Radial Magnet Assembly to Shaft

[(unknown)]

Hi,

I'm putting together a hydro power system and have an old water pump with burned coils but new bearings to use.  I was planning on using permanent magnets in a radial design to replace the original armature windings.  My question is, how does one go about attaching high-power magnets to the shaft considering that the magnets opposite one another (at 180 degrees on the shaft) will repel each other?  

Any hints would be appreciated.

[Flux]

Look through posts here on motor conversion, there is a lot of useful information.

If this is 2 pole and the magnets are at 180 deg they will actually attract rather than repel, but if you need to make each pole from multiple magnets then you will have strong repulsion to deal with and it needs some ingenuity to hold things in place while the glue sets. Some use magnetic shunts to direct the flux elsewhere to reduce the repulsion while others use brute force and clamps.

You also need to consider holding the magnets on long term with the centrifugal force trying to throw them off. Various schemes such as aluminium sleeves with holes in them have been used to hold individual magnets. Commercially a stainless steel foil band is a common method but is better suited to poles made from one magnet not built up from several smaller ones.

If you can get them positioned then casting the whole magnet block with epoxy resin and filler is usually sufficient to hold them.

Flux

[FishbonzWV]

This is how I did a conversion.

http://fieldlines.com/story/2009/3/13/233643/638

I used JB Kwik on that one but now I have changed to super glue with accelerator to temporarily hold the mags. Then I use a two part epoxy to fill the voids between mags and poles.

Bonz

[celution]

Thanks for the link w/ pics.  I was planning on epoxy resin or fiberglass for filler after super-glue for the initial attachment.

[celution]

No multiple-magnets in my plan.  Below is a simplified diagram using only 4 magnets; it would seem the like-poles facing each other through the shaft would repel, though perhaps the steel shaft alters that?

Thanks for the aluminum sleeve idea - I might use a square-tube around the shaft with cutouts for 4 magnets.  This would result a large airgap to the coils, vs more, smaller magnets, but efficiency is not a concern as I have unlimited water in the river (12 meter drop though the system around a waterfall) and only need to get 50 Watts from a formerly 3/4 HP motor.  

[ghurd]

They will stick to the shaft, unless they are so close they interact.

The pump motor is a 2 pole, slightly less than 3600RPM(60Hz) 3000RPM(50Hz)?  It will need the coils replaced differently than they were from the factory if you use a 4 pole rotor.

For the effort and cost involved in changing the coils, might consider starting with a different motor.  A 3/4 or 1 HP ~1750RPM(60Hz) or ~1400RPM(50Hz) 3-phase would be a lot simpler, and give a couple options on how use the resulting PMA.

G-

[celution]

Yep.  Might do something completely different with this old pump/motor after searching for 'motor conversion' on this site; skew/cogging could really throw a monkey-wrench into the thing - plus scrapping the 2-phase winding-layout (it is 60Hz).  

Thanks very much for all the input here - saved me a lot of potential frustration.

[ghurd]

Unless you get very unlucky, I doubt cogging will have a lot of effect in a hydro system with 12 meters of head, after it starts turning.

Can do some simpler de-gogging measures after a super glue cogging test.

Like in a 4 pole rotor, with magnets at 12:00, 3:00, 6:00 and 9:00,

can slope the 3:00 and 9:00 shaft surface some to get those magnets to 3:15 and 9:15.

Poor explanation, but you know what I mean.

G-

[wooferhound]

Here are some excellent articles on how to do a Motor Conversion

by our deceased expert "Zubbly" . . .

Part 1

http://fieldlines.com/story/2004/8/13/191519/161

Part 2

http://fieldlines.com/story/2004/8/13/214144/026

Part 3

http://fieldlines.com/story/2004/8/14/11359/0629