douglassmt
Well Known Member
Story of a partial Alternator failure
I'm posting this in the hopes that it might help someone else who encounters a similar problem. Here's the scenario:
RV-10, IO-540, ~250 hours, VP-X, AFS 5600/5500, GTN650, SL30, GTX327, Plane Power 60 amp primary, Plane Power 30 amp backup alternators.
On one recent flight, my 650 Comm circuit trips the electronic circuit breaker (ECB) on the VP-X. Hmm, that's never happened before. Reset in flight, no recurrence. Next flight, no problems. Next flight, same thing, only reset in flight doesn't work. Switch to SL30 comm, land, reset ECB on ground, stays on. Two flights later, GTX327 trips during runup. Reset, no problem. Then in flight, the 650 Comm trips, the 327 trips, and the flaps trip, not all at the same time. By this time (some might argue a little late), I'm getting concerned, the plane is grounded until I figure this out.
After discussions with Vertical Power (thanks Marc and crew), he suggests the most obvious solution is shorts between VP-X and the two devices that tripped. I'm a little skeptical because they all happened at once, the plane is nearly new, etc. However, I switched pins to the 650 comm circuit from the VP-X, tested it on the ground, it still tripped, which indicated the problem was not in the VP-X. I pulled and traced the wires between the VP-X and both units - good as new, no apparent chafing/cuts. I tested the 650 and 327 circuits with the boxes removed from the trays - no circuit breaker trips and no amperage draw at all.
What I learned at this point was that the VP-X gives a reason for the trips - either short circuit, overcurrent, or current fault (this last has to be enabled for each device). I should have looked at the reason for each trip initially but I did not. When I retested, all the trips were listed as short circuits. OK, so I've now eliminated shorts in the wires, shorts in the connectors at the back of each box, and probably the VP-X. Marc offers to look at my VP-X anyway so I send it in. They look it over but cannot find anything. They send me a NEW unit anyway! So what could be the matter? The alternator must be working fine or my battery would be dead, right?
By this time I'm getting frustrated. I repeat the runup (when the 327 now trips every time) while monitoring the amps for the problem circuits. Well now, at idle, the two circuits are drawing 0.4-0.7 amps, but it wavers a little. At about 1400 rpm, the amps go crazy, bouncing from 0.4 to 13 to 30 to 22 to .5, until eventually the 327 trips (ECB set at 3 amps). Same thing on the 650 comm circuit but it does not always trip - odd, because the ECB is set at 10 amps. The total amps drawn (as reported on the VP-X page) bounces around in the same way. However, the current produced by the alternator (Hall effect sensor) is steady. I decide to check other circuits and notice that the amps on the autopilot (AFS) and the SL30 comm are also bouncing around at runup RPMs, although neither ever tripped. The flaps ECB never tripped again, but I never flew again until the problem was resolved.
Then I repeat the runup on the backup alternator. Nothing, no trips, no amps fluctuation, no nothing. Works perfect.
Ok, now we're getting somewhere. I start to focus on the main alternator. I call Plane Power and talk to Dick, who is very helpful. He gives me some ideas for troubleshooting the alternator: supply the field voltage direct from the battery instead of through the VP-X (did not solve the problem), check for loose connections (none), watch for voltage fluctuations (aha!). At this point, I notice that the VP-X page is reporting a voltage that is below 13V when on the main alternator. I'm not sure how long this has been happening, but that is now a clear indication something is amiss.
Now I am strongly considering sending the alternator in to Plane Power for them to look over (they offered) when my hangar neighbor offered to let me swap out his exact same model alternator for mine and see if it fixes the problem. After 15 minutes the alternators are swapped and the problem has gone away. That's all I needed to know. The alternator is going in. I also noticed that the windings on my alternator were discolored in places. When I mentioned that to Plane Power, he said that is a sure sign of a broken stator wire.
Plane Power looks it over the next day, finds two broken stator wires, repairs it under warranty, returns it the third day. After installation and ground testing, flight testing shows problem resolved.
So here is what I learned...
1. The vendors in the experimental world are great - special thanks to Vertical Power and Plane Power; and to Christer @ Steinair and Bob @ TCW for some valuable help. Vertical Power did things for me they didn't have to do.
2. Alternators don't always fail outright and completely. Mine was apparently making enough power initially to supply the plane and recharge the battery but was making so much noise that the VP-X sensitive ECBs interpreted it as amperage swings and tripped several ECBs. It did apparently progress to nearly complete failure eventually, which made the diagnosis easier. My alternator worked fine at idle but not at higher rpm even at the end.
3. I should have kept a better eye on the power system fundamentals: alternator voltage should be 14.5+ and the amps reported by the VP-X should not swing wildly, check the reason for any circuit breaker trips.
4. Alternator windings shouldn't be discolored - another good thing to check at every oil change. I have no idea how long my stator wires were broken.
5. I have hangar neighbors who are great folks, willing to pull their cowl, remove their alternator, and let me try it.
6. There's a tendency to question everything about your system when these - apparently intermittent - electrical problems occur. Troubleshooting should start with the basics, eliminate possibilities until you find the problem. Don't panic, just logically work through the options and don't be afraid to get help from experts.
7. In the end, my system worked as it was intended. The VP-X protected the wires and devices and provided lots of valuable information that would have helped me find the problem sooner if I had known how to read and interpret it...hence the reason for this post.
Hope this helps someone else who might run into a similar problem.
PS - Plane Power suggested that the cause might be an out-of-balance prop. I was planning to have the prop balanced anyway - and will - but I strongly doubt that such could have caused the damage to the alternator. The engine and prop seems to be pretty darn smooth.
