Diesel heaters in classic Hymers - in detail! Think and plan carefully - it's not a simple swap.

 With Truma heaters now starting to corrode and fail after 30 years, and replacements being expensive, many owners are turning to diesel heaters - because they are cheap.

So the first rule is - think carefully - if you have the money - it is always best replace the Truma with another Truma - Carver are the same as Truma, and there are plenty of s/h ones about. There are also UK guys who can repair them. And of course there is the old originality argument - it's a classic van and original is best, but I am not a total purist, I respect the right of anybody to do what they like to their van, but it is no secret that I am a Truma and gas fan and don't like DHs in a Hymer, but I have owned 2, so it's not just based on sentiment.

You have to understand how the original Truma heater works in your Hymer - it's not a heater - it's a system. The Tuma fire both radiates, like a radiator, and it also blows hot air around the ducts in the van - so essentially it is the boiler of a central heating system. Inthe back of the Truma is a fan, and this fan draws air from the front of the fire, over the heat exchanger (that big aluminium box) and then into the ducts that run around the van. The result is that after warm up, the fire is quiet and background and all areas of the van are nicely heated - quiet and efficient.

What you need to remember is that it is that ducting system that is so important in this respect.

So when you install a DH - you have 2 choices - connect it to the ducts, or forget the ducts and just have the a single outlet from the DH blowing into the van. 

And remember that a DH is a blown air heater only - it doesn't also radiate like the Truma used to do.

So you have to think carefully where and how you install it.

Next things you have to think about are its connections. A DH needs a fuel pipe supplying diesel, an exhaust pipe system to the outside, and a solid 12v electrical connection. Plus as discussed, it either needs interfacing to the warm air ducts, or it needs either it's own set up hot air distribution ducts, or it needs to be positioned in such a place as to direct its single hot air outlet into the van, in a comfortable way - ie where it will heat the whole van efficiently.  And once you decide this, all the connections I just mentioned have to be plumbed in to that point.

The best scenario fr a DH install in a Hymer is to install it so that it blows into the existing Hymer hot air ducts - but even this is not straightforward. A DH has a heat outlet temperature sensor and if this gets too hot it will shut down the heater. A DH is a powerful beast, so the heat has to be directed into the ducts quickly and efficiently. if there is any back pressure - ie the ducts can't carry away the heat fast enough, then you can get problems, especially if you are using a  big DH - it might just put out more heat than the ducts can handle, so will overheat and shut down. See below about sizing the heater to the van.

The next ting you need to know about is that a DH is a completely different beast to any other heater you have ever known. Almost every heater you have ever known either in a van or a house, gives heat quite quickly - you turn on a gas fire or a fan heater and you feel the heat almost immediately. But a DH isn't like that. Diesel fuel is not like gas, it doesn't combust easily. If you throw a match into a bowl of diesel, the match goes out! So diesel has to be cajoled and provoked to finally combust. The way it does this is to use a glow plug - similar to the ones in your engine to start on a cold morning. The DH has a combustion chamber into which the fuel is injected. This is done by a pulsed pump - a DH doesn't use an injector like a normal engine - that would be too expensive to manufacture. A DH uses a pump that squirts a small quantity of diesel into the combustion chamber every second or so. This is the familiar tick tick sound that a DH pump makes. The hotter you want the heater, the faster the pulses. But this method takes time. The DH starts by switching on the fan and the glow plug, and this needs 12v - the plug glows red hot and after a few pulses the diesel starts to burn. But it takes a while, about a minute. The pump runs slowly at first, giving the fuel chance to burn, and then increases, eventually to the level that is preset by the control panel. It is very similar in basic content to a jet engine - it needs a spin to get it going, and then it becomes a self feeding cycle - the more fuel you inject, the faster it spins!

So what you need to understand about this process is that it takes time! And once going, if you want to switch it off, the whole process has to happen in reverse. When you switch off a diesel heater, it has to go through a cool down cycle - the fuel is stopped, but the thing is still hot, so the fan has to be run until the temperature sensor reports the temperature low enough so that the fan can stop.

So here is the big disadvantage of DHs - they take time to wind up, and time to wind down. This means that if they are being switched on and off by a room thermostat, the whole process has to be repeated. It is nothing like a gas fire where the burner ignites immediately in response to the thermostat and gives heat immediately.

And in cold weather in a van, you can experience big differences in ambient temperature as it goes through this cycle - a common complaint from DH users is that the ambient temperature goes up and down dramatically because of this long warm up and cool down cycle.

But there is a way around this - if you can set the DH up so that it just runs constantly, putting out a constant stream of heat that is just the right amount to keep the van at the temperature you want, then there is no reason for it to shut down and warm up again. But this can be more difficult than it sounds.

The reason for this is that DHs are powerful beasts. They put out a lot of heat. The Truma in your van was either a 3002  in a 5 series van, or a 5002 in a 6 series van. The 3 and 5 refer to kilowatts. DHs come in different sizes, and the bigger ones are hardly more expensive than the samller ones, so people tend to go for bigger is better. But it's not - an 8kw DH, on its lowest setting will make a 5 series van like a sauna, and it won't go any lower - if it gets too hot all you can do is switch it off, let the van cool, and then switch it on again, and believe me, I've been there, it is not relaxing. You are trying to watch TV and the heater is going from zero to hero every 30 minutes and the temperature in the van is varying by 10 or 15 degrees - ie cycling between cold and hot. It is not pleasant - I have been there! 

So the trick here is not to over-specify. Most Hymers only need a small DH - 3kw max. So that on it's lowest setting it gives out constant heat, but not too much. And then you can fine control the heat by opening windows and rooflights a crack. You want a DH that on its lowest setting will not overheat the van. You need to prevent the DH from having to go through its warm up cool down cycle - that means that it should always be running, with its lowest setting not to hot. Increasing heat from low is easy - you just press a button and the pump speed increases, and the extra heat comes quite quickly.

And this is the main point of this article - a correctly planned and installed  DH can work very well. But it has to be that - planned and installed. It is not like a fan heater you can buy from Currys and just plug it in. You need good solid DIY skills - you need to cut holes in the floor, tap into your van's diesel tank, and make good 12v connections. And then you have to be willing to fine tune.

If you don't have these skills, or access to them, then you should consider just replacing the Truma - or even fixing it. Truma fires are very fixable - the spares are still available although the dealer expertise is starting to retire. But I have always said that anybody with the skill to install a DH also has the skill to fix a Truma.

Miscellaneous things to remember are .... a DH needs 12v, and plenty of it. It will draw 10 amps for about 5 to 10 minutes - this is for the glow plug. Once the fire is running it only needs 12v for the fan - less than 1 amp. But that 10amps is quite a draw, and if your battery is either tired or getting low that 10amp draw can pull down the voltage of the battery - and if the voltage drops below a preset threshold, the DH itself will detect low voltage and then shut down. So you need a robust battery system and good cabling to minimise this risk. One of the reasons Hymer used the Truma is that if there is no battery power needed at all, you can still get heat from a Truma - but it won't blow hot air because there is no power for the fan, but it will radiate - it needs no 12v power to run in radiate mode, and turn up high it will heat the whole van. A Truma will heat a van with no battery power at all.

Another thing to think about is pump noise - the pump makes a tick tick sound, and depending on where it is located this noise can be annoying. There are silent pumps available, but these need fitting and are often as expensive as the heater itself.

Next thing to consider is running cost - you are using a road taxed fuel for heating - at 2024 prices £1.60 a litre. For occasional holiday use it's not an issue, but for full timing through a cold winter it is expensive - they don't sip so little fuel that you don't notice it - that is a myth. A DH in cold weather, used 24/7 in a full timing or winter holiday situation will use a lot of fuel. You can mitigate this by using kerosene, heating oil, which is cheaper, but then you need a separate tank and this has to be located somewhere in your van, and has to be filled, so you have to either fit a big tank, or carry a container. And don't forget that kerosene is smelly!

So in conclusion - DHs are not bad! But it's horses for courses. They are pretty much the only choice for van most van and truck conversions, but installing one to replace a Truma in a Hymer is not a simple operation. 

You have to take out this ....

And replace it with this ....

But it is possible ... this is a simple campervan motorhome installation with a single outlet installed under a bench. 

Classic Hymer Mythbusters and common situations.

Here are some thoughts and musings on questions that get asked regularly ....

