Old DC Motor Starter

[dv1976]

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?

[Cheller]

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.