Can I run 12V camper van fridge whilst 'trickle charging' the battery in van?

Question

I am running the following setup in my camper van and would like to know if there is a simple solution or device that would be effective in allowing me to run my 12V fridge whilst the leisure battery is being trickle charged from shore voltage. I recently got this van and realised the owner had removed the original charge controller and bodged a lot of the electrics.

Currently when the SPDT switch (Seen in pic above) is set to charge the battery from the charge controller, the voltage at the fridge is stable approx, 11.9V +-.2 volts. When I switch over to the trickle charger to charge the batteries (normally when its dark), the voltage is fluctuating between 8V-16V, and the fridge isn't turning on.

I'm assuming the fridge needs a stable 12v supply, and guess the trickle charger fluctuates according to battery state. With this in mind, is there a simple solution e.g. voltage regulator or a different charge controller, that I could use to stop the voltage fluctuating so I can charge the batteries and run the fridge at the same time?

Answer 1

Make sure that when you switch over, the battery is still in the circuit. Check that.

You can't run the fridge with that battery and that trickle charger. It would work if you had a much larger battery, or a much larger charger, or much smaller fridge, but not with the equipment you have. When the fridge starts to turn on, it draws so much current that battery voltage drops, then when it turns off, the battery voltage swings up.

Having said that, here's something you can try: put another big battery on the trickle charger, and leave it there. When the fridge tries to start up, hopefully the big battery will stabalise the voltage enough. I'd also add a circuit breaker and a big coil of wire, to handle the surge when the two batteries are switched in parallel.