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Another DC motor question

Have a 3 HP permanent magnet DC motor I need to nurse back to life for three days. Opened it up and the glaringly obvious problem is one of the ten magnets is broken in half. Semi-circular, with five 'half circles' down each side of the inside of the outer shell. Broken one is at the output shaft end.

Should I leave the loose piece out, or attempt to reattach it? Looks like it may have been held with epoxy. Guessing that leaving it out will reduce the power by some percentage? Not sure if reattaching is better since the broken pieces may act as separate magnets?

Bearings are a bit glitchy but should run three more days. Brushes are worn about half way down and I may even have spares. Did not see any other obvious problems but will examine it more closely in the morning. Plan "B" is to risk a

2 HP motor for the three days. Have two good spares and we can temporally lighten the load on that one location.

(Bunch of extra information below.)

Think the motor in question may possibly be a Sew-Eurodrive (my predecessor removed all the tags!) all the 1 and 2 HP DC motors on the same machines are Baldors. Since Baldor does not make a three HP in this frame style, the motor does not look like the smaller Baldors and the bottom layer of paint matches the Sew-Eurodrive gear boxes they attach to. (As well as much of the original machine.)

One of six 3 HP DC motors used in the plant and both 3 HP spares are at the re-build shop. (One for another recent failure, the other because the re-build shop missed a problem. Argh!) Have a new Century Magnetek on order but will not get it until Wednesday at the earliest. 106 Lbs so no "next day air". Decided to not go with a locally available Leeson since both of the ones at rebuild are relatively new Leesons. Unless it was replaced through the OEM at some point the one I need to patch is either 14 or 16 years old!

Reply to
William Bagwell
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"William Bagwell" wrote: (clip) Not sure if reattaching is better since the broken

^^^^^^^^^^^^^^^^^^^^^^ If you can reattach the broken magnet pieces in fairly good contact, the field will follow the proper path through them. If you can't avoid a little gap, there will be a slight amount of leakage flux, which should not matter. I think the greatest risk is that one of the magnets could fall into the rotor, if the adhesive does not hold.

Reply to
Leo Lichtman

That is good to know. The piece is roughly half of a magnet segment and I will not even attempt to reattach any tiny fragments I may find. Will swing by a store on the way in the morning and try to find some one hour epoxy. Don't trust that five minute stuff...

Thanks!

Reply to
William Bagwell

It should work in slightly degraded performancd with a slight bit of the field magnets missing.

There is a strength difference between 1-hour versus 5-minute epoxy, but it is documented and not as much as you might think. Personally I only use the millenium-cure stuff; worth the wait.

Reply to
Richard J Kinch

if it were me, I would remove the loose parts of the magnet and put it back together again - you will have a loss of power, but unless the motor is running at max power it won't make a difference to you. if it's in a critical servo application of course the story is different

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Reply to
William Noble

Ended up doing just this. Decided to not waste any more time waiting on epoxy to dry and just get it running. Was still going when I left for the day:)

Not at all. Big azz shaft with two 10' (yes ten foot!) diameter 'plates' attached then various molds bolted to the plates. The 3 HP drives the outer shaft at 8 RPM and a 2 HP spins the plates via the inner shaft at 2 RPM. Both reverse direction every 2 1/2 minutes which is why motors need rebuilding so often and we *try* to keep two spares of each size.

Rotational molding in case any one was wondering.

Thanks all!

And BTW I am following the other motor threads too.

Reply to
William Bagwell

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