Battery Cable Size

desertsun

We just ordered 8 6v 445AH lead acid batteries for our 48v system. Our old batteries are 400AH and have 2/0 battery cables which were already installed when we bought the house. They are pure copper with tin coated copper lugs. The inverter is a 4.4kw Magnum.
Someone told us the 2/0 size is not the most efficient and we should put smaller wires on. Someone else told us that having that size wires was great. We often get conflicting information about things like this. Can someone explain in layman's terms which size would be best?  We could just reuse the existing cables, unless that is not ideal. Thanks in advance.

BB.

I am a little confused... 6x 6 volt batteries = 36 volt battery bus. 8x?

• 4,400 Watts * 1/0.85 AC inverter rating * 1/42.2 volts battery cutoff = 123 Amps max continuous

I like to suggest using a 1/0.85 derating (1.25x) of NEC rated wiring for inverter/off grid battery systems:

• 123 amps * 1.25 NEC breaker/branch circuit derating = 154 Amp rated circuit/breakers (round up to next available standard sizes)

2/0 wiring is rated for (NEC basic table):

https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

145-195 amps (depending on insulation, temperature, conduit, etc.)...

And if you run 123 amps through 6 feet of 2/0 cable (one way run):
https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.2557&voltage=48&phase=dc&noofconductor=1&distance=6&distanceunit=feet&amperes=123&x=60&y=19

Result

Voltage drop: 0.12
Voltage drop percentage: 0.24%
Voltage at the end: 47.88

• 0.12 volts * 123 amps = 15 Watts
• 15 Watts loss / 4,400 Watt loads on inverter = 0.003 = 0.3% DC cable losses

I would not worry about 15 watts worst case loss in the cables.

-Bill

desertsun

Yes that was a typo, I meant 8 batteries.
Thank you very much!

t00ls

between batteries 2/0 is fine......from batteries to inverter is where a larger size might be handy depending on the distance from batteries to inverter

bigger wire = less resistance..less resistance is good....so whoever told you to go to smaller wire...doesnt understand electrical resistance

soooo...reuse those wires