Need help understanding this old DC motor wiring diagram

[741C]

https://imgur.com/a/kKPtzyP

We are making improvements to these motor controls by replacing these old resistor banks and DC generator with DC drives. But, we have learned that evidently these motors are "series wound", meaning that the armature and fields are in series with eachother. But, the peckerhead has three leads into the motor. Two positives that are spliced together just before entering the motor. What are the two positives? What is the yellow lead? The third appears to be a negative. The motor says series wound which would suggest only two leads. Cant tell if there is a shunt coil inside or not – that would be a “compound wound” motor I think but could explain the third lead.

Thanks in advance.

 

[Vic]

The third lead will be the connection between the armature and the series field. To reverse a series motor, you must reverse the polarity of either the armature or the field without changing the polarity of the other. The third lead allows this to be done.

If you are going to convert this to a DC Drive, and need the motor to reverse, you must make provision to be able to change the polarity of just the armature or field. This is best left to a integrator who is experienced with DC Drives.

 

[DSMR]

Be careful about getting the connections correct. If you put the series field in buck, it may eventually fry the motor. I used to use a 9V battery and an old anolog meter to test polarity (I found one that the leads were labeled wrong).

 

[Vic]

DSMR
You are confusing a compound wound motor, which has both a series and shunt field, with a series wound motor, which only has a series field. If the polarity of the field is reversed in a series wound motor, the motor will just run in reverse. No harm to the motor.