inhabor avatar image
inhabor asked

Battery output enough?

I have a nuwave induction burner that pulls 1300 watts. It is possible to use it with two 170AH Renogy batteries and a Victron multiplus compact? Do I'll get enough output power from the Renogy batteries?

battery charging
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1 Answer
kai avatar image
kai answered ·

you could, but based on the specs its not too healthy for the batteries in the long term.

The batteries are capable of discharging 100A each which would be more than enough for the 1300 watts. But the manufacturer is basically saying you won't get the expected lifetime if you choose to draw that kind of power - see below.

The battery's nominal specs are rated at 0.2C which means 170*0.2 = 34Amp per battery.

34A per battery * 2 = 68A all up, then *12v = 816W. You're out by nearly a factor of 2 for the burner, using the 0.2C nominal. This is before taking into account inefficiencies from the multiplus.

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inhabor avatar image inhabor commented ·

What about if I use three batteries? Would that help?

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kai avatar image kai ♦ inhabor commented ·

Battery side calc:

34A * 3 = 102A => *12v = 1224W maximum draw from battery while staying inside 0.2C

Consumption side calc:

1300 W / 85% efficiency (the multiplus compact 12/1600 has 90%+ efficiency at full load, so in practice it might be higher than 85% but I don't have a derating curve handy) = 1529W

So. The numbers look a little better with three batteries. Still over the published limits. The batteries aren't cheap so there's a few ways of looking at this:

1) If you want the comfort of staying inside Renogy's specs then no, 3 batteries won't be enough to keep the batteries from being discharged at greater than 0.2C. You would scrape past with 4 batteries.

2) The discharge rate with 3 batteries is out by 50% relative to 0.2C. Assuming the cooker isn't on 24/7, the discharge rate doesn't look outrageously high. The batteries essentially have a higher wear rate than using 4 batteries. But this wear and tear is gradual. Its not like just because you've drawn over 0.2C for a few hours here and there the batteries would suddenly decide to pack up and quit. The risk of earlier failure is there, and you would have to take on the incremental risk.

3) See if another method of cooking is viable. Cookers/heaters are one of the more challenging loads for battery systems simply because they draw so much power.

At this point I think its no longer a technical issue, its a question of risk appetite. Hope that's helpful.

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inhabor avatar image inhabor kai ♦ commented ·

Thank you very much for your help.

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