What follows is based on years of answering technical questions online and reading and analysing all the questions that get asked, and the situations that occur. 

Some of this is personal opinion, but based on what I see, but most of it is simply an accumulation of collective knowledge

DIESEL HEATERS

I have lost count of the times people say - I am going to fit a diesel heater - usually because their Truma heater is no longer working. It really isn't that simple, what is actually happening is that people see a diesel heater costing £100 online and think it's a cheap fix. It isn't, unless you are a solid DIYer with a good tool kit and knowledge - and if you are, then you also have the nouse to fix the Truma.

The Truma 3002/5002 is a brilliant heater, and is plumbed into the ducts that run around the van. It is a blown air central heating system - quiet and efficient. It is there for a reason - Hymer put it there! Spares are available, and they are usually easy to fix. But what happens is that over the years the ducts get damaged, the vents get blocked, the fan gets clogged with dust - but all of this is just routine maintenace - we all need a bit of maintenance every 15 year or so.

Diesel heaters are noisy and expensive to run, they also need battery power. Fix the Truma if you can, especially if you use the van a lot or full time.

For a full and detailed article on diesel heaters in classic Hymers ....

https://hymers700.blogspot.com/2024/02/diesel-heaters-in-classic-hymers-in.html

COMPRESSOR FRIDGES

With new 3-way fridges now well over £1200, everybody thinks 12v compressor fridges are the answer. They are not, but they can be if you take everything into consideration.

A compressor fridge is a one trick pony - it needs 12v, and only 12v - if you have no 12v, you have no fridge. So the 12v it needs has to be supplied over and above your normal 12v usage. Average use for a 12v fridge in summer is about 30 amp hours per day - that's nearly half a standard 100ah leisure battery. So a 12v fridge only makes sense if you can replace that much power - every day. The easiest way to do this is by solar. If you have 200w or more of solar and a decent battery, then you can run a 12v fridge - but there is a catch - and that is that you can only do this in summer.

If you full time or use the van for long periods in winter, then it is a completely different kettle of fish. Solar is almost non existent in winter - so you need other sources of charge - regular plug ins or regular driving. It is almost impossible to run a 12v fridge completely off grid all winter - for winter full timing, gas is the answer.

Of course if you never off grid and always plug in, then you can of course run an electric fridge - in fact you can run an under the counter 230v domestic fridge that you can buy on Amazon for £80 - all you have to do is secure it in place and fit a door catch.

SOLAR IS NOT ABSOLUTE

A 200w solar panel does NOT supply 200w of power. It will only supply 200w of power with the sun directly overhead in clear sky and clear air - ie lab conditions. In the UK and Europe the sun is never overhead. So the most you will ever get is around 180w for an hour either side of midday at the June solstice - June 21st to be exact. From that day forward, the amount of power you get reduces steadily day by day until you get to the shortest day December 21st, the winter solstice. And to make matters worse, a panel only provides the max, if it is at 90 degrees to the sun. But a panel on a van roof is flat, which only makes it worse. At midday on December 21st if the sun is shining, that 200w panel will produce about 20w - and then only for a couple of hours.

The bottom line is that you simply can't get enough power from your solar setup in winter. You have power to burn in June, and next to nothing in winter. So if you use the van in winter you have to have a completely different routine to what you do in summer - you have to drive more, or plug in more. 

Full timing or long periods off grid in mid winter is very hard on solar alone.

BATTERIES in 2024

After years of messing around and researching, I can now say that lithium batteries have arrived! A cheap crappy 100ah old fashioned lead acid leisure battery is around £100 and will last about 3 years, less if abused. A decent one - Varta etc - is now about £150 and will last a bit longer - up to 5 years. But a half decent 100ah lithium battery with bluetooth will now cost about £350, will deliver 50% more power than a normal battery - which means that a 100ah lithium is as good as a 150ah lead acid battery, and it will last 10 years or more.

Edit 2024 - I am now seeing "smart" 100ah lifepo4 batts for under £250 - Fogstar and Aolithium are 2 brands. I don't rate any "non smart" battery - ie Ecoworthy. See below.

So the longevity alone is a good reason to buy - if you intend to keep the van that long. But the number one reason to buy lithium is not any of the above .... it is INFORMATION! Most (but not all) lithium batteries are "smart" - they have bluetooth and come with an app - and the app tells you everything about the battery. This info is priceless because it allows you to plan. It tells you exactly how much juice you have in the battery, how much you are using when you switch things on and off, and how much charge you are getting. This feature and this feature alone is worth upgrading to lithium, because the app is just so bloody useful! After a few weeks of use you soon know exactly what effect every activity has on your power situation. This allows you to make decisions based on facts, not guesswork. Wonder whether you can stay an extra day off grid? The app will tell you. Want to know how much solar is giving you? or an hours driving? The app will tell you. 

Reasons NOT to buy lithium? if you only use the van for summer weekends, or you mainly use campsites and plug in, or you drive every day for at least 2 hours - then you don't need lithium. And you have never had any complaints so far.

Reasons TO BUY lithium. You use the van a lot, you prefer off grid, or at least to have the choice. You use a lot of power ... or for the last few years you have been frustrated with your power system - these are all good reasons to upgrade.

And if you love your van life and dream about lots of power - then go large! Spend £500 or more and get 200, or 300 or even more amp hours of lithium - it is life changing .... it was for me.

PORTABLE POWER STATIONS - JACKERY BLUETTI ETC

In the context of a motorhome these have zero relevance at all. A PPS is nothing more than a battery and an inverter in a pretty box. There is only one reason to buy one of these, and that is to deal with situations where you need power and you are nowhere near any vehicle or building or power source - ie camping in a tent in the wild - in those situations they are good - if you can carry them.

But in a motorhome they have no use whatsoever because you already have a battery. So if you want more power in your motorhome you simply upgrade your system to satisfy your needs. And that upgrade will be well under the cost of any of these PPS devices.

And these devices are also misnamed - they are not "power stations" - they are batteries, and just like a battery, they have so much power, and when that power is gone, they need recharging - from plugging in or solar. Which is exactly the same as the electrical setup in your motorhome.

Technically, they are rated in watt hours, which confuses many people. Motorhome owners are generally used to thinking in amp hours at 12/13v (leisure battery voltage). To convert, you just divide the watt hours by 13. So a Jackblue portable power station advertised at 800wh, is the equivalent of a 60ah 12v battery. And will most likely be at least twice the price.

I am not saying the products are rubbish, just that they are not relevant at all in a motorhome - unless you also need to have power away from your van, in a field or on a mountain.

CHARGING THE ENGINE BATTERY 

A common question is how do I charge the engine battery? The short answer is, in a classic Hymer, you don't. The engine battery has only one purpose and that is to start the engine. When the engine is started, the alternator soon puts back the power that was used to start the engine, and you should always arrive at your destination with the engine battery completely full, and it will stay that way for months, ready to start the engine again. Self discharge of a starter battery is around 3% a month, so it will hold charge for many many months.

So a classic Hymer left the factory with no facility to charge the engine battery from anywhere except the alternator.

But then as mobile phones, satnav and reversing cameras arrived - many if not most of these were powered by the cigar socket in the cab - the nearest and most convenient source of 12v power - and the cab cigar socket is powered from the engine battery, not the leisure battery, because it is a Fiat or Mercedes factory feature, not Hymer. So then owners were arriving on site and leaving all that gear plugged in, or just having the radio on for a few days, and even if plugged in to EHU, or had solar fitted, found they had a flat starter battery.

This became such a "thing" in the 90s and 00s that dealers and manufacturers were getting sick of the support and warranty claims, which were not their fault. So products started to appear on the market to "fix" the "problem". The most famous of these is the BatteryMaster - this is a very simple box that connects between both batteries and allows some charge to bleed over from the leisure battery to the starter battery to compensate for this extra load and alleviate the problem.

Then solar controllers started to appear with dual outputs, and some later vans with Elektroblocks also had a trickle charger output to the engine battery.

Another factor involved was that back when the vans were new and expensive, many owners fitted expensive alarm systems, and alarm installers just connected these to the engine battery, as they did with cars.

So just like the horrible cigar lighter socket became the default 12v source in the cab, so engine battery charging from all sources also became a thing.

But it really should not be necessary in a classic - what is actually needed is to get back to original specification and not have anything plugged into the cab cigar socket, or if there is, to unplug it while parked up. Better still, it is better to never use the cigar socket at all - they are horrible things - and install proper power sockets in the cab, powered from the leisure battery. Modern life in the 2020s is almost completely powered by USB, so having USB sockets installed is the best answer.

