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Old 10-17-2014, 01:49 AM   #1220 (permalink)
thingstodo
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Quote:
Originally Posted by MPaulHolmes View Post
My main contactor evidently has an on resistance between 7 and 300 ohms. also, either the motor now has a problem or something needs to be fixed on the controller. I don't think its the controller, but I'll check. what is a common failure mode for a 3 phase motor that has had too much current? this is happening at a terrible time. I think I got rid of just about all the bugs.
7 ohms is too much, 300 ohms is WAY WAY TOO HIGH.

Too much current heats up the coils, the insulation degrades. Depending on the insulation class, this is 60C, 80C 105C or 125C above ambient temperature (it is a relative temperature). This link seems pretty good

http://toshont.com/ag/mtrldesign/AG0...%20Rise%29.pdf

The insulation failure allows current to flow to ground (about 2/3 of the time) or between phases (the other 1/3). There are good tests for phase to ground - a megger will put high voltage DC on the phase and check for current flow to ground. For phase to phase faults, there is really no easy way to check.

By the time you take the motor apart, you can usually smell a problem (failed electrical insulation has a distinctive smell). A small scorch mark is all you are likely to see.

This is a *BAD* way to verify your hardware over-current circuit!

I would replace the contactor first. If the contactor is over 7 ohms, your controller may be starved for voltage and amps
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e*clipse (10-17-2014), MPaulHolmes (10-17-2014)