Looking for a a basic formula

Hairfarm
Hairfarm Solar Expert Posts: 225 ✭✭✭
in Solar Beginners Corner #1
Greetings,

What is the basic formula that will allow me to convert AC watts into DC amps?

In other words, if a load can potentially draw 2000 watts max from my inverter, then how many DC amps is the inverter pulling from my battery bank?

What is the formula for that?

I couldn't find this anywhere in my notes that I've taken from this forum over the last few days.

thanks,
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #2
    Re: Looking for a a basic formula

    Here is what I do... I will use "real numbers"--Just substitute your values:
    • 2,000 Watt * 1/0.85 Inverter eff * 1/10.5 volt batt cutoff * 1.25 NEC Derating = 280 Amp circuit/fuse/breaker minimum

    If you just want the amps at any typical value:
    • Power = Watts = Volts * Amps
    • Amps = Watts / DC Volts

    But, of course, inverters have losses (around 85% is a good number), the inverter will draw more than its loads:
    • Amps = Watts * 1/eff * 1/DC Volts
    • 2,000 watts * 1/0.85 inverter eff * 1/12.2 volts = 193 amps at nominal battery voltage and inverter efficiency

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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