M20F Alternator Help

[Bryan G]

I’ve searched the forum and found good info on alternator fixes…but I can’t find the specific answer to my issue.

Plane Power 12/70 Alternator and VR

Went for a flight this morning, stopped for gas, and right after wheels up I heard an odd tone in my headset and saw a flashing “11.1 Volts” on my JPI-700. I was only a short distance from home, so I shut off all my avionics and turned my com2 back on for for final radio calls at my home field and landed uneventfully.

-I noticed only 13.6v on my JPI as I was taxiing, it is usually 14.0. It didn’t change during my run up, stayed at 13.6.

-The alternator caution light did not come on airborne, but did come on momentarily on the taxi back to my hangar which was odd.

-I started going through the troubleshooting guide to check the VR, but stopped early when I saw the condition of the output connector because it looked like the problem.

-The alternator output “B+” was very corroded, very loose, and the electrical connector rubber cover falling apart. Looks like a very obvious cause to the problem, planned on cleaning it up and reconnecting.

-Attempted to remove the bolt on the terminal, and the top of the terminal/bolt snapped with hardly any force. Alternator only has about 400 hours on it (but is over a decade old…) and looks like new minus the corroded and much shorter B terminal. The second/bottom nut came off without a problem…

So to my question…new alternator? Or is the output terminal something that can be repaired. Fingers crossed it’s a cheap fix, not feeling too good about it right now.

Thanks!

[N201MKTurbo]

I’ve never done a plane power alternator. If it was a prestolite, the parts manuals are available on line and parts are readily available.
 

I would look for the parts manual for the alternator. You may end up at the NAPA store.

Edited June 13, 2022 by N201MKTurbo

[David Lloyd]

Old time automotive alternator and starter shop could likely repair plus put in new brushes. Wear your John Deere hat, mumble something about a manure spreader, and the proper answer concerning the manufacture of the alternator is “huh.”

[Shadrach]

1 hour ago, Bryan G said:

I’ve searched the forum and found good info on alternator fixes…but I can’t find the specific answer to my issue.

Plane Power 12/70 Alternator and VR

Went for a flight this morning, stopped for gas, and right after wheels up I heard an odd tone in my headset and saw a flashing “11.1 Volts” on my JPI-700. I was only a short distance from home, so I shut off all my avionics and turned my com2 back on for for final radio calls at my home field and landed uneventfully.

-I noticed only 13.6v on my JPI as I was taxiing, it is usually 14.0. It didn’t change during my run up, stayed at 13.6.

-The alternator caution light did not come on airborne, but did come on momentarily on the taxi back to my hangar which was odd.

-I started going through the troubleshooting guide to check the VR, but stopped early when I saw the condition of the output connector because it looked like the problem.

-The alternator output “B+” was very corroded, very loose, and the electrical connector rubber cover falling apart. Looks like a very obvious cause to the problem, planned on cleaning it up and reconnecting.

-Attempted to remove the bolt on the terminal, and the top of the terminal/bolt snapped with hardly any force. Alternator only has about 400 hours on it (but is over a decade old…) and looks like new minus the corroded and much shorter B terminal. The second/bottom nut came off without a problem…

So to my question…new alternator? Or is the output terminal something that can be repaired. Fingers crossed it’s a cheap fix, not feeling too good about it right now.

Thanks!

 I”ve seen SCAT tube cause an intermittent short by rubbing an unprotected terminal. A Canadian Mooneyspacer got stuck at my airport on Xmas Eve a few years ago for that very reason. Clean and protect terminals thoroughly before you dig deeper.

[EricJ]

53 minutes ago, David Lloyd said:

Old time automotive alternator and starter shop could likely repair plus put in new brushes. Wear your John Deere hat, mumble something about a manure spreader, and the proper answer concerning the manufacture of the alternator is “huh.”

+1 that it can likely be taken to an automotive electric shop if needed.  Many aircraft alternators turn backwards compared to most similar (or even equivalent) automotive alternators.   Most test benches in the shops can do either, you just gotta let them know so that they don't go down a rabbit hole trying to figure it out.   When I've done this I let them know it was out of an airplane and at least around here they don't care.   

[jetdriven]

2 hours ago, Bryan G said:

I’ve searched the forum and found good info on alternator fixes…but I can’t find the specific answer to my issue.

Plane Power 12/70 Alternator and VR

Went for a flight this morning, stopped for gas, and right after wheels up I heard an odd tone in my headset and saw a flashing “11.1 Volts” on my JPI-700. I was only a short distance from home, so I shut off all my avionics and turned my com2 back on for for final radio calls at my home field and landed uneventfully.

-I noticed only 13.6v on my JPI as I was taxiing, it is usually 14.0. It didn’t change during my run up, stayed at 13.6.

-The alternator caution light did not come on airborne, but did come on momentarily on the taxi back to my hangar which was odd.

-I started going through the troubleshooting guide to check the VR, but stopped early when I saw the condition of the output connector because it looked like the problem.

-The alternator output “B+” was very corroded, very loose, and the electrical connector rubber cover falling apart. Looks like a very obvious cause to the problem, planned on cleaning it up and reconnecting.

-Attempted to remove the bolt on the terminal, and the top of the terminal/bolt snapped with hardly any force. Alternator only has about 400 hours on it (but is over a decade old…) and looks like new minus the corroded and much shorter B terminal. The second/bottom nut came off without a problem…

So to my question…new alternator? Or is the output terminal something that can be repaired. Fingers crossed it’s a cheap fix, not feeling too good about it right now.

Thanks!

It’s part of the diode rectifier bridge.  It’s a 35$ part. It’s replaceable.    

