Voltage on M20J

[dc0341]

I have an 83J with a EDM 830 installed.  With the engine running and while in flight, the volts read 12.9 -13.2, this is also the same while on the ground with master turned on.  The ammeter needle jumps around while in flight but settles to center.  The plane has a brand new Concorde battery that was replaced 2 months ago and it's on a Battery Minder when hangered.  Does anyone know if the EDM830 measures the battery voltage or the system while charging? From what I've found, the voltage should be higher with engine running than 13.2.

I was going to check the ground cable on the battery and clean it, then the voltage regulator.  It has been over 14 years since the alternator and voltage regulator has been changed.  But the log book entries doesn't specify the make or model that were used.

If I do need an alternator or voltage regulator, what is recommended?  I was looking at the Zeftronics vr but did not know the specific model number. 

Thanks,   

[Fly Boomer]

19 minutes ago, dc0341 said:

If I do need an alternator or voltage regulator, what is recommended?  I was looking at the Zeftronics vr but did not know the specific model number. 

One thing you can do is check the OCV when the battery has been sitting without the BatteryMINDer for 24 hours.  This is from the manual.  Ignore the highlight -- my system is 28 volts.

 

[PT20J]

The voltage measured is going to depend to some extent on where you measure it. I would verify the EDM voltage by using a DVM and I would measure it at the voltage regulator sense input since that is the voltage that the regulator is controlling. Here’s the service manual section on voltage adjustments.

[201Mooniac]

4 hours ago, dc0341 said:

If I do need an alternator or voltage regulator, what is recommended?  I was looking at the Zeftronics vr but did not know the specific model number.

If yours is the same as my 1980 M20J, the Zeftronics regulator is R15300.  I have one of those with a Plane Power AL12-P70 alternator. Both have lasted over 16 years now.  I understand the Plane Power alternators have gotten very expensive though.

[dc0341]

Anyone have a Zeftronics R15300 voltage regulator for sale?  Adjusted the vr as per the service manual and on a flight yesterday, the volts were initially going to 14.2 V and down to 12.2 V on cruise.  High/low voltage light kept flashing on annunciator panel. 

[PT20J]

51 minutes ago, dc0341 said:

Anyone have a Zeftronics R15300 voltage regulator for sale?  Adjusted the vr as per the service manual and on a flight yesterday, the volts were initially going to 14.2 V and down to 12.2 V on cruise.  High/low voltage light kept flashing on annunciator panel. 

That's just an indication that the alternator is not operating. I'd check all the connections before replacing the VR.

[dc0341]

4 hours ago, PT20J said:

That's just an indication that the alternator is not operating. I'd check all the connections before replacing the VR.

It was running at 14.1-14.3 V when I left home airport, then high/low annunciator flashing light in cruise.  Then landed at another airport about 2 hrs away, volts dropped down to 12.5- 12.1V, and high/low light stayed flashing all way back home.  Ammeter was discharging on way there and charging when I was flying back.  Has a brand new Concord battery that is on a Battery Minder.

[PT20J]

The flashing annunciator, low voltmeter reading and discharge indication on the ammeter are all telling you the same thing: the alternator is not charging. I would find out why before replacing parts. The easiest thing to check is the wiring. Here’s a troubleshooting guide. 

[Ragsf15e]

As @PT20J is telling you, replacing parts will just get expensive without potentially fixing the problem.  You need to have someone knowledgeable with a voltmeter troubleshoot it. You might have something as simple as a corroded or loose connection. You’ve got to check throughout the system as it could be at several different connectors.

[OR75]

On 6/13/2025 at 8:06 AM, dc0341 said:

Anyone have a Zeftronics R15300 voltage regulator for sale?  Adjusted the vr as per the service manual and on a flight yesterday, the volts were initially going to 14.2 V and down to 12.2 V on cruise.  High/low voltage light kept flashing on annunciator panel. 

IF you need to change your VR to a Zeftronics, it may be an R15300 or an R1530B. Difference between the two is the 4 pin plug.  If you are replacing an OECO (larger metal plug), it will be a B. Check which one you currently have and use the crosscheck table in the zeftronics site before ordering 

[dc0341]

Thank you everyone for the help.  It was the the voltage regulator that was going bad.  Alternator was at 14.3V with engine running.  Change out the VR to a Zeftronics R15300 and it is constant at 14V now.