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lucien
Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM
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 Posted: Sat May 02, 2009 1:30 pm Post subject: 912ULS integrated alternator question |
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Hi all,
I'm curious for the 912 gurus, is it ok for the integrated alternater on the 912 series to have no load on it? I just discovered last night that my reg/rect is long since burnt out. At least for the last 3 or 4 operating hours anyway. finally smelled a rat after yesterday's flight that the battery took a bunch of charge where some several flights before it was still most of the way charged after the same electrics were used. My voltage would always run low when I had the electrics on so didn't notice it on the voltmeter either.
I checked the stator resistance with my ohmmeter according to the heavy maint. manual and that looks correct. Also ran er up with the meter hooked to the two generator leads and got a good 15 volts AC at high idle, on up to 25 and more as I revved it up. So the stator appears to be undamaged.
Can't find anything in the manuals about any adverse affects of operating the alternator with no load, which is what the case has been for a bit now. Anyone know? I assume it's ok since it's just a coil of wire with no current flow due to the open circuit.
Ordering new R/R on Monday. Plane is just getting newer and newer all the time!
LS
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LS
Titan II SS |
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dalewhelan
Joined: 11 Nov 2008
Posts: 105
Location: USA ARIZONA fountain hills
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| Posted: Mon May 04, 2009 7:16 am Post subject: Re: 912ULS integrated alternator question |
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I am not familiar with the 912. I use to teach motorcycle electric systems.
I get the feeling you were describing a permanent magnet charging system. It really makes little difference anyway.
You used good tests but there are ways for the stator to still be bad, although I suspect it is fine.
The easiest most conclusive way I know to test it is to use an automotive headlight. Connect High beam to one stator lead and low to another, don't use ground. If th bulb lights bright, you are good. Resist the temptation to rev the motor high and blow the bulb.
As for meter tests and other tools. You can perform an insulation test to make sure the stator is not shorted to ground by testing resistance from ant lead to ground. The reading should be infinity. They can still be bad in this may if they arch to ground during operation, a megger could be used to see this. It is likley that it would have failed the voltage output test if this was the case.
The voltage test itself can be brought into question due to the fact that it is a no load test. Have you ever had a battery that mould not start a car and then tested its voltage with everything turned off and wondered why a battery with good voltage won't start your car?
Let's just imagine a pair of 9 volt batteries in series, we now have 18 volts, will that start your car? Do you think we will read 18 volts when you turn on the cars electrics?
A stator can behave it the same way, it may pass an unloaded test when it is bad, it would fail the loaded test. The bulb provides a good load. I hope this helps
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503 powered Firestar II, Luscombe 8A
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JetPilot
Joined: 10 Jan 2006
Posts: 1246
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| Posted: Mon May 04, 2009 8:06 am Post subject: Re: 912ULS integrated alternator question |
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Lucien,
From what I understand of the system, there is not a problem with running no load on the stator / magnet system . I would replace the bad part and head on out to monument valley !
Mike
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lucien
Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM
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| Posted: Mon May 04, 2009 8:11 am Post subject: Re: 912ULS integrated alternator question |
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| dalewhelan wrote: | I am not familiar with the 912. I use to teach motorcycle electric systems.
I get the feeling you were describing a permanent magnet charging system. It really makes little difference anyway.
You used good tests but there are ways for the stator to still be bad, although I suspect it is fine.
The easiest most conclusive way I know to test it is to use an automotive headlight. Connect High beam to one stator lead and low to another, don't use ground. If th bulb lights bright, you are good. Resist the temptation to rev the motor high and blow the bulb.
As for meter tests and other tools. You can perform an insulation test to make sure the stator is not shorted to ground by testing resistance from ant lead to ground. The reading should be infinity. They can still be bad in this may if they arch to ground during operation, a megger could be used to see this. It is likley that it would have failed the voltage output test if this was the case.
The voltage test itself can be brought into question due to the fact that it is a no load test. Have you ever had a battery that mould not start a car and then tested its voltage with everything turned off and wondered why a battery with good voltage won't start your car?
Let's just imagine a pair of 9 volt batteries in series, we now have 18 volts, will that start your car? Do you think we will read 18 volts when you turn on the cars electrics?
A stator can behave it the same way, it may pass an unloaded test when it is bad, it would fail the loaded test. The bulb provides a good load. I hope this helps |
Yeah I'll try the light bulb today just to make sure. The voltage test was just the meter put across the generator leads so indeed there was no load, tho the voltages looked right to me (15 to 25 at frequencies of 150 to 250 on up, up to about 4500 rpm)...... But you're quite right it'd be a good idea to test it with an actual load on it.
I checked the resistances of each lead to ground and got infinity as expected. The coil reads close to a dead short, about .1 ohms, which is in the expected range specified in the heavy maintenance manual.
So I think I'm ok..... I hope  That stator is expensive and replacing it would be pulling the motor off the plane and driving it to Ronnie Smith's place in the pickup..... not something I'd want to do for fun....
Thanks for the info!
LS
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LS
Titan II SS |
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lucien
Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM
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| Posted: Mon May 04, 2009 11:42 am Post subject: Re: 912ULS integrated alternator question |
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| JetPilot wrote: | Lucien,
From what I understand of the system, there is not a problem with running no load on the stator / magnet system . I would replace the bad part and head on out to monument valley !
Mike |
Well tested stator on my lunch break with the light bulb test. Nearly burnt out my spare 50W landing light even at idle..... so the stator is fine which is a big sigh of relief.......
I'll have the new R/R tomorrow if lockwood had it in stock today....
LS
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LS
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