Inverters in the motorhome ... for beginners!

An inverter is 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 a 220v item - like you do at home. An inverter is specified as having an input voltage and an output voltage. A typical inverter takes 12V DC in, and outputs 220V AC, 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 device (ie laptop charger) into the socket on the inverter and away you go.

Unfortunately it is not quite as simple as that and 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. In a motorhome, you should never plug an inverter into a cigar socket, unless the only thing you are going to plug in, is a phone or tablet charger. NOT a laptop or TV. If you want to use an inverter for these higher power items, then you must connect the inverter directly to the battery with proper connections.

A good inverter will be supplied with a suitable cable, and a fuse may be in the cable, or installed in the inverter itself. You should attach these cables directly to the battery terminals, using spade or ring connectors - if you don't know how to do this properly, then get help. 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.

Every van is different, but in a simple installation, you should install the inverter in a convenient place, close enough to the battery, and where you can also get at it to plug in your 220v stuff. If you can't find a convenient place, then you can install the inverter out of the way, and plug an extension lead into it. Remember that you need to be able to get at the inverter to switch it off when not in use - most inverters consume power when doing nothing. If you are wondering if you can have an inverter feeding all the same sockets that are in your van already, that are live when you are hooked up, then yes you can, but that needs a more complex installation using an autoswitching inverter, which is too complicated for this simple guide - contact me if you want to discuss this. You should also be aware that most inverters have fans - which can be quite noisy, so bear this in mind when you locate it.

So now you have a basic simple working inverter setup - there are a few more points about inverters that i would like to touch on.

One of the hardest things to understand about inverters is that you can't just plug anything into them. In a house, you never think about it, whether it's a phone charger, a laptop, a TV, a hairdryer, a microwave or a fan heater - you just plug them in and off they go no problem. This is because in a house, you are being fed by the national grid. which for all intents and purposes is unlimited and lasts forever. There is a maximum though - most plugs are rated at 13amps, which in watts is equivalent to 3000w, or 3kw. This is a lot of power - enough for a 3 bar electric fire on full.

But in a motorhome, the power is not unlimited, it is supplied by your 12v leisure battery, and compared with the national grid, this battery is tiny. So unless you understand the sums, it is very easy to innocently overload a leisure battery, by asking it to deliver too many watts - far more than it was designed for.

This is the point at which most people switch off because they don't like sums and calculations, especially where electricity is concerned. So I have found that it easier to break it down into simple rules. In a basic motorhome installation, with 1 or 2 normal leisure batteries, and normal wiring, then you should never try to power anything through an inverter that generates heat - this means heaters, kettles, toasters, coffee machines, microwaves, hairdryers, cookers, ovens, slow cookers - this list is not exhaustive, but you get the drift.

What you can use is as follows - phone chargers, tablet chargers, anything USB, radios, CD players, small TVs - up to about 23" and laptops. Basically anything low power. Special cases - that are possible but need careful consideration are - e-bike chargers and curling tongs - these are medium power items that are on the borderline, so you need to understand how to use them in more detail.

Now here is the technical reason, for those interested. As the volts go down, the amps go up, but the watts remain constant. Lots of amps need thicker copper wire. To calculate the amps you need at 12v, you simply divide the watts (of the appliance(s)) by 12.

So - at 12v - which is the voltage of your van battery, to supply 100w of power, you need 8 amps at 12v - you divide the watts by the voltage. The wiring of your van, and the capacity of your battery to deliver amps is basically around 20 amps - any more than that and things start to get hot and stressed. As a rule of thumb, a normal motorhome battery and wiring system is capable of delivering about 10 amps of 12v - in classic Hymer vans, the fuses are 16a. The battery is capable of a bit more, but you shouldn't ask for it!

At the other end of the scale if you look at an average coffee machine, the label will say maybe 1200w - that is an easy calculation - 1200 divided by 12v = 100amps. So if you bought and connected a 1500w inverter to your battery, and switched on the machine, it would ask for 100amps. Normal leisure batteries are simply not capable of delivering that amount of power, and the result would be a ruined battery. But in your house - it's no problem - why? because the voltage is 220v, not 12v - so 1200 divided by 220 = 5.5a, which is under half of the maximum of 13a available from a house plug, so no problem, and it only needs a thin wire So that is why the simple rule states that you should only try and power low power items from a basic inverter installation in a van with a normal battery setup. A normal van setup isn't capable of delivering much more than around 15amps at 12v. Now of course you can have whatever you like - if you want a coffee machine and a toaster, powered by your battery, then you can - but it will cost - you have to install big batteries, thick cabling and proper metering and monitoring - this can easily run into thousands of pounds.

