Powering a laptop (or an ebike charger) in a van - all the issues in detail

Powering your laptop from a 12V campervan battery EDIT - EVERYTHING HERE ALSO APPLIES TO EBIKE CHARGERS - THERE IS AN EXTRA SECTION ON EBIKE CHARGERS AT THE END.

One of the most common questions I get asked online is about the best way to run a laptop in a motorhome or campervan, or any live-in vehicle. As with all things electrical, the answers can get a bit technical, but in this article I will cover the technicalities, but also try and express the main points in simple language, so please persevere!

Not everybody needs to run a laptop in a van. Many folk are happy to get away from computers in their van. If you only want Facebook, the web and email, then your phone or a tablet is often enough. For for some folk - especially those who work while on the move, powering a laptop in a van is a necessity.

The subject always seems to come down to two basic questions - Do you use the original laptop 220V charger plugged into an inverter? Or do you convert 12V DC from the battery to the DC voltage required by the laptop directly, either by obtaining a 12V charger, or by doing it yourself using a voltage converter.

Laptops and power in general

Laptops come in many shapes and sizes and their power requirements vary, but generally speaking small laptops consume about 50w and large laptops up to about 140w, and the average is about 80w. The way to find out is to look on the charger that came with your laptop. The charger is also often called a PSU (Power Supply Unit), or simply the "brick". It is usually a black plastic box with one wire that goes to a 220V plug and another wire that plugs into the laptop. The charger will always have a label on it that looks something like this.

It looks complicated, but most of it is just regulatory and legal stuff - there are only two things you are interested in and they are input and output. In simple terms - it takes one type of electricity in, and converts it to another type suitable for the laptop.

You may well ask, why can't they just make laptops that you can plug straight into the mains? The simple answer is that even with all this modern technology, there just isn't enough room inside a thin laptop to cram in the required circuits. Also, the safety regulations mean that a laptop that was powered directly from 220V would have to be engineered and insulated to a higher and more expensive standard. So all laptops have a brick - that's the way it is.

An Example

So looking at the this label, you can soon see that this Dell laptop takes an input of 100 - 240v AC, and gives an output of 19.5v DC. Hold on a minute! Where does it say AC and DC? Well it does and it doesn't. If you look closely at where it says 19.5v you will see a symbol that looks like a longer equals sign where the upper line is solid and the lower line is broken. This is the standard symbol for DC. For AC, the international symbol is usually a wavy line like this ~ and you can see this on the label, just after 240v.

An ebike charger will have a similar label

Modern power supplies are now almost always "universal" this means that they work anywhere in the world - whether it is America on 110V AC, Europe on 220V AC, or the UK on 240V AC. You can see this because it says 100 - 240v AC, which means that it will work on any voltage between these 2 numbers. If the input figure on your charger says just a single number like 220v only, then you know that it won't work in the USA.

On the output side, it says 19.5v 6.5A. 6.5A means 6.5 amps. And in the middle of the top row it says in big letters 130W. This means 130 watts. Not all charger labels display the number of watts, but most do. If you multiply 19.5 by 6.5 you get 126.75, which is rounded up to 130. This is yet another example of the universal laws of electrickery - watts = volts x amps. So if your charger doesn't display the watts, and you want to know it, then you just multiply the volts and amps together. I know that most people's eyes glaze over at this point, but if you are going to want to use your laptop in your van, and want to set it up correctly, you need to know the numbers in order to do it right.

One final point about charger specifications - the numbers quoted are maximums and have a built in safety margin. In real life the laptop will use a bit less than the max figures quoted. It will use more power when in use and on charge, and less power when in use with the battery fully charged, but for the purposes of choosing inverters or working out power requirements in your van, you should always use the maximum figure, so that the same margin of safety will be used in your van.

So now we understand the charger label, and in the case of this Dell, we need 130W.

So let's talk about inverters

For those that don't know what an inverter is, it's a box of tricks that takes 12V DC from your battery and converts it to 220V AC as you find at home. You can then plug in and use the charger that was supplied with your laptop. An inverter is specified in a similar way to a charger, but the other way round. It has an input voltage and an output voltage. A typical inverter takes 12V DC in, and outputs 220V, and the power of the inverter is specified in watts.

So in very simple terms, you connect your inverter to the 12V supply of your van, plug your laptop charger into the socket on the inverter and away you go.

Unfortunately it is not quite as simple as that if you want to avoid many of the problems that can arise if you don't understand the basic principles of power. Many inverters are supplied with wiring to connect to your 12V supply. Usually this will be a twin core wire, coloured red and black. One end is connected to the inverter, and the other end will either be bare, or with spade connectors, or with a cigar plug. It is the cigar plug that you have to be wary of.

But first - the dreaded cigar plug

Everybody knows what the cigar plug looks like - they have been around for years - they are a throwback to the days when all cars had a cigar lighter, and plugging into the cigar lighter socket was the only way to easily get a 12V supply from your vehicle. But the truth is that they are unsuitable for the job, and are responsible for the majority of problems that people report online.

Cigar plugs are inefficient. The majority of them are made very cheaply. If you look closely at one, you will see that it has a point, and two bits of metal on the side. When you push the plug into the socket, the point makes contact with the centre of the socket, and the side bits rub onto the sides of the socket. In technical terms, the point is the 12V positive, and the sides are the 12V negative. What you have to remember is that the cigar socket was originally designed for the cigar lighter, not to supply 12V to external equipment. The point only makes a very small contact with the centre of the socket, and the whole thing is completely open to the outside and is susceptible to dirt getting in. The bottom line is that it is an inefficient thing and unsuitable for powering expensive equipment. Many of you will have experienced the situation where you have something plugged into a cigar socket, and it doesn't work, so you wiggle the plug until it comes back to life. This is bad!

When mobile phones came out in the 90s, and we needed to charge them on the move, all that was available was a cigar plug adapter, so that was what we used. Then smartphones came out that are charged by USB, so we all bought USB cigar adapters. And generally, they always worked OK, and the occasional wiggle was OK and caused no problems. But it is a different story when you come to inverters and laptops - the reason being that phones don't need much power, but inverters and laptops do.

An average USB phone charger only needs about 10 watts. An average laptop, as we have already discovered, needs about 10 times more. The cigar socket, for all it's inefficiency and old fashioned design, has no problem delivering 10 watts, but it is a different matter trying to deliver  over 100 watts.

In pure technical terms the international standard for a 12V cigar socket is 10 amps, which is 120W (12 x 10). So you can see immediately that if you try and power a 130w device with it, it will be working at its maximum capacity. But you should also remember that it was only designed to power the cigar lighter - that hot thing that popped out back in the days when smoking was acceptable! But the cigar lighter would only take about 30 seconds to heat up and pop out. This is important - there is a world of difference between supplying 120W for under a minute, and supplying 120W constantly for many hours. The cigar socket simply isn't robust enough to supply its full capacity, constantly. And this is what gives rise to the problems. After many hours of use, things get hot and brittle, fuses can blow, and generally they can become unreliable and a pain in the bum.

