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BobL
24th February 2014, 03:01 PM
I have managed to find the common point of a Y wound motor and converted it into ∆ but before I assemble it I would like to re-glue and tie down the wiring that I had to loosen to get at the common point.

Does anyone have any suggestions as to what glue and what tie down material to use, it looks like plain cotton string to me.

The motor is a bit of a tricky one as it is a 2 speed jobbie with both wound as Y.

Once I have reassembled I I will get the techo at work to look at it and run a megger over it before firing it up.

RayG
24th February 2014, 04:52 PM
I have managed to find the common point of a Y wound motor and converted it into ∆ but before I assemble it I would like to re-glue and tie down the wiring that I had to loosen to get at the common point.

Does anyone have any suggestions as to what glue and what tie down material to use, it looks like plain cotton string to me.

The motor is a bit of a tricky one as it is a 2 speed jobbie with both wound as Y.

Once I have reassembled I I will get the techo at work to look at it and run a megger over it before firing it up.


Do a search for nylon lacing cord, http://www.ebay.com/itm/Gudebrod-Mil-T-43435B-NATURAL-GUIDELACE-Lacing-CORD-LONG-/291071698282?pt=LH_DefaultDomain_0&hash=item43c539a56a

and for the varnish, Ultimeg 2000/372 or

ebay http://www.ebay.com/itm/CLEAR-AIR-DRYING-VARNISH-ELECTRIC-MOTOR-COIL-INSULATING-VARNISH-100ml-/371006068830?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item5661af585e

Ray

swk
24th February 2014, 06:31 PM
Bob,
Ray has given you info on the right stuff to use... but "when I were a lad..." we used a linen thread (or it might have been cotton) of about 0.6mm. Surprisingly I still have a little bit left (see picture) but there isn't any identifying info left on the spool after all these years. Also for bigger motors (I mean really big, so probably no use to you) we used "Marlin" (Marline?) which was an impregnated jute or similar. Basically anything will do bearing in mind it will get hot later on.

If you get the windings meggered* do it after the tying and before the varnishing (and again after the varnishing if you like). Much easier to go pull it apart _if_ there is something crook (!)

Also (and Ray probably wont like me for this :-) ) epoxy resin can be used as the "varnish", particularly if it is only the leads of the windings you have exposed, but once again, redoing the windings in future becomes much more problematical.

*Meggering won't show shorted turns if you've damaged the interturn insulation on any windings. That will only be evident when the motor overheats or burns out after running for a short time.

Regards
SWK


305411

RayG
24th February 2014, 06:55 PM
Forgot to mention, use fibreglass sleeves to cover joins, and when you do the joins use silver solder.. my son-in-law who is a motor rewinder, insists on using oxy-lpg to actually melt the copper together when making joins between windings, you twist the wires together tightly and heat with the oxy until you get a ball of molten copper at the tip. Silver solder is second best but still ok. Soft lead/tin solder isn't acceptable.

Ray

PS.. SWK.... you're right about the epoxy... :)

BobL
24th February 2014, 08:17 PM
Thanks Ray and SWK,


Bob,
Ray has given you info on the right stuff to use... but "when I were a lad..." we used a linen thread (or it might have been cotton) of about 0.6mm. Surprisingly I still have a little bit left (see picture) but there isn't any identifying info left on the spool after all these years. Also for bigger motors (I mean really big, so probably no use to you) we used "Marlin" (Marline?) which was an impregnated jute or similar. Basically anything will do bearing in mind it will get hot later on.
I wonder if braided nylon fishing line would work?


If you get the windings meggered* do it after the tying and before the varnishing (and again after the varnishing if you like). Much easier to go pull it apart _if_ there is something crook (!)
Good point!


Also (and Ray probably wont like me for this :-) ) epoxy resin can be used as the "varnish", particularly if it is only the leads of the windings you have exposed, but once again, redoing the windings in future becomes much more problematical.
This will probably do me as I have only really pulled away the common point from the windings and just need something to hold the connections back down again


*Meggering won't show shorted turns if you've damaged the interturn insulation on any windings. That will only be evident when the motor overheats or burns out after running for a short time.
Shouldn't a a regular ohm meter reading of a coil should show any gross shorting across the windings of a coil? EG if two coils show 12 ohms and one show 8 than suggests something is wrong?

Thanks for the tip on the solder requirements Ray. I guessed regular solder was not suitable when I tried to melt the sliver blob on the Y connection so I used silver solder.

swk
24th February 2014, 08:32 PM
I wonder if braided nylon fishing line would work?

