Alternator Issues in IMC

[Eli Greene]

I have a 1975 M20F and have been having an intermittent issue with my alternator in IMC.
 

Back in July of last year, I went on about a 3 hour flight through IMC. About 2 hours in, while in IMC, the alternator died. We had a low voltage warning light, negative amps draw, and voltage of 11.9 volts. Circuit breakers were ok, we unplugged/turned off all non-essential equipment, and continued the flight. After a few minutes, we decided to cycle the master switch, and this worked. The alternator returned and we landed without event. The mechanic on the ground couldn’t find any issues, and our flight home was set to be VFR conditions, so we continued home with no problems. We had the alternator inspected at our home airport, and no issues were found.

I don’t fly through large amounts of IMC(being from Colorado it’s normally icy, so I didn’t see the issue arise or fly long IFR flights much after that incident. In October, we got the engine overhauled, resetting most of our stuff firewall forward. I felt that this would likely also have alleviated our issues with the alternator.

 

However, now I have experienced the issue again. First, yesterday we lost the alternator in IMC intermittently for maybe 20 seconds. Today, we lost the alternator for about 10 minutes at the end of our flight. After getting on the ground, I cycled the master switch and it reacted exactly the same as the first time, with the alternator coming right back. I have heard of issues with early model Mooneys ingesting too much water and having that hurt the alternator. I have the lower cowl enclosure which makes me believe it would be less of an issue for me but I’m not sure. Either way I’ve had the same issue 2-3 times through one overhaul. Does anybody know what this issue could be?

[PT20J]

I doubt that the alternator knows that it is IMC 

You didn’t say what was done to the alternator during the engine overhaul, but since you mentioned that “most” of the firewall forward stuff was “reset”, I assume it was either replaced or overhauled as is generally standard practice (though not required) with an engine overhaul.

Cycling the master/alternator switches resets the over-voltage protection circuit in the voltage regulator if it has tripped and shut down the alternator to protect the electrical equipment from damaging voltages. If you have an engine monitor that records bus voltage, you might check that to see if the voltage went high before dropping. It sounds like perhaps you have an intermittent issue with the voltage regulator.

Skip

 

[EricJ]

15 minutes ago, Eli Greene said:

I have a 1975 M20F and have been having an intermittent issue with my alternator in IMC.
 

Back in July of last year, I went on about a 3 hour flight through IMC. About 2 hours in, while in IMC, the alternator died. We had a low voltage warning light, negative amps draw, and voltage of 11.9 volts. Circuit breakers were ok, we unplugged/turned off all non-essential equipment, and continued the flight. After a few minutes, we decided to cycle the master switch, and this worked. The alternator returned and we landed without event. The mechanic on the ground couldn’t find any issues, and our flight home was set to be VFR conditions, so we continued home with no problems. We had the alternator inspected at our home airport, and no issues were found.

I don’t fly through large amounts of IMC(being from Colorado it’s normally icy, so I didn’t see the issue arise or fly long IFR flights much after that incident. In October, we got the engine overhauled, resetting most of our stuff firewall forward. I felt that this would likely also have alleviated our issues with the alternator.

 

However, now I have experienced the issue again. First, yesterday we lost the alternator in IMC intermittently for maybe 20 seconds. Today, we lost the alternator for about 10 minutes at the end of our flight. After getting on the ground, I cycled the master switch and it reacted exactly the same as the first time, with the alternator coming right back. I have heard of issues with early model Mooneys ingesting too much water and having that hurt the alternator. I have the lower cowl enclosure which makes me believe it would be less of an issue for me but I’m not sure. Either way I’ve had the same issue 2-3 times through one overhaul. Does anybody know what this issue could be?

An overhaul wouldn't affect the regulator, which may be causing your issues.    If all of the wiring and connectors check out, which should be checked first, the regulator might be the next thing to look at.

 

[David Lloyd]

Like Skip says, cycling the master will reset an overvoltage trip.  The OECO or Electro Delta voltage regulator on the 1975s has both a voltage and overvoltage adjustment.  I think with old age, sometimes they may require a slight adjustment.  There is a procedure in the service manual. Follow the procedure.  If it happens again after the first adjustment, replace the voltage regulator.

[carusoam]

welcome aboard Eli!
 

Most common challenge in real life alternators… is the field wire.

They have a tendency to wear out due to vibration….

This is the communication line between the alternator and the voltage regulator…

When this wire isn’t functioning… it makes it look like an alternator problem…

 

Could be a fifty cent fix…

Did the IMC include rain?

when discussing electrical problems… rain may be part of the issue more than IMC…

PP thoughts only, not a mechanic…

Best regards,

-a-

[Eli Greene]

Thanks for all the help,

 

Yea the reason that I feel that it has something to do with IMC is that it only seems to happen after spending >20minutes in the clouds. I've never seen it happen outside of the clouds or when in the clouds for a short while. Obviously the alternator's don't understand whether IMC exists around them, but I'm wiling to bet that the clouds are getting the alternator wet.

13 minutes ago, carusoam said:

 

Did the IMC include rain?