But if all you want is to charge your devices and maybe a TV and laptop, then you can, with a simple inverter setup that can easily cost around £100 all in.

But remember - there is no free power in a van - whatever charge you take out of your battery, whether it's your lights, fans, TVs, gadgets, through your inverter or not - that charge has to be replaced somehow - either by the engine while driving, solar, or on hookup. So although this article is specifically about inverters, remember that all aspects of a mobile 12v system have to be taken as a functioning whole.

So what inverter should you buy?

Pure sine or modified sine or quasi sine? These are terms that you will see in inverter ads. My simple advice, is don't bother about it - it's a technical discussion and there is lots of rubbish talked. Basically you can use any inverter that is sold either in shops or online. Most inverters nowadays are pure sine, and that's all you need to know.

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. There is also another brand called Epever, who are famous for their solar controllers, and they also make good inverters at decent money.

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, and big is most definitely not better.

However you also need to understand what the numbers actually mean. The words to look for are "peak" "power" and "constant". The Chinese are very fond of big numbers - so they will put numbers like "1500w" and "1000w" and even more, but when you read the small print, it will say "peak power". This means that the inverter is only capable of supplying that power for a few seconds. This isn't as dishonest as it sounds, because many appliances, especially those with electric motors, do indeed need a lot of power for just a few seconds when you switch them on, so it's not all rubbish - it's just that they tend to overemphasise the "peak" and under emphasise the "constant". Constant is what you want - around 500w constant is what you want for a normal low power installation as detailed above. Quality manufacturers like Victron, on the other hand, always quote "constant". So a 300w inverter from Victron will have a peak value of over three times that - they just don't shout about it!

Then there is the matter of efficiency. Most inverters nowadays are over 90% efficient so effcieincy losses are not as important as they used to be. 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.

At the time of writing in 2020 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. It is hard to argue with these for the money.

If you need more information or have questions, then ask on the Classic Hymers Technical facebook group. https://www.facebook.com/groups/297054424534823/

A typical Chinese 400w inverter showing plug sockets, 4 usb sockets and voltage displays. All for under £40

How an inverter should be wired to a battery - there will of course be other wires on your battery, but this is the basic idea - no cigar plugs or crocodile clips please!

An Epever 500w inverter - also has a USB socket.

Another no name Chinese inverter - this one is rated 150w, which is at least honest! It also looks well built.

Ring - another good middle of the road make

These are posh Victron inverters - the new ones have Bluetooth so you can see all the numbers on your phone in an app. Well worth the extra money.

Battery management for Classic Campervans........................... 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.

Typical 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. 

Replacing the plywood dashboard in classic Hymers

One of the commonest repair jobs on classic Hymers is to replace the dashboard. This is a piece of plywood that sits between the van binnacle and the windscreen - ie the big flat shelf at the bottom of the screen, with two round air vents in it. Usually it is carpeted.

The reason it often needs replacing is that it gets loose and starts to move around. It serves a structural purpose in that it forms a part of the overall integrity of the front of the van, it plays an important role in binding the front fibreglass shell of the van to the front of the Fiat/Merc chassis. If you do see this movement, it is important to fix it, otherwise you end up with the whole of the front end of the van wobbling around which can cause all sorts of nastiness if left unfixed.

Although it looks like a big job - almost taking the front of the van to pieces, it is actually quite an easy job for the average DIY enthusiast - all you need are basic tools and a jigsaw, and the plywood is readily available from builders merchants. Or you may decide to have the job done professionally - there is a recommendation at the end of this article.

So how do you know if yours needs doing? It's quite easy - if it needs doing, you will visibly see it moving, especially on rough roads and cornering. If you look at the front of the board, under the screen, you will see the board moving out of sync with the screen. Another way of testing is to get two of you to rock the van hard from side to side, while watching in the same place. If it is loose, it is pretty obvious.

