7 replies to this topic

[alicetheauto]

I need to swap the polarity of a starter motor, ie it is currently for negative earth but needs to go in a positive earth car. Apparently, it is simply a case of connecting a battery to 2 points on the motor /casing? Anyone know where you connect each terminal? Cheers!!

[tommy13]

If you have the older type inertia starter then nothing needs doing. As regards the pre-engage starter, I have never tried this but I would imagine the same to be true. Test it off the vehicle with a battery and jump leads to see if it rotates in the same direction when you reverse the polarity.

[alicetheauto]

Thanks for your reply, I have been told that there is something needed to be done to reverse the polarity. Apparently, by connecting one cable to the casing and the other cable to *another* part of the motor, it reverses the bias of the magnets inside it? We dont know which polarity to have on the casing, or what other part to clip the other wire to!!!
Anyone any ideas?
Ok, I have a confession to make, its for my Dads AH Sprite rather than a Mini, but it is using a Mini starter motor as it is the same!!

[Phaeton]

You used to have to do this years ago to change the polarity of dynamo's but not heard about having to do it to starters. Have a read HERE it talks a bit about it I searched Google for polarity change starter motor

HTH

Alan...

[tommy13]

The sprite would definately be an inertia type motor. As I said before, you don't need to alter the motor connections in any way, just reverse the battery terminals and away you go. There are other issues with changing battery polarity, the heater motor may spin the other direction. The wires on the coil should be swapped over. If you have a dynamo charging system, you will have to repolarise the dynamo. Do you have an electric fuel pump? The SU type will be fine provided it is not fitted with a capacetor or diode to reduce arcing across the points. If a Facet or later electronic pump is fitted it would be a case of swapping the wires to it. Radios, time clocks, alarms and immobilisers are also polarity specific and must be replaced before converting.
The repolarising of the dynamo is a little like the process you have described for the starter. Is it possible you are confusing the two? If you need help on repolarising the dynamo I can give the procedure.
This link may help
http://www.mgcars.or...ips/PosNeg.html

Edited by tommy13, 10 June 2009 - 08:49 PM.

[Dan]

To back up what's above, it's a dynamo that is polarised and must be flashed when you change the polarity of the car and not the starter motor.

[alicetheauto]

Thanks a lot for your help! The starter on the Sprite has fallen apart (at the MOT station..... ) and we have another motor, but its off an old Mini engine. We assume the mini was negative earth, but the sprite is already positive earth. Will try it when the laquer is on my Mini then, see which way the motor spins!!

[alicetheauto]

Thanks for that, it all works!! I dont understand how the motor turns the same way regardless of polarity, but thanks!!