So the general attitude has been that there is no point in wasting valuable leisure power by diverting it to a starter battery. But on the plus side, modern solar is now so cheap and efficient that you can afford to divert a bit to the engine battery, and that in any case, all that equipment is part of the van's general setup anyway.

So in terms of what the classic Hymer should do - the first thing is to be aware of the issues, and then take a decision based on your circumstances and lifestyle. Either you modify your van so that everything is powered from the leisure battery, leaving the starter battery full all the time, or you accept that some stuff is powered from the engine battery, and you modify things to replace that charge. It doesn't really matter what you do, as long as you prevent the classic situation of enjoying a nice stay somewhere, and then not being able to start the engine to drive home.

BATTERY VOLTAGE GOTCHAS - STATE OF CHARGE

One of the commonest mistakes that many owners make is seeing a (lead acid) battery voltage of 13v or more and assuming that the battery is full and all is OK. It's not! Any battery on charge, in any condition, flat full or empty, will display a voltage over 13v - IF ANY CHARGE SOURCE IS PRESENT! So if the engine is running, or you are plugged in, or solar panels are working in the day time, then the voltage will be over 13v regardless of the state of the battery.

The ONLY way to tell how much charge a battery has left, with minimum equipment, is to measure it's "resting" voltage. Resting voltage is a battery doing nothing - no charge sources present, and no major discharge going on - having a couple of lights on is OK. And it needs to be resting for at least 15 minutes.

Once the battery is at rest, then its voltage is an accurate indication of its state of charge - ie how full or empty it is. For a lead acid battery, fully charged is 12.8v, and just about empty is 12.0v. Google "12v battery resting voltage" and you will see lots of pretty tables you can download and print. And it's linear - so 12.4v is 50% full.  At 12v, decimal points of a volt really matter, so if you do this you need to use a multimeter - the Hymer panel voltmeter isn't accurate enough, although if you compare the needle position with your multimeter readings, you can get a reasonable idea from it - ie you know what position the needle is in at 12.8v and also at 12.0v.

But if solar is connected, even a bit of sun can up the voltage, so unless you can switch off your panels, the best time to do a resting voltage measurement is after dark. Same goes for EHU and engine - must be off.

Once you understand this simple principle, it is easy to measure and estimate lead acid battery performance.

You can also buy and fit "battery monitor" devices which do all this for you and give you a useful percentage display - but that's another subject.

OLD ALARMS

When the vans were new they cost big bucks and plenty were stolen. owners rightfully installed alarms, sometimes it was even an insurance requirement. But wind the clock on 30 years and these old alarms can literally ruin a holiday and strain a marriage! Most of the companies that made and installed them have either gone or been absorbed, and unless you have original documentation, and there is info still available online, it is really hard to unpick a problem with an old alarm. The ones with a fob that immobilises the engine are the worst - they are a time bomb just waiting to blow up in your face at the most inconvenient time. One day, they just stop working. if you are lucky, all you need is a new battery in the fob, and if you are that lucky, then buy a lotto ticket that weekend. But what usually happens is that after 30 years of solid service, eventually, after all those temperature changed and periods in storage, year after year, a bit of corrosion or vibration creeps in and one day a connection is broken or a circuit board gives up and you are bang in trouble. 

And it really can be a nightmare - these alarms were meant to be secure - so they can't just publish all the details on the internet! So troubleshooting is next to impossible. It is also quite difficult to disable a diesel engine. The Fiat engines have an electric fuel shutoff valve, which is usually disabled by the alarm, and as such is usually easy to fix. But the Mercedes (pre 95) have mechanical/pneumatic (vacuum) shutoff valves, so were much harder for alarm companies to disable, and as a result can be complex to untangle.

So what to do if you have an alarm like this? You either have to know about it in advance and how it works, so that you can un-immobilise your engine if it ever fails. Or you simply take it out - either yourself or pay a modern alarm installer to do it for you, or at least have them show you what to do and how to start the engine again if it happens to you.

Classic vans hardly ever get stolen - the thieves go for modern vans - so having no alarm is no big deal. And if you do want security, you can do a lot better with modern gear - mechanical immobilisers are easy and cheap to fit, GPS trackers are dirt cheap, and security is now at the next level with the internet of things - the same technology that gives us web cams, baby cams and doorbell cams now also offers us as much or as little security as you could possibly need for your van.

If you do decide to have security items permanently connected in your van, then make sure they are powered from your leisure battery, preferably with solar. Then solar should easily replace the power used by these devices, even in winter storage - and then no matter what happens, your van engine should always start after a period of storage. Another tip if you do suffer from flat engine battery after storage is to just remove the negative cable from the engine battery so it can't possibly discharge slowly. But this is a workaround, not a fix. You can also buy battery disconnect switches which do the same thing only more conveniently, and these can also double as useful security devices. You can even buy ones that are remotely switched with a fob.

I am not saying that security and alarms are unnecessary - just that any alarm installed 30 years ago is a problem waiting to ruin your day. 

LPG

I LOVE LPG! I really do ... the best money I ever spent (other than lithium!). But just as with solar and batteries, it is all down to how you use your van. If you are a summer user, and stay in the UK, and only buy bottled gas occasionally, then you don't need LPG. 

But if you use the van a lot, especially in winter, and travel to different countries, then LPG is a must, and it pays for itself in a few years. 

The cheapest setup is a single refillable 11kg bottle - but 2 are better. LPG is about 50% cheaper than Calor - Calor is a rip off! And no matter what you read, LPG is available everywhere except Morocco. Yes it is becoming less common on forecourts in the UK, but every big town has a supplier, all you have to do is use the LPG app and fill up when you can. LPG is NOT disappearing in the UK, it will ALWAYS be available - you just have to plan forward and fill up where you can, using the app. The only time LPG is a bad idea is if you are unlucky enough to live in the van in a remote area like Cornwall or Scotland, and you don't drive very much - ie you don't tour around - you use the van more like a static. In these cases you are better with bottled gas. But if you use the van for what it was designed for - holidays and touring, then LPG is available as you go - just not on every forecourt - and it has never been on every forecourt.

Underslung tanks are OK, but the only reason to fit a tank is if you want to use the gas locker for other things. A good example of this is so that you can use your now empty gas locker for bigger batteries.

USING CAMPSITE EHU POWER TO HEAT THE VAN - VS GAS AND WILDCAMPING - THE NUMBERS AT 2024 ENERGY PRICES. 

Power is now around 25 to 30p per unit, which is a kilowatt hour. The standard Truma 3002 is a 3kw heater, and is rarely used on full - average is about 2kw to keep a 5 series van warm in average cold weather. Same goes for any fuel. So you are looking at around 60p an hour to run a 2kw electric heater. So 24 hour use is as much as £14. And people do! That's why EHU pitches are now £25+. An oil filled rad at about 800w (0.8kw) is much cheaper, but the site owner doesn't know what you use. But many of them are now wise to the fact that owners run electric heaters, so they assume the max, or fit meters, or fit low amp breakers that will trip if you try and use heaters.

Only farmers who have big power bills anyway don't seem to bother - I can still find farm sites with EHU at around £15 but they are getting rarer - the going rate for a pitch with EHU is around £25, even more in posh places.

Now contrast that with gas. Calor is crazy expensive these days at around £50 for 13kg, but still comes in at around £2 a litre, or £4.00 a kg.

The Truma 3002 heater, fitted to most classics, consumes 30g/hour on low, and 280g/hr on max - and you rarely run it on max unless it is sub zero outside, so I suggest 150g/hr is a reasonable average. That gives you a running cost for 24 hours of around £14 - which is roughly the same as electricity at 30p a unit. So there is little cost advantage between the two, except for the difference between the power cost of the pitch and the actual cost of the pitch, which for a £25 pitch is £10. So wild camping on Calor gas is roughly £10 a day cheaper than a £25 pitch.

Now consider LPG, which is 80p a litre from a gas place, and around £1 on the forecourt. half the cost of Calor. Now you are paying £7 a day for the same heat output.

So refillable LPG is by far the cheapest way to heat a van off grid - so unless you can find an EHU pitch for a tenner or less, which is almost impossible, or any other place with "free" power, a £25 pitch with EHU is more expensive by far. Of course you have to take into consideration the installation cost of LPG, but for all year round full timers it soon pays for itself, especially if you always wild camp.

