Electrics & Fridge (Updated 12/11/10)

With the spectre of liability looming over my head, I’m afraid I am not going to publish very much on the subject of electrics. Wiring in mains and 12V electrics and connecting them up to your vehicle’s electrics does require a little care and a degree of electrical knowledge and understanding.

That said, I have put together a high-level diagram of the system I used in my conversion, in the hope that this might provide some ideas for a slightly basic, but very self-sufficient  setup.

Our electrical requirements were quite limited:

• Power a small fridge Or not – see below
• Electric lights (LEDs for lower power consumption)
• Charge the leisure battery properly while driving, removing need for hookup
• Power mobile phone/camera chargers
• Water pump and cold tap

Mk1 Electrics – Not Reliable (Scroll down for Mk2 Solution!)

You’ll have to forgive the poor quality of the graphics – I couldn’t make PowerPoint save nicely and the colours are rather dodgy… still, I hope the meaning is clear. Note that details like fusing and earthing are missing:

Most of this solution is simple and conventional and works well to this day. The unusual bit is using an inverter to power a small 240V fridge (like a hotel mini bar fridge). I gambled that by using a Sterling Power Battery-Battery Charger I could keep the 110Ah leisure battery sufficiently charged to make this work. Despite the remarkable performance of this charger, in the end, I was wrong.

The fridge/inverter combination required too much power and the massive current surge everytime the compressor started fried one inverter and blew the fuses on a second inverter. In addition, having the inverter permanently switched on drained the battery too fast – larger inverters have a significant quiescent (idle) current that will eat away at the charge of your leisure battery (0.4A in my case, equating to 9.6Ah per day without doing anything).

This design might have worked if I had two or three times as much battery capacity, but I’m still not convinced. You would be better off spending the money on a proper motorhome fridge than a huge battery bank.

Lesson Learned: I have now concluded that the only fridge setups that make sense and allow some indepedence from mains hookup are a three-way (gas & electric) fridge or a 12V compressor fridge, which is more power efficient – hence the £400+ price tags they carry.

Mk2 Electrics – Good reliable solution but no fridge

Having been too clever for our own good with our inverter/240V fridge setup, we decided to remove the fridge from the system and see how things went. Predictably, we had no problems at all and leisure battery life suddenly became more than ample.

The Sterling Battery to Battery Charger now seemed like overkill – and we discovered that as its list price had risen considerably since we purchased ours, we were able to sell our second-hand unit at a small profit on eBay! So we did.

We replaced the B2B charger with a Victron Cyrix-i Battery Combiner – basically a clever, voltage sensing relay that does not need an alternator or ignition connection. It just installs between the starter and leisure batteries in the same way that the B2B Charger did. Here’s a diagram of our current electrical setup. Note that as before details such as fusing and earthing have been omitted:

As our 240V fridge was built into the side conversion, removing it and replacing it with a different unit would involve dismantling and altering some of the cupboards. We have decided not to do this and so now do not have a fridge except when we have mains hookup (rarely). We use the fridge as a cool cupboard and for most things, this works quite well – somehow the fridge stays noticeably cool inside unless the weather is quite warm. Obviously not good enough for fresh meat, but ok for most other things, within reason.

We have found that we can manage quite well without a fridge, although it would be nice to have one sometimes. Ironically, if we had stuck to the cheapest solution of all, a 12V coolbox, we would be better off. We could run it from the cigarette lighter during the day, switch it off at night, and have most of the benefits of a real fridge.

The rest of the electrical setup works very well and our single 110Ah battery gives more than enough power to support our LED lights, water pump and charging laptops and mobiles through the inverter.

Next: Water & Plumbing

Back to the Conversion Guide Index

Disclaimer: All material is provided for information purposes and is my opinion only. I can take no responsibility for the accuracy, suitability, reliability or safety of the information in this guide.