3rd battery setup question

[glennm]

Currently have 2 batteries under the bonnet with a ctek 250s to look after the 2nd battery. I was going to add a 3rd battery behind the rear seat in the same manner as happy john has done. Question is what do i need equipment wise to charge it? Another ctek? Where would it get its power from? The ctek was all done for me but i would like to have a crack at it myself this time. Thanks

 

[oldmate45]

Depends what the third battery will be.
If its the same type & capacity as your second then easy just run them in parallel with big cable and circuit breakers either end.
How old is the 2nd battery?
If its getting on a bit it would be best to replace it as a matching pair with the third and run them both as a bank off the Ctek, if its big enough (most likely will be - 250s will comfortably look after at least 200AH and up to 300AH by their specs).

If you need to run the third as a different capacity or type then you will most likely need to run a 2nd DC-DC and opinions will be divided as to whether you should run this also off the main or 2nd battery.
My opinion - run it off the main it has the best access to the charge current available from the alternator. No point charging one battery that is then charging another, why not charge both at the same time.

Might be cheaper in the long run to replace your 2nd battery at the same time as doing your 3rd, depends if your Ctek is up to the task. At least you end up with 2 new batteries that you can run as a pair and no need for more expensive DC-DC chargers.

The other advantage if you run the two as a bank is you can just utilise all your existing cabling for power outlets, no need to change anything there. It all stays the same you just have double the capacity.
If the third is run as an isolated battery you will need to work out how you're going to get the power out of it.

 

[glennm]

Thanks oldmate
First 2 batteries are near new optima yellow and blue tops so it looks like the additional dc dc charger is the go. Wanted the extra capacity to run the 2 fridges etc. without having to be concerned if the car is unused for a day or 2 or 3. The fridges work hard in summer. Looked at solar but the quote I got was expensive and wasn't keen on having a portable unit that I had to pull out whenever I wanted to boost the batteries.

 

[Old.Tony]

Matching batteries over a distance is a problem, because the cable between them loses voltage and the battery-eats-battery issue raises its ugly head again.

They're better off separately charged and used unless they not only close together, but matched in size and age as closely as possible.

 

[glennm]

Thanks old Tony looks like a 2nd ctek will need to be forthcoming. I noticed kullkyne have them for $250 at the moment. I am presuming just set it up as per the existing one from the main starter? Need to find a place to put the ctek as well as under bonnet is getting crowded. Will sus it all out on the weekend.

 

[Old.Tony]

Hooking it up to the main means it'll take its power from the best source. If you get the D250S, you can whack a solar panel onto it as well.

Put the C-Tek down the back in the tub, no need to put it under the bonnet. From the main battery, put a (say) 40A fuse (or thermal breaker) then run your heavy cable to the tub. Because the C-Tek isn't a power source, you don't have to fuse the tub end of the heavy cable.

 

[glennm]

Excellent. thanks Tony. You must have esp as i was wondering about other locations and fuses.

 

[Old.Tony]

Pretty standard warning for me these days. If you're going to run some cable from a power source, start it with a fuse. The charger isn't actually a source unless it fails and the battery backfeeds into it, I guess, but the charger will have a fuse in it so it's all good.

Since your starter battery can dump 600A without any trouble, that's one hell of a firestarter.