But even Calor is around £10 a day cheaper based on a £25 EHU pitch cost.

But if you always prefer to pay for a site pitch with EHU, at £25, because you don't like wild camping, then using a 2kw electric heater will save you around £10 in Calor gas, or £5 in LPG. And if you prefer no heating at all while in bed, and only use a 2kw heater for 12 hours a day, then those figures reduce by 50%.

Fridge on gas and cooking are of course another factor, but they take far less gas than heating. A fridge consumes 11g/hr on gas, which is around 0.25kg per day = £1 on Calor, 50p on LPG.

OK sounds complicated, but it isn't. Once you know the consumption of the appliances - my figures are from Truma's website - and the cost of the fuel, plus the cost per unit of electricity, then it's simple arithmetic.

ENGINES and TURBOS

I have lost count of the number of posts I see about owners asking about bigger engines or turbo conversions because their van is "too slow". Forget it. An engine change or a turbo conversion is a big job, and at commercial rates is simply unaffordable. The only time it is possible is if you either have the skills, or know somebody who has the skills, for free. It is the labour that costs money and with commercial labour at £50+ an hour it is simply uneconomical. Yes there are plenty of owners that have done it, but they have done it themselves. If you don't have the skills or facilities, then forget it. It is cheaper to sell your van and buy a faster one. 

And don't forget that you spend 90% of your time living in the van, and only 10% driving it. I have done 200k and 30 countries over 15 years, and a bigger or faster engine would have meant absolutely nothing.

SILVER SCREENS

Marmite! I hate them, why live in a padded cell with no view from those magnificent panoramic windows. Where do you store them? Do you fancy putting them up in the rain? Or packing them away sodding wet?

But it's horses for courses. If you are parked up in one place living in your van all winter, then screens will keep your van warmer and you will use less gas. Ditto if you are a winter sports fan and do regular ski holidays, and don't care about the view.

But for "normal" use .... well I can't tell you what to do, but do think about it. I had them on my first van 25 years ago and they were used twice and then sold. Or maybe I burnt them.

INTERNET AND WIFI

For solid wifi internet in the van you only need to spend £50 plus a PAYG data sim card. You don't need expensive gear or roof mounted antennas, and whatever you do don't buy a Mifi. 

If all you need is occasional internet - use the hotspot on your phone, not a mifi - they are technically identical.

Read this blog on the subject.

https://hymers700.blogspot.com/2022/11/no-need-to-spend-big-bucks-to-get-wifi.html

TV

Satellite TV in a van is now dead and buried, unless you already have it, there is no need to buy it. It is expensive.

For "normal" TV in the UK, all you need is a normal TV and either a roof mounted caravan TV antenna, or one of those little internal ones by a window. Terrestrial Freeview in the UK is available almost anywhere, and signals are far stronger than they used to be.

For all other TV - internet is the way to go. A 12v router costing £50, a PAYG sim card loaded with 200gb of data for £20, and either a smart TV, or a normal TV converted to smart by the addition of an Amazon Firestick plugged into its HDMI port, and you are good to go for at least a month. 4G is almost everywhere, and is almost always fast enough for rock solid TV - Iplayer, ITVX, Netflix, Amazon prime - plus if you are a bit of a nerd like me there is no end to the stuff you can get at.

As always, roaming abroad is more difficult because of UK roaming limits, but everything is doable with local sim cards.

RADIO

If you have a working FM/AM cab radio and you are happy with it, then great. But just like TV, radio is going internet. Whenever I want radio, I just use the phone and bluetooth to the car speakers. Drop outs occasionally happen, but I once drove from Manchester to Dover and it dropped out once.

DAB RADIO

Dab radio is a failed technology - forget it. Fine if you are not moving, but in a moving vehicle it is rubbish. Use internet radio instead.

STARLINK

And for those who must have fast internet 24/7 everywhere, Starlink is almost here. I say almost because at present it is a bit too cumbersome and power hungry for "normal" use. But soon I expect them to offer a simple dome on the roof that doesn't use too much power for about £50 a month. If comms and internet are your thing, then keep an eye on Starlink. In Jan 2024 they are already trialling Starlink direct to a normal mobile phone, no need for any extra equipment. In the next 2 or 3 years high speed internet and coverage everywhere on the globe will be an affordable reality. But right now (2024) it is cumbersome and consumes about 5 amps - too much for most owners and battery systems.

THETFORD TOILET AND SOG SYSTEM

There is a world of difference between occasional holiday use and full timing!

I have seen guys on camp sites empty their cassettes every morning and then rinse it out seventeen times, and then spray it with air freshener.

Mine on the other hand has been in constant use for 15 years - I have worn out 3 cassettes. I have had my hand inside it to retrieve stuff and I have emptied it in some horrendous disposal points. You just get used to it. If we have to, we can get a week out of a cassette - don't ask me how! But if you are in a gorgeous spot with no easy disposal then you can do it. I have also carried full cassettes on a scooter and a push bike, and even carried one through a crowded village - wrapped up in black bin liners - nobody even knows. It's the reality of full timing in out of the way places - you just do it.

My conclusion is that considering what it was designed for, the Thetford cassette system is worthy of great respect. Spare parts are available, and once you understand the basic design, it is easy to work on and fix. 

But I have no time for the SOG system, but only in the context of full time use year after year. The filters are expensive, the fans break, and I have spent more time fiddling with SOG than I have with the toilet itself. But for holiday use it is fine - it does what it says on the tin. But I wouldn't bother with it for full timing - it's just another thing to break.

In terms of fluids, I have tried everything, and I always end up back with Elsan Blue. Second choice is Thetford - but it's expensive. The green eco stuff is just that - eco stuff. But eco is the least of your worries when full timing. Bio washing powder or tablets, and cheap dishwater tablets also work, to an extent - I use them when no fluid is available, which is quite often when you tour places like Albania!

Disposal - after the first few years disposal is never a problem. Best thing I ever bought was a set of manhole keys and levers and the gradual knowledge of how sewer systems work, and what you can get away with. In 20 years and 30 countries I have never dumped irresponsibly - but I have dug some pretty deep holes.

If I was building a new van from scratch I would install one of those separator loos - they are really good. But I wouldn't go to the hassle of ripping out a C3 in a Hymer and installing one - the ergonomics don't work. One day somebody will design a separator the same dimensions as a Thetford C3 bench - and I would buy that.

PLATING, WEIGHTS AND DRIVING LICENCES 

All UK driving licences after 1st Jan 1997 allow the holder to drive a van up to 3500kg - and the DVLA tax class for a van under 3500kg is PLG - private light goods. And the tax amount for this is more expensive than for vans over 3500kg - perverse, but true.

Anybody who passed their test before 1997 is entitled to drive a vehicle up to 7500kg. This is nowadays called a C1 entitlement, also known as Grandad Rights.

Any van over 3500kg is classed as PHGV private heavy goods - ie a heavy goods vehicle used privately. The tax payable on this class is less than PLG under 3500kg. Don't ask why, it just is.

Generally speaking in classic Hymer terms, the 5 series vans are 3500kg or less, and the 6 and 7 series vans are plated at 4600kg, so need a C1 licence. 

Those are the basic facts. But then the whole thing can get very murky and confusing because most UK classics are imports, and many vans - many more than you would believe - are imported with incorrect V5s. Back in the 90s the DVLA were pretty lax with imports - they would basically stick anything you told them on the V5. So all sorts of weird situations have happened. I have seen S660s that are plated at 4600kg with V5s that state 3500kg. I have seen weight plates (VIN plates) either defaced or altered. I have also seen 5 series vans with plates that say 3100kg or 3200kg and hardly any payload - but in the UK these can be legally re-plated to 3500kg - there are specialist firms such as SV Tech in the UK that do this. 

So the moral is - the V5 on an imported classic is not gospel, and the DVLA do make mistakes. So if in doubt - check. Ask on the group.

SOLAR PANEL FIXING - SCREWS OR GLUE OR BOTH?

There has been a long running debate on fixing solar panels to Hymer roofs. The argument is what sort of bracket, and what sort of fixing. 

The problem for me and the group is that we are amateurs advising other amateurs, so although nobody is expecting to be sued, there is a moral responsibility to ensire sound advice. 

