What is the Technique for Measuring No-Load Current?

Electric Motors and Controllers
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mclovin   100 W

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What is the Technique for Measuring No-Load Current?

Post by mclovin » Oct 01 2011 10:34pm

As the title says - what's the technique for determining actual Io? I guessing an ammeter would help but maybe using a shunt would be better. Also, I'm wondering how the different phase currents are handled. I expect an ammeter would measure the RMS value of the current but I'm assuming I would want the max current. Since I'm concerned with the no load current the controller would have a PWM rate of 100% so max current is desired.....I think. I though of measuring batt-ESC current but I don't know how to account for ESC losses.

Any help you guys can provide is much appreciated. :D

SamTexas   100 MW

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Re: What is the Technique for Measuring No-Load Current?

Post by SamTexas » Oct 02 2011 12:26am

I must be missing something here. Current is always zero when there is no load. So what's there to measure?

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neptronix   100 GW

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Re: What is the Technique for Measuring No-Load Current?

Post by neptronix » Oct 02 2011 12:37am

SamTexas wrote:I must be missing something here. Current is always zero when there is no load. So what's there to measure?
No load means that the throttle is at 100% and there is no load on the motor. As in... you are not on the bike, and the wheel or motor is not being used to move you or anything else...

On this forum we generally measure the output from the battery to the ESC/Controller.
I believe the same method is used with the RC guys etc.

I am not sure how you go about measuring 3 phase DC amps.. it most likely requires specialized equipment.

For measuring my current i just use a turnigy watt meter. I think it cost me all of $30? There are various other RC hobby type voltmeter/amp meter units you can use.. now they are not the most accurate pieces of equipment, definitely not accurate into the decimal range.... but they work.
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Re: What is the Technique for Measuring No-Load Current?

Post by ZOMGVTEK » Oct 02 2011 12:57am

Given the low current under no load conditions, the controller tends to have enough capacitance to essentially draw pure DC, making RMS not really apply.

Any way you measure the power from the battery into the controller should be relatively accurate. Cheap power meters, high end DMM, whatever. Don't worry about measuring the power at the phase wires, that can be a bit more tricky.

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mclovin   100 W

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Re: What is the Technique for Measuring No-Load Current?

Post by mclovin » Oct 02 2011 4:32pm

OK.

Sounds like I can use the batt- to ESC current measured on my CA. I'll go with that.

Cheers.

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Re: What is the Technique for Measuring No-Load Current?

Post by DAND214 » Oct 02 2011 7:22pm

CA?
NOW WHY DIDN'T I THINK OF THAT?

And we all thought it was so simple.

That's what I have, too.

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Re: What is the Technique for Measuring No-Load Current?

Post by itchynackers » Oct 02 2011 7:39pm

I use the CA too, but I noticed since I changed to Specialized Armadillo tires with 4 ounces of automotive tire slime, that my no load went up to 1.5A at about 62mph.
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