# OT: Generator Armature Rewind



## Kirk_Wallace (Nov 20, 2008)

Sorry if this is a little off topic, but it should be close. I have an Onan 5 kW genset:
http://www.wallacecompany.com/machine_shop/Onan_5CCK/
that I need to rewind. I need to know about materials, material sources and techniques for rewinding. Does anyone have links to information that I can study?

The original armature had what appears to be kraft paper lining the iron core slots then a mylar (slightly milky, not water clear though) sheet lining the slot. It seems to me the mylar alone should work. Should I use both, or use something else? I like the idea of fiberglass tape, but it may be too thick or abrasive?

I need to figure out how the DC windings are fixed to the commutator bars. My guess is that they are silver soldered? Typically, how much heat can the commutator take? It also appears that the wires are staked. Should I stake the wires in the un-staked area or wrap the bar or wire ends? The armature turns at 1800 RPM, so I am guessing that rotational forces aren't an issue?

The AC windings used four wires for each strand. My guess is that allows a higher packing density, but there was some room left over and I am thinking of going to two larger wires per strand to try to make winding easier. Bad idea?

What varnish should I look into? Do you varnish as you go, or can I do the winding, do a short test run to make sure it works, and then varnish the whole armature at the end? Baking the varnish seems to be common. Why is it needed?

Thank you for any help with this. I hope this list doesn't mind me asking more questions later.
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Kirk
http://www.wallacecompany.com/machine_shop/


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## TX_Dj (Jul 25, 2008)

Not a whole lot of people here have delved into rewinding motors or generators.

You might want to contact Jim Husted of HiTorque Electric. He does motor work for a living.

What will you be using the generator for? Range extender? 5kW is a little low for that, so I'm guessing not.


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## Kirk_Wallace (Nov 20, 2008)

Thanks for the reply DJ.

I have studied Jim's website. I would hate to bug Jim too much, since he seems to be quite busy and time is money.

I supply WiFi Internet to my local area and would like to have backup power. The last time power went out, I was able to get by with a 2kW Honda, but at 3600 RPM, it makes allot of noise. The Onan runs at 1800 RPM and 5 kW, so it should be more tolerable. I also have a 9.5 kW generator head that I am thinking of linking to a 1.6 liter Diesel Rabbit engine, but it's a longer range project.
--------
Kirk
http://www.wallacecompany.com/machine_shop/


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## major (Apr 4, 2008)

Kirk_Wallace said:


> I need to know about materials, material sources and techniques for rewinding. Does anyone have links to information that I can study?


Hi Kirk,

You might try the EASA website. http://www.easa.com/



> The original armature had what appears to be kraft paper lining the iron core slots then a mylar (slightly milky, not water clear though) sheet lining the slot. It seems to me the mylar alone should work. Should I use both, or use something else?


Use Nomex.



> I need to figure out how the DC windings are fixed to the commutator bars. My guess is that they are silver soldered?


Several methods are used in production. Sliver solder. Heat stake. Electric brazing with silfos. Tig welding. 



> Typically, how much heat can the commutator take?


I've seen the comm bars get red hot in production. Those machines had water cooled electrodes. You can get the comm pretty hot. But try to limit it. Maybe cool the bar right after with a large metal heat sink. Go from one side to the other as you go around it instead of adjacent bars. Solder temperatures should be no problem.



> It also appears that the wires are staked. Should I stake the wires in the un-staked area or wrap the bar or wire ends?


The comm riser should have a slot to press the wire ends into. Clear that slot and use it. Strip the insulation off the wire ends. Put them into the proper riser slot. You can stake them (smash), but not necessary, especially if you solder. Hold them tightly to the bottom of the riser slot with something like a band clamp when you solder.



> The AC windings used four wires for each strand. My guess is that allows a higher packing density, but there was some room left over and I am thinking of going to two larger wires per strand to try to make winding easier. Bad idea?


I'd duplicate the original.



> What varnish should I look into? Do you varnish as you go, or can I do the winding, do a short test run to make sure it works, and then varnish the whole armature at the end? Baking the varnish seems to be common. Why is it needed?


You use a motor or transformer varnish or polyester resin. Typically these armatures are dipped into a vat and vacuum is drawn. Because you're doing a single, you can probably get away with brushing on a thick coat. Try to get it in the core slots. Baking it properly cures the varnish. Follow instructions. I'd do it twice. Dip or coat-bake-coat-bake.

Yeah, you could do a test run prior to varnish. I suggest you do half speed. And not if it shakes, rattles and rolls (out of balance). The wires can move if not varnished and rub insulation off.

Of course, you'll need to turn and undercut the comm. And balance it.

Good luck,

major


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## Kirk_Wallace (Nov 20, 2008)

Thank you major.

I think that gets me closer to ordering materials. I am a little leary about getting started without having everything planned out, but if I put the varnishing out until the end, I suppose I can always rewind the armature until I get it done properly.

At first glance, EASA looks like it caters to professionals, which means, for me, a commitment in time and money which would need a means to justify that commitment. I am in the process of trying to figure out how to make a living out in the middle of nowhere, plus being 52 doesn't help. This may be something worth getting into.

TIG welding wire ends to the commutator bars sounds interesting. I have a Hobart TIG:
http://www.wallacecompany.com/machine_shop/Hobart_Cyber-TIG/
which should be able to deliver allot of heat quickly. I also like the idea of heat sinking the rest of the bar. What is the typical material that the commutator bars are mounted in? If I really screw up, is it possible to remake a new commutator? I may be fussing too much about this. I should probably try to find a burnt out motor to practice on.

For the varnishing, I would like to build a vacuum chamber, but I guess it would need to be large enough to hold a container filled with varnish covering the windings?

For balancing, I suppose, I need a spud to fit the armature's taper. Then level my granite surface plate and use a pair of tall parallels. There shouldn't be too much magic there. 
-----------
Kirk
http://www.wallacecompany.com/machine_shop/


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## major (Apr 4, 2008)

Kirk_Wallace said:


> What is the typical material that the commutator bars are mounted in?


Hi Kirk,

I can't tell by the picture. Older comms were built up using steel cores and mica insulation. Modern comms are molded using phenolic. I am not familiar with the combo comm/slip ring jobs. 



> If I really screw up, is it possible to remake a new commutator?


Unlikely.



> For balancing,


Most are dynamically balanced. Since you are relatively low speed, you might get away with static balance.

You ever think about having a motor rewind shop do this job for you? Might be cheaper by the time you buy the wire and materials. But not as much fun, I guess.

major


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## smith77 (May 3, 2021)

You can go to servo drive repair to know about how the DC windings are fixed to the commutator bars and you will also get to know which are the materials that the commutator bars are mounted in.


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