Maybe, check if it melts at temperature 60-70 degrees, which you could get in the motor on hot spots.





Shouldn't a a regular ohm meter reading of a coil should show any gross shorting across the windings of a coil? EG if two coils show 12 ohms and one show 8 than suggests something is wrong?


In theory, but in practice the coils will be maybe a few hundred turns for a total of less than an Ohm, so a single shorted turn will reduce the resistance by a handful of milliOhms and you can't tell. The only reliable way to detect shorted turns is to use some sort of tester which induces current into the shorted turn and measures the magnetic field of that shorted turn.

Regards
SWK

BobL
24th February 2014, 10:55 PM
Maybe, check if it melts at temperature 60-70 degrees, which you could get in the motor on hot spots.
Braided nylon or Dacron fishing line is supposed to melt at around 250C
Think about how well it can burn your hands!

Mythbusters did a thing on it

After spending a day trying to catch fish without success, the Build Team returned to the shop to test line/reel combinations. They began with a lever-drag reel and measured the maximum temperature achieved with the line running out at 20 miles per hour. Four different lines were tested, with braided Spectra (http://en.wikipedia.org/wiki/Ultra_high_molecular_weight_polyethylene) giving the highest result of 158F; it was used for all further testing. Next, the team switched to older-design star-drag reels, one of which reached 245F and showed large amounts of smoke.For full-scale testing, the team outfitted a go-kart (http://en.wikipedia.org/wiki/Go-kart) to match the mass and top swimming speed of a typical sailfish (http://en.wikipedia.org/wiki/Sailfish) and hooked their line to it from a star-drag reel. Kari drove it at 68 mph, while Tory applied drag and Grant measured the temperature. The first two runs gave a peak of 530F and smoked without any fire, even after Tory used larger amounts of flammable lubricant on the second run.
Declaring the myth busted, the team brought in a professional motorcycle racer and his sidecar rig to achieve higher speeds. Tory also changed the lubricant out for even more flammable engine starting fluid. Runs at 140 and 180 mph gave temperatures over 700F, with the second of these causing the line to melt without burning. Finally, Tory set the reel on fire by exposing it to an open flame.


In theory, but in practice the coils will be maybe a few hundred turns for a total of less than an Ohm, so a single shorted turn will reduce the resistance by a handful of milliOhms and you can't tell. The only reliable way to detect shorted turns is to use some sort of tester which induces current into the shorted turn and measures the magnetic field of that shorted turn. Regards
SWK

Yep - that makes sense - will eventually get it all back together and see if it lets out the smoke.

The motor is an Italian ABB 3HP unit that cost me $30! and is very nicely made (Tidier and cleaner looking than the never used CMG 2HP I have been fiddling with) with bearings that are super smooth and roll on on on very nicely.
The motor comes out of a very large air con system that was installed but within weeks of use was significantly modified and this motor was left over after the modification

soundman
2nd March 2014, 10:52 AM
If you are considering epoxy.
Look at the particular epoxy......Araldite and most of the retail epoxies start to fail at 60C and soften before that.

The marine epoxies may be worth a look.

Most of the varnish used in motors and transformers.....from my recolection will be either phenolic or pollyiamide.

cheers

BobL
2nd March 2014, 11:32 AM
If you are considering epoxy.
Look at the particular epoxy......Araldite and most of the retail epoxies start to fail at 60C and soften before that.
The marine epoxies may be worth a look.
Most of the varnish used in motors and transformers.....from my recolection will be either phenolic or pollyiamide.
cheers

Thanks Soundman.

I went out to work last friday and had a chat with some of the techos and they gave me some dacron thread and some Silicone 401.
We used a fair bit of this silicone when rebuilding high voltage power supplies mainly top cover sharp points and edges to prevent point discharging
This stuff is good for voltages up to 10,000V and is capable of handling 200+C on a continuous basis and can take 260C for short periods.
It also makes it a lot easier if bits and pieces need to come apart later.
I did really need the Dacron thread but it did make it easier to hold the connections in place while I applied a few small spots of silicone

BobL
2nd March 2014, 05:32 PM
I just wanted to report that this 2.2kW motor is now running very smoothly and very quietly via the VFD.

The soft start works really nicely and its been free running for about 2 hours drawing 1.4A and the shaft temperature has reached a max of 31 (ambient is currently 28C in my shed - outside its 38C)

Two 3 phase motors sorted in one weekend - I'm starting to get the hang of this.