DC motor Rotation

Good afternoon everyone.

Does anyone in here have a formal procedure in place for verifying rotation on large DC motors before they are installed. I believe there is a way to check this by using a battery across the armature and reading the polarity on the field. Does this sound familiar to anyone? I want to start verifying rotation before the motors are installed to save downtime.

Any input would be appreciated.

Original Post
Actually, the brushes are in such a position on the commutator, that you should not induce ANY voltage from the armature circuit to the field and vice versa. I believe that the convention should give you correct rotation in 99.99 percent of the cases: F1 is always positive, F2 negative. If A1 is positive the rotation should be CCW facing commutator end. Your repair shop should always check it.
What you described sounds like a 'bump' test to verify shunt field to series field polarity alignment in a compound motor.

A meter (this is one application where analog meters are easier to interpret, although a scope will also do) is connected with the (+) probe on the positive shunt field terminal (F1), and (-) probe on the negative shunt field terminal.

When a battery (3 to 6 VDC) is wired with the (+) terminal to the positive (S1) series field terminal, and (-) battery terminal to the negative (S2) series terminal, and a connection is made voltage measurement across the shunt field will bump positive, then fall back to zero; when the battery connection is opened voltage will kick back in the negative direction, then return to zero.

This shows the shunt and series fields are wired in the same relative polarity, and is useful to determine if the field leads are mis-marked.

If motor leads are marked properly (and motor connected properly to the drive) then rotation direction will be according to the NEMA MG-1 standard shown in the motor installation and operation manual.
Mustangman ,
I agree with Jank who said that with battery you can locate the neutral axis of the brushes on DC motor.And percent 99,99 of correct rotation with F1 and A1 positive is OK, but I know few old Europian manufacturer who have DC motor with opposite rotation ( ACEC , MEZ). If you not sure you must verify rotation from diagram on nameplate of the motor or good idea is that repair shop check your motor . Did someone know for another manufacturer of DC motor who have "weird" CW rotation facing commutator end with F1 and A1 positive ?

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