PDA

View Full Version : Complete newbie to rewinding 1 question?



wolfcreek
09-04-2014, 06:08 PM
No it's not should I do it lol. Generator is junk anyway so I figured I'd play with it. This generator burnt up one sector of the winding ( rest of the winding every where else is not scorched at all, not even the resin coating. I know the one sector burnt up because the insulator broke down and grounded the winding. My question is do I have to strip the entire winding ( all sectors ) and start from scratch or is it ok to solder a connection to the end of the good winding and just rewind that sector? This is a sector where the end of the rewind will be at a terminal connection. Ok so one more question, if it is possible to do that how would you make the connection? my thought is a tight solder joint then coat with resin to re-insulate but not sure on solder to use or if it should be a crimp insulated after.

J Tiers
09-04-2014, 10:49 PM
Dunno how to answer without seeing it, but.....

Depends on how it is wound, and even on what you are talking about to begin with..... Rotor, or stator? Sounds like stator.... in which case no big deal, make the most reliable connection possible. Could be crimp, but if it will be made with solid wire, as I expect, I'd solder it.

When you say "sector", that can be an open definition... First question is whether you can rewind that part without affecting any other good windings. If it's in a slot under some undamaged winding, then it can get to be a real pain.

rythmnbls
09-05-2014, 06:53 AM
Standard practice is to strip the entire winding, clean the core, re-insulate , rewind and re-varnish. Connections on smaller windings are usually welded with a small oxy-acetylene torch.

Regards.

Steve.

wolfcreek
09-05-2014, 01:21 PM
Dunno how to answer without seeing it, but.....

Depends on how it is wound, and even on what you are talking about to begin with..... Rotor, or stator? Sounds like stator.... in which case no big deal, make the most reliable connection possible. Could be crimp, but if it will be made with solid wire, as I expect, I'd solder it.

When you say "sector", that can be an open definition... First question is whether you can rewind that part without affecting any other good windings. If it's in a slot under some undamaged winding, then it can get to be a real pain.


http://wolfcreekcarvings.com/images/generator%20stator%20001.jpg
Thanks for the reply. The slots that had to be unwound were easy to get at without disturbing the other winding. I have removed the bad winding already and just have to clean out the slots for new insulation. As you can see in the pic the insulating paper between the winding groups did melt but the other winding under appears to be untouched. I figured on cleaning up the old insulation, apply a fresh coat of resin, replace insulating paper before starting the rewind on the bad sector. Because of where it burnt out it was easy to remove and would be easy to rewind this one section. I just didn't know if making a connection to the section before the damage ( where it was burn't / broken off from originally ) would work or if it would have to have the entire winding stripped from all sectors. With this being a sector that leads to a terminal connection at the end of the winding I would only have to make the one joint and begin re-winding. I know enough to know it's 19 gauge 200c wire and to keep track of the number of windings ( 32 wraps / total of 63' ), to make sure the slot insulator keeps any of the winding from touching the slot and to paper insulate between this winding group from the lower layers of windings it will be tucked against.

Alan Douglas
09-05-2014, 02:28 PM
You can replace just the burned coil. A soldered connection is fine since it won't get that hot. However you must immobilize the wire with a varnish of some sort; if it can vibrate it will wear through the wire enamel rather quickly. I have an ancient can of "Dow Corning 991" electrical varnish which I use, but can't offer any suggestions of what can be bought now. As long as you allow it sufficient curing time, probably any marine oil varnish would work. The less thinner the better (higher solids content). The dipping varnish we used at the motor shop required baking overnight to cure.

wolfcreek
09-05-2014, 04:17 PM
Thanks for the tip on the varnish! I knew I needed to apply it for insulating the connection but wasn't aware that the varnish also prevents vibration wear on the windings. Now I know to seal the entire new winding. I have "Super Corona Dope 4226" varnish for high voltage, says it's self curing and made for sealing coil winding.

J Tiers
09-05-2014, 09:29 PM
OK, looks like you can do it with that item....

As far as insulation.... don't skimp. and varnish the insulation too, that's part of the insulation "system". Generators get transients from "load dump" that are at least as bad as what comes from a VFD.

davidh
09-05-2014, 11:19 PM
that appears to be a very ambitious project but you sound like you've schooled yourself well. good luck.

J Tiers
09-06-2014, 09:12 AM
It's very common to have windings where one slot has the coil "on top" and the other has the same coil "under". Even if you can pull out the side where it is "under", the remaining coil likely will not allow the full winding to go back in, no matter what sort of contortions to attempt. For those, it is more practical to re-wind the whole thing.

I can't quite tell which you have, but it being a generator, and apparently single phase, it appears you are in luck and have coils which in at least some cases may not even share a slot, since one of the open slots appears to have nothing in it. Was it that way to begin with?

wolfcreek
09-06-2014, 11:49 PM
It's very common to have windings where one slot has the coil "on top" and the other has the same coil "under". Even if you can pull out the side where it is "under", the remaining coil likely will not allow the full winding to go back in, no matter what sort of contortions to attempt. For those, it is more practical to re-wind the whole thing.

I can't quite tell which you have, but it being a generator, and apparently single phase, it appears you are in luck and have coils which in at least some cases may not even share a slot, since one of the open slots appears to have nothing in it. Was it that way to begin with?

If I understand what you are asking .... yes the slots that you see in the pic which are empty and clean were like that. Only the slot which I marked with an arrow is what I unwound. That sector simply runs through that slot tucked along the rest of the winding ( with insulation between ) and in through a slot on the opposite side. Then once the final 32nd wrap is done simply ends off with a terminal connection. I assume the empty slots are because these are different sectors of the coil. The 3 packed slots + one slot to be rewound is a divided sector from the others. Which is why this is paper insulated from the rest of the winding when it's being tucked together. I'm not explaining this to you because I think you may not know. I'm just laying out my thoughts on it the best way I can explain figuring it would clarify if this is what you were thinking with your post. Thanks.

Alan Douglas
09-07-2014, 05:21 PM
I remember one contractor who came into the shop with a motor needing rewinding. It was holding up his job and he absolutely had to have it immediately, even though the boss told him that unless it were dipped and baked overnight it wouldn't last. We did it, but he was back the next day with a shorted motor and let us do it properly.