M20j voltage reg.

[Guest]

Just taxied out to take my family up in our new (to us anyway) M20j. Got the voltage light, taxied back, mechanic is not available for about a month. He gave me some tips to troubleshoot myself.  Voltage light came on, according to poh that indicates overvoltage. Ammeter was discharging so alt was off line. I reset the field breaker and the light went out for two minutes then came back on. I question the poh because the voltage light is on when I switch on the master, which would be under volt. Should I just buy a regulator now?

[N201MKTurbo]

There were a couple of different arrangements. Some got the light signal from the regulator and some got it from an external circuit. I believe it always shows that the alternator is not charging. If the overvoltage circuit senses an over voltage condition, it turns off the regulator and you have no charge, so having a light that only shows an over voltage fault wouldn’t show any other failures like a broken field wire.

The maintenance manual doesn’t do a good job of describing these systems. You can get the most information from the schematics, but you still have to infer a bit.

[Utah20Gflyer]

Generally speaking you don’t want to buy parts until you have verified a part is bad.  Otherwise you will end up spending money unnecessarily on things that won’t fix the problem.    
 

I am not an expert on Voltage regulators but I do understand their basic function.   Seems like step 1 would be to verify what the voltage coming into the regulator is and what it is putting out.   

[ArtVandelay]

1st make sure your alternator belt is properly tensioned so it’s not slipping.

I believe Zeftronics has a short diagnostics handout you can follow.

[Marc_B]

I keep thinking I've seen a step by step electrical troubleshooting process somewhere around here, but can't seem to find what I was thinking about.  check battery voltage, check bus voltage, check connections...etc. 

Specifically regarding VRs, there are some manufactured by International Avionics, Inc (IAI) that need to be sent to them for service/overhaul and calibration.  If not IAI, they can be serviced by Don Maxwell or Consolidated Aircraft Supply.  If you do have an overvoltage it may be your VR is going out.  Many of these are not field adjustable, so would need to be sent in to be calibrated and serviced.  Depending on your set up there may be an aftermarket upgrade available (i.e. Zeftronics), but for me with a dual alternator 28V system there wasn't any other option other than lots of money or just send it to IAI for service.

[Marc_B]

@ArtVandelay I don't think that was the one I had seen before but it looks pretty thorough...is this the one you were referring to?

https://zeftronics.com/wp-content/uploads/2014/06/Z14PS.pdf

[ArtVandelay]

[mention=11849]ArtVandelay[/mention] I don't think that was the one I had seen before but it looks pretty thorough...is this the one you were referring to?
https://zeftronics.com/wp-content/uploads/2014/06/Z14PS.pdf

Yes.

[Guest]

Thanks y’all. Will get out to the hangar with a multimeter and see what I’ve got. It is a 76 model. I assume they are vibrator type regulators. This airplane sat for 5 years, so I think the points could be sticky if that is the type. 

[PT20J]

There are two types of over voltage protectors (OVP). Some just remove the field current to shut down the alternator and some “crowbar” (short) the field circuit to trip the field breaker to shut down the alternator. A flashing annunciator indicates low voltage and a steady annunciator means the OVP tripped. 

If the OVP trips the field breaker, I believe the correct procedure is to cycle the master switch to reset the OVP as well as resetting the field breaker. Resetting the field breaker alone probably isn’t sufficient. Check the emergency procedures section of your POH.

Lot’s of things can cause no output from the charging system (most common failure mode), but about the only things that can cause over voltage are a regulator failure or the field wire being shorted to the battery bus.

From the PlanePower website:

[PT20J]

If the annunciator light is now on steadily when you turn the master on and the engine is not running, it sounds like the OVP has failed and will not reset. 

[Guest]

Yes the light is on, but if I recall, it was always on before start. Just now, it stays on and ammeter shows discharge. It never popped the field breaker. I popped it manually to see what would happen and the light stayed off for about two minutes then came back on. 
 

Is the OVP separate from the regulator or integral to the unit. From my A&P class the vibrator type unit incorporates overvoltage protection through the points and electromagnet…

[EricJ]

39 minutes ago, Kerrville said:

Yes the light is on, but if I recall, it was always on before start. Just now, it stays on and ammeter shows discharge. It never popped the field breaker. I popped it manually to see what would happen and the light stayed off for about two minutes then came back on. 
 

Is the OVP separate from the regulator or integral to the unit. From my A&P class the vibrator type unit incorporates overvoltage protection through the points and electromagnet…

The light is an undervoltage light that detects that the alternator is not putting out >13V-13.5V or so, so it is on when the engine isn't running.   Even a new battery won't be above that, so the light is always on under battery power if the alternator is not producting >13-13.5V (or so, I don't recall the exact trigger).

It sounds like the regulator may be having issues.  In a J model it is not a vibrator, it is a linear regulator.   It is under the panel on the passenger side and is difficult to see, but if you have a Zeftronic it has an LED on it that provides generally reliable diagnostic information, e.g., it'll tell you if there's a field short, etc.   Getting an endoscope or something in there where you can see the LED is sometimes tricky.

Probably the most common failure is the field wire getting loose or breaking off at the alternator, but if it works a bit after resetting the breaker that suggests something else.

[Guest]

I think you are right because that is how it behaves in my short experience with it. However, the poh makes the statement that it will flash for under volt and be a constant light for over volt. 

[EricJ]

1 minute ago, Kerrville said:

I think you are right because that is how it behaves in my short experience with it. However, the poh makes the statement that it will flash for under volt and be a constant light for over volt. 

