Voltage Regulator , Alternator, or….

[201Steve]

Hello friends. Looking for some feedback on an electrical problem with a 77J. I went to takeoff today, all ops checked good on the ground, went to takeoff and got a voltage warning, reading 11.8 or so and a battery discharge showing on the ammeter. I came back around the pattern to check it out. Back on the ground I started fiddling with it, I pulled the alt field circuit, pushed it back in and the problem went away. 
 

Then, I went to takeoff again and during taxi the voltage started to actually spike, up to 15.3V as seen on my engine monitor.  
 

so it seems, I’m going from alternator totally offline, to getting over voltage readings. 
 

I think, probably the voltage regulator. Maybe the alternator, maybe a wire. 
 

I eventually got it stabilized again, took off, flew home and it only faulted once over two hours. A reset of the field CB in flight settled it back down. 
 

Any experience out there with similar?

[PT20J]

The over voltage protection circuit within the voltage regulator will shut off the alternator when an over voltage condition occurs. Cycling the field circuit breaker probably resets it although the POH procedure is to cycle the master switch. You should get a steady HI LO VOLTS annunciation if the OVP trips.

Check all the wiring to the voltage regulator, master switch and alternator for security first. If all the connections are good and it keeps happening, then replace the voltage regulator. 

[EricJ]

+1 that the first step is to cycle the master to reset the regulator.   If it keeps doing it after that, then there are a few things to check.

[N201MKTurbo]

It’s probably the regulator. My regulator went out a while back with similar symptoms. I replaced it. I haven’t trouble shot it yet, but I suspect it is the output transistor. It looks like it might be in a socket. I have found that socketed TO3s get corroded after a few decades. If you just remove it and replace it it usually fixes it. 
 

The problem with the VR is it is a PITA to R&R, so I just replaced it. I still have it, maybe someday when I’m bored, I’ll see if I can fix it.

[RoundTwo]

I had the exact same situation on my J earlier this year. After a lot of digging and testing components, my problem was traced to the regulator getting an improper voltage reading on the sense wire. Since the regulator was sensing low voltage, it was over driving the alternator which led to tripping the over voltage protection circuit. These problems are difficult to troubleshoot using standard mechanical/electrical knowledge. I eventually got my problem figured out by getting into the wiring diagram and tracing each wire, looking for the problem.

Good luck!

Chuck

[201Steve]

4 hours ago, RoundTwo said:

I had the exact same situation on my J earlier this year. After a lot of digging and testing components, my problem was traced to the regulator getting an improper voltage reading on the sense wire. Since the regulator was sensing low voltage, it was over driving the alternator which led to tripping the over voltage protection circuit. These problems are difficult to troubleshoot using standard mechanical/electrical knowledge. I eventually got my problem figured out by getting into the wiring diagram and tracing each wire, looking for the problem.

Good luck!

Chuck

This sounds terrible. Replacing the VR sounds a lot nicer. 

[201Steve]

4 hours ago, RoundTwo said:

my problem was traced to the regulator getting an improper voltage reading on the sense wire.

So, is that a long way of saying you had to replace the VR or was it a faulty wire or something?

[201Steve]

@EricJ do you know where the VR is on the 77? I’m pretty sure it’s on top of a small equipment shelf mounted to the side wall of the co pilot side, behind the panel. It almost looks like you have to pull it out from the top at the glare shield. 

[EricJ]

29 minutes ago, 201Steve said:

@EricJ do you know where the VR is on the 77? I’m pretty sure it’s on top of a small equipment shelf mounted to the side wall of the co pilot side, behind the panel. It almost looks like you have to pull it out from the top at the glare shield. 

It's in that region.    It may be attached to the firewall there, too.

[PT20J]

My 1978 J had a big OECO attached to the firewall up high under the windshield.

 

[RoundTwo]

12 hours ago, 201Steve said:

This sounds terrible. Replacing the VR sounds a lot nicer. 

That was the general consensus as well, but I sent my regulator out for testing and it came back fine. 

12 hours ago, 201Steve said:

So, is that a long way of saying you had to replace the VR or was it a faulty wire or something?

I took the long way intentionally to illustrate that these electrical gremlins are tough to figure out and solving the problem is usually a lot more involved than just replacing a part. I’m sure my problem is unique to my plane, but someone had moved the sense wire and butt spliced it into the annunciator panel power wire. Moving it back to the correct breaker on the panel cleared up the problem.

[201Steve]

2 hours ago, RoundTwo said:

someone had moved the sense wire and butt spliced it into the annunciator panel power wire. Moving it back to the correct breaker on the panel cleared up the problem.

