# Sevcon Encoder Offset



## remy_martian (Feb 4, 2019)

Does this help?


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## darren2162 (8 mo ago)

remy_martian said:


> Does this help?


thank you for the link. 

I do have this and have been through it a few times. I verified my motor phase order with this and hooked it up accordingly. The document goes on to say that the motor should be able to be commanded to spin and some adjustments will be needed for the encoder offset.

When I try to command my motor to move it is pretty much locked up or it may try to spin but gets a control current fault.

Maybe it’s not my offset yet, maybe it’s other parameter.?


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## cricketo (Oct 4, 2018)

Try spinning the motor (like using a cordless drill) while watching the RPMs in DVT. If the encoder is working correctly you should see some reasonable numbers in both directions.


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## darren2162 (8 mo ago)

I did spin motor in both directions and the speed read correctly in DVT. The one motor parameter that does not match in the Stator Inductance (Ls). The range allowed in DVT is from 0 to 3906 uH. The motor I am using is 16500uH but I cannot put this value in DVT so I put in 3906 instead. Think this would be causing my issue?


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## cricketo (Oct 4, 2018)

What is your motor ? Are you sure there is no unit scale issue, like micro vs milli ? I have a suspicion it should be 16.5 instead of 16500


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## darren2162 (8 mo ago)




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## darren2162 (8 mo ago)

The motor is 16.990mH per its datasheet


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## cricketo (Oct 4, 2018)

The magnitude of those numbers is odd, though I am certainly not an expert. Here for example consider a typical PMAC from Motenergy : https://sep.yimg.com/ty/cdn/yhst-129399866319704/ME1304outlinedrawing.pdf

Phase Resistance 0.006 Ohm
Inductance 0.066mH (that's 66uH)

One possibility is that maybe the numbers are from a different context ? I.e. there can be multiple inductive/resistive characteristics of an electrical system.


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## remy_martian (Feb 4, 2019)

mH and uH could definitely mess it up


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## kennybobby (Aug 10, 2012)

What is the subscripts "tt" represent on the Resistance and Inductance?

An 8 ohm winding with 16mH of inductance will have a L/R time constant of about 2 msec, and would limit current switching to a really low frequency.

Do you have a picture of the nameplate on the motor, or a motor model and part number?


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## remy_martian (Feb 4, 2019)

16 microhenries, 8 ohms -> 2 microseconds time constant.

The box should be filled in as "0.017" not "16.99", as @cricketo's comparative showed.

Industry is sloppy with mH and uH.

I'm guessing tt is terminal to terminal


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## darren2162 (8 mo ago)

The "tt" represents terminal to terminal measurements. The motor is made by Moog Inc. It is a 600volt motor
Here is a link to their website regarding the servo motors: CD Brushless Servo Motor Family
The model is a G463-800


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## remy_martian (Feb 4, 2019)

Why are you using an AC motor controller with a servo motor?


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## cricketo (Oct 4, 2018)

remy_martian said:


> Why are you using an AC motor controller with a servo motor?


Their marketing does say they're synchronous AC...


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## remy_martian (Feb 4, 2019)

Yeah, but they spin up super fast


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## darren2162 (8 mo ago)

It should not matter that it is a servo motor. It is still a permanent magnet motor synchronous AC motor that I was hoping would work with my sevcon drive. We have other drives that we could use from our company but this seemed to be an off the shelf somewhat cheap option to try.


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