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It has taken a while but at last I have fitted the auxiliary battery in my car so I can run a fridge or any other electric gear when travelling or when there is no mains power available. It charges off the main battery/alternator via a DC/DC charger but it also has facilities for solar.
I fitted a 120Ah Deep Cycle AGM battery which is probably a bit of overkill as 100Ah would undoubtedly have done. My fridge only uses about 0.8 amps at 12v and most of the time I am stationary mains or 240v generator power will be available. Even assuming I am away from mains and don't use the car three days running the fridge will only half discharge the battery.
Made a base out bits of pine which fitted nicely beside the drawers in the back of my car.
One of the hardest part was finding places to fix it all to the floor of the tray because of the struts, fuel tank etc underneath. You can see one fixing bolt here plus the earth connection to the chassis and the main battery feed in the split conduit.
Battery fitted into place nicely though it was a tight fit.
I had to butcher the battery box lid to fit it over the battery fixing mount (a bit of 25mm by 3mm steel bar). To be honest the battery box was another overkill; I wish I had bought a plain one and added my own fittings, this one has enough to connect a small town.
Finally the proof of the pudding once connected to the main battery the charger when straight into float mode.
It only remains to put the fridge in the back and test that out.
The local wiring at the rear was all 8sq mm but I used two bits of 8sq mm wire between the main battery and the DC/DC Charger while the local earth was a 13.3 sq mm cable. If I hadn't already had the twin 8sq mm cable I would have used 13 sq mm for the battery lead. The larger wire for the longer runs was to reduce losses - I squared R and all that.
That looks good Bruce, we've alway bought ready made systems for home made camper vans, never quite had the confidence to go it alone like you have. So I'm very impressed, very impressed indeed.