non reversing dc motor?

[crumblebear]

Hi all,

Wonder if anyone can help me as this isnt really my area! we recently had and electric tractor witha strange fault. The tractor uses to 2 brushed dc motors (parallel fields i believe) driven by a basic chopper system (Power mosfets and current sensor switch them to negative with freewheel diode system) After fitting a new motor to one side we had the following issue;

New motor spins very slowly (15rpm max)clockwise
The second motor spins at around 80% of its normal speed clockwise
Neither motor spins anti clockwise

The only fault was with the original motor and the rest of the system has been thoroughly tested all mosfets, controller, current sensor etc and motor wiring etc are ok

The only difference is we used a different rebuilder to do the new motor? What could they have done to with the motor that would stop both from turning in one direction? All motor connections are external so could be an internal connection wrong but i cant see what would cause a dc motor to run in one dorection only??

Thanks in advance
Harry

 

[DickDV]

Harry, would you please provide us a wiring diagram on how the two motors are connected together. You said the fields were in parallel but how are the armatures connected and how is reverse or anti-clockwise accomplished.

Also, do these motors each have four leads, F1,F2,A1, and A2?

 

[waross]

I once had a similar condition where a DC motor on a printing press would not reverse. One of the connections was loose and had been generating heat. This caused corrosion of the copper conductor to the point that copper oxide was rectifying and would only pass current in one direction. I would check for poor or rectifying connections.

Bill
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