There are some model year dependencies, and as mentioned previously sometimes it takes tracing out the wiring diagram to see what it really does.   It may also depend on what regulator you have actually installed.   It is primarily a low voltage detector, at least in the early models.    My POH doesn't say anything about overvoltage indication, and I've never seen it flash, even when I've had an alternator failure, even though the POH says it should.

[PT20J]

What year and serial number do you have? The 1977 M20Js are a little different because, except for the aerodynamic mods, they are essentially M20Fs. Mooney made a lot of changes to the M20J in 1978. 

I have owned a 1978 J and a 1994 J. Both describe flashing for low voltage and steady for high voltage in the POH. The flasher circuitry is within the annunciator panel and the voltage regulator has an overvoltage output that sends a signal to activate the flashing circuit. I don't know if the 1977 is different.

I suppose it is also possible that the flashing circuit has failed causing a steady annunciation during low voltage. 

Skip

[N201MKTurbo]

I replaced my voltage regulator with a Zeftronics. It worked fine until I left my master on and killed the battery. I was at a field with no services so I couldn’t charge the battery. I found someone to jump the plane. The ammeter was pegged as you would expect. I let it charge on the ground for a while and then took off. It soon blew the field breaker. I reset it and it was charging again. After a few minutes it blew the breaker again. I reset it again and it wouldn’t charge. I returned to the airport and found another way home. Actually, a guy with a Bonanza was getting ready to fly somewhere and I asked if was going to the Phoenix area by any chance. He said no, but I was just looking to get some flying time in. Why, do you need to go somewhere? I explained the situation and he said “oh, I’ll take you there.” So he flew me to my hangar, two hours away and wouldn’t accept a penny for fuel!
 

The point of all this is the Zeftronics doesn’t have any field current limiting. The only protection is the field breaker. The Plane Power regulator has field current limiting. It will limit the field current to 5 amps, so it won’t blow the breaker, or burn out its own field drivers like the Zeftronics did.

The M20J is not on the approved model list for the Plane power regulator. But the alternator is, so I used that as the approved data. The reason it isn’t specifically approved for the M20J is the annunciator circuit of the Plane power is the wrong polarity for the Mooney (PNP vs NPN) or visa versa, I don’t remember. It took about 5 minutes to fix that so the light works. It has been in for a couple of years and has behaved flawlessly.

[EricJ]

48 minutes ago, N201MKTurbo said:

I replaced my voltage regulator with a Zeftronics. It worked fine until I left my master on and killed the battery. I was at a field with no services so I couldn’t charge the battery. I found someone to jump the plane. The ammeter was pegged as you would expect. I let it charge on the ground for a while and then took off. It soon blew the field breaker. I reset it and it was charging again. After a few minutes it blew the breaker again. I reset it again and it wouldn’t charge. I returned to the airport and found another way home. Actually, a guy with a Bonanza was getting ready to fly somewhere and I asked if was going to the Phoenix area by any chance. He said no, but I was just looking to get some flying time in. Why, do you need to go somewhere? I explained the situation and he said “oh, I’ll take you there.” So he flew me to my hangar, two hours away and wouldn’t accept a penny for fuel!
 

The point of all this is the Zeftronics doesn’t have any field current limiting. The only protection is the field breaker. The Plane Power regulator has field current limiting. It will limit the field current to 5 amps, so it won’t blow the breaker, or burn out its own field drivers like the Zeftronics did.

The M20J is not on the approved model list for the Plane power regulator. But the alternator is, so I used that as the approved data. The reason it isn’t specifically approved for the M20J is the annunciator circuit of the Plane power is the wrong polarity for the Mooney (PNP vs NPN) or visa versa, I don’t remember. It took about 5 minutes to fix that so the light works. It has been in for a couple of years and has behaved flawlessly.

Hm...something sounds amiss there.   Which Zeftronics regulator did you have?   Mine limits field current to 5A.

[Bartman]

Check the field wire where it connects to the alternator. It is notorious for problems there due to vibration and the wire breaks where it crimps to the connector. 

[Guest]

Wilco to checking the field wire. It is a 76 serial 24-0040. 

[N201MKTurbo]

1 hour ago, EricJ said:

Hm...something sounds amiss there.   Which Zeftronics regulator did you have?   Mine limits field current to 5A.

It was an R1530B. I read the manual after it fried and there was no mention of field protection, but now they all say field ground fault protection, 

It seems like the highest field current would be turning the regulator on with the engine off, unless there is some mechanism that lowers the impedance of the field with it running. Seems weird. 

[EricJ]

1 minute ago, N201MKTurbo said:

It was an R1530B. I read the manual after it fried and there was no mention of field protection, but now they all say field ground fault protection, 

It seems like the highest field current would be turning the regulator on with the engine off, unless there is some mechanism that lowers the impedance of the field with it running. Seems weird. 

Yeah, mine's an R15300, so I don't know what all the differences are, but it seems to have all the expected limits and protections.    It figured out my field short when I crimped a wire hair from the shield into the terminal on the field wire.   It indicated it correctly on the LED even when I couldn't see it.

[N201MKTurbo]

1 hour ago, EricJ said:

Yeah, mine's an R15300, so I don't know what all the differences are, but it seems to have all the expected limits and protections.    It figured out my field short when I crimped a wire hair from the shield into the terminal on the field wire.   It indicated it correctly on the LED even when I couldn't see it.

There might be a difference between a short and an over current. It would be easier if they just gave us the service manual.

[Yetti]

Check the belt, Build and install a new wiring harness, replace the brushes in the alternator, can be done while on the engine.   Buy a zephtronics regulator and enjoy 10 more years of flying pleasure. .