Cable size- check my math

Yurtdweller

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I'm connecting 2 to 4 PCs LiFePo4@280ah/12v. Each BMS has max output of 100 amps, and max draw will be from a 12v 2000 watt inverter (166 amps). I am planning to connect each battery pack separately to 5 lug buss bars. I was going to use 2/0 cable for the full 166 amps, but I got to thinking that since each battery pack is limited to 100 amps output, and I think, 100 amps input, could I not use 4gg or 2gg cable instead?
 
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rmaddy

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A 12V 2000W inverter can pull up to 200A from the batteries (2000W / 12V / 85% efficiency).

You are correct that each battery will provide up to 100A. So you can wire each battery to the bus bars using 4AWG (though 2AWG would be a better choice). But you still need 2/0AWG from the bus bars to the inverter. Make sure you fuse each battery with a 125A fuse and put a 250A fuse between the bus bars and the inverter.

Also be sure the two positive wires from the batteries to the positive bus bar are the same length as each other. Be sure the two negative wires from the batteries to the negative bus bar are the same length as each other.
 

Yurtdweller

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Thanks. The inverter came with it's own doubled cables. Not sure of their sizes, tbh. I will follow your fusing advice. I've been living fast and loose as far as fusing goes🙄. I've built my batteries in milk crates, and was running a circuit breaker in one, and not another, and it sure futzed things up. The batt with the breaker had a lot more resistance, and wouldn't charge right. I'll correct that. But the smaller cables will save me at least 50 bucks:)
 
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rmaddy

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Cables that comes with inverters should only be used for decoration.

Don't skimp on fuses. Buy quality name-brand fuses. Saving $20 isn't worth burning down the house. That's really true of all components.
 

time2roll

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Mine is similar. I used #4 wire and 125 amp fuse on each. Works fine.
4/0 from bus to inverter but that a bit more than needed depending on length.
I was pleased to see how the higher voltage of the LFP significantly reduced the amp draw on the inverter vs the old FLA and sagging voltage.
 

Yurtdweller

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I've ordered the victron lynx power in and will be fusing each battery and will get a circuit breaker for the inverter. Thanks gang.
 

Yurtdweller

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One other question. I travel to four states each year. My system moves from my van to my yurt, and back again. I cannot lift and load 4 batteries and all the circuitry, so my system will be modular. When the system is in-vehicle, I don't use all four batteries, and I don't have charging capabilities in my van yet, so my system runs total loss, and my batteries get out of sync. When I arrive at my destination, everything gets reassembled. Obviously, I need to make sure the batteries are at similar voltages before they are reconnected in parallel. Here's what I want to do.

I will connect a battery lead to each lug in the Lynx Power In unit. Then, I need an easy way to connect or disconnect each battery, so that each one can be isolated while it is charging to my predetermined target voltage. I would consider simply connecting each lead into the Lynx as needed, but that seems problematic, and sloppy/arc-y. Would Anderson plugs be sufficient, or should I use switches too? And if I use switches, would the 7 buck harbor freight cutoff switches be acceptable, or should I splurge and get the 25 buck flush-mount, dial type switches? I am concerned about arcing. 12v system.

I hope all of this is clear :/
 
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