ammeter discharging - thoughts?

[JamesMooney]

About 60 hours ago, on the ground, I got a low voltage annunciator, ammeter showed a slight discharge, and voltage meter in cigarette plug read 12.4V. I reset the master switch 3 times, and on the third time, everything returned to normal. Flew the plane for another 60 hours with no issues.

This Saturday on final approach in KHHR, the same thing appeared: low voltage annunicator, ammeter showing discharge, and 12.4V.

Plane is at KHHR right now. That's not my home base, and the one maintenance shop there said they may not look at the plane for a week.

Thoughts?

1. Possible solution?

2. Other airports with recommended A&Ps around Los Angeles?

I'm not very keen to fly it very far around the busy LA airspace with the possibility of losing my battery, radios, etc.

Thoughts? Thanks!

PS. The only electrical work done recently was at annual inspection (in May), they adjusted the voltage regulator up (it had always been drawing about 13V, so they adjusted it up to get 14V). I guess it was shortly after that when this first instance happened - but then no problems for 60 more hours until now...

[M20F]

How old is your battery and how much corrosion is on your cables from the battery to the front.  

[JamesMooney]

5 minutes ago, M20F said:

How old is your battery and how much corrosion is on your cables from the battery to the front.  

Battery is new - about 18 months old.

Haven't looked at the cables - they are old / haven't been changed for many years.

[Kodiakflyer]

Any idea of how old the voltage regulator is?

[JamesMooney]

Believe its original - 1976

[bcg]

How old is your battery and how much corrosion is on your cables from the battery to the front.  

Sounds like a problem with the cables to me as well. Either corrosion on the connections or in the wires. I would start by taking them off and cleaning everything up with a wire brush.

I recently had this exact same situation with an air compressor and cleaning the cables and connections was the solution.

Sent from my Pixel 5 using Tapatalk

[Ragsf15e]

From your indication, it’s not just low voltage, the alternator is completely off line.  Nothing wrong with checking the cables at the battery and airframe connection for security or corrosion, but I don’t think that’s your problem.

Sounds like the VR is intermittent, and if that’s what they adjusted, maybe they were hiding the real problem - not on purpose though, just masking it.

Id crank the airplane and check for positive amps.  If not, pull field CB which really isn’t the field wire, but power to the VR.  At least in mine.  You can check your wiring diagram. Reset it.  This won’t fix your issue but maybe it’ll reset it or help you isolate it.  Some VRs have an over voltage protection too.  Maybe @PT20J knows which ones?

Another thought… if you were seeing 13v before, maybe you had some corrosion causing that, but now that they cranked up the Vr to indicate 14, your poor alternator is actually putting out like 15 or more just meeting some corrosion/resistance somewhere.  You need a smart person with a dvm.  Good luck.

[Guest]

By all means check for corroded terminals in the alternator wiring and battery cables, it’s cheap maintenance.  Open the right side cowl, with the master/alternator field switch on you should have battery voltage at the field terminal on the alternator.  Power here says the circuit breaker, switch, regulator and wire are likely OK.  If there is no power work backwards through the system till you find the cause.

If there is suitable power at the field terminals pull the brushes for inspection, many start wearing down above 500 hours in service.

[PT20J]

Maybe this will help

Troubleshooting-Single-Engine-Externally-Regulated-Alternators.pdf

[JamesMooney]

Had an A&P have a quick look today - they couldn’t immediately pinpoint the problem. Advice was to charge the battery, and then day VFR fly the plane back to my home base. Would be a 90 minute flight out of the LA Class B up to KSBP. Ugh….

[Ragsf15e]

15 minutes ago, FlyingCanuck said:

Had an A&P have a quick look today - they couldn’t immediately pinpoint the problem. Advice was to charge the battery, and then day VFR fly the plane back to my home base. Would be a 90 minute flight out of the LA Class B up to KSBP. Ugh….

All the stuff @M20Docsaid to check is easily done with a dvm and the left cowl off.  Did the person who looked at it even have a dvm?  No offense to mechanics, but it’s tough to find one that can properly troubleshoot electrical issues.  Doc is an outlier on the good side.

[Guest]

59 minutes ago, Ragsf15e said:

All the stuff @M20Docsaid to check is easily done with a dvm and the left cowl off.  Did the person who looked at it even have a dvm?  No offense to mechanics, but it’s tough to find one that can properly troubleshoot electrical issues.  Doc is an outlier on the good side.

Good enough to know the alternator is on the right side, or is this a test?

