caravan battery

If your van battery is identical to the existing deep cycle battery you may get away without using a second isolator. If the battery is different then I would definitely use a second isolator. For a second Isolator I would probably use a high current relay or solenoid controlled by the run position on the ignition switch.

However if you have a solar charging installation on your van I suggest you do not connect the van battery to your vehicle alternator. After the motor has warmed up (ie after 1/2 hours running) the temperature compensation in the alternator will lower its output voltage to be lower than the solar panels would be charging your battery without the alternator connected. This will mean that the battery charge rate will be reduced.

When you have a deep cycle battery in a van you should also have a good 3 or 4 stage battery charger for when you are on a powered site and to maintain the battery when you are at home. The most efficient way to way to charge your battery from your tug is to feed the battery charger from an inverter fed from the 12V system in the tug. Mount the inverter near the battery charger so that you can transfer the charger 240V power plug from its power point to the 240V outlet on the inverter. Doing it this simple way will mean that you do not need to employ an electrician. If you desire to have an inverter connected to the vans existing wiring then this must be done by a licensed tradesman.

PeterD

Chris,

How old is the "100ah cranking battery"? Sounds like a waste of a deep cycle battery there mate. Cranking batteries require Cold Cranking Amps (big grunt for a short time) rather than Amp Hours. (continuous deep drain over a long period of time)

Anyway, there are two options to consider for the third battery in the Van.

1. Providing you use heavy enough cable to limit voltage drop, you may get away with running a dual cable from the Auxiliary battery terminals to an Anderson connector at the back of the vehicle and then to the caravan.

2. Alternatively, you can run a lighter duty cable from the Auxiliary battery terminals to an Anderson connector at the back of the vehicle and then to the Van, but terminating in an Arrid Twin Charge unit which "boosts" the voltage charge going to the Van's battery.

In either case the one Isolator in the vehicle is all that is required to give the Starting battery priority preference when recharging and keeping it and any other batteries electrically separated.

Hi kukmasta, as long as you run thick enough cable in the first place, say 6B&S ( 13.5mm2 ), from your vehicle’s auxiliary battery to your proposed new battery in the caravan, you will have no problems.

It won’t matter what type of battery either one is, because when connected together while driving, your alternator will be supplying a much higher voltage than any of your batteries so the alternator will charge all batteries at the same time, at what ever current level each individual battery will require.

With the motor off and your Isolator has your cranking battery separated from the two auxiliary batteries, your two auxiliary batteries can stay connected in parallel and supplying your caravan while stopped and any load needed to supply the caravan will simply be drawn at the same voltage level from both batteries.

Again, there is no problem with having two batteries of different types, size and/or age, even if you have two identical batteries of the same type, size and age, you are still going to end up with differences in charge levels in either battery and charging and usage is no different to having mixed types of batteries or identical types.

The only thing to avoid if possible, is when connecting the tow vehicle to the caravan, try not to do this until you are ready to actually drive. If you do connect and your motor is not running and if you have a fully charged auxiliary battery in the two vehicle and a fairly low battery in the caravan, your going to end up with two fairly low batteries.

There is not going to be a problem if you do connect and don’t have the motor running. There won’t be a sudden rush of huge currents between the batteries and it would take at least a few hour to lower the vehicle’s auxiliary battery voltage, it’s just a waste of power that you may not be aware of and you do a short drive and think you have heaps of power in your vehicle’s auxiliary battery.

Use 50 amp Anderson plugs to connect the battery cables between your tow vehicle and caravan and as you are only adding a 100 A/H battery in the caravan, fit 30 amp automotive type automatic reset circuit breakers at either end of the positive cable, as close as practical to each battery’s positive terminal.

Cheers.

Chris, my set up is exactly as Drivesafe describes. Only variations for my set up are 25mm sq cable, 175 Amp Anderson Plug and 50 Amp Circuit breakers. Reason for my larger dimensions is that I often carry two x 120 AH AGMs in the camper trailer.

Leaving aside the difference is size of components, the system has worked very well for me.

Thank's to all who helped, I am now able to go ahead. I have chosen to run heavy duty cables to an Anderson plug and charge the Aux battery in the van in parallel with the ute aux battery.

Hitting the road up to Gulf next week Cheers all.

Chris

P.S. What a great forum.

Hi Chris

There is an article here on the site to help you with this project.

Article

You will have no problem with charging these batteries if the alternator and isolator are in good condition.

I run an AGM 120 a/h battery in my own van and a MRV70 (dual purpose battery) in the car as an aux. I was running a pre-trip test yesterday and my AGM at 60% SOC was pulling 28 amps initially and then settled to 18 amps after 10 mins at fast idle. I use 8 B&S cable from front to back.

Regards

Derek.