How do I know if my battery is charging when towing

G'day Toby

Q1. Probably the easiest way is to check across the terminals of the 2nd battery with the engine running at fast idle or up to say 2000 RPM (you may need to get the boss to hold the throttle). Should read well above 13V probably >14V. If so, it means the alternator is supplying charge to the 2nd batt. Use a multimeter for this.

Q2. As a general rule you should always use a battery management unit when running an aux batt (even the one in the van). That will take care of isolating the 2nd batt from the cranking batt when necessary.

Of course you will need to consider very heavy wiring if the batt is in the van + a suitable plug.

May I suggest an auto sparky if you feel you're getting out of your depth.

By using an additional two wire plug the wires can run from the van battery to a digital voltmeter on the dash and it will indicate the voltage when the charging system, whatever it is, is delivering charge to the aux battery.

Because of the sensitivity you should also be able to see when the fridge is ON or OFF.
Some learning of the charging and voltages happening will need to be observed to do that though.

If charge not happening then volts will go down and then rise when charging is occurring.
Cheers
Ross M

Hi Toby I am asuming because of the type of questions you are asking that you are new to towing a caravan if you read electricity for camping do a search for it on this site it will answer many of your questionsand some you dont even know you want to ask yet After reading that you will find you will have most of your questions answered and can come back and ask us some that may be more particular to your circumstaces
Have fun Steve

Toby,

You wrote in a follow-up:
" just brought a new car with an ECU Alternator. Now that is new to me. bTW it is a 3 way fridge :)"

At the risk of starting another 12 volt war ....

If you are now sure that your new vehicle has an ECU-controlled alternator and you want to properly charge your caravan batteries while driving, then I think you need a DC-DC charger located in the van, near the battery, with a 6 gauge supply from the car all the way to the charger via Anderson at the back of the car.

Your 3-way fridge running on 12V draws relatively high current, probably in the range 10 to 15 amps. I don't know what your present wiring arrangements are, but it would be better not to have that sort of load connected to the van battery while you're trying to charge it. Instead, have it powered directly by the supply from the car. Reason for this is that the fridge will absorb a large part of the output from the charger instead of that output going toward charging the batteries. You will need an isolator in the car to ensure that the 6 gauge supply from the car is energised only when the engine is running.

In my Avan when I had it, I had the 6 gauge cabling all the way from car battery via isolator and Anderson to a fused terminal block in the van. The supply to the charger was connected to that.

I had a relay so that when the supply to the charger was live (car engine running), the 3-way fridge ran directly off the supply from the car, and when it was dead (engine off) the fridge ran off the van batteries until I switched it over to gas or 240. Reason for that was to keep the fridge going if stopped for an hour or so .

That system worked very, very well for me.

If you don't like the idea of running your fridge off the van batteries at all then you'd supply the fridge directly from the terminal block and forget the relay. The isolator in the car would ensure that your fridge will not flatten your car battery when the engine is not running. You could do without the isolator, but then you'd have to remember to unplug your Anderson every time you stop for lunch, shops etc or risk flattening your car battery. Not worth it, IMO.

A simpler, and in my opinion NOT recommended, way is to not have the isolator in the car and connect the fridge direct to the van battery (still need the dc-dc charger). Much of the output from the dc-dc charger will be taken by the fridge so you won't get the full benefit of the charger and you may need a longer drive time to charge the battery. When the tug's engine is off the dc-dc charger will act as an isolator to isolate the fridge and the rest of the van electrics from the car.

Are you contemplating a second battery for the tug?

Cheers