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Thread: Dead Stator - ideas?
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20th Apr 2020, 11:51 AM #16
Have you googled for information on the particular model of pump / motor you have ?
I dont know what model yours is so just looked for general Grundfos info:
http://net.grundfos.com/Appl/ccmsser...ature-6692.pdf
In section 10.8 it has instructions for stator removal
4. Block up the stator housing so that it stands on the flange at a height where the stator can come outunderneath.
5. Heat the stator housing until the stator drops out. Heat the stator housing uniformly so that it is not deformed.When using a gas burner, to approx. 200 °C. When using a pre-heated oven, to approx. 300 °C.
Other video's I found online show Grundfos stator being pressed into the housings in a robotic production line.
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20th Apr 2020, 12:07 PM #17Diamond Member
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I hadn't thought of Googling for that (I did hunt around to see if I could get the stator and housing as a spare part).
Useful info, suggests I might be on the right path?
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20th Apr 2020, 02:33 PM #18Most Valued Member
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20th Apr 2020, 07:09 PM #19
Hi Rusty,
What is all that stuff ringed in red ? It looks like Epoxy or varnish to me !
IMG_3081.jpg
There looks to be a small lip of laminations, but whether you can get underneath it to lock puller lips onto it is debatable.
Edit: When I posted this, I had not seen the previous posts.Best Regards:
Baron J.
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20th Apr 2020, 08:05 PM #20Diamond Member
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I think it's kapton tape or something similar.
There looks to be a small lip of laminations, but whether you can get underneath it to lock puller lips onto it is debatable.
However, for the moment I'm going to continue with the freeze-heat-smack down on the bench approach. I had one attempt today: -20C out of the freezer, one pass around the outside to bring it up to 100C then a second to bring it to 200C, then smacked it face down numerous times onto a sheet of cement board protecting the bench. No movement in the stator, so I think I'll just repeat the process up to 300C. Bit iffy about bringing one side up to full temp in one go, but may have to go that way if I want maximum difference in temperature between the stator and the housing.
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21st Apr 2020, 12:47 AM #21
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21st Apr 2020, 02:15 PM #22Diamond Member
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Yep, kapton tape.
https://www.jaycar.com.au/heat-resis...-50mm/p/NM2817
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21st Apr 2020, 02:25 PM #23Diamond Member
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Success!
Well that was all rather satisfactory.
IMG_3096.jpg
Brought it out of the freezer and up to 250 degrees, tapped it on the bench and the stator slid out part of the way, stopping as it met the bench, so set it face up and re-applied heat, trying to make sure I didn't get any heat on the exposed portion of the stator, and after a few seconds, the stator dropped down again into place, so I quickly flipped the housing over and the stator just dropped onto the bench, no thumping required.
Stator was only about 100C or so, so hopefully haven't triggered any other thermal fuses in the windings (assuming that's what the culprit is).
So now to let it cool, and work out how best to unwind the suspect coil.
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21st Apr 2020, 08:11 PM #24Diamond Member
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The next bit, unwinding the faulty coil, ended up being a less than pleasant nor quick process.
While I couldn't see any varnish on the outer windings, it certainly had it throughout the rest of the coil, making removal a fairly destructive process. But I got it all off in the end.
IMG_3097.jpg
So it turns out there was no fuse, but a small, burnt out break in the second or third last winding before reaching the former. There was slight discolouration in the enamel of the winding below, but no evidence of widespread heating, making me think it was a damaged (pinched or nicked) part of the wire that had higher resistance and initiated the failure, so perhaps it was just a manufacturing fault, and nothing to do with getting wet. However, the coil in question was the lowest in the motor, so would have been immersed for the longest period, making hard to dismiss immersion as a factor.
Next challenge is rewinding the coil. The wire measures 1.02mm dia, so I'm going to assume it's nominally 1mm dia wire, although I'd have thought the enamel would be thicker than 0.01mm. I weighed the chopped up bits of wire at 88 grams, I can get a 100g roll locally for $16. So I could have a go at rewinding it, but there's a few challenges: I don't know how many windings to apply. I could either try and measure the total length of the removed bits, and cut my new wire to that length and wind on all of it, or I could use weight to do the same. Given the chopped up bits are not straight, the error between the length versus weight approach might be pretty similar.
IMG_3099.jpg
Then there's the varnish. I think it has to be there, otherwise the coil will buzz and maybe heat up, but I think I'd need to apply it layer-by-layer somehow.
I'm tempted to take it to the local rewinder to see what they think...
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22nd Apr 2020, 01:20 AM #25
Hi Rusty,
Just weigh out the wire and wind it on the former, keep it neat. 10 grm isn't going to make a lot of difference. When finished just dribble shellac or yacht varnish over it and let it dry. Wire it all back up and reassemble and test.Best Regards:
Baron J.
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22nd Apr 2020, 09:16 AM #26Then there's the varnish. I think it has to be there, otherwise the coil will buzz and maybe heat up, but I think I'd need to apply it layer-by-layer somehow.
As for failure, yes the water would have played a major part, for whatever reason there has been a failure of the insulation water getting in corrodes the wire causing a higher resistance. The heating from the higher resistance multiplies the effect until it fails, the heating can be very localised and only appear as a spot on the winding.
Dipping the coil in varnish should protect it from any localised minor damage to the enamel caused during the winding process.
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22nd Apr 2020, 01:36 PM #27Diamond Member
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Between school and uni I worked in a power tool shop for a year that also did rewinds, in hindsight I probably should have paid more attention to what the rewinding guy did. At the time I just used him for a supply of really nice silicone wire for an amplifier I was building.
I can't really dip the coil in varnish, but I'm thinking I could try using aerosol circuit board laquer which might serve the same purpose. Also toying with the idea of using the odd dot of superglue to hold the windings in place as I go.
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22nd Apr 2020, 04:19 PM #28Senior Member
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Could you elaborate on why you can't dip in varnish?
I am Iikely missing something, but tin - varnish - dip- drain?
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22nd Apr 2020, 07:58 PM #29Diamond Member
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Well, first I'd need some varnish I guess, and I'd need to remove it from the outside of the stator before putting it back in the housing, but apart from that, I probably could.
I'll see how I feel after winding it all on. Which I've started. I think I've done maybe 8 turns so far. Not a fun process.
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23rd Apr 2020, 09:32 AM #30
Interesting repair you're working on. There is a freely available old textbook on motor rewinding available at the internet archive, might be useful:
https://archive.org/details/Armature...agen5/mode/2up
Also look at the 'similar items' that come up at the bottom of the screen - there are a few books on aspects of motor repair there on ia.
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