So it's OK for phones, but no good for laptops. I have friends in the motorhome trade and they all say the same thing - cigar sockets are completely unsuitable for powering inverters and laptops and are a huge source of problems. In fact it is fair to say that their use should be avoided completely.

Motorhome and campervan owners have an additional problem on top of all this, and this is that in most vans, the cigar socket in the dash is supplied from the vehicle starter battery, and not the leisure battery, so taking a lot of power from the the cigar socket can run down the vehicle battery.

So now you know the technical reasons why never to use a cigar socket to power an inverter/laptop setup. Phones are OK, because they are low power, but even a couple of phones can run down a vehicle battery in a few days.

Back to inverters

So what is the correct solution? The inverter must be connected directly to the battery, through a suitably sized and fused cable. A good inverter will be supplied with a suitable cable, and the fuse may be in the cable, or installed in the inverter itself. If the supplied cable isn't long enough, then it is OK to extend the cable using a wire of equal or thicker dimensions. If the ideal cable length for your particular installation is longer than about 2m, then you should use an even thicker cable, because longer cables at 12V DC can suffer from voltage drop. This is the reason that most inverter cables are quite short, and also the reason that most van inverters are located quite close to the battery.

So having connected your inverter properly, you are good to go, and you should never suffer from any of the problems just described.

You now have the power - or do you?

The next thing you need to know is just how long your battery will last. A laptop is probably going to be one of the most powerful devices running off 12V in your van. It may sound strange, but it is true. Van lighting takes very little power, neither do phones and tablets. A 12V TV is a medium power device, usually about 30W or so, but a decent sized laptop, like the Dell we are using as an example, can take around 100W while charging, and around 50W while in use, plugged in, but fully charged. Anything that uses more than 20 or 30W of power, has the potential to run down your battery quite quickly.

The way to work it out is this. You divide the watts by the supply voltage - which is 12V. Yes I know that the charger label says 19.5V, but the actual supply voltage is the voltage of your battery - which is 12V. So taking 100W as the average, divide 100 by 12 and you get 8.3. That is 8.3 amps. And when your laptop has finished charging its internal battery, then the power will drop to about 50W while you are using it, so that is about 4 amps. The exact numbers will vary a little bit depending on your laptop, but these figures are a good average.

You will also know how long your laptop takes to get fully charged from flat - this is usually about 2 hours, sometimes more, sometimes less. So you know that to fully charge your laptop will take about 2 hours at 12 amps, which is 24 amps in total.

Now you need to know the capacity of your battery. The commonest van battery is a 100ah leisure battery. The AH stands for amp hours. A 100ah battery should supply 1 amp for 100 hours, or 10 amps for ten hours - it's a simple calculation. So in our laptop case, 24 amps represents roughly 25% of the battery capacity. But normal 12V leisure batteries are generally only capable of delivering roughly 50% of their capacity before the voltage drops to below 12V. So the real world figure is more like 50%. So charging your laptop from flat could easily use 50% of a 100ah leisure battery. So you can see that a laptop can be a hungry beast, a beast capable of eating a battery! For this reason, people who need to have their laptop available at all times should pay close attention to power management. They usually need bigger batteries, solar panels and monitoring devices so they can plan their activities accordingly.

And here is the point about laptops in a van - it doesn't really matter whether you use an inverter or some other method, like a DC converter - people argue for hours online about whether inverters are efficient or not, and how it is daft to convert 12V to 220V and then back to 19v again. The truth is that all methods are better than 90% efficient, and that 10% isn't really relevant in the grand scheme of things. 10% doesn't make much difference - it might mean you can get an extra 10 minutes of use on top of the 2 hours. Purists (and trolls!) love to argue the point to show how clever they are, but based on my experience, people just want things to work reliably.

Use the original charger for peace of mind

This brings me onto another issue about using an inverter, and that is that using an inverter enables you to use the original charger that was supplied with your laptop. Even though a purist would say that it's inefficient to invert 12V to 220V to plug in a charger that then converts 220V to 19v, I would say that this is still the best method because a modern laptop charger doesn't just convert voltage - most modern chargers are "smart" chargers - they communicate with the laptop and are designed specifically to give the laptop just what it needs. There is also the matter of warranty. Try explaining to the Apple Shop why your £2000 Macbook is broken because you used a different, non Apple, charger. It's just not worth the risk.

This is the main reason I generally advise normal non technical people to use an inverter and the original charger - not because it is "technically" a few percent more or less efficient, but because it is convenient and safer for the laptop.

Apple MacBooks

Talking about Apple … A quick note about Apple MacBooks. They have white chargers that have no labels - however the specs are online. MacBook chargers are called "Magsafe Adaptors" and are between 60W and 90W. The electronics inside the adaptor are tightly integrated with the MacBook itself so it is generally impossible to use any other adaptor. Apple used to offer a 12V car charger for their laptops - but they don't any more - they disappeared several years ago. The story went that they were experiencing too many warranty claims. So generally it is easiest to use an inverter for a MacBook. And safer in terms of warranty and the wellbeing of the MacBook.

More on inverters

There are a few more points about inverters that i would like to touch on.

You will see references and online discussions about "pure sine" inverters, "modified sine" inverters and "quasi sine" inverters. For years now there has been much discussion about which is best. It gets technical, but for all intents and purposes it doesn't matter. It used to be that the "pure sine" inverters were much more expensive than the other type, but this is no longer the case. Technology has moved on and prices have come down, and in purely laptop terms, a laptop charger is happy with either type. Despite all the online discussions, I have yet to see anybody tell a story about having a major problem with either type. There are a couple of items of equipment that occasionally give problems with the wrong type of inverter, but these are rarely found in a van. "Pure sine" inverters are usually the most popular these days because they are about the same price. Some cynics say that many cheap inverters are advertised as "pure sine", but are the other two types. I have never come across this myself, but you need an oscilloscope to know for sure, and these are expensive.

The next discussion point is what inverter to buy. Ebay and Amazon are chock full of a bewildering array of inverters of all shapes and sizes and at prices from £25 upwards. Again, lots of folk have opinions and love to make statements on Facebook on what is best. A favourite opinion is that cheap "chinese" inverters are "crap", and you get what you pay for. My answer to this is that while there is always a possibility that any electronic product can break, it is bad business to sell a faulty or unreliable product - Ebay and Amazon function on the principle of feedback, and nobody survives very long if half the stuff they sell comes back for refund. The reality is that chinese stuff isn't all that bad, and all you have to do is look at a range of prices, check that the supplier has decent feedback, and choose the middle way - not the cheapest, not the most expensive.

