Magnet failure and repair

Cliff Coggin · 2007-09-02T13:10:48+00:00

This might be a little off-topic, but the breadth of knowledge here would beinvaluable to me, as I have been unable to find answers with Google.I am trying to repair a 12 volt DC fan motor from my car in which two of thesix permanent field magnets have become detached from the casing as a resultof failure of the adhesive. One is undamaged and can be glued back in place,but the other has broken into several fragments. I am puzzled to find thatmany of the fragments will not fit back together because their polarity hasreversed and they repel each other, so I have a few questions.[1] Is polarity reversal normal when a magnet breaks, or is it the result ofthe magnetic flux created by the rotor?[2] Is there any way to repair the broken magnet, or a company to do it forme?[3] If repair is impossible, is the motor likely to work with one of sixmagnets missing? ( I don't know what sort of motor it is, but it has twobrushes and a commutator.)I should point out that a new Ford part is over £300, and that Internetsearches of car breakers have not revealed a working replacement motor.Cliff Coggin.

Sep 02, 2007 21 Replies

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pentagrid 18 years ago

snip

Sounds like an electrolytic capacitor for RFI suppression - would object strongly to reversed polarity but not damage the motor.

Motor should work fine without it in either direction. The value for RFI suppression is not critical. If you can't decipher the markings 10uF 40v working should be OK.

Jim

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Chris Holford 18 years ago

snip

Could be a diode? -to short out back emf. If so, then polarity would be relevant. The end with the silver hoop should go to the +ve terminal. (Diode would probably look like a solid cylinder of black plastic-epoxy- ) If this the case it's easy to replace from RadioShack or similar.

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