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grolly Regular Member Joined: 19/05/2007 Location: AustraliaPosts: 62
Posted: 11:26am 29 Aug 2008
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Hi all , would anyone have any sugestions as to what I could do to this burnt out unit, it spins beautifully, but smokes when spun at 3000 rpm. is there any use for it as is, other wise I will start stripping the copper wire out of it, it did have a 12V 10A DC outlet, is that the small windings at the top, or is that the exciting winding, as there is only one magnet, a small one that the nail is stuck to?
I have bought the farm...now I AM powering it...
Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510
Posted: 01:11pm 29 Aug 2008
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If it were mine I'd certainly be tempted to try to repair it. A working 5.5kVA generator is always nice to have and worth much more than its copper scrap value.
In the top picture, the top part of the rotor (with the 6 pole shoes) appears to be the excitation generator that supplies power to the field (2-pole part of the rotor, below the excitation coils on the rotor).
Can't be hard to find the fault. By the look of the blackened stator coil in the top picture it appears to be burned out. Shouldn't be too hard to remove the statorwindings and rewind. Throw in some new bearings for good measure and she'd be as good as new.Edited by Dinges 2008-08-31
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 10:30pm 29 Aug 2008
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Grolly,
If you feel a rewind is too much, you can resort to a barbaric act.....
If you can carefully remove the faulty winding (hack it out), and replace it with a piece of wire(bypass it) to complete the circuit, you may get it to work pretty well. You can not just short the faulty winding, it must be removed or it will probably try to toast itself.
(It's about now that Dinges will fall off his chair I suspect and mutter about wild animals in the southern oceans......)
.........oztules
Village idiot...or... just another hack out of his depth
Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510
Posted: 10:40pm 29 Aug 2008
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Nope Oztules, didn't fall off my chair. I had it in mind too when answering the OP, it's just that I've got a name to keep...
Bypassing a defect winding is what Rosenberg suggests too for DC motors. The machine should probably be derated (by how much?), but it could be a quick and dirty fix. And if he's going to chisel out the copper anyway... it might be an idea to carefully remove (or *completely* chisel through the coil) and bypass the burned-out winding first and give the genny a try. With a bit of luck it works. If it doesn't he can still scrap it or do a complete rewind if that tickles his fancy.
But, if it were mine I wouldn't accept anything but a full rewind. And I think you'd rewind too; you just can't resist the opportunity... Edited by Dinges 2008-08-31
grolly Regular Member Joined: 19/05/2007 Location: AustraliaPosts: 62
Posted: 05:38am 30 Aug 2008
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Now now you two.... the burnt coil is the one conected to the red(+) wire, and the three coils next to it have one wire blackened too, would your " Hack fix" just cause the next winding to fry? and by how much would it be de-rated?
BTW, priced a rewind for it, for $100 more, bought an NEW 8KVA....
The bearings are perfect.
What speed would I have to turn it at to get some useable power out of it( not AC ,maybe rectified DC),It was ment to run at 3000 rpm.
I would like to run it on my VWT, only spins at 100 to 150 rpm, it has the torque to take a 5:1 step up, and I have the wind here to keep it turning.
If I can find a use for it, it would be worth more to me than scrap value.
Thanks Grolly I have bought the farm...now I AM powering it...
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 10:15pm 30 Aug 2008
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Hmmm..
Dinges knows me too well. I think I would try the hack first just to glean some knowledge..... but I would have to rewind it as Dinges would..... although probably not with new wire...
Grolly, if a few more coils are cactus, then total rewire is in order, or scrap it. It is not for a vawt
........oztulesVillage idiot...or... just another hack out of his depth
grolly Regular Member Joined: 19/05/2007 Location: AustraliaPosts: 62
Posted: 09:25am 04 Sep 2008
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Thanks Oztules and Dingles,
I found on further examination that one compleate side of the windings were burnt, so I am attempting a rewind.
Now, there a re a few things that I have no idea how to find out...
What speed would the exciting winding have to reach to excite the core windings?
Would it be easier to rewind it to put out 240V AC @ 50 Hz, or rewind it to produce an AC output that I could rectify to 48V DC ?
There are 36 slots, so assumeing that I can spin it at 3000 rpm, what would be the output if I rewound it useing a coil 6 slots wide and haveing 18 of these coils?
Or haveing coils 3 slots wide and haveing 12 if these..
Or am I barking up the wrong tree?
If this won't work, I have about 3 kg of copper wire to sell...
GrollyI have bought the farm...now I AM powering it...
Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510
Posted: 08:05pm 04 Sep 2008
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To attain full rated output power of your generator you'd have to run it at rated RPM. At what speed the excitation winding starts exciting ? Impossible to say. Probably at 0.1 RPM, but the output would be immeasurably small.
Either 48V-ish ac or 240Vac could work, as long as you make sure you wind it in exactly the same slots as the present windings. If you'd go for 240Vac it'd be a simple copy of the present situation, guaranteed to work; if you want to have 48Vdc battery charger at 3000 RPM, you'd have to do a little math as you're basically re-designing the generator. (just guessing here; but if you rectify you'd want at most 60Vdc for floatcharging, so 60/1.41 = 42Vac (at 3000 RPM))
For 42Vac, you'd need 42/240 = 0.175 times the amount of turns the coils have now. Also, to have same rated output power (5.5 kVA), wire diameter would have to be 2.4 times as large.
If you start unwinding the generator, measure wire diameter and count the number of turns each coil has. Then choose a wire diameter that's 2.4 times as large and wind a test coil of 0.175 times as many windings. See if it fits. If it does, wind the other coils and insert them in the right slots.
The above w.r.t. rewinding for 48V only applies if there's no 'feedback' of main power to the excitation field. I can't tell if there is from here. If part of the stator output is used to supply energy back to the field (the single magnet is probably only there for bootstrapping the system) then rewinding to any other voltage would be much more complicated (if not practically impossible without rewinding the excitation generator too).
At 3000 RPM you should be able to get full rated output power, as long as you have the same 'slot fill' (amount of copper per slot). That's why you want to calculate how many turns and how thick wire you can still fit in there.
I'm not sure what to make of your drawings; whatever you do, make sure that you're rewinding EXACTLY the same as it is now, only with different thickness wire and different number of turns.
Edited by Dinges 2008-09-06
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