However it is worth bearing in mind that there are a couple of manufacturers who are famous for the quality of their products and the most famous of these is Victron. Victron are a Dutch company who have a vast array of quality products, and are generally regarded as the best available. There is another company called Sterling, who are UK based and have a similar reputation, although as with most things, opinions always differ. Victron make a wide range of inverters, and their small inverters are priced similarly to the bigger models of other manufacturers. When asked, my standard answer is usually, I would rather have a small Victron than a big chinese one.

Don't over-specify!

A common mistake that many people make when choosing an inverter is over specifying. You will see ads that offer 1000 watt inverters, or more, and it is easy to think that more is better. However this isn't the case. You should size an inverter for the purpose you need it for. We are talking laptops in this discussion, and we have agreed that an average laptop needs about 130W. So why buy a 1000w model when you only need a tenth of that? Big chinese inverters are less efficient than small quality ones, and even though we have already discussed that efficiency isn't everything, there is another aspect to efficiency that is quite important in a van, especially if you are a "normal" owner with a single leisure battery. This is about "no load" or "standby" power. This is the amount of battery power an inverter uses while switched on, but doing nothing. A big 1000w inverter can use 1 amp of your battery every hour it is switched on. This may not seem like a lot, but that 24 amps if left on all day and night. So a good rule to obey when using an inverter is - switch it off when not in use. I have seen many a flat battery because of this - people think that if nothing is plugged into an inverter, then it is using no power. This isn't true.

So generally speaking, if the main purpose of owning an inverter is to power your 130W laptop, then a 200w or 300w inverter is more than enough, and smaller high quality inverters use less power on standby than bigger cheaper ones. Victron inverters take this one step further by having "auto sensing" - they take hardly any power at all until they sense the need. This is a useful feature to have if you forget to switch it off as it won't drain your battery. Other manufacturers also offer auto sensing.

Of course there are many other reasons why you might need a big inverter, but as we are talking laptops - small is better. If your budget allows, a small Victron is a good choice, I have installed many, and can testify to this fact. But I have also installed many cheap chinese inverters and know many more folk who have, and they can also give good service. The main thing to remember is not to over specify - very few van owners have a valid reason to own a 1000w inverter.

At the time of writing in early 2019 I have started to notice a new type of chinese inverter on the market that not only supplies around 400w reasonably efficiently, it also has built in USB sockets to charge phones and tablets, and it also has a digital display so you can keep an eye on your battery voltage - and all for £40.

So having discussed inverters, and why I think they are the best method, for the sake of completeness let's discuss the other methods.

12v laptop chargers

The first of these is to use a dedicated laptop charger that takes 12V as its input and outputs the required voltage to the laptop (usually, but not always. 19v). This cuts out the need for an inverter. Even though I think an inverter is the best bet in general terms, there is no real technical argument against it. The only problem I have with it is that, as stated above, you are replacing the warrantied charger with a third party charger that is not warrantied by the laptop manufacturer. This means that if you do get a problem, and need warranty, you will have no choice but to hide the fact that you were using a third party charger. However, it is unlikely that a third party charger will actually damage a laptop - not impossible, but unlikely. Any problem will more likely be with the charger itself ie it stops working, leaving you stranded with no laptop. Ebay and Amazon have plenty of 12V chargers for most laptops, but at the end of the day you are trusting an unknown supplier. I have seen plenty of folk online who have suffered this way.

At the end of the day I think it is swings and roundabouts. The cost of an extra third party 12V charger will be about £50 - less for a cheap one, more for a quality one. The same money will buy you an inverter, allowing you to use the original charger, plus have the added convenience of being able to use the inverter for other uses.

But in terms of efficiency - there is very little in it, as discussed above.

DC to DC converters - the DIY way

There is another method of powering a laptop from 12V, and it is the cheapest of them all. I include it here for completeness, but with the caveat that it is really only for folk that have basic DIY skills and a basic understanding of 12V electrics. Do not attempt this unless you know what you are doing.

It is based on the fact that, as discussed above, most laptops run on 19v DC, and most vans/vehicles run on 12V DC, so why not just convert 12V to 19v and plug in the laptop? No reason at all, especially if the laptop is out of warranty and you don't mind a bit of DIY.

On Ebay and Amazon you will find devices that cost around £10. They are called DC to DC converters, also known as "buck converters" - please don't ask why! They comprise a circuit board with a few transistors and chips and have a set of terminals to attach a 12V supply wire, and another set to attach the wire to supply the laptop. This wire must have the same plug on it that fits the laptop socket - they are available online, but you have to make sure it is the right plug. You may have to solder the plug to the wire. Another method is to find an old broken charger and cut the wire and plug off it and use that - like I said it's a DIY job, there is no off the shelf product that saves all this work. In effect you are home brewing your own 12V charger.

The main thing to remember if going down this route is that you must make sure you buy the right converter - it must be capable of delivering a constant output voltage for a varying input voltage. The reason for this is that a fully charged battery gives about 13v, which reduces as the battery discharges down to 12V and below. But a laptop must have a rock solid and constant voltage. The other thing you have to look out for is to make sure that the unit you choose has the correct power and cooling.

Like I said - it's a home brew DIY project that needs basic skill, but there is no reason for it not to work if done properly. The problem is that guys who have the skill to do this love to go online and advise others to do the same, saying it's easy and that you are daft to go to the expense of an inverter. It is! As long as you know what you are doing. But not everybody knows what they are doing - they just want to plug it in and it works.

And finally ...

So those are the 3 basic methods of powering a laptop in a van. Here are some bullet points in conclusion.

• An inverter is the easiest method in terms of ease of use for non technical people
• 
  
• An inverter allows you to use the original charger
• 
  
• An inverter is a useful thing to have around anyway
• 
  
• Cigar sockets to supply power to a laptop are a no no
• 
  
• Third party 12V laptop chargers are OK, but don't offer any real benefit over an inverter
• 
  
• You can homebrew your own 12V laptop charger with basic DIY and electrical skills
• 
  
• Laptops take more power at 12V than most people realise

Any questions please leave a comment or contact me directly.

EDIT - NOTES FOR EBIKE CHARGERS

Everything above applies equally to ebike chargers, except that ebike chargers are generally more powerful - generally they are about 180w, so they will draw about (180 / 12) 15amps, roughly 50% more than a decent laptop. And if the battery is empty, it needs about 3 to 4 hours. This means that if you have a fully charged 100ah leisure battery, it will be pretty much all used up, although generally it is not as bad because most riders won't use a full battery on a ride.

So it makes sense to charge your ebike batts while you are driving or on hookup. If you do need to charge while off grid, then the only other charge source available is solar. So you need enough solar both to charge the ebike battery, and have enough left over to put enough charge in your LB for your normal use.

In a UK summer, a 500w solar system with 200ah of battery should cope with it, but you have to monitor it closely - a few cloudy days would be problematic. Again, as suggested above, the best tool for this is a decent battery monitor, so you know what you have left and can plan accordingly.

