I’ve recently purchased 2x new 115AH AGM 12v batteries that I want to cable in parallel so as to get 230AH from them. I’d like to confirm what size cabling to use for each link shown in the picture, they are located next to each other and within 500mm of the J35 unit.
Thats the way, I use 8 B&S cable since the distance isn't great and at 85amps more than capable as the van wiring wouldn't handle half that anyway, 6 B&S is just too bulky, keep the lengths the same and use proper terminals not the light weight jobs ........... I would also fit a maxi fuse or breakers on the POS and NEG leads going to your BM, 35/40amp is plenty big enough in most cases, this will safeguard the battery and make for easy disconnect. The only leads I would have hanging off the batteries other than the ones for the BM is if you have an Inverter.
So am I correct in thinking that the 230AH combine battery would never actually flow at that current as the draw/ input current from the J35BM is 35A? At present the cable from battery to J35BM is 10mm2
AH is a measure of battery capacity not current. For example a 230AH battery could (in theory) supply 23 amps for 10 hours or 230amps for 1 hour which is why Drover said to use a master fuse - ideally as close to the battery terminals as possible. The j35 manual (page 14) specifies a 40A fuse.
And no surprise, the J35 number has nothing to do with what it can actually do. The specs say "The J35 can simultaneously deliver up to 20A (J35A) or 35A (J35B-L, J35D) to the caravan battery and loads from the mains input source, with a maximum charging current of 15A (J35A) or 30A (J35B-L, J35D)"
With 230ah of storage that means you technically only have 115ah, being 50% of storage for AGMs is usable if you want your batteries to have a long life, in reality I would say you should have 100ah to use, stated capacities of batteries and solar panels are always on the wishful side ........... ideally do a audit of power draw to see how much in an average day you need, noting that not everything is being used for hours on end ............. with everything turned off, turn one unit on at a time, take the reading then switch it off and go to the next, work out how long you would use it each day, do the math and add them all up. My rig I work on 40amp a day as a general figure for a busy winters day, using diesel heater, HWS, pump and with my Foxbox on, thats with a 3 way fridge fitted not a compressor fridge , compressor fridge would want that much at least. .......