The bottom line is that adhesive only can work, and is used by professionals, often on newer vans. But pros work to a formula - a carefully designed formula, and they never deviate. Adhesive only fixings are all about surface preparation, choice of adhesive and final application, plus curing time. But for the amateur, there are too many variables, not the least of which is their own ability and experience.

The Facebook group has several professionals and ex professionals in the background, and they report that this is argued about even within the industry. But our professionals (and me!) are unanimous - when installing panels on a classic van, using both is the easiest and safest option, because it offers the best of both worlds.

Our professionals are adamant - all the stories of panels coming off are usually always those that were adhesive only, and the majority of these could be narrowed down to bad surface preparation - if you use glue on a dirty surface you are asking for trouble. Even using the wrong type of solvent cleaning fluid can be a factor.

Of course owners are free to do whatever they like, but if the question is asked on the group, screws and adhesive is the answer. My panels went on using this method in 2015 and every year I inspect and give a really strong pull. No change after 8 years. So at least I have some evidence to back it up. 

With regard to brackets - the big plastic ones do not have a good reputation - aluminium is more popular. 

And while we are on the subject of panels - flex panels are rubbish and a nightmare to get off when they break. Rigid panels are the way to go.

OLD AWNINGS - NURSE THEM DON'T ABUSE THEM

Old awnings develop wear and tear character just like the rest of the van. They are often reluctant to pop out when you wind out, and reluctant to go fully back in when you wind in. But If you rely on the winder alone and just keep winding harder, you will accelerate its eventual demise. The way to deal with an old awning is to help it like an old lady across the road. Better to make it a 2 person job - one stands in the doorway and gives a helping hand, and the other winds. Usually all it needs is a shake and a wobble in and out of its cassette. This is far easier than trying complicated repairs and hard to get spare parts. With care an awning should last as long as the van.

Mine is a really old model, and it complains loudly when I occasionally disturb it. It comes out with a bit of a pull, and just so I know who's in charge, it refuses to go back in its box at one end. I have to give it a slap and shake and in it goes - nothing abusive, just common sense.

REPLACING THE ORIGINAL ROOFLIGHT WITH A HEKI 

 If you ask any question for help with a broken or leaking original rooflight, many will tell you - replace it with a Heki. A Heki is a different style of rooflight. It is expensive, more expensive than a new dome, and YOU HAVE TO MAKE THE HOLE IN THE ROOF BIGGER! Which is a big job involving jigsaws, and Hymer purists, myself included, regard this as a crazy idea, especially since the old one is usually fixable. The other problem with the Heki is that although it looks posh, with its wide opening and clear glass, the wide opening is only any good in a heat wave, plus it easily catches the wind. The Heki lacks the fine adjustment of the original, which winds up and down and allows very fine adjustment - you can have it open from just a tiny crack, to 6 inches. This fine adjustment is very useful in all weathers, including rain - it allows as much or as little air circulation as you need, and used in conjunction with the excellent Truma blown warm air cetral heating that a Hymer has, you can have any mixture of fresh and warm air in all seasons. You lose all this with the Heki - it has very coarse adjustment. So bear all this in mind when you consider the Heki. It is a downgrade not an upgrade. But of course you can fit what you like - it's your van, this is just an alternative view from me and other owners.

What is an EBL? All about the Elektroblock - in detail. Updated 2026 with notes for lithium batteries.

If you just want the very basics of what the EBL is, then all you need is this first section in bold.

The EBL is a box fitted to later post 95 (approx) classic Hymers which handles all of the habitation electrics.

Earlier pre 95 vans have separate components - ie fuse box, relays and mains charger, but the later vans have all this incorporated into one box - the EBL.

So an EBL contains a 230v charger, split charge relays and 12v habitation distribution and fusing. It is connected to both the engine battery (EB) and the leisure battery (LB), to the alternator D+ signal cable, to the fridge for 12v fridge operation and to the various habitation circuits - lights, pumps etc. The EBL is also responsible for driving the control panel, where the meters are etc.

It also has a socket into which a solar controller can be connected - but there are limits to what can be connected to this - see below.

At first glance it looks a complicated beast, with a whole plate of spaghetti on the front of it. But you only have to study it for a while and you will discover that it has typically efficient German design and common sense going on. All you have to do is learn a few new words - "block" and "pin".

All the cables are connected to the EBL via multi connectors - these are called "mate n lok"  - it's a brand name. These are good connectors, but the downside for the amateur is that you need special tools to attach the pins to the cable ends, and then the pins push into the holes and have a tang which locks them into place. This means they can't easily be taken out - you need a special tool. However the good news is that the average owner rarely needs to do this - modifications and repairs can usually be made without special tools or pin removal.

The sockets on the EBL are called "blocks", and they are lettered - A B C etc. And within each block, the pins are numbered. if you look closely you will see that the pins are numbered in such a way as you can work out which pin is what. So for example Block A may be a 3 x 5 block - the lower left hand pin will be numbered 1, the end of the row will be numbered 3, and the top right is 15. So that is telling you the numbering scheme - start at one and count across in rows. So if you want pin 7, that will be third row up, first pin .... all very logical.

So when you are talking technical with EBLs, you will often see - Block A pin 7.

All the EBL models are made by a company in Germany called Schaudt, and they are used in many other vans - not just Hymers - and all the technical manuals and diagrams are available online. The diagrams show the function of each pin.

So looking at this diag you can see that Battery 2 positive - the leisure battery - is connected to Block C pin 2 .... and if you look closely, you can see that pin 2 is also paralleled with pin 5 - this is common in EBLs to allow more current carrying capacity. Note this is an example and does not mean that all EBLs have the LB connected to these pins.

So now you know how to identify the connections on your EBL - but remember that there are several models of EBL - EBL99, EBL104 and EBL105 are common ones, but there are others - but the principles are the same for all.

So now let's look at some of the functions of the EBL.

230v Charging.

All EBLs have a 230v connection. This is to power the internal charger. There is usually a switch on the EBL marked on/off and this switches on and off the 230v supply to the charger. usually it is left on, and so when the van is plugged in to EHU, the charger is live and delivering 12v charge to the battery.

It is important to remember that the EBL has nothing to do with 230v distribution to the 230v sockets around the van. The sockets are fed directly from the EHU connection, via the breaker box (consumer unit), and the EBL also takes its 230v power from here also. The switch on the EBL only affects the charger.

Most classic EBLs only charge the leisure battery, but some also charge the engine battery as well. You have to consult the documentation to see if your EBL has this function.

The other thing you have to remember is that even when you are plugged in to EHU, everything in the van, except the 230v sockets, is still powered from the LB. All the lights and pumps etc are powered from the LB, and the EBL charger replaces the battery power used as you go. This means that if the EBL charger fails, or is switched off, you can still end up in a situation where the LB goes flat and the lights go out even if you are plugged in - although this is a rare situation, it can cause confusion. The EBL does not provide 12v power directly to the van - it just replaces the battery power used in real time, and any left over goes to top up the LB.

Engine charging

The EBL is also connected to the engine battery (EB). And of course the EB is connected to the alternator - and the alternator charges the EB. But of course when you are driving you want the LB to be charged as well. This is achieved by relays inside the EBL. Relays are the same as switches. 

All alternators have a signal line called the D+. This is the same signal line that operates the red battery light on the dashboard instruments of your van. When the engine is on, the alternator is spinning, and the D+ line goes to +12v. This D+ 12v is used to switch on the relays inside the EBL. So when the engine is on, the relays are operated and the two batteries - EB and LB are connected together - in parallel - and this allows alternator power to flow to both batteries while engine is on. As soon as the engine is switched off, the relays switch off, and the LB is no longer connected to the EB. This arrangement is traditionally called a split charge relay system and is common to all motorhomes and caravans. The reason it is done this way, with relays, is so that the LB can go flat while the van is parked, but the EB always stays fully charged so that the van engine will always start.

You can see this in action by looking at the meters - the voltage on both batteries will rise to the same level - above 13v, with the engine on, and the relays are working properly. Conversely if you do not see this then that indicates a problem either with the relays (rare) or the D+ line (common). At the factory Hymer had to add an extension to the D+ wire, and the connector they used to achieve this can get corroded after 30 years, leading to failure of the D+ voltage getting to the EBL.

Fridge on 12v

The same system is used to power the fridge on 12v while driving - assuming you have switched the fridge to this mode. A typical fridge takes 10 amps on 12v, which would soon flatten a leisure battery, but is no problem to an alternator, so the fridge is only allowed to run on 12v while the engine is running.