This old dash was rotten all along the front edge

So the first thing to know is how does it all fit together? It's not complicated. It is usually a single sheet of plywood, cut to shape. There are some differences between Merc and Fiat family vans, and also of different ages, and bear in mind that we are talking pre 95 vans here, which is the general (but quite loose) definition of a classic. Merc vans are usually all the same - a single sheet of plywood and 2 circular fresh air vents which are connected to intakes at the bottom of the front spoiler. On Mercs there is no connection to the heating system - the Merc demisting vents are in their original position just in front of instrument binnacle, and as such are quite far away from the windscreen, and consequently don't perform very well demisting such a large screen. On Fiat family vans, certain years and models have demisting vents mounted on, or integrated with, the front of the dashboard, and these are fed with hot air from the heater. This often takes the form of a plastic duct mounted on the front edge of the dash. Even more rarely you may find a multilayered dashboard that incorporates ducts - this is quite rare and may be the work of a previous owner. So as you disassemble it is most important, particularly on Fiat family vans, to note how everything is connected and mounted, so you can replicate it exactly when you reassemble the new dash. 

Below the screen there is a lip of fibreglass about 30mm deep, and the front edge of the board is screwed to this. The rear of the board is screwed into the metal front edge of the Fiat or Merc dash/binnacle - basically where the original panel van windscreen would have fitted if it had been a van and not a coach-built motorhome. At each of the two ends there is a metal angle bracket that is screwed to the walls to form a lip for the board ends - see photos. Sometimes you will find rubber strip or foam, depending on the van, and also if the dash has been replaced by a previous owner.

Dash removed on a Merc - you can see the fibreglass lip below the screen

On the underside of the original board, Hymer installed foam insulation for soundproofing. Unfortunately after several decades most of this has turned to dust and has fallen away. This is another reason why many owners replace the dashboard - it is also a great opportunity to really upgrade the soundproofing, giving you a quieter van. I can tell you from experience that a new dashboard, using thicker ply, modern soundproofing, good carpet on top, plus an upgrade to the cab carpet with underlay .... all this can totally transform the sound levels in the front of the van.

Mounted in the dashboard there are usually two circular air vents. These are fed by ducts that are mounted in the lower part of the front spoiler and provide fresh air while driving. Don't be tempted to do away with these - used properly they are very useful - in all weathers. They have vane controls on them, and they rotate - they can be configured to provide anything from a trickle to a roar or air, and in any direction. To remove them the tops come off, and you will see tiny screws that are holding them into the holes, screwed into the edge of the plywood. The ducts are removed by unscrewing the small screws on the underside, and then pulling off. It's a really simple mechanism and can be cleaned and serviced at the same time.

Some van dashboards have had holes for speakers cut in them. Personally I don't think this is a good idea - especially for large speakers. Big holes can reduce the structural integrity of the board, and cab also let in more than their fair share of engine noise. This is less of a problem for small speakers of course, but small speakers are not really any good. The other thing you should think about with regard to speakers is that from an acoustic point of view, the front passenger space of a Hymer is a really crap sound stage. If your speakers are facing upwards, the sound is reflected off the underside of the bed, and it really doesn't sound very good. I found this out quite by accident when I took out the front bed in my S700 during a major upgrade, and was astonished at how much better the stereo sounded, both on the move and static. My advice with speakers, is to mount them in pods if you can, firing forward, or at least up 45 degrees. Also consider not having speakers at all - in these modern times of really high quality high power reasonably priced bluetooth speakers, there is much less need to install traditional car stereo speakers in the dash. Nowadays I use a pair of Ultimate Ears Megaboom 3 Bluetooth speakers, and they are fantastic, and can be placed anywhere, inside or out - and no wires. This is just background info - the choice is yours - but a dashboard replacement is also an opportunity for upgrades and new ideas.

So you have detected movement, and have decided to do the job, then it's time to proceed! The first job is to expose the board. Remove the carpet and any other layers, but before you remove any vents or speakers, or anything underneath - inspect the board. In many instances you will find the board in decent condition, and all that has happened is that the screws have come loose. In which case, if you are really happy that the board is otherwise solid and strong and not damp along the front edge, then you can leave it in place and refix it with new screws - or nuts and bolts - as discussed later. Even if you find that your board is reusable you might still want to take it out entirely to replace insulation. But in most cases, you will probably find that the front edge of the board has gone rotten or damp, and is loose all along the front edge. This is usually caused by a lifetime of use and vibration, coupled with condensation running down the inside of the screen and soaking the board. So it's time for a new board.