How do I get online in my van?

Warning! This is a long article, so put the kettle on. But if you persevere you should get a full understanding of mobile internet, with minimum jargon.
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Nothing seems to generate more confusion and questions than getting internet in a vehicle.

So here at last is what I hope is the definite answer, in simple language.

There are two methods to get online while out and about - WiFi hotspots, or through the mobile networks - Orange Vodafone etc.

But first we have to deal with terminology - the use of the word "WiFi". Many people now use the word WiFi to mean the internet in general, and most of the time we know what they mean. "Is there any Wifi?" generally means "is there any internet?".

But the true definition is that WiFi is just a delivery system - it is not actually the internet. But because WiFi is everywhere it's easy to see why it has become a generic word. Just about every home computer, gaming console and hand held device nowadays connects to the internet via WiFi. 

Access via public WiFi

In order for WiFi to work, it has to be broadcast by a router, and that router must be connected to the internet. Most of us are familiar with this because at home, we have a broadband connection that delivers internet down the phone line to the router, and the router broadcasts WiFi so that all our devices can connect to the internet. We also know that if you go too far away from the router, the signal becomes weak and eventually fails.

As well as your home WiFi, there is also public WiFi at bars, restaurants and airports etc. This works in exactly the same way as at home in that somewhere in the business building there is a router that is connected to the internet (usually via broadband over a phone line) and it broadcasts a WiFi signal for customers to log on to - sometimes with a password which is provided by the business, sometimes no password is needed. McDonalds is quite famous for offering free WiFi in its restaurants, and this often extends into the car park which sometimes enables you to sit in your vehicle and use their WiFi.

There are thousands and thousands of these WiFi "hotspots" as they are known, all over the country, all over the EU, all over the world. They are very popular. The advantages of WiFi hotspots is that they are usually free and are not limited to how much data you can use. However the disadvantage is that they can get very busy and are often quite slow as a result. It is similar to the situation at home with a big family - if everybody is online at the same time, the speed will often be slower, because a fixed line speed is being shared by several users - it's the same with public WiFi. Many people will be familiar with the internet being really slow or unusable when using a busy public hotspot.

So using Wifi to access public hotspots is one way of getting online, and if you are in a vehicle, and your vehicle is in range of the hotspot then you can also get online from inside your vehicle this way. However you can often be frustrated because you may not be able to get close enough to get a reliable signal. It is the same on campsites that offer WiFi - if you are too far away from the router then you either get a slow patchy connection compared with somebody who is closer - or maybe no signal at all.

The reason for this is that routers only broadcast the WiFi signals with so much power, and this power is limited by the regulations. It is designed as a short range service, so that many routers can broadcast on the same frequencies without interfering with each other. Generally speaking, the power is designed to be just enough to cover the average house. But as many will know, this isn't always the case. Radio waves don't like travelling through brick walls or metal, so you often get a situation where one room has a weak or no signal, or that the signal will just cover outside the house, but won't extend to the bottom of the garden. Every situation is different. The other reason why this is so is that although the router usually has a decent sized aerial on it, the receiving devices - phones and tablets etc, usually have much smaller built in aerials - aerials that you can't even see because they are built in to the device - usually round the edge of the screen.

So it follows from this that if you had a bigger aerial, then you could receive WiFi further away from the router. But it is impossible to fit a bigger aerial to a phone or tablet, so the tech world came up with the concept of the WiFi extender. This is a device that looks similar to a router, almost identical in fact. It has one or two aerials on it - nice big ones! This device, also called a repeater, receives the original signal from the router and then re-transmits it through its bigger aerial, with the result that devices now have a stronger signal to connect to. So for example, if your original router was in the living room at the front of your house, but could not be received down on the patio at the back of the garden, installing an extender/repeater in the back bedroom window would probably be enough to extend the signal down the garden. As long as the extender/repeater is within range of the main router it can the rebroadcast the WiFi signal over a wider area and everybody is happy. The extender/repeaters can even be daisy chained together so that a large building can be covered quite easily. 

The same thing applies to a vehicle. WiFi reception in a vehicle is a particular problem because most vehicles have metal bodies, and metal is a terrible material for radio waves to travel through. In fact the only way radio signals can get inside a metal vehicle is through the windows. This is why things often seem to work better near windows. Many people in vehicles, in particular motorhomes and campervans, can benefit from using a WiFi extender/repeater in their van. In this situation the extender would use it's bigger aerial to pull in the WiFi signal from, say, a restaurant or bar, and then rebroadcast it inside the van so that all the van occupants can use it. You still have the same problems as you would have if you were sat inside the bar or restaurant - if it's slow and busy in the restaurant it will be no better in the van.

You can improve things even better in terms of distance by using an even bigger aerial than the one supplied with the repeater/extender by buying a roof mounted aerial and connecting it to the box by coax cable. This is known as an external aerial. The golden rule of all radio aerials is that they need to be as high as possible and as big as possible. Radio waves travel in straight lines, so being up in the air is a huge advantage. A bigger aerial like the ones that attach to the back of a router or extender is at least 10 times more efficient than the little one built into a phone or tablet - and an aerial on the roof will perform better still.

So that is my description of the first method of getting online through public WiFi hotspots. The basic rules are that you have to find one, know the password, and be close enough to it for it to work. Plus you have no control over how fast or reliable it is - you have to make do with what you are given. If you are too far away, you can use an extender/repeater, but this will only increase the distance at which you can access, it won't improve the quality.

Access via the mobile phone network

The second method for accessing the internet from a vehicle or while you are out and about is through the mobile networks. As well as enabling you to make calls and send SMS messages, modern smartphones can also access the internet as well. Today this is known as 3G, 4G and soon 5G will be along as well. As you would expect 5G is faster than 4G is faster than 3G. Before 3G there was 2G also known as GPRS, but this is now all but obsolete. Most people with either a contract or pay as you go - PAYG - will have a data allowance included. This is measured in gigabytes - Gb, and you will usually have a set monthly allowance of Gbs of data as part of your deal.

The main thing to remember about mobile data is that unlike home broadband which is usually unlimited data, with mobile data you have a set allowance and once you have used it, you either have to wait until your monthly allowance resets, or you have to pay for more. There are a also few mobile contracts that allow unlimited data, but not many. 

So if you have a smartphone like an Iphone or Android, you can access the internet via 3G or 4G on your phone very easily. You also know that your smartphone can access the internet via WiFi as well. The way you can tell the difference is by looking at the little symbols on the top of your phone display - it will either say 3G or 4G if you are connected to the mobile network, or it will display the little fan shaped icon if you are connected to a WiFi hotspot - the one at your home for example. Most people have their smartphones set so that they access the internet through WiFi if it is available, or if not the phone switches to 3G or 4G automatically.

