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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I have a 240v motor with FLA 32 for 120v and 16A for 240v service. The current draw is related to the load on the motor. What happens if I run 240v at 20A by subjecting the motor to a higher load? The wire is meant for the higher current. Is there a problem here?
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Yup, there's a problem. The motor has 2 identical windings, each sized to handle 16 amperes with tolerable temperature rise. When wired for 120 volt operation they are in parallel, and when wired for 240 V they are in series.
That tolerable full-load temperature rise may well be more than 100 degrees C. Your overload would increase I^2 by a factor of (20/16)^2, for 56% additional temp. rise. Which could increase the copper resistivity to 22% above design maximum, for yet another 22% increase in power dissipation and temp. rise. etc. yada yada
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
All of what Klugesmith said is true for continuous operation. However if you want to overload the motor only with a short duty cycle and respect the maximum temperature, then you should be OK, but you'll need to do measurements to see what you're allowed. Winding resistance will be a good measurement, better than a thermometer on the case, as it will give you the winding insulation temperature, which is the stuff that will get damaged, while the case temperature will lag that somewhat.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Thanks for the replies. I should have realized the two winds would be in series. I was thinking of overdriving the motor, but this would be for long periods and I don't want to do that. I will stick with what I have.
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