code to change the motor amp limit

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devin
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Re: code to change the motor amp limit

Postby devin » 29 May 2017, 21:09

Last edited by devin on 30 May 2017, 06:01, edited 1 time in total.

devin
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Re: code to change the motor amp limit

Postby devin » 30 May 2017, 06:01


rew
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Re: code to change the motor amp limit

Postby rew » 31 May 2017, 04:46

As 1.414213562373095048801688724209698078569671875376948073176679737990 specifies sqrt (2) to an accuracy of a single atom should you use a compass the size of the visible universe(*) , I don't see why your drawings could be more accurate than using a finite amount of paper. If you want to visualize things, go ahead an draw things. That's useful. But please keep nonsense claims of "100% accuracy" away from me. What you believe yourself I don't mind, but you're not going to convince me.

We can transform motors to keep the same KV with different configurations. I think that for every KV and copper volume there are exactly two configurations with the same KV: delta and Y. Those configurations have very similar performance.

We can transform motors to keep the same KV while we change the copper volume. Maximum performance will change, even though the motor parameters will be the same.

Suppose that through a few examples, I formulate the theory that total energy is described by 1/2 . m . v. Funny to note that "height" is not present in this formula. Interesting observation that height doesn't matter. But when we realize that according to my formula an object at the top of the skyscraper has the same energy as one at the bottom we have to reject the hypothesis that the formula is correct.

So... if your formula predicts that it is possible to transform every motor into a smaller version with precisely the same performance, then something went wrong.

There are lots of mathematical proofs that prove that say 1==0. It is sometimes tricky to find the problem in such a reasoning. But if the result is absurd, you must have made an error along the way.

In the case of your formula: either the formual is not valid, or you are applying it wrong.


(*) That's a guess. I don't feel like doing the math. At worst my guess is off-by-a-factor-of-two and you'd need another 50-80 decimals.

devin
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Re: code to change the motor amp limit

Postby devin » 31 May 2017, 13:35

Last edited by devin on 01 Jun 2017, 11:45, edited 1 time in total.

rew
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Re: code to change the motor amp limit

Postby rew » 01 Jun 2017, 06:57

I have abused my moderator powers to edit your post to become more readable. This forum is about motors, not about "perfect sqrt (2)".

Ah... You've fallen for the fallacy of thinking that the third leg in Y configuration is not powered.

The best way to drive a three phase motor is with three sinusoidal waveforms. That's what the VESC does in FOC mode. Each of the phases is driven with a sinusoidal voltage, no phase is undriven any point in time. THAT is the "normal" situation.

Now if you move to BLDC the motor will lose some efficiency. This could very well be different in DELTA or in Y configuration. I just don't know. Fact remains that if the winding is not getting hot because it is unpowered, it is "saving" for being powered stronger during the next commutation step.

This might mean that if you have a Y wound motor with hall sensors providing torque at standstill... you may have to derate the allowable current a bit.

devin
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Re: code to change the motor amp limit

Postby devin » 01 Jun 2017, 11:57

Image

^ @Rew -- Taking a glance at the circuit diagrams of wye and delta in reference to the equal enclosed copper volume 100kv delta vs 100kv wye example (which in theory have indistinguishable performance)... it would appear in the 100kv Wye example at 100% duty cycle, 2 of the 3 phases are part of the conductive circuit or "powered" at any given time (2/3rds or 0.666... copper volume) while in the 100kv Delta example, all 3 phases appear to be part of the conductive circuit or "powered" at the same time given the 2 conductive pathways available for the electricity to follow (3/3rds or 1 or "whole"... copper volume). These motors theoretically have identical weight, performance, resistance, enclosed copper volume, rpm per volt and torque per amp-- and yet while there is an identical mass of "enclosed" copper, there seems to be a 1/3rd volume differential in "simultaneously energized" copper-- so it appears to me that it would be non-fallacious to say that identical performance is possible "using" different volumes of copper.

I note that lead-to-lead conductance, resistance, "enclosed copper volume" and kv are identical & consistent between the 2 examples despite the 33.33% difference in "same-time-energized copper volume."

There is simply no time when more then 2/3rds of the Wye's copper volume is used simultaneously. [& the Delta 100kv with identical "enclosed" copper volume energizes a factor of 1.5 times as much copper volume as the Wye 100kv simultaneously to achieve indistinguishable performance]

Image
Image

rew
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Re: code to change the motor amp limit

Postby rew » 02 Jun 2017, 05:09

You are applying the wrong voltages to your motor.

Apply:
V= Vmax * sin (0*2*PI/3 + ω.t)
V= Vmax * sin (1*2*PI/3 + ω.t)
V= Vmax * sin (2*2*PI/3 + ω.t)

You can visualize that by taking a fidget spinner, and using the Y-coordinate of each of the three arms as the voltage for each phase wire, while you spin the spinner and the motor.

Now, when you skimp on driving electronics and simply drive two phases to the power rails and leave the other alone, the Y configuration gets the situation where one part is undriven, while in the Delta configuration you might be driving current through coils that doesn't help in turning the motor. Which of these inefficiencies is more important, or if they maybe cancel out, I don't know.

devin
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Re: code to change the motor amp limit

Postby devin » 06 Jun 2017, 18:37


rew
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Re: code to change the motor amp limit

Postby rew » 06 Jun 2017, 21:01

You seem focused on BLDC mode.

Actually in the beginning motors required sinusoidal excitation. Then people got more control over the back EMF waveform and could actually make motors that accepted the "simplified" driving scheme. Since a few years, motor manufacturers know that you could drive their motor with FOC, so they no longer try to make hte back EMF compatible with BLDC. It still works, but not optimally.

So. I say you need to drive the motor with sines, you ignore me and post again about full-rails-BLDC-mode. Fine. Goodluck.

devin
Posts: 255
Joined: 08 May 2017, 01:55
Location: San Francisco, California, US
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Re: code to change the motor amp limit

Postby devin » 06 Jun 2017, 21:03

Last edited by devin on 06 Jun 2017, 21:08, edited 1 time in total.


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