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Robbins & Myers G30


Andrew White

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8 hours ago, David Deloria said:

I'm following this thread. I have the same fan, same cooked motor. Interested in seeing if you end up rewinding and the results if you do.

After researching it and reading Mark's great advice, I think this is something I am capable of (and very interested in) doing. It won't be right away as I have lots going on for the holidays and such, but I hope to at least start working on it within the next few weeks. Thanks for expressing your interest in it David, I will make sure to document my process and share it with you. Maybe we can save a couple R&Ms!

Mark (or anyone who has an opinion):

1) Is polyimide (as opposed to polyamide or polyurethane) coating the way to go for magnet wire? For example: https://temcoindustrial.com/electrical/wire/magnet-wire/?ProductLine=GP/MR-200

2) How many feet of wire are in the average fractional hp motor? To my eye, maybe the run windings in mine are 20 AWG (small paperclip thickness) and start windings are a little smaller, so say 24 or 25 AWG. So, maybe a couple thousand feet of wire?

2) Should I bother trying to figure out a way to vacuum the varnish into the windings or is the spray and bake method sufficient?

3) Is it advisable to use low voltage direct current instead of low voltage alternating current when baking varnish using the resistive heat of the coils, or same difference?

4) How exact do I have to be with my wrap count? Over a few thousand wraps, if I am off by even 1/10th of an inch on my coil pack length, I could inadvertently be +/- a few hundred inches of wire. Perhaps having a dozen or so more or fewer wraps than what it originally had from the factory wouldn't have a large impact, however, it seems to me that having any variance between my newly made coil packs within a single winding would be bad and have any number of negative noise, heat, efficiency implications. Am I thinking correctly?

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On 11/17/2022 at 9:24 AM, Andrew White said:

After researching it and reading Mark's great advice, I think this is something I am capable of (and very interested in) doing. It won't be right away as I have lots going on for the holidays and such, but I hope to at least start working on it within the next few weeks. Thanks for expressing your interest in it David, I will make sure to document my process and share it with you. Maybe we can save a couple R&Ms!

Mark (or anyone who has an opinion):

1) Is polyimide (as opposed to polyamide or polyurethane) coating the way to go for magnet wire? For example: https://temcoindustrial.com/electrical/wire/magnet-wire/?ProductLine=GP/MR-200

2) How many feet of wire are in the average fractional hp motor? To my eye, maybe the run windings in mine are 20 AWG (small paperclip thickness) and start windings are a little smaller, so say 24 or 25 AWG. So, maybe a couple thousand feet of wire?

2) Should I bother trying to figure out a way to vacuum the varnish into the windings or is the spray and bake method sufficient?

3) Is it advisable to use low voltage direct current instead of low voltage alternating current when baking varnish using the resistive heat of the coils, or same difference?

4) How exact do I have to be with my wrap count? Over a few thousand wraps, if I am off by even 1/10th of an inch on my coil pack length, I could inadvertently be +/- a few hundred inches of wire. Perhaps having a dozen or so more or fewer wraps than what it originally had from the factory wouldn't have a large impact, however, it seems to me that having any variance between my newly made coil packs within a single winding would be bad and have any number of negative noise, heat, efficiency implications. Am I thinking correctly?

Andrew,

I am sorry that I missed this post.

Short answers:

1: All magnet wire today has far superior insulation than what they had back in the day.

2: A pound of each will be more than enough.

3: Vacuum impregnation is nice, but this is an antique fan. Spray-On varnish is a fine fixative.

4: Count the turns as well as you can. You have as many chances as your motor has poles. You will find that they are almost the same. A speed coil is a different animal, and care must be taken. There are typically only a few hundred wraps, not thousands.

I hope this helps, BTW, a mechanical winder with a turns counter is a great asset.

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A gram scale is a great asset for motor rewinding. 

Using it and some math, you won't even have to count turns in the old coils, just weigh them. Pull off say a foot, weigh it, then weigh it and the whole coil together.

It's as simple as, say your sample is 1.2g and the full coil plus the sample is 600g. Now you know you have (on average) 500' coils of magnet wire.

I'd repeat this process for all the coils so you can get an idea of what kind of tolerance the motor was made with. You might find a variance of a few feet between the largest and smallest, which comes out to be 1-2% "error" off an exact length. Obviously, closer is better, but knowing you don't have to measure to the inch to avoid a fireball can be reassuring.

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On 12/26/2022 at 5:59 PM, Mark Olson said:

4: Count the turns as well as you can. You have as many chances as your motor has poles. You will find that they are almost the same. A speed coil is a different animal, and care must be taken. There are typically only a few hundred wraps, not thousands.

I hope this helps, BTW, a mechanical winder with a turns counter is a great asset.

Counting turns to cut your teeth is nice, but sampling and weighing coils cuts out 99% of the stress and crap. You won't ever need to know the turns, either in the old or new coils. If you use the same gauge wire and your coil forms are accurate, all you will need to do is sample, weigh, and gauge the old coil, and use that to spin off however much you need of new wire. Having an identical empty spool to the one holding the wire you're weighing is a must, so that you can tare it off.

 

If you can weigh anything to avoid counting and you have a trustworthy scale, ALWAYS WEIGH!

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48 minutes ago, Nicholas Denney said:

Counting turns to cut your teeth is nice, but sampling and weighing coils cuts out 99% of the stress and crap. You won't ever need to know the turns, either in the old or new coils. If you use the same gauge wire and your coil forms are accurate, all you will need to do is sample, weigh, and gauge the old coil, and use that to spin off however much you need of new wire. Having an identical empty spool to the one holding the wire you're weighing is a must, so that you can tare it off.

 

If you can weigh anything to avoid counting and you have a trustworthy scale, ALWAYS WEIGH!

Weighing has its place. Some motors had cloth covered wire, and it weighs different than enamel insulated wire.

I like the accuracy of counting, and in the grand scheme of work, it is but a small part of the overall time consumed, and the chances of getting a motor wound with the correct current draw, or power consumption, increases.

Lastly, a speed coil turns must be counted, as otherwise one would not know where to bring out the taps!

Edited by Mark Olson
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