# F+, F-, D.C. Motor Connection Question?



## 8V71 (Dec 23, 2011)

The field is polarity sensitive as in direction of rotation. But that is all.


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## John Valdes (May 17, 2007)

Field connections are fully dependent on voltage. Series for high and parallel for low.
Since your motor is relatively small, it probably has a fixed field voltage.
The nameplate will give you the armature and the field voltage.

Yes the field connection is polarity sensitive.
Its good practice to interchange armature leads to correct rotation.
You can wire for the rotation you need. So you can be assured it runs the right direction without moving any leads.

Someone gave you a link to the Baldor DC motor publication in the other thread.
It will show you how to connect for rotation.


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## DriveGuru (Jul 29, 2012)

If the motor is a "shunt wound" motor the field polarity is irrelevant for proper operation( other than maintaining polarity of F1 to F2 with respect to F3 to F4), direction may be changed by reversing either the armature or the field. 

If the motor is a "compound wound" motor, care must be take to maintain the same polarity of current F1 to F4 with respect to S1 to S2, failure to do so "WILL RESULT IN BURNING UP THE SHUNT FIELDS", direction must be changed by only changing A1 & A2.


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## Jayc316 (Jun 30, 2013)

Thanks DG. That post lite up some of the formally dark corners of my understanding of D.C. motors.


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## John Valdes (May 17, 2007)

Jayc316 said:


> Thanks DG. That post lite up some of the formally dark corners of my understanding of D.C. motors.


Did you download the Baldor PDF?
It has every DC motor connection shown plainly on the last page.
I like to use it or try to remember how to connect for correct rotation first time.


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## Jayc316 (Jun 30, 2013)

Yes I did. I have saved it and am still working on digesting it. The Boston Bata II D.C. speed controller for the motor from this original post was putting out @225VDC on the field without motor connected. After connecting the motor, with 4 field wires in sires, the field voltage dropped down to @107VDC. The motor is running fine. Now I am working on understanding: 1)when do I wire the field in parallel? 2) what to do if I open a motor junction box and find S1 and S2 wires along with 4 field wires?


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## DriveGuru (Jul 29, 2012)

Sound like that may be a current regulated field supply, you need to look at the drive parameters concerning the field, and wire the field in accordance with the set field current compared to the motor nameplate, the voltage should not have decreased if it were a fixed field bridge.

To check polarity, black meter lead on F1 red on F4, measure and observe polarity, then black lead S1 red lead S2 measure and observe polarity, polarity should be the same. Note S1 to S2 you will read milivolts to a few volts depending on the motor. But what you're concerned with is polarity. Also remember when testing that the S leads are at the same potential as the A leads with respect to ground, so be careful.


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## John Valdes (May 17, 2007)

Jayc316 said:


> Yes I did. I have saved it and am still working on digesting it. The Boston Bata II D.C. speed controller for the motor from this original post was putting out @225VDC on the field without motor connected. After connecting the motor, with 4 field wires in sires, the field voltage dropped down to @107VDC. The motor is running fine. Now I am working on understanding: 1)when do I wire the field in parallel? 2) what to do if I open a motor junction box and find S1 and S2 wires along with 4 field wires?


What does the nameplate say the field voltage is?
Series for high voltage and parallel for low voltage.
Its on the nameplate.

You must connect the field for the correct voltage.

Look at the download for the S1 and S2 connections. It explains it for you.
Just because its running does not mean you connected it correctly.
It (motor) could be severely hampered by wrong field connections.
Low field voltage increases speed and reduces torque.
So you may be able to achieve the desired speed while reducing the torque required for the application.


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## DriveGuru (Jul 29, 2012)

John Valdes said:


> What does the nameplate say the field voltage is? Series for high voltage and parallel for low voltage. Its on the nameplate. You must connect the field for the correct voltage. Look at the download for the S1 and S2 connections. It explains it for you. Just because its running does not mean you connected it correctly. It (motor) could be severely hampered by wrong field connections. Low field voltage increases speed and reduces torque. So you may be able to achieve the desired speed while reducing the torque required for the application.


The rules change a little when you are using a drive, what you are saying is correct for a fixed field supply. If it is on a drive that has a current regulated field supply, the drive is going to regulate to the set point amperage. If the field is wired in series or parallel, the drive will still regulate that same current setting by raising and lowering the voltage to do so. So you could get yourself in trouble pretty quickly if care isn't taken. Since after he connected the field, the voltage lowered, I'm assuming it's current regulated.


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## DriveGuru (Jul 29, 2012)

I forgot to mention earlier, on the motor, use he "hot amps" field current if it's listed. Sometimes they don't list the field current. In that case measure the field resistance after the motor warms up with the field wired in series. Applied field voltage(name plate voltage) / measured resistance (with the winding physically hot) = Hot field current. The reason you need to measure after the winding is up to temp is that your field resistance can increase 5-25% as the winding heats up as compared to when it's at room temperature. It's important to have it set for hot amps or you will be over exciting the field, and thus causing it to run at a higher temperature. Hope this helps.


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