How critical is magnet gap ?

Dacflyer

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Joined
Apr 20, 2022
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Fayetteville , NC
Hi all, I finally found some magnets to repair a hub motor ( no info available on this motor )
48V Watts ???
has a 10" rotor 36 poles 32 magnets.
I thought it was missing a magnet, So hunting hi and low, I finally found a place that had the exact size i needed..
Today, I was excited to start assembling it all back..only to find ( thru learning ) that the gap was too small for the extra magnet.
I read somewhere that the magnets require some gap. Not touching.
So, i started looking around for some card paper, of different thicknesses. The thickest i have was a card paper that Del Monte cans come in.. I'm so close.. the sections really closed the gap. but right at the last/first magnet, there's still a gap that i can fit in 2 papers.
only other way to close the gap is to use regular paper with the card paper. that'll be really tricky to do...
would it mater much on motor operation with such a gap ? or should i just go ahead and add the paper + card paper to close the gap better??

Does this look ok?
20220516_195401.jpg
 
I'm not sure how much of an effect it would have for the magnets to be slightly asymmetrical around the rotor; it should still run ok; might be noisier than normal, or it might use a little more power than usual.


Just be sure to install them like the originals were, regarding polarity: If they were alternating polarities, do that. (that's usually how they would be).


And don't catch your fingers in anything when you put the motor back together...that can really hurt. :(

If you used a gearpuller to take the stator out, use it to put it back in, too, to slowly lower it in; it's safer.
 
Thanks for the idea on the gear puller idea,, I been thinking on how i'll het it back together without it pulling me with it.
Might have to use hands and feet if my puller isn't long enough. Motor was already apart when i got it..
still hunting for an affordable adhesive. I found some adhesive that is used for glueing motor magnets and Speaker magnets etc.
but it's $50.00+ for a small 25Ml tube of it. and even then, I'm not sure if it would even be enough.
Any other suggestions ?
Maybe I'm looking for something too strong ?
 
The gap between magnet sections won't make much difference in performance unless it gets up to about the magnet thickness. Perfectly symmetrical spacing is more important.
I've seen various recommendations for glue. You want something that stays strong at higher temps. Normal epoxy can get pretty soft when it heats up to motor temp. I've used high-temp epoxy and some kind of polyurethane stuff that both worked out OK.
 
I did some researching and asked various companies, and i finally settled on Loctite 324 + 7387 Activator.
these are actually recommended for magnet use.
they call it Acrylic Structural Adhesive.

It is specially suitable for joining dissimilar materials, e.g. ferrite to plated materials in electric motors, loudspeakers, etc.
good for up to about 300F.

thanks...
 
I haven't tried that before. They say it's a urethane methacrylate ester acrylic. The temp rating is great.

Let us know how it works out. Also interested in how long it takes to set up and cure. Super fast stuff like cyanoacrylate sets up too fast and you have a hard time positioning the magnets before it grabs.
 
The stuff was said to have about 5 min working time. I was a little worried that the last magnet was a super tight squeeze to fit in,
but i got it..I used the same spacers as i did in Mock Up. I don't know why it was slightly tighter in real assembly.
But they all fit, so that's more important..
I let it cure in the sun for 2 days, took the papers out yesterday,, had to cut most of them free..
I'm pretty sure they aren't going anywhere now. Might assemble it tonight..
I'll be so glad if this fixes it..
 
Dacflyer said:
I don't know why it was slightly tighter in real assembly.

THe glue adds a little thickness (even squished down by the magnets). This pushes the magnets into a very slightly smaller circle since they're closer to the center this way. Makes very slightly smaller gaps between them.
 
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