Once you decide that it has to come out - do your best to remove it carefully - this is important because it is your template for cutting the new board, so don't break it up - get it out in one piece!

You will also have to remove the two gadget trays either side of the dash - the square ones made from soft plastic. These are fixed by 4 screws - the screws are under the plastic dome covers - if they are still there. On the drivers side, there is often a ventilation duct - this has to be pulled out also. Look for a small fixing screw.

What board do you buy? Purists will say - marine grade plywood - and there has been some online discussion about this. It's up to you, but personally I, and others, don't think it's worth the extra for marine ply - as used on yachts - what your local builders merchant sells as "plywood" should be more than enough. I have also seen a grade sold known WPB, or waterproof board. This is what I used. It's about £30 a sheet if I remember correctly (about 2017). What is worthwhile upgrading is the thickness. The original was around 9mm and most owners replace with 11 or 12mm. This is pretty much the standard procedure nowadays - you get a much stronger and quieter job that should also last longer. The only slight problem with using thicker board is that it might stand up just a mm or so higher on the front lip, and catch the underside of the window-screen rubber, preventing a snug fit. So offer it up and check, and if necessary toy have to chamfer the front edge of the board - ie file a bit off the corner. Using a power tool makes this a job of a few minutes, but even with a hand file it only takes 10 minutes. Don't be tempted to use any sort of MDF, chipboard or blockboard - it must be some form of laminated plywood.

Next job is to cut the board with a jigsaw. Lay the old board on the new, and trace round with a pencil or felt tip. I can't teach you in writing on how to actually do this - but it's just common DIY skill - if you are unsure, get help from a friend. If you are really unsure, you can just take the original dash to a local wood shop and ask them to make you one - it won't cost a fortune.

A new dash being prepared for a customer by Peter Curry at North Cotswold Motorhome Services

So now you have a new dash board, cut and shaped and chamfered - don't forget the ventilation duct holes! Now is the time to prepare it. At this stage you should glue your chosen insulation to the underside. What to use is another much discussed topic (check out the Facebook Group for specific recommendations). Insulation varies from cheap and cheerful, right up to weapons grade dedicated sound insulation as used by professional sound engineers, that costs twice as much as the plywood itself! Basically it's up to you and your level of OCD perfection desire. But there are plenty of basic insulation products on the market at reasonable money - if it looks a bit thin - use 2 layers - that's what I did, and was very happy. Another good idea is to apply a coat of varnish - this gives you an extra layer of waterproofing. However it is not mandatory - the old dash lasted over 20 years and the new one will last even longer, and a coat of varnish, while belt and braces, won't really shorten the life of the job, so if you are needing to do the whole job in a day and don't want to wait for varnish to dry, then fine. I did mine on a summers day and I found that a reasonable coat of polyurethane varnish was almost dry to the touch in about an hour.

Now we come on to the most important aspect of the job - fixing it. General opinion nowadays is that Hymer were lazy in only using simple self tapping screws to fix the board to the front lip. Along the back lip, you are screwing into metal, so it doesn't matter as much, but at the front you are screwing into fibreglass and over the years it has become obvious that simple screws are not enough - they work loose with time. To be fair to Hymer, maybe they didn't really expect their vans to last 30 years!

Offered up, prior to fixing - check everything!

The answer is to use nuts and bolts, and clamp the plywood firmly to the fibreglass lip. But even this isn't enough - you have to incorporate some form of locking washers to prevent them shaking loose. I have been involved in at least 4 dash replacement jobs over the years, and even nuts and bolts can work loose after a few years. You probably know that there are several methods to prevent nuts coming loose - nyloc nuts are very popular and common, but I have known even these to come loose. Another problem is what style of bolt to use, what head, and what washers? As I write this I know that there are several vans out there using different variations of fixing nuts, bolts and washers, and the jury is still out as to what is the best. Another problem is that the original screws were screwed in from the top, and were countersunk - resulting in flush heads. If you upgrade to bolts, the heads will be proud. Usually you can't notice this under the carpet, but just bear it in mind. 

