Power in Flux
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Thread: Overclocking controllers and motors

  1. #11
    Seņor Member podolefsky's Avatar
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    Oct 2010
    Boulder, CO
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    Quote Originally Posted by nedfunnell View Post
    Hmm. Is that true for all kinds of controllers? I know brushless/AC controllers do their own thing with phase currents, but that's new to me for PMDC motor controller. I've got an Alltrax that is a duty cycle/voltage control- would it be the same for a torque-control style controller?
    It's the same for all controllers.

    To go 55 you need, say, 5kW. The power required is just from rolling and air resistance, so it's independent of gearing (ignoring any small difference in efficiency).

    To get 5kW you need 70A @ 72V. Since sag depends on current, there's only going to be one current/voltage combination that gives you 5kW for a given battery.

    The relationship between battery current and motor current is actually simplest for PMDC controllers. Pin = Pout, so Vin*Iin = Vout*Iout. Vout ~ RPM (at steady state), so for a given Pout, as motor speed goes down motor current goes up proportionally.

    AC systems follow roughly the same rule, although the voltage/speed relationship isn't as straight forward as for PMDC.
    - Noah Podolefsky -
    The GSX-E

  2. #12
    Member 4dollarjoe's Avatar
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    Aug 2014
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    I'm using nissan leaf batteries that can do the continous and max currents, so I think that isn't the problem. However voltage sag is prevalent. But it's within the C rate limits listed on hybrid auto.
    I am also next door to a battery company that has a bunch of academic papers on their computer. They were nice enough to let me look up the same cells and if I remember correctly they could handle 300 amps per cell so since the nissan leaf modules are 2s2p it should handle it.

    Definitely outdoor temps are affecting it to. Today is really humid and my controller fan started right up as soon as I turned on the ignition. The other day when I got slogged back to 45mph was really hot.

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