Modern smartphones also have what is known as a personal hotspot feature. This allows the phone to receive internet over 3G and 4G and then rebroadcasts it via WiFi, using the tiny WiFi aerial built into the phone. Smartphones have 2 aerials - one for receiving and transmitting 3G and 4G, and another for receiving and transmitting Wifi. In effect, modern smartphones have a built-in router. 

So in a vehicle for example, if your phone has a decent 3G or 4G signal, you can use it to re-broadcast the internet it gets from 3G and 4G via WiFi so that your other devices can access the internet through your phone's hotspot service. These devices can be anything that has Wifi - tablets, laptops, smart TVs etc. and the internet data they consume will come out of the same data allowance you have on your phone. It is important to remember what is going on here - your devices connect to your phone using WiFi, and your phone connects to the internet over 3G/4G.

However you have the same constraints with the mobile networks that you have with public WiFi hotspots - if you are too far away from the nearest mobile cell tower - ie no signal - then you will have no access. So it follows from this that if you have a bigger aerial then you have a bigger chance of getting a signal - especially if you are out and about in rural areas. Modern mobile coverage is pretty good, but as we all know sometimes you get "no service".

So how do you get a bigger aerial? You achieve this by using an additional device that has the facility to use a much bigger aerial. This is called a mobile router. A mobile router is a small box that is basically a mobile phone, but can't make calls - it has no keyboard or speaker or microphone. But it takes a sim card that only handles 3G and 4G data - usually called a "data only sim". All the mobile networks offer data only sims, either on contract or PAYG. A mobile router takes a data only sim card, connects to 3G or 4G and then rebroadcasts it as a WiFi hotspot - just the same as using a personal hotspot on your phone, but because it has a bigger aerial it will still have a signal in a weak area when your phone has none. A mobile router will usually have a bigger aerial sticking out of the back of it, quite often more than one aerial - as many as three, depending on the model. In fact it looks very similar to a typical WiFi extender/repeater that I described before, so it is easy to confuse the two, but they are quite different, and this is what causes people confusion. A Wifi extender/repeater connects to an existing WiFi hotspot (say McDonalds) and repeats it. A mobile router connects to the mobile 3G 4G networks from Orange, Vodafone O2 etc and then repeats it locally as Wifi. So both devices offer WiFi to your devices, but they get at the internet by different methods. To put it another way, one is WiFi to WiFi, the other is 3G/4G to WiFi.

MiFi

So what is a MiFi? Some clever guy a few years ago came up with this term, but has caused endless confusion! A MiFi is a small mobile router like I have just described. It takes a data only sim, and rebroadcasts the internet locally via Wifi. The reason they are popular is because they are small and cheap and battery operated. They allow you to set up a personal hotspot just like a smartphone, but without having to tie up the phone itself. If you use a smartphone as a personal hotspot then quite often this can be inconvenient - if the phone rings it can slow down the data connection, or indeed if the owner of the phone wants to go somewhere and take the phone with them, then the hotspot goes with them, and anybody left behind no longer has internet. So MiFis were introduced to get round this and are popular with travellers. But MiFis still suffer from the same constraints as smartphones - they only have a tiny built in aerial which is nowhere near as good as a full sized aerial. However a small number of MiFis do have tiny aerial sockets to which you can connect external aerials and as a result these particular models, mainly from Huawei, are very popular for use in campervans and motorhomes.

So a MiFi is exactly the same as a mobile router - it is just another name for the same thing. However although they do the same thing, there are subtle differences. A MiFi is a small device that is usually battery powered and is charged up by USB whereas a mobile router is generally a bigger device that has bigger aerials and proper aerial sockets to which you can easily connect external aerials. A full sized mobile router will also be usually directly powered by 12v and have no battery. This is an advantage because MiFi devices that have an internal battery when plugged permanently into a USB power source are effectively "permanently on charge" and in hot weather they can get quite hot and the batteries can expand. So the best technical solution for a motorhome is generally to use a 12v mobile router that is designed for permanent connection to 12v.

A mobile router with either a big aerial plugged into the back of it and sited near a window, or with a roof mounted aerial connected to it via coax cable, will pull in a mobile signal at least 10 times better than a phone or MiFi aerial.

So which is best?

So which should you use - public Wifi or 3G/4G? It's horses for courses. If you only want to check email and browse the news and keep up with Facebook, and not being able to access the internet occasionally doesn't bother you, then public Wifi should do you OK. But if you need to have a fast reliable connection available all the time, for work perhaps, then 3G/4G is the way to go and if you tend to travel a lot to out of the way places where mobile phone signals may well be weak then a mobile router with a big aerial will give you the maximum chance of getting online. The only time you will not be online is if you are in a location that has no mobile signal, no matter how big your aerial is. I have been travelling in a van for a very long time and nowadays I find it a very rare occurrence that I have no mobile signal with an external aerial, but it does occasionally happen.

Personally, I very rarely use public WiFi - for me it is just too unreliable, but I am online constantly and demand a lot from my connection. However I do possess an WiFi extender/repeater for occasional use. I have found campsite WiFi to be either expensive or slow, but occasionally I find that in the off season there are not many vans on site and the WiFi is fast - and if I am a bit too far away from the reception office where the router is, then that's when I get out my extender. It is also useful when I am parked outside friend's houses and their home WiFi isn't quite strong enough to penetrate inside the van. But mainly I am on 3G/4G home and abroad. I have a professional quality mobile router and a MIMO dome aerial on the van roof. This provides data to 2 phones, 2 tablets, the satnav, the smart TV and the laptop. I have a UK contract data sim which roams, and in addition while abroad I buy local PAYG data sims as needed. On average I probably pay about £50 a month for data. It sounds a lot but I regard it as an essential utility like electricity and water. I get electricity for free in the van, so it balances out.

Which data sim?

This is a complicated subject and the mobile networks are always coming up with new offers. The basic choice is contract or PAYG. You tend to get more Gb per pound on contract, but PAYG is of course better for occasional use. Then there is the matter of roaming abroad, which is a complex subject in itself, especially with Brexit looming at the time of writing.

Generally speaking, in 2019, and having travelled in many countries, the price of data has come down a lot in the last few years. In most countries now you can buy data for around 50p per Gb or less. How much data you need is entirely up to you. The biggest consumer of data is video - Netflix, Iplayer etc. Most people who have unlimited broadband at home and are used to watching video on demand as much as they want can get a shock when they try to do the same thing on the road via the mobile networks. So you have to shop around. As a general rule of thumb 1Gb will give you about 2 hours of online (not HD) TV. At the time of writing the Three network offers a "Go Binge" option which allows you unlimited video from Netflix or Iplayer and a few others, and is popular. They are also still offering, at the time of writing, an unlimited data package, they are the only UK network to do so to my knowledge. (Go Binge is limited to 10Gb when roaming)

The best approach is to buy a few PAYG sims and see how you go. Once you know what your average usage is you can then start to shop around for a good deal. Right now in March 2019 I am reading that Vodafone have a new deal offering 200Gb a month for £20 on a 12 month contract, and that it will work while roaming. I will believe it when I see it (the roaming!), but it is a sign of the way the market is going. When 5G comes out it is going to be fantastic for watching video - I can see a situation where mobile satellite TV systems costing several thousand pounds become obsolete when you can get HD video over 5G very cheaply. We can but dream.

