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I have purchased a sewing machine motor from aliexpress. The issue is that it spins in the wrong direction. I opened it and only see 2 wires going to the brushes.enter image description here

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  • \$\begingroup\$ See What to check for when buying an electronic component or module. \$\endgroup\$ – Transistor Sep 17 '20 at 11:27
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    \$\begingroup\$ @Transistor If I may make a comment as an 'everyday group member' :-) (ie not intended to have any sort of official standing): I suspect that beating people with Andy's (or other) 'you should have been smarter' response is not going to help them either feel better this time or solve their problems. | As advice for next time its great. \$\endgroup\$ – Russell McMahon Sep 17 '20 at 12:06
  • \$\begingroup\$ Point taken. Thanks for the feedback. \$\endgroup\$ – Transistor Sep 17 '20 at 12:44
  • \$\begingroup\$ @HazenAL Besides trying to change the rotating direction, I hope that you asked the vendor about this failure? Beware that most of time the sellers from AliExpress try to prevent you from raising a claim to AliExpress, they almost always try to fool you with words and empty promises, in order to delay the question untill past the final day that you have to raise a claim. The fact is that if you raise a claim before the final date, chances are that AliExpress will exam your claim and you can get a full, or at least a substantial refund for the deffective product. \$\endgroup\$ – mguima Sep 17 '20 at 15:09
  • \$\begingroup\$ I'll hazard a guess that with the possible exception of machines with motors buried deep inside (either cheap or advanced servo drives) traditional "sewing machine motors" essentially always spin the same way across the industry as the layout of a machine and the use of a belt drive have been fixed for over a century (some have gone so far as to claim the machines are all "left handed" though that sounds more like an urban legend). Seems like the asker probably wants the motor for something else; changing the mounting or power transmission setup to use an unmodified motor might be warranted. \$\endgroup\$ – Chris Stratton Sep 17 '20 at 15:44
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Summary:

  • Disconnect the wires from the two brushes.

  • Reconnect the wires to the brushes that they were not connected to before.
    (A little extra wire will probably be required).

  • Done.


Universal motors are what is known as "series wound" - they have the whole motor current flowing in series in both the field coils and the armature.
When the AC supply reverses the current flow to both field and armature also reverse so the same relative polarity is maintained.

To reverse the motor direction you thus either need to swap the wires to either the brushes or to the field (but not to both). eg
Wire previously going to brush A now goes to brush B.
Wire previously going to brush B now goes to brush A.

There is a chance that the motor is designed mechanically to work better one way than the other but if there is no prospect in using the motor as supplied reversal may still be acceptable.


As @BrianDrummond notes -

in some cases brush holders are adjustable in rotational position over a small range. Adjusting the position [with due care to avoid electric shock] can optimise the position and reduce commutator sparking.

Brushes optimised in position for one direction of rotation may be slightly off position in reverse.

As @Charles Cowie notes -

"If the brush mounting assembly has a lot of room to rotate, and if the wires are long enough, you may be able to reverse the motor by turning the mounting assembly 180 degrees."

This is electrically the same as swapping brush leads but may be easier. It's unlikely to be possible in the present case (based on the photo).

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  • \$\begingroup\$ And if the brush mounting is adjustable you might be able to improve its working in reverse (rotate it a few degrees to reduce sparking). \$\endgroup\$ – Brian Drummond Sep 17 '20 at 12:16
  • \$\begingroup\$ @BrianDrummond Thanks. Yes. I considered adding some comments about offset brushes and just maybe angled brush holders. I'll do so. \$\endgroup\$ – Russell McMahon Sep 17 '20 at 12:19
  • \$\begingroup\$ If the brush mounting assembly has a lot of room to rotate, and if the wires are long enough, you may be able to reverse the motor by turning the mounting assembly 180 degrees. More pictures would help. \$\endgroup\$ – Charles Cowie Sep 17 '20 at 12:21
  • \$\begingroup\$ @CharlesCowie Good point. Electrically the same as swapping brush leads but may be easier. Unlikely in the present case (based on photo). \$\endgroup\$ – Russell McMahon Sep 17 '20 at 12:23
  • \$\begingroup\$ @RussellMcMahon Thank you very much for your reply. I fully disassembled the motor and found that there are 2 wires in the whole assembly. They go directly from mains through the field windings to the brushes. I think that if I do as you said, and switch the brush wires it would be the equivalent of desoldering the board containing the brushes and rotating it 180- nothing will be changed. Im not an EE experet so please correct me if I am wrong. I have reassembled it because I decided I will 3D print a gear box, but if you think it is still possible I will disassemble and take pictures. \$\endgroup\$ – HazenAL Sep 19 '20 at 6:39

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