over-voltage

edasmus · #1 10-04-10, 09:36 PM

Thanks Mark...

I have been meaning to update for the last day or two but just been short of time. The voltage has been successfully set to 28.5 volts. We also found signs of arcing on the master switch contacts so that was replaced. One alternator circuit breaker was replaced because of wandering resistance or voltage variations through it. You could tap the breaker and watch the variations on the meter. A diode was also added to the landing gear power pack because a consistent "pop" was heard when the gear hit the stops on the up cycle. That was the moment I was getting the over-voltage system to trip off the alternators. Since this work has been completed, the electrical system has been behaving normally. Nothing but the sound of silence in my headset other then the voice of the friendly ATC. I have about 6 or 7 hours on it in the last week with no problems so she is slowly regaining my confidence.

Ed

hharney · #2 10-05-10, 01:30 PM

Great news Ed
Thanks for posting all the trouble shooting. This will be of great help to someone else in the future.

edasmus · #3 10-29-17, 10:24 PM

Hello all! Well, it looks as though it has been 7 years since I last posted on this thread about my over-voltage issues! Well a Halloween horror story, the beast is back. Dang it!

Started two flights ago. In cruise climb about 10 minutes after departure all is well and a little zap and pop in my headset and sure enough, the over-voltage relay has tripped and the alternators are off. Crap, hmmm, well I reset and all goes well the rest of the day for the remaining two hours of flying. Passing anomaly I hope. Time will tell.

Next flight this past weekend, in cruise, level flight on auto-pilot for 30 minutes or so with absolutely nothing going on other than to enjoy the view. Then, out of no where, little zap and pop and there is that damn beast. Reset, complete the flight and while I'm taxing to the ramp, the beast hits again. WTF.... I say.

Well, I enjoy my Halloweenie party for the night, next morning, fly home. First 30 minutes, all is well, and then in cruise, on auto-pilot, doing nothin, the beast strikes again. I reset and 5 miles from home while leveling to slow for the pattern, he strikes again. I do a quick reset to get the gear out, fly the pattern turning from base to final all configured for landing, the beast strikes again. He's an active mother f---er. It's simply fascinating to me how for 7 years and probably 400 hours of trouble free electrical operation and then all of the sudden out of no where the monster awakes.

Well, Ill be headed to the shop in the morning but in the mean time, if anyone has ever had this symptom (and I realize many of you have, I have read all the horror stories on this forum) and found a "SMOKING GUN" that cured it (as I have when I started this thread), please do tell. I'm sure we will do all the usual connection cleaning and ground checking, etc. That zap I hear in my headset, is an arc. I need to find that arc. The breaker box will be the first place I go, but the problem will likely not be there. I remember that repair like it was yesterday. That insulator box that holds the breakers will last 1000 years.

For all that are interested, stay tuned for how this Halloween horror story evolves!

Note: I love my Skymaster, the Halloween story is for dramatic effect! ;o)

Bye for now....

edasmus · #4 02-24-18, 05:19 PM

Well folks, here's my update on this issue. It's been several months however I'm cautiously optimistic that this problem has been resolved. Time will tell as I fly along but here is the story.

I flew around 10 or so hours last November (2016) running the electrical system on one alternator or the other. The symptom would only appear while running on the front. Usually the over-voltage sensor would trip within an hour of running on the front. Switching to the rear alternator would yield several hours of trouble free electrical system operation. That seemed like reasonable evidence the problem was with the front side of the electrical system.

Also what I observed on my digital volt meter during operation on one alternator versus the other was that the front alternator was indicating plus/minus 2 to 2.5 volts rapid fluctuation but while running on the rear alternator, the voltage would only fluctuate plus\minus 0.1 volts. The rear was very stable. While running both alternators simultaneously, the wild fluctuation was present though not as amplified. Hmmmm, interesting.

The airplane went into it's annual inspection in December and that all went smoothly. My IA kept his eyes open for anything that looked unusual during the inspection regarding the electrical system. Nothing seemed amiss. For lack of a better plan, he removed the front alternator and sent it out for an IRAN. Neither one of us had much confidence that the front alternator was the problem but it is quite old so I was up for the experiment. Both of my alternators have been running trouble free for the life of my engines which are now beyond TBO. The shop (which I've used countless times with excellent service) opened the alternator and said "yes," it looks old in there but nothing inside the alternator was causing the problem. They cleaned it up, put it back together, and said "keep looking." Running the front engine with the freshly serviced alternator still yielded the same voltage fluctuations. The alternator shop was correct.

Well, one of the young ones in my maintenance shop who has been working under my primary IA went looking some more and discovered one of the diodes on the front firewall that is in the circuit which controls the over-voltage protection system appeared to have a defect. I'll attempt to describe.

The diode looks like a cylinder maybe an inch long and having a diameter of about a half an inch. The thing was enclosed inside a plastic case. There is a small metal pole protruding from this cylinder that a wire attaches to. Now for all I know the diode is encased inside this cylinder or maybe the entire cylinder is the diode. I have no clue how all this stuff works. That's why I pay these guys. Well, the little metal pole that is protruding from the cylinder was loose. You could actually wiggle it around inside the cylinder. Comparing it to the other diode on the firewall, that one was very tight. No play whatsoever. Replacing that $8.00 diode seems to have solved the problem. Voltage across the system running on a either single or both alternators is rock solid at 28.5 volts plus/minus 0.1 volts and no over-voltage tripping has yet to occur. Granted, I haven't flown much yet since the repair but so far so good. It's been a long winter. Better Wx ahead. Stay tuned.

kilr4d · #5 02-26-18, 03:38 PM

Quote:

Originally Posted by edasmus

The diode looks like a cylinder maybe an inch long and having a diameter of about a half an inch. The thing was enclosed inside a plastic case. There is a small metal pole protruding from this cylinder that a wire attaches to. Now for all I know the diode is encased inside this cylinder or maybe the entire cylinder is the diode. I have no clue how all this stuff works. That's why I pay these guys. Well, the little metal pole that is protruding from the cylinder was loose. You could actually wiggle it around inside the cylinder. Comparing it to the other diode on the firewall, that one was very tight. No play whatsoever. Replacing that $8.00 diode seems to have solved the problem. Voltage across the system running on a either single or both alternators is rock solid at 28.5 volts plus/minus 0.1 volts and no over-voltage tripping has yet to occur. Granted, I haven't flown much yet since the repair but so far so good. It's been a long winter. Better Wx ahead. Stay tuned.

Interesting.

Could you grab a picture the next time you have the cowl off?

Thanks,

John

edasmus · #6 02-28-18, 07:29 PM

Here's your photo....

kilr4d · #7 03-01-18, 01:00 PM

Quote:

Originally Posted by edasmus

Here's your photo....

Thank you.

general · #8 04-24-18, 08:55 AM

https://www.slideshare.net/mobile/St...oting-test-box
If you're working on electrical systems on Skymasters this PowerPoint from my friends at Airscan in Florida is well worth looking at. There are actually quite a few power points that they've done. The one for the IO 550 engine conversion for the 337 is pretty interesting also