Battery Bank cabling

Re: Battery Bank cabling

My personal suggestion.

For one string or two parallel strings, size the battery cables (and fuses) to the maximum sustained load (charging and discharging)...

If you have a 2,000 watt 12 volt AC inverter, and want to run near 2,000 watts max continuous through it, that would be:

• 2,000 watts * 1/0.85 inverter 1/10.5 volts inverter cutoff * 1.25 NEC derating = 280 Amp minimum fuse/branch circuit

If you have three or more parallel strings, I would humbly suggest that you would rate, at a minimum, the bank wiring for 50% of maximum rated load (or charging) current per string.

From the battery side--The most current you can pull from a flooded cell deep cycle battery "reliably" over all charge, age, and temperature conditions would be ~C/2.5 (recommended design limit for a reliable off grid system).

A golf cart battery is rated at ~225 Amp*Hours, so:

• 225 AH * 2 parallel strings * 1/2.5 maximum short term surge = 180 Amps
• 180 amps * 1.25 NEC derating = 225 Amps "practical" current limit from suggested bank

-Bill

Re: Battery Bank cabling

vtMaps is correct,

I got a little confused between designing for the Inverter side and the battery side--problem with "generic answers"...

My recommended "practical" maximum current from a single battery would be:

• 225 AH * 1/2.5 maximum short term surge = 90 Amps
• 90 amps * 1.25 NEC derating = 112.5 Amps "practical" current limit from suggested bank

So, from this bank, should you expect 90 Amps maximum surge/short term current or can you use 180 amps.

If the batteries share 50% each--then 180 Amps... In practice, batteries and their wiring don't always share at 100%... And worst case would be 100% from the one "good string"...

So, back to that is the maximum AC or DC load (or charging current) that is expected?

-Bill