12V Guru – How to power 12V DC fridge while driving?

Question to 12V Guru: is my 12V DC fridge charging while I am driving?

 My question relates to keeping 12V DC power to the fridge whilst driving. I understand 12v is supplied by the tow vehicle to the fridge whilst the car is running. When stopping for a break or refuelling does it continue to draw from the car (auxilliary) battery or does the power management unit in the van switch to the van batteries? If so will the solar panels on the van roof kick in to assist in preventing a rapid voltage drop?

At the moment my van fridge flashes a warning light soon after the car is turned off, which indicates to me that the van batteries are not being utilised. The fridge is a 3 way Dometic that requires manual switching between 12v, AC and gas modes.

Paul Lodder,  Belgrave, VIC

12V Guru answers:

Hi Paul, thanks for your question and happy to answer this promptly as firstly we don’t want your drinks and snags warming up on the journey and secondly, we have been asked similar questions before.

Like all power managements systems installed in caravans in Australia the BMPRO systems do not have an inbuilt charging system that comes standard inside the unit which allows for the charging of batteries in the caravan from the vehicle when the vehicle alternator voltage drops. That being the case probably means that whilst you will be getting a charge it will only be when the voltage in the caravan is lower than that across the terminals of your auxiliary battery.

You have correctly questioned as to whether the caravan battery is still draining power when the car is not running. It depends upon how it was setup. If you have installed in your car a battery isolator then most like this should be wired to your ignition and when the ignition is turnoff it prevents the flow of electrical current back to your caravan. This should be your first stage of investigation. The fridge will not be powered directly off the line from the car it should be wired to the batteries and the fridge is then wired directly from the BMPRO unit.

Where to look for possible faults

We are aware that on some older system, which yours may be as many of the newer vans are moving to the 2 way compressor style 12V DC fridges, the fridge was being wired with very thin gauge wire and thus there was too much resistance and with voltage drop the fridge was not able to accurately record the voltage and thus flashed the error codes. Need to ensure running at least 8AWG thickness.

Also suggest after turning off the car, disconnect from the vehicle and then see how it runs from the batteries on DC the DC switch. Try turning off and switching back to 12V as I have heard this sometimes help. There is also the chance that there is something wrong with the fridge but I am guessing not as you don’t mention that on gas or AC you get the flashing lights.

Following this I would check that your caravan batteries are still in reasonable condition. It could be that if they are getting a bit tired, they will show a reasonable terminal voltage when under charge but when left idle and the car is no longer running the fridge may pull down the battery voltage to a level that forces the fridge warning light to activate. This would mean you need to switch over to gas or AC relatively quickly.

If the batteries are still good and you are not able to charge enough whilst travelling from the AUX or the Solar you should consider installing something like the DC-DC BMPRO Miniboost beside the BMPRO system as this will boost the voltage from the vehicle to ensure the batteries are perfectly charge with a multi stage charging algorithm.

Charging from solar panels

In regard to the solar on the roof of your van it will also provide a charge to the batteries. Depends upon how many panels you have on the roof, but we have seen many systems where 3 x 140W panels can adequately power a 3-way fridge for days without gas or AC. Does depend upon how many times the fridge door is opened and the outside ambient temperature.

Overall, I think the issue is going to be in your wiring setup between the car, caravan and fridge. Map the layout and chat with your local auto-elec.

Tips and tricks

An idea is to remember to cool your fridge down for a day or two on gas or AC power before you travel to really give the thermal properties of the fridge a chance to chill.

This will prevent a massive drain on the batteries before you take off on a trip or move campsites.

Happy cool travels – 12V Guru

The article is written for Caravan World Magazine.

Like this Post? Share it!

Share on facebook
Share on linkedin
Share on email

Leave a Comment

Your email address will not be published. Required fields are marked *

Covid-19 update – our online shop is open for business and the orders are shipped daily. Please allow longer delivery times for any orders with the current pressures on Australia Post.