Fusing

There is a big row of fuses on all EBLs - and the function of each fuse is written on the EBL next to each fuse. They vary from van to van, but basically all the habitation circuits - ie everything in the living side of the van is fed from the cables on the EBL, and all are fused. So if something stops working, these fuses are the first place to look. You can use google translate in camera mode to decipher the fuse labels. The main ones are "KREIS" which means circuit. Just like the pre 95 non EBL vans, there are 2 or 3 main habitation circuits that feed the lights and stuff around the van, usually in zones. The EBL often takes this a step further and has separate fused circuits for the water pump and heating - all marked in German.

Metering

Because both batteries and all the hab circuits are connected to the EBL, it is logical for the control panel to also be connected to the EBL. The voltage and power meters are fed by a multi core cable from the EBL to the panel. On some vans there is a master 12v on/off switch on the panel - this operates another relay switch inside the EBL which switches on or off main 12v power to the van hab circuits.

Solar

Solar and the EBL confuses a lot of people. There is a socket (block) on the EBL marked "solar". This is to connect solar controllers into the EBL, but the only solar controllers that plug straight into this socket are those made by Schaudt, and another German company Votronic. These are PWM controllers - which are now regarded as old technology - don't forget that the basic design of everything electrical in a classic Hymer is 1980s and 90s technology. Back then solar was expensive, and much less powerful than today. Most EBL manuals state that the maximum solar power that can be plugged into the EBL is around 10 amps - roughly equivalent to a 100 or 150w solar panel. 

But these days solar panels are much more powerful - 200w and above, and more efficient MPPT controllers have replaced the older PWM controllers, so if modern or upgraded solar is fitted to a van with an EBL it is normal to not use the solar input on the EBL and to connect solar controllers directly to the battery.

Upgrades and bigger batteries - including lithium.

So what does a modern classic owner do when they want to install bigger batteries, bigger solar panels or bigger chargers to a van that has an EBL?

There is a limit to how much power input an EBL can handle - after all it was designed over 30 years ago. So if you want more, then it has to be thought about. The simple answer is to connect all of these more powerful components directly to the leisure batteries and to disable all functions of the EBL except for 12v power distribution and fusing. So lets look at all these functions in turn.

230v charger upgrade

Most EBLs have a charger of around 10amps. The basic configuration of a van 30 years ago was a 100ah LB. So if you fit a bigger battery, then it makes sense to fit a bigger charger, especially if you plug in a lot, or if you want to spend as much time off grid as possible, and then get a rapid overnight charge from EHU ready for going off grid again. If fitting a newer bigger charger, then all you have to do is unplug the 230v plug from the EBL - this will disable the internal charger. Then connect the new charger directly to the LB.

Notes for Lithium - if you are fitting a smaller lithium battery, say 100ah to replace the original, then you may wonder if you can use the original charger. There are plenty of armchair pundits who will scream NO at you online, and the more loony of them will offer doom and gloom explosion and fire. I have written about this at length in another blog, but te bottom line is that using the EBL to charge lithium is not dangerous, but it is not optimum. If your EBL has an AGM selection switch, and you had AGM batteries previously, then deselect AGM, this reduces charging voltage slightly. An original EBL charger will happily charge a lithium battery, but it may not charge it fully - it may stop just short - around 90%, which to be honest is no big deal. And most vans with lithium will also have modern solar, which will have a lithium profile, and as solar is connected all the time, it will happily work with the old charger and top off the battery.

The other issue is that a lithium battery will work the charger harder - it won't abuse it, but it will be asking it to work hrder than it has in the past. Plus the van is 30 or more years old, so a sudden change to  harder work may well see off a charger that was getting old anyway. This has given rise to memes that "lithium killed my charger" or "the charger sacrificed itself to save my family" and over the years this has morphed into "you must not use a non lithium charger". However, if you are spending money on a major upgrade, a charger upgrade is a good investment anyway.

And if you are fitting big lithium - ie 200ah and more, then a charger upgrade is a no brainer. My favourite is the Victron Blue Smart IP22 30a charger. Beware of cheaper dedicated lithium chargers - these can have noisy fans on all the time you are on EHU which can be a pain if the charger is near where you sleep.

But if you are experimenting, or upgrading a bit at a time, you can use the EBL charger on lithium.

Solar upgrade

The same goes for solar - ignore the solar input on the EBL and connect your new panels and MPPT controllers directly to the LB. Modern MPPT solar controllers have lithium (Lifepo4) profiles. Victron, Epever and Renogy make good controllers for lithium.

Engine charging upgrade - this is the hardest one! And how it affects the fridge on 12v.

If you are fitting bigger leisure batteries and need more charge from your alternator, then things start to get a bit more complicated.  A lead acid battery will take charge at roughly 20% of its rated capacity - so a 100ah battery will take 20a - a 200ah battery will take 40a, and so on. But most EBLs were only designed for 100ah batteries (occasionally 200ah) so the relays and cable sizes are too small to handle more alternator power.

Notes for lithium. Like the 230v charger, the EBL relays maybe asked to work a bit harder, but internet memes about ruined alternators are to be safely ignored.

So to bypass the relays inside the EBL so that more power can be delivered from the alternator, the split charge relay system inside the EBL has to be disabled and new bigger cabling and more powerful external split charge relays have to be fitted externally. Or in some cases a relay is not used, and a b2b - battery to battery charger - may also be installed. A b2b is the better choice for lithium, but a good voltage controlled relay such as the Victron Cyrix will also work well.

The easiest way to disable the split charge relays in the EBL is to simply cut the D+ alternator line to the EBL - usually a yellow wire. This will then stop the internal relays from operating. However this will also stop the fridge relay from operating, so just cutting the D+ line also disable the 12v supply to the fridge while driving. 

If it is important to preserve this function then there are several ways - either the internal split charge relays can be disabled - this means opening the EBL and going inside, so is only for owners with this competence. Or, an external fridge relay can be fitted. This external relay would be operated by an extension to the D+ line, and the new relay would be connected to the branch from the incoming EB line to the EBL, and the 12v feed to the fridge from the EBL would be removed from its plug, and connected to the output of the new relay, via an inline fuse. This sounds more complicated than it is but is achievable with basic 12v wiring skills.

Other possibilities are to run the fridge on gas while driving, or even run the fridge on 230v via an inverter - this might sound daft, but with a bigger battery system and more power from the alternator, then diverting 10amps to the fridge to power it on 230v from an inverter is no different to the original 12v arrangement. And of course 12v only compressor fridges are becoming more and more popular, because these big power upgrades have the ability to power them. A 12v only compressor fridge needs nothing more than a connection direct to the LB - this can even be done via the EBL - and many EBLs have a dedicated fused connection specifically for a comp fridge, so all you have to do

Once you have decided which method you are using, then you should run a thicker cable via an inline fuse from the engine battery to either your new b2b or relay, and from there direct to the LB.

EDIT I now have more information on how to deal with the EBL104 and EBL99 (the 2 most common ones in classic Hymers) when fitting lithium. Contact me directly via Classic Hymers Technical FB group.

So a typical big lithium (or lead acid) battery upgrade will result in the following.

• EBL unplugged from 230v - disables the internal charger.
• Solar connected directly to LB.
• Internal relays disabled by several methods as discussed and external relay or b2b fitted.
• Alternative arrangements made for powering fridge on 12v if desired.

This will result in the EBL being only used for 12v fused distribution. The panel meters will still work for voltage, but will no longer be accurate for power "STROM", because previously all power in and out went through the EBL, which measured it and sent it to the meter but this is now disabled because power is flowing externally. But this is now no problem as you will have chosen (didn't you!?) a lithium battery that has bluetooth and an app, and the app will give you all the information and more than the panel meters ever did. If you have fitted "dumb" lithium, or lead acid, and you want accurate metering info, then you can fit a battery monitor such as a smart shunt and app, which I have written about elsewhere. 




So that covers most aspects of EBL modification. There are now many vans with EBLs on the road sporting big solar and chargers and lithium batteries where the EBL is only used for 12v fusing and distribution, and all other functions have been bypassed.

Differences between pre 95 and post 95 classics.

Or to put it another way - differences between EBL vans and non EBL vans. Non EBL vans have basically the same functionality, but it is in separate components, not just in one box. So the early vans have a separate fuse panel, and the relays are in a box behind that panel. They also have a separate 230v charger. If an early van has solar, then it is always connected directly to the LB.