The next problem is how to tighten them - if using screws, all Hymer had to do was screw in from the top - nice and easy, which is probably why they did. But if you are going to do a proper job and use nuts and bolts and washers, then this means that you have to get a spanner or socket on the underside to hold the nuts as you tighten from the top. This is quite easy for those in the middle, but if you are doing a really strong job, you need strong fasters at the sides as well, and getting a spanner or socket on the underside of these is a real contortionist stretch in through the front access panel - so be warned - it's a 2 man job. But don't be put off - it's doable. I'm just explaining things I found out the hard way. Also see below about an alternative method using teenuts.

For fixing the front lip and the sides to the angles (more on the angles later), you should use minimum 5mm fasteners - many have used 6mm. The length should be enough to get through the 12mm ply, and the lip, with a bit extra - this makes it easier to find the bolts when you are stretching - but bear in mind that if you make them too long, then you won't get a standard socket on them - but whether you use sockets or not depends on your tool kit. You may be using spanners - if you use spanners, then ring spanners are better. 25 or 30mm long bolts should be about right.

In terms of bolts - you have to choose a head. This will either be a screw head - slotted or pozi, hex heads - these need a spanner or socket and will stand proud, or even hex socket - ie allen screws. The choice is yours, each has its merits and demerits. Screw driver heads mean you might not get them tight enough, but can be used if you just hold the heads with the screwdriver from the top, and tighten from below with a a socket driver. You can use hex heads (normal bolt heads) but these will stand proud, and will also dig into the ply wood, which isn't actually a bad thing. My personal favourite is dome head hex bolts, with large washers. If fixing from below, screwing up into the board, you must use either hex head or socket head - screw heads - pozi or slotted will be impossible to get to from underneath - you need something that you can do by feel because at the sides you will be at full stretch.

On the underside you want nyloc nuts and large washers - but not so big as they stick over the edge. If you can get your hands on serrated washers - those with teeth that stick into the wood, so much the better.

Serrated washer

Conventional bolts, washers normal nuts and  Nyloc nuts

Teenuts - clever stuff!

Yet another method, used successfully by several owners is to use "captive nuts" - the commonest of these for use in wood is called a teenut. This is a threaded socket mounted in a metal collar that has sharp teeth - or tangs - that enable it to be hammered into the wood and fixed. The picture explains it better than words! The beauty of using these is that you don't have the problem of the whole bolt rotating when you are trying to tighten them up - this also makes it into a one man job - you don't need somebody holding the screw from the top. The down side is that you need just that little bit more preparation. You have to decide in advance where the holes are going to be, then drill the board, and knock in the teenuts. Then you have to drill through the teenuts into the fibreglass lip and the end angles, making sure that everything lines up. Then you have to widen the holes so that the M5 bolts pass through, and up into the teenuts - don't forget to put washers under the heads to spread the load and prevent shaking loose - preferably use serrated shake proof washers. You have to be very careful with your measurements because the teenuts are close to the edge of the board, and there is only so much space on the fibreglass lip - so make sure everything lines up and looks good before you commit. 

You may think I am going into too much (confusing) detail here - this is because the job has been done by many owners over the years and each one swears by their system! So I really have to explain all the options. I am also going into deep detail to hopefully help you avoid mistakes - you only want to be doing the job once. The first time I did it, it was loose again in a year and needed a days work to re-fix - that's how I discovered that screws were useless and nuts and bolts were needed. Don't underestimate the power of the front of your Hymer to shake those fasteners loose! All I want to stress is that you want to clamp that new board as tightly as possible, using fasteners that have the least chance of shaking loose with time. And diary to check them a year later!

But having said all that - if you have understood all the discussions about the different ways of fixing, my personal advice is to use teenuts, but the alternative of conventional (nyloc) nuts and bolts is almost as good ... but definitely avoid using self tapping screws as the original.

All the above concerns fixing the front and sides of the board. Along the back lip, where it joins the instrument panel, you will see the original holes that Hymer used. Just make sure that you use a good quality screw - maybe go up a size. The rear screws are not so prone to shake loose - but make sure you get a good fix on them.

Now lets talk about the metal angles at the sides. Take a good look at these, and you will probably shake your head and wonder. They certainly don't look very strong do they. So what you must do is to re-fix them, using extra fasteners if necessary, and make them as strong as you can. Then you want to fix the new dash board to them using at least two good solid nuts and bolts - but be warned these are the really hard ones to get at.

