Obsolete Industrial


Old DC Motor Starter

dv1976

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Old DC Motor Starter
« on: July 31, 2015, 04:31:AM »
Folks,
I have been haunted by a vintage DC motor starter. It consists of a series of contactors, a resistor bank, some vintage timers, and a lot of old wiring. It is the starter for a 240VDC motor at 75 HP.

There is a ghost in the system. Most of the time it starts appropriately, and sometimes it just won't start the motor. I started checking the coils for resistance and noticed that one of the contactor coils that steps through the starting resistors has a lower resistance reading than the other two.

My question is if the contactor is closing, would the lower resistance have any effect of the rest of the sequence?
Thank You!!


Cheller

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Re: Old DC Motor Starter
« Reply #1 on: August 10, 2015, 04:05:AM »
How old is the starter? (year of manufacture) What brand is it? (Westinghouse, Allen Bradley, Cutler Hammer, etc)

I really don't see a small difference in resistance having anything to do with your problem. I believe a lower resistance in a coil will do nothing but draw more current through that particular coil. It shouldn't affect the operation of the motor starter.

These old coil operated DC motor starters are a thing of beauty. State of the art at the time and there are still some of these floating around out there.
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