What is a VPN?

It gets a bit complicated, but in simple terms a VPN is a service that prevents people from knowing which country you are in. Many people know that BBC Iplayer won't work when you are roaming abroad. To get round this you can use a VPN service. It costs a few pounds a month. However if you are using a UK sim, roaming in the EU, then you may find that Iplayer works without a VPN, so it pays to check first.

I hope this helps - please ask questions in the comments below and if you like my blog, please subscribe.

Battery management for camper vans - No excuse not to!

Battery management is about knowing how much capacity your battery has left in real time - similar to how a fuel gauge works on a fuel tank. It is very useful and informative to know just how much charge is flowing into and out of your battery, and how much power is left in the battery. 

To do this you need a gadget that measures all the current going into and out of a battery and uses these measurements to calculate the state of charge of the battery. Such a gadget is called a battery management system. Another name is a battery monitor.

A battery manager consists of 2 main components - the sensor, and the display. The sensor measures the current and the display gives you the information.

Technical alert! Don't worry if you don't understand this paragraph! The sensor device that enables these measurements and calculations to be made is called a shunt. In simple terms, a shunt is a lump of copper through which all current in and out of the battery must pass. The shunt is actually a carefully designed piece of copper that has a precise resistance which can be measured as a tiny voltage - and these tiny voltage are directly proportional to the current. By sampling these voltages many times a second, a simple computer on a chip can calculate and store these values, and if it already knows the capacity of the battery, then it can calculate how much power is left in the battery. Not only that, it can calculate how much longer the battery will last under the current load, and in a charge situation, how much longer the battery will take to get fully charged for a given amount of charge.

For the non technical, all you need to know is that a shunt measures the power in and out of your battery.

In terms of our beloved Classic Hymers, they actually do include a shunt, which is buried inside the back of the fuse box, but this was long before cheap chip computers were available, so all that was possible back then is to use the shunt to drive a meter - the famous "Strom" meter on the panel, Strom being german for power. If the battery is receiving charge, the the meter would deflect into the green, if the battery is giving power, then it goes the other way into the red. The Strom meter is also calibrated in amps - plus or minus 25 or 30, but because of the technology of the time and the tolerances of the shunt, this is only a rough indication.

But nowadays you can do so much better!

So how do you fit a battery management system (BM) to a Classic? It is a lot easier than you would think.

As already mentioned a BM consists of 2 main components - the shunt, and the display. The shunt goes on or near the battery, and the display goes wherever is convenient.

Although the original Hymer shunt is fitted in the positive side of the battery system, and buried inside the fusebox, the modern convention is to fit a shunt on the negative side of the battery, and the easiest way to do that is to simply fit it directly to the negative post of the battery. You just take all the connections that were on the neg of the battery, attach them to one end of the shunt, and then attach the other end of the shunt to the battery neg. It's that easy. Some shunt designs are now so clever that they attach directly, and can be fitted in a couple of minutes. This means that it is easy to fit a shunt to a Classic Hymer.

The other component is a display, and this is also much easier to install than in the past because it doesn't need any additional wiring between it and the sensor because it communicates to the sensor wirelessly - via radio. All it needs is a 12v supply from the nearest convenient point. 

The display contains a small computer chip which does all the calculations - all you have to do is to program it with the total capacity of your battery in amp hours (ah). It needs a few charge cycles to settle down and make its calculations, then after that it is quite accurate.

Here are 2 typical displays (there are many others) - you get an accurate display of system voltage in this case 12.29v. Below that is the number of amps - in this case the battery is discharging 2amps. If it was being charged, the number would be preceded by a + sign. To the left there is a simple battery meter which is showing less than half full - the exact figure is shown below 33%. There are other numbers that represent amp hours and watt hours, as well as a clock and battery temperature gauge.

Recent developments have seen a whole new raft of products come on to the market. One of these is Bluetooth. You can now use your phone or tablet to display the information, and the data is sent from a shunt that has Bluetooth - also known, strangely enough, as a Bluetooth shunt! These are very popular, but you should think about it carefully before you buy one. The main thing is that in order to see the state of the battery, you have to get out your phone or tablet and launch the app - not always convenient. So you might prefer to have a permanent display, so all you have to do is glance at it, in which case you get a BM that has a dedicated display. However some folk are having the best of both worlds by dedicating an old phone, or cheap tablet, to be a permanent van display. This can also be used for many other things - limited only by your imagination.

Once installed and working, you then have access to a whole new world of information about your battery system. There is quite a lot of information on the display, but the three most important values are voltage, amps and a percentage bar graph that tells you the state of your battery - similar to a fuel gauge. 

Here are some examples.

Every time you switch something on in the van, the display changes and tells you exactly how much power that item is using. You can then, if necessary, modify your behaviour to suit how much power you have left. For example, if you switch on your TV or computer, you will be able to see just how many hours of use you will be able to get from the power available. 

If you have solar panels then you can tell how much solar power is going into your battery, less any power that you are using. At a glance you can tell how long it will take for the battery to reach 100%. This is particularly useful when there is not much sunshine about. Many solar controllers have power displays already, but they only tell you how much power your panels are generating - they don't tell you the overall state of charge of your battery - ie how full it is.

While driving, the display will tell you how much charge is going into the battery from the van engine. You can then work out how much driving you need to do before your battery is fully charged.

When on hookup, you can tell how much power your mains charger is delivering.

Power management in a van is important, especially if you spend a lot of time in the van, and more especially if you use quite a lot of power - using a laptop or watching TV are usually the main consumers of battery power. It is very useful to be able to tell at a glance how much power you have left, and also what you need to do in order to get power back into the battery - either from solar, engine or hookup. It is particularly useful with solar, because after a few weeks or months of use, you will get a feeling for just how much power you can expect from solar in any given weather situation. Solar gives you much less power in winter and it is very useful to know exactly how much you can expect from solar, and modify your plans accordingly.

Another great advantage of a battery monitor is that it enables you to avoid abusing your battery, which can shorten its life. Most people know that a lead acid battery should not be discharged below 12v, which is roughly half of its rated capacity. This means in theory that a 100ah battery should give you 50ah of usable power before it drops below 12v. In practice this is almost impossible know without a battery monitor. With an accurate battery monitor you can see the voltage and capacity of your battery on the display, and you can tell exactly how much power you have left. This enables you to make decisions about reducing your power usage to get the best out of what you have left, and ultimately, to switch everything off and go to bed. 

