SW inverter to battery cable calculation [RE-wrenches]

[Allan Sindelar]

Joel,
The upper example has been the one that I have most often seen. It's used by
Wiles on page E-16 of his PV/NEC book. If you extrapolate these numbers to
the SW5548, I think you will get 5500 watts divided by 0.85 inverter
efficiency divided by 44 volts = 147.05 x 1.25 NEC = 184 amps battery cable
rating.
I have no idea where you got the part about adding "28 amps RMS AC current"
to the DC calculation.
Allan at PosE


----- Original Message ----- 
From: "Joel Davidson" <joeldavidson at earthlink.net>


> Last week I asked someone at Xantrex technical service for the fuse,
> breaker and wire loss calculations for the cable between the SW inverter
> and the battery, but the person I talked to did not know the
> calculations.
>
> One system designer uses this calculation for the SW4024:
> 4000 watts divided by 22 volts divided by 0.85 inverter efficiency =
> 213.9 (for the 250 amp breaker) and an additional 1.25 NEC = 267 amps
> for the 300 amp fuse.
>
> Another system designer uses this calculation for the SW5548:
> 5500 watts divided by 0.8 inverter efficiency divided by 40 volts = 172
> amps DC plus 28 amps RMS AC current = 200 x 1.25 NEC = 250 amps battery
> cable rating.
>
> Does anyone know the correct efficiency multipliers for the SW inverters
> and the calculation to use?

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