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Wire size and breaker size protection

At 12 volts, 1500 watts will pull 125 amps. So of course you can't use the maximum rated output of your inverter. A 150 amp breaker will protect the wiring but will leave the BMS as the primary circuit protection. As to what gauge wire that depends on the length of run. You can use this calculator to determine proper wire gauge:

 
The fuse or breaker needs to be the safety link Not the wire so depending on how long your run is going to be you may need to re-think what wire and or breaker your going to use.
 
I plan on the inverter being close , total wire length would only be 4 foot, 2 foot each way.A quick check on the wire calculator says 6 gauge is good for 160 amps at that length. So now I just need to find a breaker.
 

The breaker spec says 3k AIC. That's the maximum short-circuit current it is rated to interrupt.
Likely a 70 Ah lithium battery can deliver considerably more, so that breaker isn't ideal protection. (Although, it's specs are for 48V so likely provides some greater undocumented protection at 12V)

I plan on the inverter being close , total wire length would only be 4 foot, 2 foot each way.A quick check on the wire calculator says 6 gauge is good for 160 amps at that length. So now I just need to find a breaker.

Better use another chart. This one says single 6 awg wire with 90 degree C insulation in free air is good for 105A


Just use 1/0 or 2/0 and don't worry about it.
 
I think I'll just use 2/0 since it's a very short run.
Hedges, you got a breaker that you might recommend and work with the 120 amp bms?
Thanks for the input everyone!
 
Especially for lithium batteries, which can deliver something like 20,000A into a short (probably less for your smaller 70 Ah), I prefer fuses.
Class T fuses are rated 20k AIC. MRBF are rated 10k AIC at 14V, probably good for your size battery.


Do the cells have an internal resistance (IR) spec? That would allow calculation of short circuit current.

Fuses should be sized so they never blow under any inverter loading conditions. It is not likely they will protect the BMS, which hopefully protects itself under normal conditions. There are some "semiconductor" fast fuses used for variable frequency drives and the like, but VFD limit their current draw while inverters draw a big surge to start motors.

1500W/10V/90% efficiency x 1.25 margin x 1.12 ripple factor = 233A
I would rather size the system for 250A, including a BMS that could handle that. Or use 24V for half the current.

Does inverter have wires for remote on/off switch? Could let BMS control that rather than carrying current through its FETs.

Fast fuses can blow just due to inrush current. People here set up precharge circuits with a resistor to avoid damage to switch contacts. If you get a rotary switch meant for two banks, one position can be precharge resistor and the other direct to battery. I'd like to find one "Off On On", but here's an "On Off On" switch.

 
I plan on the inverter being close , total wire length would only be 4 foot, 2 foot each way.A quick check on the wire calculator says 6 gauge is good for 160 amps at that length. So now I just need to find a breaker.
2' of wire that is fairly well protected and attached to a BMS that will shut down for overcurrent.... I am thinking I would use #2 wire and skip the fuse.
 
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