# Electric motor help?

**URL:** <https://boards.straightdope.com/t/electric-motor-help/507178>\
**Category:** Factual Questions\
**Created:** [August 21, 2009, 6:09am UTC](https://boards.straightdope.com/t/electric-motor-help/507178 "2009-08-21T06:09:17Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![3trew](https://avatars.discourse-cdn.com/v4/letter/3/13edae/32.png) [@3trew](https://boards.straightdope.com/u/3trew)\
**Post date:** [August 21, 2009, 6:09am UTC](https://boards.straightdope.com/t/electric-motor-help/507178/1 "2009-08-21T06:09:17Z")

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I have a rotary tool. The other day I had to open up the casing. When I did so, a red wire with a paddle shaped end became dislodged. There was a black wire on the other side which went into a small box where it was held by a spring. I know nothing about electric motors, but it looked fairly symmetrical so I decided to try putting the red wire into the corresponding box on the other side, where it would be held by the spring. When I closed the unit and tried it out, it spun right up.

Today I tried to use it with a metal cutting disc and found that the disc assembly was being unscrewed by the motion of the drive shaft. I appear to have somehow reversed the direction of the drive shaft.

The Googles do nothing. Any advice on how to fix this and any fairly non technical explanations for how it actually happened would be appreciated.

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**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\
**Post date:** [August 21, 2009, 11:39am UTC](https://boards.straightdope.com/t/electric-motor-help/507178/2 "2009-08-21T11:39:00Z")

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You reversed the brush’s or the magnet’s polarity. There are too many ways to wire a motor for me to help you.

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**Author:** ![HongKongFooey](https://avatars.discourse-cdn.com/v4/letter/h/c4cdca/32.png) [@HongKongFooey](https://boards.straightdope.com/u/HongKongFooey)\
**Post date:** [August 21, 2009, 12:55pm UTC](https://boards.straightdope.com/t/electric-motor-help/507178/3 "2009-08-21T12:55:57Z")

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It’s a series motor. Reversing the voltage applied to any coil in the circuit will reverse the direction. Your black and red wires are the armature leads. Reverse them and the motor direction will reverse. That won’t explain why the direction got switched in the first place though.

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**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\
**Post date:** [August 21, 2009, 5:48pm UTC](https://boards.straightdope.com/t/electric-motor-help/507178/4 "2009-08-21T17:48:52Z")

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Are you sure there isn’t a “reverse” switch somewhere that you accidentally moved, like on a drill?

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**Author:** ![HongKongFooey](https://avatars.discourse-cdn.com/v4/letter/h/c4cdca/32.png) [@HongKongFooey](https://boards.straightdope.com/u/HongKongFooey)\
**Post date:** [August 21, 2009, 7:03pm UTC](https://boards.straightdope.com/t/electric-motor-help/507178/5 "2009-08-21T19:03:37Z")

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> [@HongKongFooey](#):
>
> It’s a series motor.

This is why I shouldn’t post right after a night shift. I meant to say _universal_ motor.