 

When it first happened, I was in the clouds, no rain but quite a bit of water/water droplets. Second time it happened we were in pretty heavy rain. Third time it happened no rain, just in the clouds. All three times I had been in the clouds for at least 20 minutes, although in the first 2 cases it was about an hour before anything happened. This leads me to believe that clouds/water from the clouds getting onto the airplane and into some connections could be causing the issue... From what little I understand, I guess the water may be causing an overvoltage for some reason, leading to an overvoltage trip. This would be consistent with being able to reset the alternator, and would be consistent with water getting in. I'm guessing that this all points towards a new voltage regulator, but I will check over the connections obviously before immediately going that route.

 

-Eli

[A64Pilot]

If your airplane is like mine the alternator field power is also run through the master, if memory serves there are four spade connectors, the alt field ones are the two closest to the passenger seat one above the other, remove and clean them and reinstall. I like deoxit to clean things like this. Make sure they make a good connection.

Often you can reach under the panel and wiggle these wires, if the alternator comes back then you have likely found the culprit.

Mine is a J so I’m assuming yours is like mine, easy to check and costs no money

https://www.donmaxwell.com/fluctuating-ammeters

[BravoWhiskey]

I had a belt get hung up/slip as a result of bad bearings.  Did the same thing.  Worked then didn’t work then worked the snapped a belt then flipped another one… needed an overhaul.

[McMooney]

6 hours ago, carusoam said:

welcome aboard Eli!
 

Most common challenge in real life alternators… is the field wire.

They have a tendency to wear out due to vibration….

This is the communication line between the alternator and the voltage regulator…

When this wire isn’t functioning… it makes it look like an alternator problem…

 

Could be a fifty cent fix…

Did the IMC include rain?

when discussing electrical problems… rain may be part of the issue more than IMC…

PP thoughts only, not a mechanic…

Best regards,

-a-

Mine did this today,  strange thing the ammeter showed charging but the voltage steadily dropped. 

[EricJ]

1 hour ago, McMooney said:

Mine did this today,  strange thing the ammeter showed charging but the voltage steadily dropped. 

Ooh, that's not good.   Something is not right if the ammeter showed charging and it wasn't.   Might be time to test the ammeter functionality.

[carusoam]

Another common challenge for everything working but not actually charging…

Slipping belts…

There is a strong torque setting for it… the procedure is possibly found in the MM…

Best regards,

-a-

[carusoam]

The over voltage warning is interesting…

That sounds more like voltage regulator not being able to regulate…

See if you have the sticks, stones, and springs VR or something more from this century called zeftronics…

 

The sticks and stones can boil away an expensive battery…

The zeftronics has option for warning lights…

Best regards,

-a-

 

[PT20J]

15 hours ago, carusoam said:

Another common challenge for everything working but not actually charging…

Slipping belts…

There is a strong torque setting for it… the procedure is possibly found in the MM…

Best regards,

-a-

SI1129D Alternator Belt Tension, Methods of Checking.pdf

[Marauder]

Thanks for all the help,
 
Yea the reason that I feel that it has something to do with IMC is that it only seems to happen after spending >20minutes in the clouds. I've never seen it happen outside of the clouds or when in the clouds for a short while. Obviously the alternator's don't understand whether IMC exists around them, but I'm wiling to bet that the clouds are getting the alternator wet.
When it first happened, I was in the clouds, no rain but quite a bit of water/water droplets. Second time it happened we were in pretty heavy rain. Third time it happened no rain, just in the clouds. All three times I had been in the clouds for at least 20 minutes, although in the first 2 cases it was about an hour before anything happened. This leads me to believe that clouds/water from the clouds getting onto the airplane and into some connections could be causing the issue... From what little I understand, I guess the water may be causing an overvoltage for some reason, leading to an overvoltage trip. This would be consistent with being able to reset the alternator, and would be consistent with water getting in. I'm guessing that this all points towards a new voltage regulator, but I will check over the connections obviously before immediately going that route.
 
-Eli

Eli - I would suspect the voltage regulator. I have a 75 F as well and saw some weird voltage fluctuations on an IFR flight as well. Unfortunately, I had to have the charging system troubleshooting done at my destination because my return trip was going to be IFR. The alternator was replaced and my run up and flight around the pattern showed at steady 13.8V.

About an hour into my 1+30 return flight, the voltage dropped into the 12 voltage range. Cycling the power brought it back for the remainder of the flight. I replaced the regulator with a Zeftronics and have seen a solid 14.1V for the past 4 years.

BTW - Zeftronics sells a version for our model that has the Cannon plug end. Makes for a quick and easier (mounting them is a bit challenging) swap.




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[carusoam]

+1 for the modern Zeftronics VR…

Getting the sticks and stones and springs VR to produce the proper voltage is a challenging adjustment…. (Follow the MM)

The Zeftronics is more of a set it and forget it kind of device….

PP thoughts only, not a mechanic…

Best regards,

-a-

[thinwing]

the other thought I had was while in cloud you wouldnt by any chance have pitot heat on??That puts quite a draw on the system and is unlikely to be used in vfr conditions

[carusoam]

Good thinking tw!

Thanks for sharing the idea…

Best regards,

-a-