# Reversing Direction on Shunt Wound Motors



## order99 (Sep 8, 2008)

Still dreaming of my first EV-and still hampered by a non-existent budget. 

The good news is that I have acquired an old VW generator from 1972. It's a shunt-wound motor, so i'm assuming that makes it a SepEx and capable of Regen. My original plan was to mount it on a bicycle I have rescued from a dumpster and recently refurbished (an old Huffy with bulletproof single speed) and although I still can't afford batteries i've had one successful test with a borrowed pack.

This is the setup I blatantly copied for my test:
http://www.angelfire.com/oh/PetesCafe/vwgen.html

So far, so good...

Here's my problem(besides my poverty of course)-i've come up with a more efficient way to mount my motor, but in order to make it work I need to reverse the rotation. Is that possible with a shunt-wound at all? If so, would I need to fabricate a special controller to make it happen or just alter an existing one? For the test I just used a plain old rheostat and a fuse.

On a related note, is it possible to use a Shunt-wound motor as a Series motor without rebuilding the entire thing? Regen is a nice option but hardly seems worth it for a vehicle this lightweight...


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## Dennis (Feb 25, 2008)

> Here's my problem(besides my poverty of course)-i've come up with a more efficient way to mount my motor, but in order to make it work *I need to reverse the rotation*. Is that possible with a shunt-wound at all? If so, would I need to fabricate a special controller to make it happen or just alter an existing one? For the test I just used a plain old rheostat and a fuse.


Reversing a shunt wound motor is very simple. It can be accomplished either by polarity reversal of the shunt field circuit or polarity reversal of the armature circuit, *but not both*, else rotation will not change.


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## order99 (Sep 8, 2008)

(facepalm) 

Many thanks. So given that the Field Coil was wired D+ to DF and the Armature was wired from D+ to the ground screw, I should simply reverse the battery wires? I could have sworn I did that, but i've been misplacing things lately, soooo... blast it, 40 is TOO YOUNG to get senile! 

Also, given the scheme above, I could leave the terminals alone and switch the ground screw to DF, right? Despite hanging around the Forums awhile this is my first actual motor, so i'm being EXTRA cautious before breaking it. I'm on a VERY tight budget...


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## major (Apr 4, 2008)

order99 said:


> So given that the Field Coil was wired D+ to DF and the Armature was wired from D+ to the ground screw, I should simply reverse the battery wires?


No, that won't reverse rotation.



> Also, given the scheme above, I could leave the terminals alone and switch the ground screw to DF, right?


No. You have to reverse the field coil leads inside the motor. The coil lead which now goes to D+ must be moved to DF. And the coil lead currently connected to DF must be moved to D+. Then wire the battery the same as before and she'll rotate backwards.

Regards,

major


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## Dennis (Feb 25, 2008)

> Many thanks. So given that the Field Coil was wired D+ to DF and the Armature was wired from D+ to the ground screw, *I should simply reverse the battery wires?* I could have sworn I did that, but i've been misplacing things lately, soooo... blast it, 40 is TOO YOUNG to get senile!


The polarity change has changed both field circuit and armature circuit resulting in a net motor rotation being unchanged. Remember either armature circuit or shunt field circuit must be reversed in polarity, but not both. Your motor as it stands is non-reversible and will need modification. The leg of the shunt field going to the D+ terminal needs to be removed and mounted to its own terminal.


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## order99 (Sep 8, 2008)

So if I want to reverse the coil I need to go inside and do some surgery. Sounds easy, but it always does on paper...

I think i'll leave the motor mount as is for now-if I can find another motor as cheaply as I got this one though, i'll open that one up for practice.

Thanks with your patience with a guy finally beginning to get his hands dirty!


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## dschill (Mar 19, 2009)

Good luck and let us know how it turns out!


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