More info

There are 2 firms in the UK that specialise in EBL repair

They are Apuljack Engineering and A & N Caravan Services

Both come up on google first page.

The A & N web site is a mine of information on EBLs, but is not for the faint hearted - the author uses technical language and assumes that the reader has the same ability.

For more info and discussion, join and ask on the Classic Hymers Technical Facebook group.

https://www.facebook.com/groups/297054424534823

Lithium in the Classic Hymer (pre 95 non EBL)

Too busy for a long article? Can you just “drop in” a lithium battery into an unmodified classic Hymer? Basically yes you can, as long as you keep an eye on it, and the best way to do this is to choose a "smart" lithium battery that comes with a bluetooth app for your phone or tablet that shows you exactly what is happening to the battery in real time. Then you are in control. There is really no point in installing a "dumb" lithium battery - unless you are quite technical and have other means of monitoring and testing.

For the technical discussion .... read on.

Can you just “drop in” a lithium battery into an unmodified classic Hymer? I am afraid that there is no definitive black and white answer. I asked 3 leading lithium leisure battery manufacturers this question. One said yes, the other said their advice was to always fit a battery to battery charger, and the other didn’t reply!
So lets take each of these charging sources in turn, and try and assess their suitability for charging lithium.

The main issue is that lithium has different charging parameters to normal batteries, and the implied danger is that charging devices might get overworked, because a lithium battery can usually take all the charge presented to it. This could result, for example, in components only originally designed for charging a standard 100ah leisure battery with around 20a of charge, to deliver much more than that when a lithium battery is installed.

Alternator charging

The standard pre 95 classic, Fiat or Merc has an alternator of around 50 to 70a, and cabling between the engine battery and the leisure battery, via the split charge relay behind the fuse panel, of around 10mm2 copper, and intended to handle around 20a. Hymer fitted a 70a relay, but it is important to remember that this was over specification by Hymer so that the relay would last for ever - not to actually handle 70a.  But the bottom line here is that you are starting with a charging circuit with a design capacity of around 20a. But this isn’t self regulating - it doesn’t limit itself automatically - if asked to do more, it will, but then every component in the chain of the circuit will be working harder than before and problems can occur. In practice, if an original charging circuit is used, then it needs to be monitored for the first few weeks and months. The limiting factor is usually cable thickness, but connections can also be a problem, especially old ones that may be corroded or tired.

But some owners can and do charge lithium directly from the alternator - by upgrading cables and relays. Bt these owners are usually technically minded, and have metering and monitoring in place to ensure that every component in the chain is solid, and that the alternator isn’t being asked to work too hard. You have to keep and eye on it, and have the metering in place to monitor it.

The other worry that you read about online is that a charging system designed for lead acid batts is not suitable for lithium. This is actually not really a problem. A lead acid charging circuit will deliver around 13.8v maybe a bit more. But the limit for lithium is 14.6v, and even if this voltage was reached for some reason, the lithium bat's BMS would kick in and disconnect the charge. And if you look at the cgarge vs voltage chart for lithium batts you will see that even a charge that goes no higher than 13.8v will still result in a 95% charge. And in practice, with most vans that have lithium will also have solar, with a solar controller that has a lithium profile, solar will take care of the remaining 5%.

What many forget is that lithium batts are not dumb like lead acid, they have brains - the BMS, Battery Management System, and the job of the BMS is to prevent abuse. So the BMS will simply switch off the battery if the voltage or current falls outside of preset safety values. So in reality it is actually almost impossible to damage a lithium batt by giving it wrong voltages - it will just shut down.

But when it comes to alternator charging the simple solution for most owners is to fit a battery to battery charger - a b2b. This is a device that sits between the engine battery and the leisure battery. It has two main functions - to limit the amount of strain put on the alternator, and to present the leisure battery with a near perfect charging profile. A b2b is easy to fit - it has just 3 connections - to the engine battery, to the leisure battery, and the D+ alternator control line. (some b2bs don’t even need D+ - they are auto sensing). The only other issue for classic Hymer owners when fitting a b2b is that the original Hymer split charge relay (discussed above) needs disabling. This is easily done by removing the original relay from the fuse box. All other original cabling is left intact, which preserves the original function of 12v fridge operation while driving. Then a new cable has to be installed from the engine battery to the b2b, and from the b2b to the new lithium battery. The size of this cable is dictated by the size of the chosen b2b. And the size of the b2b is dictated not by the size of the new battery, but by the max rating of the alternator. The general sensible rule is 50% of the alternator rating - for te vast majority this will be 30a.

If fitting a b2b which needs D+ switching, then the original D+ line to the original relays in the fuse box has to be identified and tapped into, and a new wire run to the b2b.

In the case of classic Fiat vans, where the engine battery is under the front bonnet, a longer cable to the b2b is usually needed, and the D+ line can be run alongside it - the original D+ wire is usually able to be found in the area of the engine battery.

In the case of classic Mercedes, with the double battery box next to the drivers seat access is easier - the b2b can be easily connected to the engine battery and from there to wherever the new lithium battery is located. An easy way to obtain a D+ signal in the Mercedes battery box is to open the trunking that leads across the bottom edge of the door (if fitted) and locate the 12v power feed to the fridge, and carefully split the cable and tap into the fridge feed. The 12v fridge feed is relay switched by the D+ in the fuse box, so is in itself a D+ proxy - this method just makes it easier. Please note this is a tip for certain types of install, not a mandatory requirement. Most modern b2b chargers, such as Victron orion, have voltage sensing and don't need D+. 

The other factor that needs thinking about when considering alternator charging, is just how much you want. There is a trend with lithium batteries to “go large” and fit batteries of 200ah or more. So you have to think about just how much driving time you will need the next day, in addition to whatever you get from solar, to replace the power you have recently used. With most classics having around 60 to 80 amp alternators, and a sensible limit of around 50% of this, then that means no more than about 30 to 40 amps per hour of driving will be available. This is usually enough for most owners, but if you want more, then the only alternative is to fit a bigger alternator. But before you do, consider this ...

Solar keeps working all the time, and many vans with lithium also have solar, and those that don't should have! And modern solar panels are big, and cheap. In 2025 you can get a 425w black panel that is 1700 x 1100mm and will fit perfectly on the front of most Hymer roofs. And if you have such a panel, or even 2 or 300 watts of other panels further back - these panels don't stop working while you are driving. On a sunny day in summer I have regularly seen 70a of charge while driving - 40a from the alternator and another 30 from the solar! So factor in your solar ad your driving habits (winter/summer) before you go to the expense and hassle of a bigger alternator. In my experience a bigger alternator is rarely justified if thought out properly. It depends on your lifestyle and intended power use.

EHU (230v) charging

Pre 95 vans have a separate 230v charger. Most owners have replaced the original separate charger, so what charger you now have dictates what mods if any are needed. The original factory charger, if you still have it, will work with lithium, but will not be optimum. But if you do need to use it, you can.

But most owners fitting lithium will opt for a new charger. The Victron Blue Smart IP22 30a is ideal. 

When fitting a new more powerful charger for lithium, the next question will be whether to use the original Hymer cabling or not. This is particularly relevant on vans that have the charger in the back and the battery in the front, it is tempting to use the old cable because running a new one is a big job.

You can use the old cable - it will handle 30a, but you have to take into account that the original charger was only 10a, and the 12v cable from the old charger to the front of the van goes to the fuse box, and then via a 16a fuse, and then to the battery. Not only will the fuse blow if you fit a 30a charger in the back, but the length of cable, with old and possibly corroded connections along the way, will lead to an unacceptable voltage drop - ie won't charge the battery optimally.

So what do you do in this situation? And remember we are only talking about vans with the charger in the back and battery in the front. You have 2 options. The first is to move the charger to the front and connect directly to the battery. This means you will have to supply the charger with a new 230v supply. How easy this is depends on your van layout and your DIY skills. The second is to use the original cable, but disconnect it from the fuse box and run it directly to the battery. This takes out the problem of the original fuse and the old connections in the fuse box, and it also shortens the cable run considerably. I have performed this mod on many vans and it works well. But there are different tricks to identify the cable and do this, depending on the van. Anybody wanting more info on this can contact me direct.