Location of metal side angles.
Also note the little black box, on many vans this is the amplifier for a wire loop radio antenna that goes around the windscreen hidden in the rubber.

Now I will tell you about a modification that you can do to give even more strength, courtesy of Peter Curry, who as you might know, is an expert. There is no actual fixing of the angle bracket to the side wall - this has been a criticism of the design. But there is a way of doing this, but you have to be keen and careful. It is only worth doing if your van has suffered more than most from a loose front end - it may be high mileage or had a hard life and you just want to make it as strong as possible. What you have to do is to locate the aluminium trim of the outside wall (see photo) and remove the plastic strip. then you have to carefully drill a hole through the trim, through the wall, then through the bracket, so you can get a 5mm bolt all the way through. But it won't be any bolt - you will use a countersunk head bolt that you will file carefully so it just fits snugly in the bottom of the aluminium trim, so that when the plastic strip is re-fitted, you can't see anything. Then you bolt it all together from the inside. This has the effect of clamping the angle bracket to the wall, and adding to the strength of the end fixing of the dashboard. Now I must stress that this is not a "necessary" modification, but if you are either engineering minded, or have a particular problem and need to beef up your front end, then this is a useful mod. But for most vans that are in decent condition for their age, it isn't necessary - just make sure the angle bracket is fixed as strongly as you can, with good quality fasteners that have a good chance of not shaking loose.

I don't have a photo of this mod to hand - I will add one soon.

Another thing to take into consideration is the area where the windscreen wiper motor is fitted. You will notice from the photos that you have to cut out a small bit of the wood to allow for the bolts that fix the motor bracket. Dashboard replacement time is the ideal time to service, or even replace your wiper motor and mechanism. These jobs are 4 times harder with the dashboard in place, so if you have any issues at all with your wipers, then you should get them fixed at the same time.

Other things you can do at the same time while the dash is out are have a look at the washer bottle, which is hard to access. Check the wire and tube connections and service as necessary. Also take a peer with a torch right down to the are near the wheel arch where the Hymer fuse box is located. On many vans there is a lot of road water and dirt thrown up here and it can benefit from a bit of TLC. Non of this is mandatory - just things that you should look at while the dash is out. Also check the rubber boots, if you can see any, that keep the water out where the wires go through the bulkhead. It's all common sense really - it's quite fascinating being able to peer into the engine compartment from the top!

Once the dash is back in and looking like a masterpiece of modern construction, all that remains is to upholster it with the trim of your choice. A tip here is to use a dark material, otherwise you might get to much reflection from a lighter material. If in doubt, test it first before glueing - also ask yourself - do you really need to glue? Was it a real mess taking off the old stuff? Get creative!

Finished!

So that's about it - All the above isn't just my opinion, it is the collective wisdom of many other owners too - I am just the guy collating it all into one place. There is no definitive correct way to do the job - but as long as the result is solid and will remain that way for many more years, then that is the main objective. You can get creative and you may have special skills, but I must stress again - all you need is a drill, a jigsaw, basic tools and basic household DIY skills to do a good job.

For those owners who would prefer to have the job done by a professional, I have a recommendation for you. Peter Curry is one of the UKs leading experts in all things Classic Hymer. His company, North Cotswold Motorhome Services, will replace your dashboard, insulated and trimmed, for between £400 and £500 inc VAT (2020 prices), depending on model and final finish required - there are options. NCMS is near Stratford on Avon and is a pretty place to visit out in the countryside. info@northcotsmotorhomeservices.com or 07917 863703.

If in doubt and for further info, ask on the Facebook group "Classic Hymers Technical". Join this group, and then look in the index for "dash board replacement". There you will see a link back to this blog, but also you will find links to the discussions that were had in writing this article. There will be more photos, and also suggestions of what people have used for insulation, and suppliers, and lots more photos.

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

Gallery - here is a gallery of photos of different jobs and methods - sent to me by various owners.

A Fiat showing the plastic ducting - but not all vans have this.

Nicely soundproofed board with steel battens

Nicely finished and varnished Merc

This owner used steel plates to offset the fasteners and captive nuts - lovely job!

This owner also added extra side insulation

Really high quality insulation work