I'm posting this in the hopes that it might help someone else who encounters a similar problem. Here's the scenario:
RV-10, IO-540, ~250 hours, VP-X, AFS 5600/5500, GTN650, SL30, GTX327, Plane Power 60 amp primary, Plane Power 30 amp backup alternators.
On one recent flight, my 650 Comm circuit trips the electronic circuit breaker (ECB) on the VP-X. Hmm, that's never happened before. Reset in flight, no recurrence. Next flight, no problems. Next flight, same thing, only reset in flight doesn't work. Switch to SL30 comm, land, reset ECB on ground, stays on. Two flights later, GTX327 trips during runup. Reset, no problem. Then in flight, the 650 Comm trips, the 327 trips, and the flaps trip, not all at the same time. By this time (some might argue a little late), I'm getting concerned, the plane is grounded until I figure this out.
After discussions with Vertical Power (thanks Marc and crew), he suggests the most obvious solution is shorts between VP-X and the two devices that tripped. I'm a little skeptical because they all happened at once, the plane is nearly new, etc. However, I switched pins to the 650 comm circuit from the VP-X, tested it on the ground, it still tripped, which indicated the problem was not in the VP-X. I pulled and traced the wires between the VP-X and both units - good as new, no apparent chafing/cuts. I tested the 650 and 327 circuits with the boxes removed from the trays - no circuit breaker trips and no amperage draw at all.
What I learned at this point was that the VP-X gives a reason for the trips - either short circuit, overcurrent, or current fault (this last has to be enabled for each device). I should have looked at the reason for each trip initially but I did not. When I retested, all the trips were listed as short circuits. OK, so I've now eliminated shorts in the wires, shorts in the connectors at the back of each box, and probably the VP-X. Marc offers to look at my VP-X anyway so I send it in. They look it over but cannot find anything. They send me a NEW unit anyway! So what could be the matter? The alternator must be working fine or my battery would be dead, right?
By this time I'm getting frustrated. I repeat the runup (when the 327 now trips every time) while monitoring the amps for the problem circuits. Well now, at idle, the two circuits are drawing 0.4-0.7 amps, but it wavers a little. At about 1400 rpm, the amps go crazy, bouncing from 0.4 to 13 to 30 to 22 to .5, until eventually the 327 trips (ECB set at 3 amps). Same thing on the 650 comm circuit but it does not always trip - odd, because the ECB is set at 10 amps. The total amps drawn (as reported on the VP-X page) bounces around in the same way. However, the current produced by the alternator (Hall effect sensor) is steady. I decide to check other circuits and notice that the amps on the autopilot (AFS) and the SL30 comm are also bouncing around at runup RPMs, although neither ever tripped. The flaps ECB never tripped again, but I never flew again until the problem was resolved.
Then I repeat the runup on the backup alternator. Nothing, no trips, no amps fluctuation, no nothing. Works perfect.
Ok, now we're getting somewhere. I start to focus on the main alternator. I call Plane Power and talk to Dick, who is very helpful. He gives me some ideas for troubleshooting the alternator: supply the field voltage direct from the battery instead of through the VP-X (did not solve the problem), check for loose connections (none), watch for voltage fluctuations (aha!). At this point, I notice that the VP-X page is reporting a voltage that is below 13V when on the main alternator. I'm not sure how long this has been happening, but that is now a clear indication something is amiss.
Now I am strongly considering sending the alternator in to Plane Power for them to look over (they offered) when my hangar neighbor offered to let me swap out his exact same model alternator for mine and see if it fixes the problem. After 15 minutes the alternators are swapped and the problem has gone away. That's all I needed to know. The alternator is going in. I also noticed that the windings on my alternator were discolored in places. When I mentioned that to Plane Power, he said that is a sure sign of a broken stator wire.
Plane Power looks it over the next day, finds two broken stator wires, repairs it under warranty, returns it the third day. After installation and ground testing, flight testing shows problem resolved.
So here is what I learned...
1. The vendors in the experimental world are great - special thanks to Vertical Power and Plane Power; and to Christer @ Steinair and Bob @ TCW for some valuable help. Vertical Power did things for me they didn't have to do.
2. Alternators don't always fail outright and completely. Mine was apparently making enough power initially to supply the plane and recharge the battery but was making so much noise that the VP-X sensitive ECBs interpreted it as amperage swings and tripped several ECBs. It did apparently progress to nearly complete failure eventually, which made the diagnosis easier. My alternator worked fine at idle but not at higher rpm even at the end.
3. I should have kept a better eye on the power system fundamentals: alternator voltage should be 14.5+ and the amps reported by the VP-X should not swing wildly, check the reason for any circuit breaker trips.
4. Alternator windings shouldn't be discolored - another good thing to check at every oil change. I have no idea how long my stator wires were broken.
5. I have hangar neighbors who are great folks, willing to pull their cowl, remove their alternator, and let me try it.
6. There's a tendency to question everything about your system when these - apparently intermittent - electrical problems occur. Troubleshooting should start with the basics, eliminate possibilities until you find the problem. Don't panic, just logically work through the options and don't be afraid to get help from experts.
7. In the end, my system worked as it was intended. The VP-X protected the wires and devices and provided lots of valuable information that would have helped me find the problem sooner if I had known how to read and interpret it...hence the reason for this post.
Hope this helps someone else who might run into a similar problem.
PS - Plane Power suggested that the cause might be an out-of-balance prop. I was planning to have the prop balanced anyway - and will - but I strongly doubt that such could have caused the damage to the alternator. The engine and prop seems to be pretty darn smooth.
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