Once you get used to the information at your disposal you can then plan your activity accordingly. If you need to work on your computer for a few hours, or watch a movie tonight, you can tell at a glance whether you have enough power to do so. If it has been a cloudy weekend, wildcamping, and you want to stay put, then you will know how much battery you have left, and ration out the power - ie read a book instead of watch TV.

It may sound a bit daft, but 12v battery systems are not simple mechanical devices that are either on or off, with a fixed capacity. They have character! Battery systems perform differently according to conditions - how much charge, how fast, the temperature ... and they also change as they age. Only with a battery monitor can you get intimate with your battery!

So who would benefit most from a battery monitor? The simple answer is - anybody to who battery power is or has been an issue. If you have ever run out of power unexpectedly or wondered how much power you have left, then you will benefit. The only people who don't need a battery monitor are those who always have enough power for their activities, and never run out. Many people don't run TVs or laptops and only need power for lighting and reading. If you always use EHU then you don't - if you always wildcamp - you do!

Other options - more technical stuff that you can skip!

There is another way of measuring current that doesn't use a copper shunt. This involves using a sensor known as a "Hall effect" sensor, named after the man who discovered it. This works by sensing the magnetic field generated by DC current flowing in a wire. It is the same effect as used in those test multimeters you can buy known as "DC Clamp meters". A hall effect sensor works by having the negative cable passing through it.

These have only become available recently - mostly from China. I have used one, and found it to be very good, but slightly more temperamental than a copper shunt. They also have to be located carefully, as they are easily damaged by knocks etc - we want things to last for years not months.

Another recent development is that fixed displays can now be fed from the shunt by radio - which means no wiring. This makes installation easier. You may ask what is the difference between this and a Bluetooth shunt? Good question - the answer is not much - one used a dedicated display but with no wires - the other is a phone app.

A typical Hall sensor - the negative wire goes through the hole

So what should you buy?

Here is a list of the battery management systems that I know about

Victron - Victron now do a SmartShunt - a snazzy bluetooth shunt that drives their phone app - it is reasonably priced. 

Victron SmartShunt and the App

If you want a dedicated display, then Victron do several - they are called the BMV battery monitors, and there are several in the range.

Victron BMV - you get the full kit with Victron

NASA - NASA is a manufacturer of yacht instruments - not space rockets - and they have produced a very reliable and quality shunt/display BM for years - I have used one myself for 5 years and it is still going strong. They produce the BM1 and the BM1 Compact - the compact has a smaller display.

Nasa BM1, BM1 Compact, and the NASA shunt

NASA have also just brought out a Bluetooth shunt and app.

The new NASA Bluetooth unit

BMPRO - BMPRO are an Australian outfit that produce quality gear - and their latest product is called the Batterycheck. This is a very simple design that blots directly to the battery, and displays on a phone app. They also have some other really fab products, and I believe they are just starting to get UK distribution.

Lovely product ... just bolt one side to the battery, and everything else to the other side! Google "BMPRO" for their other stuff.

China - China has a bewildering array of products available. The reason for this is that BMs are not just for motorhomes. They are used in electric bikes and electric vehicles and in off grid power setups - the principles are all the same - counting amps and calculating capacities. These are available on Ebay, Amazon and Ali Express. I can't possibly review them all. Some use shunts, some use Hall effect sensors. Most cost between $20 and $50 - that's US dollars. Anything cheaper will be no good. The problem is the specifications - the english is always bad. You want something that has a shunt, is for measuring DC and looks like these pictures here. If in doubt get in touch with me. Not all these products are crap - if money is tight, then no reason why not. At these prices you can just play! Most are unbranded, but Juntek seems to have a decent reputation.

Here is a selection of Chinese products - these are the main ones - my personal favourite, which I have used, is the bottom one, often labelled Juntek - available in several versions - including copper shunt, Hall effect sensor, hard wired, non wired (radio).

Finally - a note about Lithium. Lithium batteries are not like normal lead acid batteries. A lithium battery ALWAYS has an electronic battery management system, also called a BM or a BMS. Do not get these confused with what I am talking about here. This article is about BM systems for lead acid batteries.

If you want more information on this subject message me, or contact me on "Classic Hymers Technical" Facebook group. I also offer a fitting service.https://www.facebook.com/groups/297054424534823/

Oil all over the road and the engine? Don't panic until you have checked this.

Oil all over the road and the engine

It's easy to get that sinking feeling when the oil light comes on and when you look under the van there is oil everywhere.

That is exactly what happened yesterday to my brother in his S670. It's not a common thing - in all my years with the van and answering questions online and reading forums I have come across it very rarely, if at all. So when it happens you can be forgiven for fearing the worst. After all there are very few places where the oil actually has access to the outside world - and most of them horrible and expensive - head gaskets, blown engine etc ...

But as it turns out, there is one place where the oil can escape in panic inducing quantities - but is easy to fix and only costs a tenner plus labour, and you can find it and do it yourself. I am talking about the oil pressure switch. This is a small circular component with a wire attached that screws into a hole in the engine block. It is located under the inside engine cover at the lower left of the block as you face the front - see photos.

As you can see the oil gets everywhere so it can be difficult to see where it is coming from at first. In my brother's case the van was running fine and did not cough and splutter or make strange noises and no smoke from the exhaust - just the oil light came on, so he stopped immediately. After a bit of discussion we decided to wipe away as much of the oil as possible and then start the engine again for a few seconds to see if we could spot the leak. The dipstick was reading just under full, so we knew there was plenty of oil in the sump. taking off the inside cover we were greeted by what you can see in the photo - not pretty! - so we cleaned and looked here first.

Neither of us are expert mechanics, just amateurs, and neither of us actually knew the details of just how the oil pressure light is operated. I made a call to my mechanic friend Wayne in N Wales and sent him the pics on Whatsapp. Straight away he said that it would most likely to be the oil pressure switch located as in the photos. After just a few seconds of the engine running we could see it oozing out, and when we gave it a few more revs the light flickered a bit and went out and then back on again. Wayne then said as long as there was oil in the sump and showing on the dipstick then it was safe to drive a short distance. Sam was only a couple of miles from base so he limped back, ordered a new switch and fitted it the next day. It's an easy DIY job, all you need is a spanner and brother Sam had to replace the wire connector because it was seized on - been there since new over 20 odd years ago so we'll forgive it. The switch has a plastic body and this had eventually cracked with age.

Of course it goes without saying that if you are pouring out smoke and the engine sounds like a spin dryer with a brick in it then it is unlikely to be the pressure switch. You should never ever drive with the oil light on unless you are absolutely sure you know the reason, as in this case.

So if a similar thing ever happens to you, don't panic until you have checked that it's not the oil pressure switch. Panic over!

If ordering online search for "Mercedes T1 oil pressure switch", or "OM602 oil pressure switch". It was used in lots of other vehicles and there are many different oem part numbers.

