The ten unbreakable rules for motorhome and caravan electrics

Here is a list of what I consider the 10 most important rules when designing, building and using a motorhome or caravan electrical system

1.SYSTEM VOLTAGE – Keep the vehicle system voltage and the house system voltage the same. If your vehicle is 12 volt – then make sure the house system is also 12 volts. For larger motorhomes 24 volt is much better – but do not mix voltages! I know that there are mixed systems out there – but these are complex and very difficult to fault find when they have a problem.

2.AIR CONDITIONING – You cannot run Air Conditioning (normal compressor type) from a solar powered system. Aircon uses far too much energy to practically be powered from a battery/solar system. You will need a large generator if you intend to run aircon. (That is not to say that you can not use solar for the 10 months of the year when you don’t need aircon).

3.CHARGING – There are no “free lunches”. Whatever energy you take out of a battery, you must put back (with a little interest).  If you take 25 amp/hours out of your battery system overnight, you will need to produce and put that back during the day (in addition to whatever you use during the day) .

4.FUSES – Fuse EVERYTHING! When a fault occurs in a circuit that is correctly fused, the fuse blows. When a fault occurs in unfused circuits things melt and fires start. I know which I would rather deal with! Make sure you know where all the fuses are and be sure they are correctly labelled – Murphy’s 3rd law states that “lighting fuses will only blow at night when your torch batteries are flat”.

5.APPLIANCE VOLTAGE – Run everything you can at the native voltage. If your house system is 12 volts – your lights, fans, TV, fridge and every other electrical item should also be 12 volt if possible. This is the most efficient configuration. It costs energy every time you convert it – the very best inverters approach 90% efficiency. Even these are throwing away 10% of the energy that your poor solar panels are working hard to produce each day.

6.WIRING SIZE – Use the correct sized wiring. You may save $10 by fitting a cable with less copper in it – this is insignificant when compared to the issues you will have when the fridge stops (and the beer gets warm) due to voltage drop in the cable or the solar array does not produce what it should. (Don’t listen to auto electricians recommendations regarding cable size – do the math yourself or find someone who knows about this stuff).

7.PHANTOM LOADS – Make sure you do not have “phantom loads”. Phantom loads are appliances that use a small amount of power all the time. 24 hours times “a small amount” is a lot of power to throw away. For example a phantom load of just half an amp will consume 12 amphours every single day. This is enough power to run our microwave for 15 minutes each day!

8.WIRING DIAGRAM – Always carry an up-to-date “as built” wiring diagram. Even if you cannot resolve an issue yourself, it is about 100 times easier for a tradesman to find a fault if you have a diagram. If something gets added or changed, make sure the diagram is updated.

9.MAINTENANCE CHECKS – Make a list of routine maintenance checks: Battery water, terminal tightness etc. Discovering a problem BEFORE it happens is one of the most joyful things ever.

10.   BATTERY LIFE – Be kind to your batteries – avoid deep discharges. Flattening lead acid batteries is almost the worst thing you can do to them. Remember – a 100aH battery should not be expected to regularly deliver 100aH  – it may do it once or twice – but this kind of abuse will surely kill the battery almost as fast as driving a 6 inch nail into it.

Have I missed any?

Have you broken any of these rules – what happened?

We would love to hear from you about your experiences. Use the “Leave a reply” box below to let us all know.



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18 Responses to “The ten unbreakable rules for motorhome and caravan electrics”

  1. Alex Says:

    I just want to thank you for all of the info you have published. I will be taking the plunge in 12 months time, and thanks to you i now know what I’m looking at when i go shopping for a bus. You have possibly saved me tens of thousands of dollars. Just a note on the top ten above i would add that any second hand converted bus will also need a certificate of compliance with the electrical work. At least it will here in Victoria otherwise i wont be able to obtain a rwc. Maby one day we will catch up and the drinks will be on me!



  2. Alby Says:

    When I first added batteries to the van a couple of years ago I forgot to put a fuse in the line from the Anderson plug to the battery. Anyway, Murphy’s Law says that anything that can happen will eventually happen or something like that. We were on a trip to Bright, Vic when the hitch between car and van broke a few bolts and we ended up dragging the van on the WDH which kept the rig together until we stopped. The van had to be transported to Bright on a flat top which the RACV provided. However, as it was dragged on to the flattop the 12v wiring got caught under the A Frame and fused causing the wiring to heat up and melt all the way to the battery. We ended up with a van full of smoke as we desperately went in to disconnect the wire from the battery. The batteries were located under the lounge seats inside the van. A scary moment!! as we thought the van would catch fire.
    The RACV recommended electrician fixed the wiring in Bright and installed a fuse inline to stop that sort of thing happening in future. Lesson learned and now make sure there are fuses on all wiring as needed.
    Enjoy reading your blog. Learnt a lot from your articles.

    Cheers, Alby

  3. Hobo Says:

    Hi Alby,

    Thanks for the comment. I see lots of DIY caravan and motorhome wiring jobs where people have forgotten the fuse – easily done, but oh so dangerous!

  4. Hobo Says:

    Hi Alex,
    I agree, a certificate of compliance is very important. However people should be aware of the limitations of the testing done to obtain this certificate. Most of these certifications are undertaken by household electricians. These guys are well trained in detecting the dangerous issues with 240 volt wiring and earthing in caravans and motorhomes, they do very little testing (if any) of the low voltage systems. (BTW – I trained and worked as a household/industrial electrician for a number of years).
    If you purchase a second-hand motorhome or caravan and want to be sure about the electrical safety or I would recommend getting a low voltage expert to look at it after the compliance cert has been issued.
    The low voltage may not have the same ability to electrocute as 240 volts – but it is far more likely to cause a fire if not correctly installed.


