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Generators & Electric Motors General Discussion Antique Generators and Old Electric Motors: Questions and answers about restoring and showing old power generation systems.

Generators & Electric Motors General Discussion

Pincor PTO overheated?


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  #1  
Old 01-01-2010, 06:51:52 PM
Rob vds Rob vds is offline
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Default Pincor PTO overheated?

I just bought an old pincor 25kw cont. pto generator and have 7 days to try it and return if not satisfied. While it was still in the pickup box at a comfortable working height I removed the rear cover and was a little perturbed by the armature windings . The coils show deeply darkened varnish one one side and there are a couple of blobs of hard solder stuck on 2 places. I find it hard to believe it is solder that has run out from somewhere but neither does it look like professionaly applied balancing weights.
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  #2  
Old 01-02-2010, 02:13:46 AM
Andrew Mackey Andrew Mackey is offline
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Unhappy Re: pincor pto overheated?

Looks like it has been severely heated. look over any soldered connections, and test for shorts.
Andrew
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Old 01-02-2010, 04:26:48 AM
Ironsides Ironsides is offline
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Default Re: pincor pto overheated?

Two ways to go in my opinion,return it or offer them scrap value.It has been way too hot and cooked something in there somewhere.Norm
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Old 01-02-2010, 10:19:09 AM
Rob vds Rob vds is offline
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Default Re: pincor pto overheated?

As the varnish is darkened on only part of the circumference of the rotor coils is it logic to assume the armature was stationary when the heating occurred? The heat would almost have to have come from inside the rotor not the stator. I have no idea how these things are built, is this possible? Is there something other than heat that could discolor the varnish?
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Old 01-02-2010, 04:00:39 PM
Jim Rankin Jim Rankin is offline
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Default Re: pincor pto overheated?

Single or 3 phase? If 3 phase, how was it connected?

Imbalanced amperage loads on a 3 phase stator are supposed to create circulating currents in the rotor. Normally this is OK within the operating limits set by the manufacturer (most common rule seems to be... applying no load greater than rated 3phase amperage on any phase....... will keep you out of trouble).

With a PTO unit, the normal relationship between prime mover and generator that you have built into a set by the manufacturer can be very different.....
Could have had a large tractor hooked to it and plenty of power to drive it into overload conditons without overheating the tractor, so it got abused. That would say something about the exciter capability though if it had the capacity to force the field for an extended overload.

I wonder what it would look like if the generator were backfed from the line for a (very?) short time.

My tendency would be to keep it if it pulls the load fine and I hadn't paid a lot for it.

I would worry more about one pole winding being darkened while the others weren't instead of all of them being the same, but with a difference around each coil.
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Old 01-02-2010, 06:37:01 PM
Rob vds Rob vds is offline
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Default Re: Pincor PTO overheated?

This is a single phase 120/240 unit. I would have thought the 125 amp breaker would protect it? The 15 kw unit I have borrowed would sometimes trip it's 80 amp breaker. That is why I was pleased to find a 25/30 kw unit. This machine will have had a good workout during the 1997 ice storm when I had no power for 15 days but some areas were much longer. Many dairy farms bought new 65kw models after that storm. The major issue with pto generators is driveline wear, I don't see why the generator should wear out if not overloaded and I am sure the build quality will be better than a new one. The price is 1200$ and I find that reasonable but it would be expensive if it needs repair the first time I need it in earnest!
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Old 01-03-2010, 12:53:46 AM
Jim Rankin Jim Rankin is offline
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Default Re: Pincor PTO overheated?

I would load it to maximum and keep it that way for a while before accepting it.
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Old 01-03-2010, 12:18:27 PM
David K David K is offline
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Default Re: Pincor PTO overheated?

Is it solder or is it epoxy? To me, it looks more like a dark gray (like J-B Weld) than it does a bright gray/silver (like solder). Although old solder does darken over time. Give it a scratch with a pocket knife and see if it is shiney underneath. I don't think it is solder because if it got hot enough to melt solder, the centrifugal force of a spinning rotor would have thrown the solder off of the rotor and spread it around the stator or housing (like the generator I have sitting on my bench, see "solder recommendation - added pictures for clarity").

If it is epxoy, I don't know why it would be there.

Good luck.
Dave
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Old 01-03-2010, 04:05:19 PM
Jim Rankin Jim Rankin is offline
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Default Re: Pincor PTO overheated?

Guess I didn't notice the blobs of "solder" you were referring to in the picture. If you mean the ragged grey stuff there on the end of the pole iron above the winding, it does look like it might have been put there to balance the rotor. I had a small brushless exciter rotor winding that had some similar looking epoxy/putty like material applied to it presumably to balance it. It had been stuck inside the end windings and looked like the bond with the iron had failed and the stuff pushed the windings outward under centrifugal force causing a short. This was a used purchased non running generator, so I don't know the history on it. The rotor came back from the rewinder without any similar putty stuck in it and it performed well under testing without any noticable shake.

I would wind this generator up to synchronous rpm and feel it carefully for vibration. Might feel it better at some rpm less than synchronous, but certainly do not leave a load attached or even excitation on it at low rpm.
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Old 01-03-2010, 07:27:05 PM
Rob vds Rob vds is offline
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Default Re: Pincor PTO overheated?

Yes I think it is epoxy and there is no sign that it has come loose anywhere or at anytime. It does seem a pretty insignifigant mass to tame an unbalanced rotor that must weigh over a hundred pounds and it seems pretty messy to have been factory installed.
Back to the discoloured varnish it doesn't seem logic that the copper winding didn't dissipate the heat if that is what caused it. To me the cutoff between colours is too sharp. I need to talk to a rebuilder in case they have ever come across this, I have only ever seen the whole coil toasted. I will speak to the seller's agent tommorrow before running it as I don't want to be blamed for burning it out completely.
There are 4 little diodes being fed from a transformer. I presume they supply dc to the brushes for excitation? What actually controls the voltage? Should the voltage be adjustable or is it fixed at sync. speed. (1800rpm)?
Thanks for the help so far, please keep the suggestions coming, Rob
P.S. Is there a spell checker incorparated in here somewhere?
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