Intermittent electrical issue

[flyby201]

I have a 77 201 and have been experiencing an intermittent electrical problem for some time.   When this issue occurs, maybe every 3rd or 4th flight, the alternator will stop charging leaving the plane to operate on battery power.  Usually when I notice this I can recycle the master switch a couple of times until it comes back online.  Because it is so intermittent, it has been difficult for my A&P friends to diagnose.  We attached a wire to the field wire connection at the alternator and ran it up into the cockpit.  I attached a volt meter to it so I can monitor what is going on when this happens. (Trying to determine if the problem is the alternator or voltage regulator).  Yesterday, I went to fly and during my run up on the ground I was turning on the landing light, pitot heat and anything else to put a load on the electrical system.  During all this my field wire voltage was around 8 volts and bus voltage was around 14.1 volts.  I looked away for a few seconds to attend to something else and when I looked back I had 0 volts on field wire and 12.3 volts on the bus.  Recycling the master switch brought everything back to normal operation.  I haven't had a chance to share this information with my A & Ps but wanted to put this info on MooneySpace to see what the consensus was here.  Your input will be greatly appreciated.

[PT20J]

Sounds like the over voltage protection circuit in the voltage regulator is tripping.

[mooniac15u]

57 minutes ago, nosky2high said:

FWIW I highly recommend plane power voltage regulators, 2000+ hours behind them and never a problem. Same with their alternators. 

Plane Power voltage regulators are part of the STC generator to alternator conversion which doesn't apply to the M20J because they all came from the factory with alternators.  Zeftronics is pretty much the only option.

[Yetti]

yep.   Same issue.   I ordered a set of brushes and installed.  Brushes took about an hour to install with altenator on the plane.   Easy just time consuming.    When start up it will produce power for like 30 seconds.   Being lazy I decided to order a Zeftronics voltage regulator seeing the first one lasted 40 years.   Should be in this week will let you know.  

The zefttronics is plug and play with a matching cannon plug.

[flyby201]

I sent an email to Zeftronics tech support and got a phone call the next day.  The guy that called me had a VERY heavy foreign accent and I had trouble understanding him.  He suggested I call Don Maxwell if I had questions.  Don told me he gets at least one call per month about this problem and 99% of the time it is the ground wire on the field circuit at the alternator (bad connection at the terminal connectors).  He said to replace this wire and it should resolve the problem.  We removed the wire and it looked ok,  terminal connectors appear to be solid but we made a new one anyway.   We were putting it back on when we noticed the nut would not tighten all the way.  Closer inspection revealed the threads on the terminal stud on F2 had worn away.  I’m guessing that the nut loosened over time due to vibration and the washer and/or terminal connector wore away the threads.  I’m waiting on new terminal studs and will advise if this fixes my problem.  The problem with intermittent issues is that you don’t know if it’s fixed until it never happens again 

[larryb]

Perhaps you could add some washers so the nut grabs on the threads near the top of the stud which still look OK. New studs would be preferred of course but if it takes too long to get them this could work temporarily. And use new a new nut of course.

[Marauder]

Perhaps you could add some washers so the nut grabs on the threads near the top of the stud which still look OK. New studs would be preferred of course but if it takes too long to get them this could work temporarily. And use new a new nut of course.

I wonder if a low profile locking nut might work until his replacement studs show up.

https://www.aircraftspruce.com/catalog/hapages/an363_1.php?clickkey=3015656


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[flyby201]

I didn’t discover this until late Friday afternoon and this being 4th of July weekend I won’t have a chance to source the studs until tomorrow.  I’m going to call some of the companies that overhaul alternators and see if they will sell me a couple.  If i have a problem finding them I had already thought of using washers temporarily or even using a new #6 bolt.  The only thing I see special about the studs is that they have a carriage bolt design with a square section between the head and threads.  But, in the end, I want it fixed correctly.

[Ragsf15e]

On 6/28/2022 at 8:19 AM, Yetti said:

yep.   Same issue.   I ordered a set of brushes and installed.  Brushes took about an hour to install with altenator on the plane.   Easy just time consuming.    When start up it will produce power for like 30 seconds.   Being lazy I decided to order a Zeftronics voltage regulator seeing the first one lasted 40 years.   Should be in this week will let you know.  

The zefttronics is plug and play with a matching cannon plug.

I got a new zeph VR a while back and it didn’t match the existing cannon plug in my ‘68.  The existing one was a larger metal cannon plug and the zeph came with a smaller plastic one.  There’s only like 3 wires in/out, so it wasn’t hard to rectify, but I think the cannon plugs changed over the years.

[EricJ]

It looks like that stud is part of the brush assembly, so if you can't change the stud by itself it probably won't be too difficult to find another brush assembly and replace the whole thing.   Shouldn't need to remove the alternator to do that.

 

[flyby201]

We've already removed the alternator and I've removed the stud just to look at it and see what it so special about it.  Fairly easy to remove and replace.  I just hope obtaining new studs aren't too difficult.

Edited July 4, 2022 by flyby201

[Guest]

44 minutes ago, flyby201 said:

We've already removed the alternator and I've removed the stud just to look at it and see what it so special about it.  Fairly easy to remove and replace.  I just hope obtaining new studs aren't too difficult.

I’ve seen brushes sold separately, as well as entire brush holders, but never just the stud.

Clarence

[Yetti]

Finally got some time to install Zeftronics Voltage Regulator.     Plug and play.   Brushes probably due and the were replaced first.   So we are good to go.