[Ragsf15e]

15 minutes ago, M20Doc said:

Good enough to know the alternator is on the right side, or is this a test?

That was a test.  I figured you’d pass, but I knew that was enough to keep many mechanics guessing. 

In all honesty, they all know where the alternator is because that’s the easiest thing to just replace, “alternator no worky, must replace!” However, with electrical, that’s rarely the answer.

[carusoam]

Make sure you have a portable radio working before the battery dies in flight…

The most common killer of alternators around here… the field wire breaks, and the alternator goes off line…

Find your field wire… is it in pieces?

 

If the alternator is sort of working… are you getting rpm dependent whine in your headset?

 

 

PP thoughts only…

-a-

[JamesMooney]

10 hours ago, carusoam said:

Make sure you have a portable radio working before the battery dies in flight…

The most common killer of alternators around here… the field wire breaks, and the alternator goes off line…

Find your field wire… is it in pieces?

 

If the alternator is sort of working… are you getting rpm dependent whine in your headset?

 

 

PP thoughts only…

-a-

You know what's interesting... on my last flight, I heard a weird (intermittent) whine in my headset. Sort of an electrical noise. It was intermittent and went away after a while.

[JamesMooney]

Update on this saga: looks like the wiring is good, battery is good, and there is voltage at the field wiring suggesting that the voltage regulator is functioning. The A&P working on it suspects the alternator slip ring/brushes have gone. There's another Mooney on the airport with the same alternator, so they are going to try swapping alternators and/or slip rings/brushes, to see if that is the issue.

[carusoam]

If the brushes are worn….

The surface they are riding on… commutator… will probably need some refinishing….

Pp thoughts only,

-a-

[ArtVandelay]

There's another Mooney on the airport with the same alternator, so they are going to try swapping alternators and/or slip rings/brushes, to see if that is the issue.

If I was the owner of that other Mooney I would not be happy having my plane disassembled and parts pulled.
If the alternator has 500+ hours on it I would just have it overhauled, probably could use it anyway.

[Guest]

17 hours ago, FlyingCanuck said:

Update on this saga: looks like the wiring is good, battery is good, and there is voltage at the field wiring suggesting that the voltage regulator is functioning. The A&P working on it suspects the alternator slip ring/brushes have gone. There's another Mooney on the airport with the same alternator, so they are going to try swapping alternators and/or slip rings/brushes, to see if that is the issue.

If it’s a Prestolite alternator the brushes come out with two screws, certainly faster and more ethical than trying someone else’s alternator on your plane.  Time to seek out a more qualified maintainer.

[Fly Boomer]

On 8/22/2022 at 2:45 PM, bcg said:

had this exact same situation with an air compressor and cleaning the cables and connections was the solution.

This is pretty far out and long ago, but I once had a cable that looked perfect, but I cleaned and tightened the connections to no avail.  In desperation, I replaced the cable — problem fixed.

[ZuluZulu]

The good news about being "stuck" in LA is you're close to Aero Accessories at Van Nuys, which is one of the best alternator and mag shops around.  And that's coming from someone who once had to drive his alternator up there for an IRAN while AOG at SNA.  (Turned out to be the voltage regulator but I still felt better having had them inspect it!  This was early in my ownership and zero alternator problems since.)

P.S. If your voltage regulator gives you problems, call Don Maxwell.  Mine was an orphan no longer supported or offered by Mooney (maybe you're lucky to have a more common one) and Don was the only one I could find in the entire country who will work on it.  Otherwise it's an expensive retrofit to install a different V/R.

@FlyingCanuck

[JamesMooney]

Update: my 'home' maintenance shop were able to look at it. Verdict was: missing field ground wire (missing! interesting...).

$0.86 in parts later...

 

[carusoam]

Interesting follow-up FC!

Field wires don’t usually go missing…

But, if it broke off on one end… it may have broken the other end as it fell away…

 

Great price!

PP guesses only, not a mechanic…

Best regards,

-a-

[JamesMooney]

Don't ask me how it got from LA to SMX for that inspection.

But if you want to talk about calculating amp hours on various electrical devices versus the health of a new battery, I'm happy to offer my amateur opinions

[BDPetersen]

Just had a positive experience with my Plane Power system which began to whine in headset and show low voltage. A call to PP support had me talking to a fellow who talked me through troubleshooting with a digital voltmeter. Determined it to be the alternator not the regulator. Had me fill out a warranty claim on their website, sent me an RMA and I shipped it off for replacement. Waaay out of warranty.