Isolator-Combiner Ampacity

[Training Wheels]

My son’s motorhome has a G24 starting battery and 2 G27 house batteries, all 12V. I’m moving the house batteries toward the rear and replacing them w 3 125A Lifeline G31XTs 12V (375A). Newmar OE installed a 100A Battery Isolation Manager (BIM). This is NOT a B.I.R.D.; but for you who have only used BIRDs, the overall concept is the same. BIMs are just made differently and do things more magically.

I need to know what size Pos wires to connect the BIM. Newmar OE is ~4AWG which I’ll remove. I know how to use ampacity, voltage drop, ANL Fuse Blow, ABYC, and NEC charts, and have used them all for this project. Unfortunately, the one thing I need and don’t have is the current amp draw for the BIM. One side to the starting battery will be ~2’; but the other Pos side to the Pos Source buss (house batteries) will be ~21’.

The BIM is from Precision Circuits, Inc.; and I’ve talked to them with little help. They sell 160A and 225A versions now ILO the 100A they sold Newmar in 2014. Their best idea was to get the big 225A, just ‘cause biggest is best.

My alternator, BTW, is 220A and would normally default production to the starting battery. The BIM sorta overrides the alternator’s regulator and combines the circuit based on the voltage of both battery systems.

Does anyone have an idea how I can determine how the maximum current the BIM can send down my long 22’ run? With that, I can figure wire size and breaker size. I guessed using the 225A of the new BIM and got a result of 4/0 for the wire. I can run 2 2/0s in parallel and get the same result. That seems like too much wire just for the BIM to transmit what amounts to maintenance current, but that’s just my ignorant side thinking.

Jerry

[myarmar]

Jerry, BIM doesn't regulate current, it is acting as a "smart" ON/OFF switch. The current will be determined by charging source and batteries state of charge. I don't think you need to account for max possible current because this current will last only a minute or two. I would run single 2/0 cable.
Mike

[twinboat]

The alternator current is always sent to the chassis ( starting ) battery.

The BIM connects the chassis battery to the house battery when conditions are right.

It will not connect unless the chassis battery is receiving and maintaning a steady 13.4 or more volts.