On vans with the charger already in the front, things are much simpler, but you still have the problem of the original charger cable going via the fuse box. So in these cases it is usually best to simply run a new cable, and leave the old charger cable unused and safely insulated and tucked away. But it can be used if you are willing to put a bit of extra work in - it can be disconnected from the fuse box and re-routed directly to the battery. Again I have hints on this if needed.

Solar charging

This is probably the easiest of all. Solar power is free from the sun, and is the only charge source that is available “off grid”, so is ideal for wild camping. Solar panels and MPPT charging are now so cheap, and powerful, that if you are fitting lithium batteries it makes sense to fit as much solar power as your roof will easily take. On most vans this will be between 200 and 400w. This means that on a summers day, you can reasonably expect to replace between 80 amp hours (200w panel) and 160 amp hours (400w panel) on a sunny summer day, based on 6 hours of sunshine. But in winter the figures can be as low as 20% of this because the sun is much lower and the days shorter in winter. This is no problem if you don’t use your van in winter, but for full timers it is a major factor in your off grid capability. Full timers who want to be off grid as much as possible need to fit as much solar as they can. This goes for any battery system, not just lithium. A common misconception is that a 200w solar panel is a constant - it is not! In December it is a 40w panel! And that is assuming that the sun shines in December.

Technically, modern solar MPPT controllers usually have a lithium profile, but you can still use those that do not. If the controller has user definable settings, just set everything to 14.2v. If this isn’t possible, then just leave it set to the lead acid profile, it won’t do any harm.

So those are the main points to consider about charging lithium.

The result of all or some of this work is that the new lithium battery will have some or all charge sources (EHU, engine, solar) connected directly to it. But power still needs to get from the battery to the habitation circuits - so the original Hymer cables are left in place - black positive and brown negative. These feed direct to the fuse box, and then to the van.

If you are fitting high power devices such as an inverter, then this should be connected directly to the battery via suitable fusing. More complex installations may use busbars or connection posts.

Types of lithium battery - what to buy.

The next subject to discuss is "what type of lithium battery"? All lithium batteries for the leisure vehicle industry are lithium iron phosphate - known as lifepo4. These are the safest type.

Prices are now so low that lithium batteries are hardly more expensive than lead acid. The choice nowadays is do you opt for "dumb" lithium or "smart" lithium. Smart means the battery has a bluetooth BMS that talks to an app or display. In the motorhome context, the choice is a no brainer - always buy smart. Having an app in your hand which tells you exactly what is going on in real time (see screen grab below) is the killer app of modern battery technology. It is daft to fit a dumb lithium battery to a motorhome. But for those that have fitted dumb lithium, all is not lost, because you can make a dumb system smart by adding a Victron Smart Shunt (or cheaper chinese version) which will then offer you the same valuable info as a smart system. But note that if you shop around, you can now buy smart lithium 12v batteries for roughly the same price as dumb ones - Epever and Fogstar from Bimble are 2 solid recommendations. Note that when browsing 12v lithium leisure batteries online, if it doesn't specifically say "Bluetooth BMS", then it will be dumb. There is a huge amount of old stock flying around, and also a lot of cheap chinese lithium leisure batteries. Chinese batteries from either AliExpress, or UK/EU suppliers and importers are everywhere now. There is great debate about quality. There are Youtubers who cut open cheap chinese batteries and dissect them and analyse at length. I have even done it myself. My conclusion - and I am by no means the last word on this - it is just based on experience, is that there is nothing wrong with cheap no name chinese lifepo4 batteries - as long as they are smart bluetooth, and you have to be careful with the ad small print. There are lots of dumb batteries around - used in golf carts and fishing boats (trolling motors) and many other applications that don't need smart - but for a motorhome owner, smart is essential, because having all that info in your hand is a game changer for van life - it puts you in control - no more unwelcome surprises of the lights going dim half way through the weekend.

To my mind, the choice comes down to whether you want UK support and warranty - if you do, you have Bimble, Fogstar and several others, and you will pay a bit extra. Renogy and Ecoworthy also deserve a mention - their support is not quite as good, but it does exist if you push. But the unknown suppliers on AliExpress, you will get little or no support.

But little or no support isn't as bad as it sounds because these batteries are pretty reliable. The reason for this is that unlike lead acid batteries, which are easy to abuse, and fail as a result, it is actually very difficult to damage a lithium battery because they have a computer brain - the BMS - protecting it. If you abuse it, it just shuts down. 

So basically cheap lithium smart batteries are fine for motorhome use. By all means pay a bit extra, but if budget is tight, you are usually OK.

But there is one area where it pays to go big on quality and that is high power. Big lithium at a reasonable price means that things that were only dreamed about in the past are now possible - I am talking about high power - microwaves, airfryers, hair dryers, coffee machines, toasters, even kettles, these can all be powered with a big lithium battery through an inverter. Putting aside that the installation has to be solid and well installed, and that any power you use for these luxuries has to be replaced somehow .... but just concentrating on the battery .... if you power a 1500w device that will be drawing over 100amps from the battery. That is a lot of power, so now quality does become a factor. Big power needs lots of copper, and generates heat, so build quality is important. So if you are planning big power then probably best to buy a battery at the top end of the scale. Reputable suppliers will publish detailed specs, and 200amp continuous discharge is easy to find.

But having said all that, as long as you have done things right in terms of cable spec, there is nothing wrong with a 20 minute airfryer session from a cheaper battery. Even the no name suppliers don't want warranty returns and bad online reviews.

many owners have no idea about power  - they are used to just plugging anything in at home and it works - for all intents and purposes power at home is limitless. But it is completely different in a van. It takes a LOT of 12v power to convert to 230v.

So here is a list of common appliances to guide you.

Low power, no problem under 50 watts- phones, pads, any small battery appliance -shavers tec.

Low-ish power - 50 to 200w - TVs, laptops, ebike chargers.

Medium power - 200w to 800w - small coffee machines, small kitchen appliances such as whisks.

High power - 800w to 1500w. Small airfryers, small kettles, microwaves, big coffee machines, hairdryers. Basically anything that generates heat - check the label for the watts, divide by 12, that is how many amps at 12v you need.

Air conditioning is a special case and a separate conversation.

Finally .... do you really need it?

There is also one more big thing to think about - and that is - “do you really need it”??!!

There is nothing special about lithium - it is exactly the same volts and amps as any other battery. So you have to really identify the need.

The three main advantages of lithium are power density, long life and better information. Power density means you can get more power out of the same size - so a rough example would be if you only have space for 1 traditional 100ah leisure battery, and you don't want or can't relocate the battery, then you would get roughly double the power from the same space.

Long life is exactly as it sounds - they last longer. In regular use a standard leisure battery is only good for a few hundred cycles of charge and discharge which in average use means they need replacing every 2, 3 or 4 years. Lithium batts are good for thousands of cycles. The jury is still out because it's new technology but it is generally accepted that a decent lithium battery setup should last decades. So if you use your van a lot and intend to carry on doing so for years, then the financial deal alone can justify it.

But the third reason, better information, is for me, the best reason by far - better monitoring and information. The latest lithium batts come with bluetooth monitoring, and a phone app that displays accurate battery information. This tells you exactly how much power is left in the battery, how much charge you are getting (from all sources), and how much power you are using. Basically it is an accurate battery fuel gauge. After a few days of use you soon get a feel for your battery system, and can plan your activities accordingly. This is particularly useful for those who like to be off-grid as much as possible, or for those who may need to run devices that potentially use a lot of power, such as coffee machines, ebike chargers etc. You soon get to know exactly how much power these devices use, and how much charge you need to replace that power used - from solar etc. It is incredibly useful and gives you complete control, with no nasty surprises. With a standard lead acid battery - it is quite difficult (but not impossible) to get this sort of accurate information. Having used these Bluetooth lithium battery systems for over a year now, for me, it is by far the best reason to do the upgrade.

But none of that is to say that lead acid batteries are old hat or obsolete - they are not. A lead acid battery with a good solar system can easily provide enough power for normal summer holiday use. One of the best reasons to upgrade is when your existing system simply isn't giving you the power you need.

But now that lithium is only slightly more expensive than lead acid, it should be considered. And for the hobbyist and technical enthusiast, a lithium upgrade is a fascinating project.

Lifepo4 charge discharge characteristics

Epever 100ah smart bluetooth Lifepo4 battery

A typical BMS phone app, showing exactly what is being used, being received and how much is left.