Outer Limits 4x4 Board

Hello all. I've just bought a 2nd hand caravan with its own battery and Anderson plug. I had a plug put in the tow vehicle to suit, and was wondering... How do I check that it is actually charging the van battery ? Without going to an Auto Electrician....

Connect the van to the car. Put a multimeter on the van battery and check the voltage with the car off. Should be around 12ish obviously.

Then start the car, the voltage should rise to around 14v, 14.4v to be exact but you probably wont get that due to the length of the wire running to the van. However if it is much lower then 14v then you will need to run a larger cable to the van or it will take forever to charge the batt in the van.

Hi twocs, phil94delica pretty well had it.

As above, before connecting the caravan to the tow vehicle, measure the terminal voltage at the caravan battery.

Next start the tow vehicle and then measure the voltage at the caravan battery again.

If the caravan battery’s voltage is less than 12.7 ( less than fully charged ) then the voltage at the battery MUST BE at least 1 volt higher than what the caravan battery’s voltage was before you connected to the tow vehicle.

It does not have to be 14 volts when the caravan battery’s voltage is less than 12.5. It just has to be at least 1 volt higher to be able to raise the charge voltage of the battery.

The problem with reading the voltage at the caravan battery is that you need to allow for a voltage drop caused by the corresponding current draw that a low battery requires.

As the battery voltage rises, the current draw reduces and the voltage drop reduces.

Even with thick cable, you will get a voltage drop and it is actually better to do this test with a low caravan battery than it is with a fully charged caravan battery as there will be very little current being draw by the caravan battery so you will not have a really accurate idea of whether the cable is suitable for the job required.

An additional point, if the caravan has a fridge and the fridge is going to be power directly from the caravan battery while you are travelling, make sure the fridge is running when you do the test and again, with the fridge running, there must be at least a 1 volt increase when you have the motor running.

Thanks heaps Drivesafe and Phil. Great help. Will be straight onto it...Cheers...