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Dennis Johnson
Joined: 10 Jan 2006
Posts: 89
Location: N. Calif.
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 Posted: Mon Dec 06, 2010 8:05 am Post subject: Intermittent Generator Problem |
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While on a cross country flight last week, I got a low voltage indication in my Lancair Legacy, wired using Z 13-8. I turned on the SD-8 aux alternator and the voltage increased to the low end of the normal range. I also noticed a whine sound in my headset. If I turned off the main alternator, the whine went away but the voltage sagged. (I have an all electric airplane and the SD-8 won't carry the full load unless I shed loads, turn the master switch off, and run on the E-bus.)
I turned the main alternator back on and the whine sound in my headset returned and the voltage returned to the low end of the normal range. I flew that way for about 15 minutes and the whine suddenly stopped and voltage jumped up to normal. I turned off the aux alternator and completed the flight normally.
Everything was perfectly normal for the two hour flight home.
Any ideas what caused this? Since the first symptom was reduced output and a whine in the headset, I initially suspected failed diodes inside the alternator, but when it healed itself, I thought it might have been a brush problem inside the alternator. After 15 minutes, whatever was causing poor brush contact went away? I'm grasping at straws here.
I am so thankful for Bob's Z 13-8 architecture, which allowed me to continue the flight without breaking a sweat! Thanks, Bob!
Supporting information:
Lancair Legacy, Continental IO-550 engine, 12 volt gear-driven main alternator, SD-8 permanent magnet aux alternator, Z 13-8 architecture, all electric panel.
Dennis Johnson
[quote][b]
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n8zg(at)att.net
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| Posted: Mon Dec 06, 2010 1:05 pm Post subject: Intermittent Generator Problem |
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I suspect you’re losing an output diode in the alternator.
neal
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Dennis Johnson
Sent: Monday, December 06, 2010 9:59 AM
To: aeroelectric-list(at)matronics.com
Subject: Intermittent Generator Problem
While on a cross country flight last week, I got a low voltage indication in my Lancair Legacy, wired using Z 13-8. I turned on the SD-8 aux alternator and the voltage increased to the low end of the normal range. I also noticed a whine sound in my headset. If I turned off the main alternator, the whine went away but the voltage sagged. (I have an all electric airplane and the SD-8 won't carry the full load unless I shed loads, turn the master switch off, and run on the E-bus.)
I turned the main alternator back on and the whine sound in my headset returned and the voltage returned to the low end of the normal range. I flew that way for about 15 minutes and the whine suddenly stopped and voltage jumped up to normal. I turned off the aux alternator and completed the flight normally.
Everything was perfectly normal for the two hour flight home.
Any ideas what caused this? Since the first symptom was reduced output and a whine in the headset, I initially suspected failed diodes inside the alternator, but when it healed itself, I thought it might have been a brush problem inside the alternator. After 15 minutes, whatever was causing poor brush contact went away? I'm grasping at straws here.
I am so thankful for Bob's Z 13-8 architecture, which allowed me to continue the flight without breaking a sweat! Thanks, Bob!
Supporting information:
Lancair Legacy, Continental IO-550 engine, 12 volt gear-driven main alternator, SD-8 permanent magnet aux alternator, Z 13-8 architecture, all electric panel.
Dennis Johnson
01234567890123456
[quote][b]
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skywagon
Joined: 11 Feb 2006
Posts: 184
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| Posted: Mon Dec 06, 2010 2:39 pm Post subject: Intermittent Generator Problem |
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About intermittent alternators..... Once I had to chase a mystery problem. Alternator would go off line, later come on line. I later chased down a hairline crack in the stationary stator windings in the case where it entered a swaging boss. When the alt. go hot, the hairline crack would open and after the alt. cooled a little the wire would make continuity and charge again. I suspect that the heavy wire was damaged during manufacture and would not show up until the alt. put under heavy loads in hot conditions. I had to use a magnifying glass to finally view the crack.....
If it is not diodes, then look for this stator wire problem.
David
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Tue Dec 07, 2010 2:50 pm Post subject: Intermittent Generator Problem |
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It could also be a sticking brush on the field coil.
Noel
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of David Lloyd
Sent: December 6, 2010 7:05 PM
To: aeroelectric-list(at)matronics.com
Subject: Re: Intermittent Generator Problem
About intermittent alternators..... Once I had to chase a mystery problem. Alternator would go off line, later come on line. I later chased down a hairline crack in the stationary stator windings in the case where it entered a swaging boss. When the alt. go hot, the hairline crack would open and after the alt. cooled a little the wire would make continuity and charge again. I suspect that the heavy wire was damaged during manufacture and would not show up until the alt. put under heavy loads in hot conditions. I had to use a magnifying glass to finally view the crack.....
If it is not diodes, then look for this stator wire problem.
David
[quote]
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Noel Loveys
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nuckolls.bob(at)aeroelect
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| Posted: Fri Dec 10, 2010 10:14 am Post subject: Intermittent Generator Problem |
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Any ideas what caused this? Since the first symptom was reduced
output and a whine in the headset, I initially suspected failed
diodes inside the alternator, but when it healed itself, I thought it
might have been a brush problem inside the alternator.
Could be a grounding issue too . . .
After 15 minutes, whatever was causing poor brush contact went
away? I'm grasping at straws here.
I am so thankful for Bob's Z 13-8 architecture, which allowed me to
continue the flight without breaking a sweat! Thanks, Bob!
Let's replace the 'straws' with data. What kind of
alternator/regulator combination are you flying?
If an externally regulated alternator, consider
adding a temporary instrumentation wire with 1000
ohm resistor as close as possible to to the
alternator's field terminal best. See:
http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z22K_23K.pdf
Get some cheepy volt-ohmeter to monitor voltage
at the cockpit end of the wire in flight. An analog
meter is best suited for this. This would be a good
choice:
http://www.radioshack.com/product/index.jsp?productId=2103957
Tape the meter up where you can watch it. Note the
readings when the system is operating normally/
abnormally. Review the topic of Alternator Fault
Isolation in chapter 3 of the 'Connection.
Bob . . .
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