  5. robert Says:

    Hi Gavin,
    Love your site, its a great help.

    In one of your other articles, which I can’t find now, you say to fuse everything, both positive & negative wires.
    I understand the “everything”, but….
    I was always advised that only the positive wire required fuses!!

    Why the negative???


  6. Hobo Says:

    Hi Robert,
    So glad you asked about fusing the negitive side. There are two reasons to do this…
    1. Plasmatronics (the makers of the solar controller) insist that a fuse should be installed in BOTH the negative and positive lines from the battery.
    2. A little more difficult to explain – but here goes… Some devices install in and switch the negative line (the PL40 for example) thus the positive lines from the solar panels go directly (via a fuse) to the positive of the battery. If the negative from the panels, was unfused AND this wire happened to come in contact with say the positive terminal of the battery, it would instantly destroy the electronics of the PL40 and potentially cause a fire.

    I do not fuse EVERY negative line – but I do fuse the one that have devices in the negative line and the negative from the solar panels.

  7. stephenabrahams Says:

    i have been motorhoming for many years now in a 40ft converted hino bus and i have learnt many lessons the hard way. The best advice for travellers i could give is use electricity for light and electronic appliances, and use gas for anything that requires heat (ie cooking, hot water and heating). using electricity for heat is just not feasible (even with generators) unless you have access to mains power. You would be surprised how much petrol a generator can go thru when trying to heat an electric hot water service! Cheers

  8. tony lawn Says:

    hi hope you can help i have a coaster 24 vbus which i plan to slowly convert however i plan to use straight away for some short holidays i dont have house batteries as yet so i plan to use fridge off bus batteries maybe not ideal but ok being temporary i hope. here is my question what 240 volt battery charger should i buy so i can mount and wire in permanant and then at a later date wire up to house batteries when fitted i always have a genset while camping so i plan to use this to charge with. i will be sticking with 24 v for house batteries thanks in advance

  9. Hobo Says:

    Hi Tony,
    I’d look for a good quality smart charger. The best are made by Ctek, but there are now some good quality copies of these sold in Repco and SuperCheap stores. The size (number of amps) is important if you will use a generator to charge the battery. The larger the charger, the shorter the charge time and thus the less you will run the generator. Depending on the size of the battery bank, 15 – 25amps is a good size. Bigger is of course better.

  10. Klaus Says:

    Hi there,

    I just bought a camper on a 24V truck, the house being equiped with a 12V system. completely detached from the truck, the house batterie being charged by 3x120W solar panels.

    Looking at rule 1, I am thinking of going to 24V is the house.
    So I guess I need a batterie management system, like for example the REDARC BMS1215S2. But then that seems to cope wiith 12V house batteries only, is that right?

    You say mixed systems are hard to debug. Why is that so?

    Thanks for your ideas to a humble newbie

  11. Hobo Says:

    To be honest, if the camper is already setup and working with a 24v/12v system, it is probably not worth the effort to change (especially given that it is not a large vehicle).
    Redarc do make some very good gear for charging 12v house batteries from a 24v alternator – this would be a better option.
    Regarding the issues with fault finding – a faulty earth on a 12/24v system can do all sorts nasty things including putting 24v onto the 12v system (not good!).

  12. Lyn Says:

    Dear Gavin

    Thanks for all the useful info. It is definitely helping me to think though lots of issues while on the road.

    In particular, given you say: “Run everything you can at the native voltage…It costs energy every time you convert it…” I have been thinking about my computer and how wasteful it seems to charge it using a a 150 watt DC to AC inverter connected to the AC adapter that came with the computer.

    Hoping you can help me find a more efficient way.


  13. Hobo Says:

    Hi Lyn,

    If the vehicle voltage is 12v, there are 12v power supplies available for most laptop computers. Jaycar electronics sell some good ones. Be sure the output voltage and current matches the power supply that came with the computer.

  14. jilly Says:

    Hi gavin—–i am working my way through your pages and tutorials and finding them very helpful. Quite exciting actually as I am beginning to understand what my husband has been saying over the past six months. To me a battery that was say 11 out of 14 full sounded pretty OK but I am learning. Thank o all the work that has gone into your website. The adverts are interesting even….lol……cheers jilly

  15. Ken and Linda Says:

    18months ago we purchased a brand new 30 foot scenic van until late we have had no problems but they are stating to show .the biggest problem we have is there is no wiring diagrams for the 240 or the 12v systems in this van bye law is this van required to have a wiring diagram in the van so electrical experts can identify any faults

  16. Hobo Says:

    No laws that I am aware of – there should be. Fault finding on an unknown motorhome can be very time consuming.

  17. Peter Says:

    My Vitrifrigo dangfos compressor only working on 24v refuses to start on 12v any ideas . Have just upgraded to 6mm wiring 12volt runs from house batteries 24volt of vehicle batteris all batteries are in good nick have double checked connections would appreciate any help regards Peter

  18. Hobo Says:

    I would suggest you attach a diagnostic LED to get a info about what is going on. I would suspect a faulty connection somewhere. Measure the voltage at the danfoss controller as the compressor is trying to start. If there is a faulty connection, the voltage will drop significantly.

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