ST3 Generator Head output half voltage

[dkwflight]

Hi Call george at utterpower.com  He seems to be the most experienced with these gen heads. I believe Joel is the importer.
Mean while don't panic. There may be a simple repair you can do. It depends on where the short is. I believe I would bake the windings over night at a low tempereture and recheck with the Megger. If the readings improve you can coat the windings. a motor shop can do this. I'm told the rotor has to be balanced after the coating process.

Maybe you need to remagnetise the unit. Or possibly clean the brushes and sliprings?
Over 2 megohms doesnt sound bad to me. An ohm meter even a good one doesn't use a high voltage like a megger

The bearing are bad in my 20k head too. I will be pulling it down soon. I sort of expected to repace the bearing when I bought it. I don't see a reason for it tho. The chinese can make quality bearings.
Dennis

[Jim Mc]

Baking might improve the megger reading, but won't fix the problem of 1/2 output voltage.  Nor will remagnetising.  If you're getting to 1/2 voltage, there's plenty of residual magnetism.

Here's what I'd do:  First, I'd set out to prove that the stator main output windings and the field coils are OK.  To do this, excite the field with a DC supply, of whatever the rated field voltage is (about 48V DC on some that I've seen, but yours may differ - hopefully the field rating is on the nameplate.).

If this tests out OK, meaning you can get rated AC output with nominal field excitation, I'd proceed to buy or build a solid-state voltage regulator and simply not use the "harmonic winding'.  If you can't get the rated AC output with nominal field excitation, it's probably scrap.  Has anybody here ever rewound an ST head?  I have my doubts, but jump in if so.  Having a motor shop do it would be prohibitively expensive on a 3 kW ST.

[BruceM]

Applying DC to the field coil is a good diagnostic idea Jim.  If only I could spin it up here in my shop where I have a variable DC supply!

I had already flashed the field coils for testing purposes. I suppose it is possible that the field coil on the rotor could possiblybe the guilty party, since the harmonic winding output only starts the pulsing when loaded by the field coil. But since there's not evidence of heat or shorting on the rotor, the harmonic seems more likely.

There are strips of bamboo locking the windings in place, and the coils are wound on the interior of the stator  cylinder in groves that are "C" shaped with the bamboo closing off the narrow opening of each "C". I expect the bamboo will be destroyed in trying to remove it.  It looks like an real bugger to mess with.  But I will play it with a bit when it cools off a bit this evening.  We're having a heat wave, temps over 100 the last couple days.  That's a bit much for us mountain dwellers.

Thanks and Best Wishes,
Bruce

[Doug]

For all practical purposes the minut you decide to start picking away at the winding an pulling edges your stripping it. Its kind of like being a little pregnant....
Somebody said contact George, thats good advice see what he has to say there might be a simple reason for the trouble. I wish I could help more, if you were up the road with a case of beer I'd have my nose in it and if need be I'd strip and rewind it just to see what I make it do.

Ask George for the name of the maker, again it if its a dud I think we should email the factory. From what I understand about George, he's likely to cover something....

Doug

[BruceM]

My ST3 was not from George (alas), as at that time (last fall) he was out of stock on 6-1's and his new shipment was few months out.  He has kindly offered me a replacement at a bargain basement price, but is also suggesting that I go to an ST5, which is what I originally wanted but was also out of stock and a few months out when my 'oid finally got shipped.  There is aparently a very big difference in induction motor starting capability from the ST3 and ST5.  (And George is never trying to "sell" anything.) It's a pain to change my mount now in the midst of a construction project, but I may go for it.

The freight from the NW to AZ is a bugger, so I'm still thinking.

Thanks very much Doug, for sharing your expertice so generously! You're a big asset to this forum.

Best Wishes,
Bruce

[Doug]

Bruce don't scrap the ST-3, put it a side. When we have a little more time we can take it a part and if need be I'll walk you threw a simple rewind.
For you or anyone else remotely intersted in trying to spin a few coils, try and find the US navy service and technical manuals for electric motors and generators. I stumbled across a copy at the local Library ( who knows how it ended up in Canada ) and it is probably the best place to learn how to service and do fieled repairs of rotating electric machines


Doug

[BruceM]

Thanks again Doug.  I think I have a book on rewinding, but have never tried it.

[Doug]

There are some tricks and shortcuts, have a look at otherpower.com the way they spin coils on home made jigs and use fiber glass boat resine and rosin cloth. Its not the prefered method of winding a head but it can be done....

Doug

[dkwflight]

Hi It seems like there must be an open some where on the machine. THat is the only way to loose half the out put like that. It would help you to use a needle for a probe tip on your multi meter. you can use the needle to break throught the insulation on the wires to make sure there is not an open some where. Be methodical and test every joint and coil individually. Its possible the slip rings arn't connected to the windings. or some such.
good luck
Dennis

[BruceM]

With some outstanding email from Bill Rogers, I was able to get this ST3 back on line yesterday.  Ended up the the half voltage problem WAS a diode bridge fault, but then I had a doghouse AC meter failure resulting in erroneous low volatage reading (200 glitching to 150VAC), and I got confused and didn't recheck the output on my VOM.

The harmonic winding output on an ST (at least on a ST3 and ST12) is supposed to be a short pulse before and after each AC output peak.  So my harmonic output, which surprised me and didn't look right, was normal. 

Thanks and best Wishes,
Bruce M

[Doug]

Thats a huge relief!

I would still like toknow why your VOM gave such low readings on the insulation. Could you try it again warm and cold and repost. If its still low can you borrow a meggar from someone and check it out. I find it odd that a new head should read so low....

Doug

[dkwflight]

Hi Congratulations on the repair.
It pays to be methodical in your trouble shooting.
Dennis

[BruceM]

Doug- the stator and harmonic windings, as well as rotor windings checked out at greater than 20mega ohms with my bench meter (limit of meter).  The meter I tested with before was limited to 2mega ohms, which is why I reported >2megaohms. So nothing suspicious, it was just the way I reported it.

So once again I learn that George B's CD admonition about the doghouse vibration on the AC meter there is right on the mark.  It's also a relief to have the "Power Solutions" ST head windings vindicated.  I know George's next "to spec" batch will have modern bridge diode assemblies, and I think no dog house.

Best Wishes,
Bruce