Basic Battery Power Revisited

battery

I first saw the term “battery horsepower” and looked into it here.  Let’s get a refresher, in the context of the CBRe project.

Let’s see.  Talking about battery power, you’re looking at the wattage a pack can make.  Watts = Volts x Amps.  So if you take a pack, and know the voltage and the amps it’s capable of, then you can figure what it can do for watts.

I have a 100kw motor for a target.

I want to run it at around 200V…  at least that’s what I’m thinking.  So let’s look at the Leaf cells.  The voltage of that pack is 182V, and the testing I’ve seen says it can do 5C – so we have our amps, if we know what 5C means.  Bear with me.  Here’s my post on C-Rates.  Simply, though, the formula is: rating x capacity = current

So our rating is 5C, the capacity of one cell is 30ah, so the current from one cell is 150amps.  Now, for the pack I showed, you have two paralleled strings of cells, so a total capacity of 60ah.  The total current from the pack is 300A.

Next step.  Let’s find the total wattage of the pack.  at 300A, and 182V, we get a 54.6kW pack.

See how this can work?  Let’s say we want to double the voltage to 400V (for round numbers).  Starting with a 54kW pack, we divide by the voltage to get the current – 136.5A.  Bigger volts, less current.  Thank you Mr. Ohm.

Here’s the real exercise, though. We have a system that is rated for 100kW, so what do we need to get that out of a pack?  Let’s double the C Rate.  At 200V and 10C with a 60Ah capacity we’re looking at 600A.  At 600A and 200V we’re getting a 120kW pack.  Or, with that first pack, if I double the voltage to 400V, I now have a 108kW pack.  Suddenly the ultra-high C-rates of the RC lipo cells starts to look promising again.

There’s got to be some online calculator for this.  Right?  In any case, it’s the next step to making the battery decision, and it’s going to be a matter of sitting down and running the numbers.

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2 responses to “Basic Battery Power Revisited

  1. Small typo where you state you double the C-rate you should end up with 120Kw (600 *200). So as you said you could double the C-Rate, double the Voltage or double the Ah…. all ends up the same Kw.

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