Author Topic: Reversing D.C. Motor Direction  (Read 602 times)

Offline raynerd

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Reversing D.C. Motor Direction
« on: July 17, 2018, 05:40:05 PM »
Evening, Iíve got a D.C. electric motor. Itís old, probably 30 years. Iím not totally familiar with motors but after some research, and a picture below, Iíll try and explain what I have inside. So when the rotor is out, Iíve got the magnets and what looks like a wound stator (googling has suggested that!) that is wrapped. These are two semi circles and a wire coming out of each. Two wires going to each of the brushes and one going to live and one to common.

I appreciate that I clearly havenít a clue what I am talking about I should be capable of editing the configuration if I know what I have to do. In an ideal world, Iíd add a switch to flip the rotation but Iím already getting ahead of myself.

Is there any way to change the direction of rotation?



Cheers
Chris

Offline John Rudd

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Re: Reversing D.C. Motor Direction
« Reply #1 on: July 18, 2018, 01:14:21 AM »
I dont comoletely understand what you have there, given your description.....

A dc motor has magnets, no wound field coils....it will run on a dc supply only

A universal motor doesnt have magnets, but wound field coils....will run on either ac or dc supply

Any how, in either case, swapping over the wires to the brushes will change the direction of rotation....

Do be careful..... :zap:
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Offline raynerd

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Re: Reversing D.C. Motor Direction
« Reply #2 on: July 18, 2018, 02:08:33 AM »
That John, is because Iím talking out of my .....
It is not a D.C. motor at all...it is most definately running on AC!

However, you have answered my question. Thank you very much!

Offline Pete.

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Re: Reversing D.C. Motor Direction
« Reply #3 on: July 18, 2018, 02:21:25 AM »
I dont comoletely understand what you have there, given your description.....

A dc motor has magnets, no wound field coils....it will run on a dc supply only

A universal motor doesnt have magnets, but wound field coils....will run on either ac or dc supply

Any how, in either case, swapping over the wires to the brushes will change the direction of rotation....

Do be careful..... :zap:

My lathe has a DC-only motor with field windings.

Offline PekkaNF

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Re: Reversing D.C. Motor Direction
« Reply #4 on: July 18, 2018, 03:52:22 AM »
If I understand it correctly you have series connected universal motor.

https://en.wikipedia.org/wiki/Universal_motor

This thread should answer you question more clearly than I can:
https://electronics.stackexchange.com/questions/253867/reversing-direction-of-an-ac-universal-motor

When these motors are run in DC, you just swap polarity and it runs then opposite direction. Obiviously this does not work on AC, there you neeed to reverse the field connection with respect to the armature (often easiest to swap the wires on brushes).

However, there is one caveat: some motors may be optimized to run one direction:

1) Radial fan may have curved blades pull the air more effectively when the shaft it rotating the correct direction. Axial fan is allways designed to cool primary the commutator.

2) brushes might be "advanced" to improve efficiency or increase RPM. You see that easy when you look at the rear of the motor and compare bruches axis with the field winding, if all looks symmetrical you are good to go (same charachteristics, both direction). If the brush holder is rotated or tilted, you will notice different performace. Sometimes the parts can be remounted.

About the brushes this is pretty good introcuction:
http://www.morganelectricalmaterials.com/media/1996/technicalhandbookglobalproof_0.pdf

p.12-15 is good info on how to read bruches or commutator to identify problems.

Pekka

Offline John Rudd

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Re: Reversing D.C. Motor Direction
« Reply #5 on: July 18, 2018, 04:07:42 AM »
I dont comoletely understand what you have there, given your description.....

A dc motor has magnets, no wound field coils....it will run on a dc supply only

A universal motor doesnt have magnets, but wound field coils....will run on either ac or dc supply

Any how, in either case, swapping over the wires to the brushes will change the direction of rotation....

Do be careful..... :zap:

My lathe has a DC-only motor with field windings.

Ok, a generalisation, there's always an exception like a car's starter motor

In your case ..presumably the field windings are in series then with the armature? That is the same configuration as a universal motor that can run on ac.....
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Offline Pete.

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Re: Reversing D.C. Motor Direction
« Reply #6 on: July 18, 2018, 09:08:37 AM »
No it's shunt wound.