Location of switch - and source of oil leak

Oil cleaned away and leak exposed after running engine for a short while

Switch taken out 

New switch ready for installation

Cleaning the Truma blown air heating fan makes a difference! And general background info on Truma heaters

On most 5 and 6 series classic Hymers, heating is provided by a Truma heater - see photo. It is usually either a Truma 3002, or a 5002. (The Hymer S700 has a 3002 in the back, near the bed and an additional Truma 2800 heater under the table in the front - this article is not about the 2800, which is a completely different beast).

The difference between the 3002 and the 5002 is that the 5002 is higher power and used in the bigger vans - in particular the S660 and S670.

These heaters work both by radiating heat from the front of the heater and by drawing air through the front of the heater by a fan mounted on the back of the heater which then pumps the heated air through a system of pipes to outlets around the van. The heater is switched on by the knob on top of the heater, and the fan is operated by a small control box marked "Truma Vent" - the location of this control varies according to the van. This control has an on off switch - which only controls the fan, and another switch which selects low or high speed. The on/off switch is three position - centre is off, up is automatic, and down is manual. There is a large rotary knob which in automatic mode controls the temperature by varying the fan speed according to the temperature, and in manual mode simply controls the speed of the fan. If the heater is switched off, then the fan simply circulates cold air, which is useful for keeping the air in the van moving around, but in practice is rarely used - it's easier to open windows. The automatic function quite often degrades with age owing to deterioration of the temperature sensor in the control box. You have to experiment to see what works best for you.

The fan does not take much electricity - about half an amp. A full battery should run the fan non-stop for at least 3 days.

(I have seen forum posts from owners asking if it ok to run the heating system all night - the answer is yes - it is designed this way! You should experiment with your system in different outside temperatures and you will soon find the settings which work best for you)

Like all things in the van, things need cleaning and servicing occasionally and the heating system is no different. The most common problem is a gradual reduction in efficiency which is caused by the blades of the fan becoming caked with years of dust and grime. It is important to remember that the air is drawn from inside the van, not outside, so all the cooking smells and particles contribute to this over the years. If you have bought an old van you have no way of knowing just how furred up your fan is - it will always work, but the system will only work at maximum efficiency if the fan is clean and shifting air at its designed capacity. 

It is also important to keep an eye on the air distribution pipes (ducts) because after many years of use and vibration, they can occasionally get damaged or disconnected at one of the many connections around the van. It pays to know where the pipes run in your particular van, and keep an eye on them. A disconnected or damaged pipe can ruin the efficiency of the whole system.

A particular characteristic of this system is that in many old Hymers when the fan is running, it can "sing" - a high pitched gentle whine. This isn't a design feature - when the fan left the factory the fan would not be singing, all you would hear is the gentle rushing of air, depending on the speed of the fan. The singing sound develops over many years and is either due to a build up of dirt on the fan, which affects the balance, or the gradual wear of the fan motor bearings. 

If the fan is noisy - ie singing - then the first thing to do is to clean it. It probably has over 20 years of dust and dirt in it. The fan is mounted on an aluminium hood (also called a cowl) that is mounted on the back of the fire. The fan is mounted on the cowl, and the pipes are connected to the fan. When switched on, the fan draws cold air through the front of the fire, over the heated body, and then pushes the hot air into the pipes and around the van.

You can use the heater in "radiator only" mode - ie with the fan switched off. This is often useful for background heating the van because it uses no battery power at all in this mode. However I have seen some vans where the fan is always forced to be on to prevent over heating - S670 for example.

To get at the fan you have to get access behind the fire. Access depends on the layout of your van. Then you should be able to see the fan. Disconnect the wires and pipes from the fan - make a note or take a photo of where everything goes - it is very simple, just 3 or 4 screws. Then remove the fan - it is attached by just 3 screws. The fan may have a plastic cover which is easily removed. You will then be able to see inside the fan and you will see that the wheel is caked with a lot of dirt and dust. Clean everything carefully - compressed air helps. Then re-assemble. The only tools you need are screwdrivers and common sense.

This does not guarantee that the singing noise will stop - every fan is different - but it should reduce the noise, and it will certainly improve the airflow. What used to be just a gentle trickle of warm air from the vents might now be a proper flow - I have been amazed at the improvement in some of the heaters I have worked on. 

It is a characteristic of Truma fans that after many years some of them sing - some more badly than others! If you do not like the sound of your fan after cleaning, then the only option is to change it. New fans are still around if you look hard enough, and I have read online that some owners have replaced the motor only.

While researching this article I found this web page which is very useful for manuals and schematics. There is also a load of info on Trumas if you Google - particularly on German forums - use Google translate.

https://dealernew.truma.com/_anweisungen/Truma_Katalog/2%20gb/s_heizungen_gb/trumatic_s_ues_gb.html

Other Truma problems ...

Ignition. I covered ignition problems in this blog - 

https://hymers700.blogspot.com/2017/01/truma-3002-fire-wont-light.html

I have also been asked can you run the fire when driving. The answer is no because airflow down the chimney will blow out the fire. However many owners forget to switch off the fire and drive away ... the fire will blow out and the safety interlock will kick in. At the end of your journey when the van is quiet somebody will say "what's that ticking noise?" - it is the ignition circuit. Many owners have a pre-drive checklist and switching off the fire should be on it!

Most other problems are not DIY jobs because they mean disconnecting the gas supply, the flue and removing the heater body. Jobs that needs this include replacing the ignition HT lead - covered in the other article, or replacing the burner assembly. The control valve at the bottom of the long rod from the control knob can also be replaced. These jobs should not be attempted unless you are fully confident and are absolutely comfortable working with gas and flues and can be fully confident that you have reconnected gas and tested for leaks. Gas engineers are certified for a reason - gas can kill you, as can carbon monoxide from an improperly connected flue.

However I must stress that the main subject of this article, cleaning the fan, has nothing to do with gas and can be done by most DIY persons. Or if you are not confident, a dealer (who knows his stuff!) should take a couple of hours to clean a fan, depending on how easy it is to get at the back of the fire. You could ask for this to be done when you are having other work done.

Front - you don't usually have to take off the front to service the fan

Behind the Truma. Every van is different - this one is easy access! You can see the aluminium hood and the fan is inside the cream plastic cover which is attached to the hood with 3 screws. Disconnect the pipes from the fan, and also the wires.

Also in this photo you can see the hot air pipes (also called ducts) leading off into the van - trace yours and check for damage and disconnections. If there are any then the whole system will not be at the right pressure and not efficient. You should have even heat coming out of all the round vents - if you have one or more vents noticeably cooler than the others, then that is a sure sign of a problem.

These are the blades you must clean. I have seen them much worse than this - so dirty that hardly any air flows at all!

These photos were taken from a German forum and I acknowledge this.

There are more photos and info on this German forum

https://www.wohnmobilforum.de/w-t64969.html