## would this method be accurate to determine a motor winding resistance?

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devin
Posts: 255
Joined: 08 May 2017, 01:55
Location: San Francisco, California, US
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### would this method be accurate to determine a motor winding resistance?

Hello,

Does anybody know if this method for determining a motor's winding resistance from data logging videos will give accurate results?

Thanks,

Devin

----------

Example 1:

From this screenshot of a data log I want to determine the resistance in ohms from lead to lead of the motor's winding.

Proposed Method:

On the log at 6.8 seconds, we can gather the following numbers:

Speed (mph): 0mph
Battery Amps: 10a
Motor Amps: 88a
Battery Voltage: 47v

From the 0mph speed, I first determine the back emf voltage is 0v

Back EMF Voltage: 0v

From the Battery Voltage and Battery amps, I next determine the electrical watts:

10a Battery Amps x 47v Battery Voltage = 470w Electrical Watts

Speed (mph): 0mph
Battery Amps: 10a
Motor Amps: 88a <----------
Battery Voltage: 47v
Back EMF Voltage: 0v <----------
Electrical Watts: 470w <----------

Since Back EMF Voltage at 0mph (stationary) is 0v, I next make the assumption that the motor current simply behaves according to ohm's law...

Therefore I go to the ohm's law calculator and enter 470w and 88a:

...and "Calculate"...

The resistance result comes back as "0.0606921488ohm"

Is this accurate?
Last edited by devin on 11 Mar 2018, 15:53, edited 1 time in total.

devin
Posts: 255
Joined: 08 May 2017, 01:55
Location: San Francisco, California, US
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### Re: would this method be accurate to determine a motor winding resistance?

Second Example:

This is a still frame from Benjamin Vedder's electric skateboard logging video:

Speed (mph): 0mph
Battery Amps: 1.26a
Motor Amps: 27.33a <----------
Battery Voltage: 33.2v
Back EMF Voltage: 0v <----------
Electrical Watts: 41.8w <----------

Since Back EMF Voltage at 0mph (stationary) is 0v, I next make the assumption that the motor current simply behaves according to ohm's law...

Therefore I go to the ohm's law calculator and enter 41.8w and 27.33a:

...and "Calculate"...

The resistance result comes back as "0.0559624885ohm"

Is this accurate?

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.
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### Re: would this method be accurate to determine a motor winding resistance?

devin
Posts: 255
Joined: 08 May 2017, 01:55
Location: San Francisco, California, US
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### Re: would this method be accurate to determine a motor winding resistance?

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