What’s interesting about that is, presumably this wiring faux paus had been performed a long time before it presented a problem under your ownership. It worked incorrectly installed for many years and then one day it just didn’t. 

[RoundTwo]

17 minutes ago, 201Steve said:

What’s interesting about that is, presumably this wiring faux paus had been performed a long time before it presented a problem under your ownership. It worked incorrectly installed for many years and then one day it just didn’t. 

Exactly! I’m sure you’ll get yours figured out as well. Hopefully it will be easily identified as a crapped out part that can be quickly replaced.

[Ragsf15e]

3 hours ago, RoundTwo said:

That was the general consensus as well, but I sent my regulator out for testing and it came back fine. 

I took the long way intentionally to illustrate that these electrical gremlins are tough to figure out and solving the problem is usually a lot more involved than just replacing a part. I’m sure my problem is unique to my plane, but someone had moved the sense wire and butt spliced it into the annunciator panel power wire. Moving it back to the correct breaker on the panel cleared up the problem.

Occasionally people get lucky and it’s a bad battery, alternator or vr.  More typically, these electrical gremlins take some reasonable troubleshooting with a digital voltmeter.  Replacing parts before really nailing down the problem can get costly and frustrating. Ask me how I learned that one!

[Guest]

Similar problem just recently. I changed both the battery and the regulator and it went away…

[201Steve]

I wanted to run this by the group for feedback. My airplane is a 77 J the first year of its' production. It's in many respects, an F with aerodynamic changes. A lot of the internal changes to the J came in 1978. We've got the Voltage Regulator out of the airplane. It's a OECO 20082 with a fat cannon plug. When going to the Zeftronics cross reference list, it shows the R15300 for the J model. But, in a part number cross reference, OECO 20082 it crosses with a Zeftronics R1530b (listed under models for a M20F not an M20J).

My assumption is that the model chart doesn't know the difference between a 77j and later years. It is also my assumption that the part number to part number cross reference is more important than the model list. It is a fact that the R15300 does not have the correct cannon plug. It is also a fact that the R1530b DOES have the correct cannon plug for my airplane.

So, is there anything I'm missing that should concern me installing the "F model" version instead of the "J Model" version? Again, the direct part numbers cross correctly, but the model list doesn't look right (wrong cannon plug) for my very early J.

 

 

I've affixed a picture of its' location for anyone in the future trying to identify the location of a voltage regulator in a 1977 M20J (it's under the glare shield, Right side, firewall).

[201Steve]

Pinging @EricJ and @PT20J

[N201MKTurbo]

You should be installing the F model regulator. Mine uses the same regulator.

Its more expensive because the cannon plug cost more than the plastic connector.

[Yetti]

Get the plug that matches.   I think I had the same question on a 75 F model.  The matching plug will be plug and play.    My Regulator is outside the cabin on the firewall.  While you are in there you might want to check for two black inline fuses.  Check the fuses.  

[201Steve]

TBH - the only reason I questioned it is bc @EricJ also has a 77 but in an old thread, he said he had r15300 installed in his airplane. Maybe they switched over to the newer style sometime in late 1977.

[N201MKTurbo]

1 minute ago, Yetti said:

Get the plug that matches.   I think I had the same question on a 75 F model.  The matching plug will be plug and play.    My Regulator is outside the cabin on the firewall.  While you are in there you might want to check for two black inline fuses.  Check the fuses.  

The two black inline fuses are for the ammeter shunt.

[Yetti]

2 minutes ago, N201MKTurbo said:

The two black inline fuses are for the ammeter shunt.

yep, but he may have popped one in the overvoltage state.  Probably not, but you are in there.

[EricJ]

They do the same thing and are probably electrically identical, so use the one that plugs in and is easiest to install.    Our airplanes are all old enough that what's in there may not have been what it left the factory with, so if the R1530b fits and crosses with the one that came out, I'd run with it.   Have the conversation with your IA, but I doubt it'll be an issue.   Mine does have an R15300 but I don't know whether it left the factory with it or it was swapped in at some point.

[PT20J]

I agree with @EricJ and @N201MKTurbo - they are most likely the same regulator and the difference in part number and price is due to the connector. But, a phone call to Zeftronics would clarify.

[Ragsf15e]

I have the one with the metal connector, but was still having some issues, and (before I troubleshot it myself), an avionics shop thought the connection might have corroded pins.  long story short, they removed both sides of the connector and spliced the wires directly.  It works fine but will be harder to replace someday.