Thread: Triple battery wiring suggestions

Originally Posted by ytt105

Dual/triple battery wiring question?

RR P38 with standard battery in the front, 65 amp/hour deep cycle in the boot, 100 amp/hour Fullriver deep cycle in the camper trailer which is charged by an 80 watt solar panel. My intended wiring system is:

Twin 3 or 4 BS wires from original battery to boot battery via a voltage sensitive relay and 50 amp fuse or circuit breaker?
Twin 6 BS wire from boot battery to 50 ltr Wacoe fridge in boot
Twin 6 BS wire from boot battery to trailer battery via 50 amp Anderson plug
Twin 6 BS wire from trailer battery to three way fridge in trailer, via ignition operated relay so 3 way fridge is not on unless car is running.

How am I going, any comments?

How are you going.......Sounds like you've done some research.

I try to keep mine as simple as possible for reliability and longevity.

I often wonder about voltage drops with what you are doing. Although deep cycle don't pull the amperage as will only trickle charge so will make around 14V over time depending on load. I have found the voltage sensitive relays to be a pain at times.


More eleco crap on the p38 to play up

Hi ytt105, here are two diagrams which will give you an idea on the way to set up your vehicles for 3 batteries.

So DriveSafe

It appears I don't need to use 3 or 4 BS wire. Its overkill. That will save a few dollars.

Could you please explain the pro/cons of fuses/circuit breakers. Which should I use where, and why.

PS. Love your diagrams!

Hi ytt105, the diagram is intended to give you an idea of all the hardware you will probably need but the cable size in my diagrams is what is used in our standard kits.

In your case, while 6B&S would work, with 2 auxiliary batteries and a 3 way fridge, if I were you I would be running 4B&S Twin from the cranking battery all the way to the camper trailer battery. Those fridges draw heap.

With a compressor type fridge, the fridge cycles and even when on, they only draw about 5 amps on average, and while they are off, the battery can get extra current while charging.

With a 3 way fridge, they constantly draw around 10 amps and this load in itself will cause a fair bit of voltage drop. Add what the load a low battery will pull and the voltage drop will mean a much slower charge for the battery which means a longer drive is needed to charge the battery.

Again, while 6B&S will work, as you have already posted, you need to weigh up the cost verses better charging ability.

In a circuit where the maximum current is known, a fuse is fine as it can sized correctly for the protection needed.

In a circuit where the maximum current can vary particularly in a dual battery set up where the currents not only vary but can be very high, an automotive type auto resetting circuit breaker is a much safer protection device and because of the operating characteristics of an automotive circuit breaker, you can use a much lower current rated device which makes the whole circuit not only safer but you can tailor the circuit breaker to act as an overload protection device, all without effecting the dual battery operation.

If you use a fuse in a dual battery set up, it has to be much bigger than the maximum current that is ever likely to be handled, which means it is only there for short circuit protection and it also means your cable has ot be much bigger, although in your case, if you go with the 4B&S, it wouldn’t be as much of a problem.