The Low Rpm Efficiency Myth - Busted?

[Leeps]

Ok well you got another post in while i was typing, but the last graph really just showed what i was saying.
im still up for the pulses of energy gig
by the way i thought the title of the thread was low rpm efficiency myth, not current warping myth or pwm effect myth, just that something doesnt feel right
Joe

[safe]

....I'm willing to tackle the little extra pulses of energy also if you want to go at it and put an end to this debate.

That was what the "myth" was centered around... the idea that the pulse effect allowed a little extra energy through than the voltage would normally suggest. We don't need to go too far into it becuase it's actually a pretty small influence, but since it shows up at low rpms it does help a great deal those people with fixed gear machines. However, that little "extra" boost doesn't change the overall truth that if the motor / current limit as a whole is inducing a bad efficiency situation the PWM "current warping and boosting effect" won't "miraculously" turn things around.

I think I've had enough typing for a while too... I think we are on the same page more or less now, so that's good.

(there was a moment when I was thinking "Oh my gosh, have I been wrong with this stuff for weeks now?" until I realized what was going on)

[safe]

I thought the title of the thread was low rpm efficiency myth, not current warping myth or pwm effect myth,

I take full credit for that mistake... terrible title on my part...

[Leeps]

Well you are right if the switching frequency is too low for a given motor inductance the current can rise to dangerous levels for the controller. In any case this would show itself at higher throttle levels, with a worse mismatch getting you into trouble at lower throttle levels. I seem to remember hearing older curtis motor controllers having this problem with axial flux motors. This effect is hardly desirable and is dangerous for the motor controller.
I had a thread about a new idea for a different approach to motor controllers that would match switching frequency to motor inductance, i have enough on my plate to work more on it.
I'm glad this is over
Joe

[fechter]

There you go, the controller should dynamically adjust it's on-time to maximize efficiency in the system. The iron and copper in the armature are acting like the inductor in a switching power supply. Those laminations are typically very inefficient at high frequencies, which can result in heating and loss. At the same time, you don't want the field to reach anywhere near steady state current, so the switching frequency can't be too low either.

I've seen some power supply circuits that measure the dI/dt to figure out the switching point.

I guess this idea should be a new thread.

[Leeps]

Fechter i had a thread on that. Remember my thread, new approach to brushed motor controller. Granted i didnt do anything with it, it was just an idea. And to boot my thread just went off on a tangent, maybe we should bring up the subject again, just doesnt seem like theres much to discuss on the subject.
Joe