Alternator disassembly

by M0GXB Tue Feb 04 2020, 12:58

I hate it when manuals give an instruction without any explanation. This is what I am looking at:

"The generator is a totally enclosed, permanent magnet inductor alternator.
The rotor MUST NOT BE REMOVED FROM THE STATOR UNDER ANY CIRCUMSTANCES"

So the obvious question: why?

I can see this dividing into "you will beak it" or "it is impossible to reinstall".
Anyone know the likely answer?

by Robotstar5 Tue Feb 04 2020, 16:43

If it's anything like the permanent magnet servo motors I've worked on, the magnets are that strong they will pull the rotor into the stator possibly causing damage. The correct way is using a purpose designed frame that holds the rotor shaft central to the stator/body as it is withdrawn or inserted, not something you find in many sheds Very Happy

by M0GXB Tue Feb 04 2020, 17:18

I did wonder, but this is 1945 - so not the latest exotic-material magnets.

by maryalice Tue Feb 04 2020, 17:49

Exotic magnets have been around for many many years their only main difference is size.

Martin P

by mattblack Tue Feb 04 2020, 21:17

I may be barking up the wrong tree, but could it be that the magnets will lose their magnetism without the rotor in place? Just thinking how a horseshoe magnet should have a 'keep' on it to stop it losing it's magnetism.

by tony RA Tue Feb 04 2020, 22:05

M0GXB wrote:I hate it when manuals give an instruction without any explanation. This is what I am looking at:

"The generator is a totally enclosed, permanent magnet inductor alternator.
The rotor MUST NOT BE REMOVED FROM THE STATOR UNDER ANY CIRCUMSTANCES"

So the obvious question: why?

I can see this dividing into "you will beak it" or "it is impossible to reinstall".
Anyone know the likely answer?

by georgineer Wed Feb 05 2020, 10:26

The simple answer is that if you take it out without a keeper it will lose a great deal of its magnetism. I discovered this the hard way as a teenager when I dismantled a Sturmey Archer Dynohub to clean and lubricate it. When I re-assembled it I couldn't get more than a feeble glow out of the lights.

George

by M0GXB Wed Feb 05 2020, 17:14

Oh that is interesting. I had always assumed that the "keeper" effect was a long-term thing, so it would gradually fade away over months (due to thermal cycling) rather than seconds - especially since magnets with keepers were meant to be used by taking the keeper off, of course.

by Gaudin98 Fri Feb 14 2020, 08:37

If you remove the magnet you will demagnetise it. we have similar problems on the stone turbo generators as fitted to south African steam locomotives. you have to remagnetise the rotor before refitting.

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