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!
--
William

"William Bagwell" wrote: (clip) Not sure if reattaching is better since
the broken
pieces may act as separate magnets? (clip)
^^^^^^^^^^^^^^^^^^^^^^
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.

On Mon, 06 Oct 2008 00:30:04 GMT, "Leo Lichtman" wrote:


"William Bagwell" wrote: (clip) Not sure if reattaching is better since
the broken
pieces may act as separate magnets? (clip)
^^^^^^^^^^^^^^^^^^^^^^
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.

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!
--
William

William Bagwell writes:

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...

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.

"William Bagwell" wrote in message
...
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.


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



** Posted from http://www.teranews.com **

On Sun, 5 Oct 2008 23:00:32 -0700, "William Noble" wrote:


"William Bagwell" wrote in message
.. .
Have a 3 HP permanent magnet DC motor I need to nurse back to life for
three days. (snips)

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.

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

if it's in a
critical servo application of course the story is different

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.
--
William