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Motor conversion
By windy, Section Homebrewed Electricity Posted on Wed Oct 04, 2006 at 03:15:55 AM MST
Will this work?

I have an idea I would like to try but I'll post it first and see if anyone thinks it might work.
I have a 7.5hp motor that is burnd't out that I will use as a motor conversion. It has a 36 slot stator and I was thinking of winding 18 coils,using slots 1 and 2 for the first coil,slots 3 and 4 for the second coil and so on for a total of 18 coils. Each coil would be rectified independantly and the DC voltage from each diode would be tied to a common terminal. A 1/2" wide x 4" long magnet would span a single stator bar. My next question is, being that I'm not concerned about anything being in phase,would it work to use 24 magnets on the rotor without the magnets being skewed. I would not skew the stator laminations either.I'm thinking an odd number of magnets would keep cogging to a minimum. I got this idea from the axial flux alternator(9 coils-12 magnets). Would the losses from 18 recifiers make this idea not possible? Would it make so much noise and vibration that it would drive the neighbors nuts? I'm I nuts?
Any comments or suggestions!!!
windy

Motor conversion | 4 comments (4 topical)

Re: Motor conversion (3.00 / 0) (#1)
by Flux on Wed Oct 04, 2006 at 12:57:23 AM MST

It doesn't seem to be possible to get the message through that cogging is associated with magnetic attraction of non uniform iron (core teeth normally)

Axial machines have no iron THEY DO NOT COG.

Your thing may work, it WILL cog. It may or may not make a pulsating torque on load, that is not cogging.

Most electrical machines make some noise on load, even dynamos (in the dc days) made a whine. With lower frequencies as with most of these things the whine turns into a growl.

I don't see why it wouldn't work but I also fail to see any advantage.
Flux

Re: Motor conversion (3.00 / 0) (#2)
by zubbly on Wed Oct 04, 2006 at 04:01:15 AM MST

hi Windy,

all i can say is you are dealing with quite a few un-knowns. if your 24 mags in a 36 slot stator does not defeat cogg, you will likely need a 3 foot long pipe wrench with you standing on the end to turn the rotor. coil spans and 18 rectifiers are other issues. i hate to see a lot of work end up useless. i have tried some wacky things in conversions with most ending up in the garbage.

if it is the stator skewing you wish to get away from, then use round mags skewed on the rotor. with 1 inch round mags and coil span of 1-4, you can have a beautiful 12 pole machine that will really reward you for your effort. you could also try 18 rows of 3/4 inch round mags skewed on rotor for a 2 phase machine with coil span of 1-3. i can draw the coil layout if you wish. a 2 phase winding is much easier to wind into the stator slots than a 3 phase.

good luck and let us know what you decide,
zubbly

Re: Motor conversion (3.00 / 0) (#3)
by dinges on Wed Oct 04, 2006 at 05:33:59 AM MST

I agree with Flux. Despite endless repeating, the message that axial fluxes don't cogg seems to fall on deaf ears.

It's perfectly possible to make the 24 magnets completely coggless in that motorconversion. Just read up on the subjects of Zubbly skewing, or offsetting the magnets like JacquesM did (see my IRC gallery & diary for it too).

You could use 2"x1"x.5" magnets, if you manage to fix them properly to the rotor. If you use JacquesM's offsetting method, no skewing of the stator would be necessary. And you'd have absolutely no cogg. But, you've got to know what you're doing & how to offset the magnets. Main worry I'd have would not be the cogg, that can be overcome, but fixing those magnets to the rotor in such a way that they'll never come off again.

Only thing to add: before you convert, be absolutely sure you understand exactly what you are doing. Just throwing magnets on a rotor is sure to end up as a failure. Myself, I still don't quite understand the coil-part of a motorconversion, which is why I'm not messing with new coils yet. I've got my hands full with just the cogging issue.

As far as 2phase goes; you decide. I've tried loading my 3 phase alternators with only 2 phases, and the vibration/pulsed torque was terrible. Loaded on all 3 phases, it was very smooth. Which is why I never will go back to 1 or 2 phase.

[ Parent ]

Re: Motor conversion (3.00 / 0) (#4)
by windy on Wed Oct 04, 2006 at 10:03:39 PM MST

Thanks for the comments.
I'll stick with the zubbly's method of motor conversions.
I did a 3hp motor conversion that works great using the stock windings but the 7.5hp motor would have to be rewound.What I don't like about using the stock windings is that the genny has to be turning at six to seven hundred rpm's to fully load the generator.That may be fine for a small conversion but for a 7.5hp or larger conversion,I can't see how it would be possible to turn a blade larger than 10 feet at that speed and be able to utilize the full output of the generator.
I thought that my idea would generate higher voltage at lower rpm. It looks like it would not generate anything.It was just an idea!

windy

Motor conversion | 4 comments (4 topical)

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