[jetdriven]

This is the rectifier for an AL12P70 plane power alternator.  Easy to swap. https://www.maniacelectricmotors.com/100mm-alternator-rectifier-denso-60-80-amp-8mm-post-inr720xhd.html

[Bryan G]

Epic! Ordered, MS is the best. Thanks everyone, I’ll update once I have her back together again.

[Browncbr1]

I have the same alternator and voltage regulator. I understand this alternator is OEM in a Suzuki samurai. It is normal to have a lower voltage reading on your JPI sometimes if your battery is fully charged. I would see a higher voltage if it is charging the battery up from being drawn down. As the flight progresses, it is normal to see 13.6 to 13.8. Keep in mind you can calibrate the voltage on the JPI. There is some voltage drop from the battery to the screen of the JPI.   If I saw 13.6 on my JPI, I would understand that my battery is fully charged.   If I have used the radios on the ground and ran the lights before starting the engine and then had to use the starter a lot, I would expect to see 13.9 or 14.0 for 20 minutes or so and then it will gradually come back down as the battery charges.  
 

always check the tension of your drive belt that it is not over or under tight.  A few years ago I was getting erratic voltage readings, and I went and ordered a new rectifier from an automotive source, which was an easy swap. It did not solve the problem. It turned out to be a loose connection from the alternator to the bus bar.   If you’re reading is stable on 13.6, I wouldn’t see any problem.   However, it seems in new rectifier is in order for you since the terminal broke.   When bolting back on, do not over torque the copper threads.  A little blue thread lock wont hurt

Edited June 13, 2022 by Browncbr1

[Ragsf15e]

56 minutes ago, Browncbr1 said:

I have the same alternator and voltage regulator. I understand this alternator is OEM in a Suzuki samurai. It is normal to have a lower voltage reading on your JPI sometimes if your battery is fully charged. I would see a higher voltage if it is charging the battery up from being drawn down. As the flight progresses, it is normal to see 13.6 to 13.8. Keep in mind you can calibrate the voltage on the JPI. There is some voltage drop from the battery to the screen of the JPI.   If I saw 13.6 on my JPI, I would understand that my battery is fully charged.   If I have used the radios on the ground and ran the lights before starting the engine and then had to use the starter a lot, I would expect to see 13.9 or 14.0 for 20 minutes or so and then it will gradually come back down as the battery charges.  
 

always check the tension of your drive belt that it is not over or under tight.  A few years ago I was getting erratic voltage readings, and I went and ordered a new rectifier from an automotive source, which was an easy swap. It did not solve the problem. It turned out to be a loose connection from the alternator to the bus bar.   If you’re reading is stable on 13.6, I wouldn’t see any problem.   However, it seems in new rectifier is in order for you since the terminal broke.   When bolting back on, do not over torque or copper threads.

I don’t have the same take on voltage.  However, I’m no EE either…

your alternator should sit at 14+\-.1 regardless of if your battery is fully charged.  Your vr should keep the electrical system at that same 14+/-.1.  Mine definitely does on my edm930.  While the battery is charging, the amps indication on the 930 indicates higher amperage to the battery - which is all the amp meter measures for most of us, current to/from the battery.  However, the voltage doesn’t change when the battery is “topped off”.  The VR keeps it at 14.

If you’re showing 13.6 or so in flight, you’ve got some resistance somewhere in your system.  Probably a corroded connection and easy to fix once found.  I had similar and traced voltage back from the alternator until I found it (couple years ago).  Sanded the connectors, 14v steady ever since.  

I bet if you start the engine and let it idle but then check the output from the alternator with a dvm and alligator clip wires, you’ll see the alternator is putting out 14v.  Your system is losing it somewhere along the way.

zephtronics has a low voltage troubleshooting guide for less than 13.9V.

[Shadrach]

I have a 50A gen and it is a rock solid at 14.1V above 2000rpm. If I saw a fluctuation, I would be concerned.

[Ragsf15e]

A good place to start looking for added resistance is at your ground attached from the battery to the airplane.  So first (everything off), check bat voltage at the battery with a dvm.  Then battery (pos) to the airframe (neg).  They should be almost exactly the same.  Then with master power on, check battery and then power bus which is behind the circuit breakers.  The zeph guide takes you through a few more steps.

I didn’t find my issue until I started the airplane and followed the 14v out of the alternator until it dropped to 13.5 through one bus connection at a circuit breaker.

 I would say these are difficult to locate but cheap to fix.

[Bryan G]

I wish I had a better picture, but a fire proof (fuel line?) sleeve was rubbing against the B+ and I can only assume was the problem…hopefully there aren’t any other issues with the alternator. You can’t see where it rubbed through, but you can see the orange sleeve and where the alternator output terminal was.

I’ve got it all taken apart, mechanic will help look over a few things when the new parts arrive. Fortunately it was very simple to do and didn’t require dropping the lower cowling.

My belt started slipping a few months back when I turned my taxi light on and caused a voltage drop, so I swapped to an LED light and had the belt tightened at my annual. After that, I’ve made sure to keep the volts in my scan post start and occasionally cycling through during flight on the 700, but it’s always been 14v.

Edited June 14, 2022 by Bryan G

[Bryan G]

4 hours ago, Ragsf15e said:

A good place to start looking for added resistance is at your ground attached from the battery to the airplane.  So first (everything off), check bat voltage at the battery with a dvm.  Then battery (pos) to the airframe (neg).  They should be almost exactly the same.  Then with master power on, check battery and then power bus which is behind the circuit breakers.  The zeph guide takes you through a few more steps.

I didn’t find my issue until I started the airplane and followed the 14v out of the alternator until it dropped to 13.5 through one bus connection at a circuit breaker.

 I would say these are difficult to locate but cheap to fix.

I’ve read through your previous electrical issue, definitely helped cage my brain and get moving in the right direction. Once I get it back together, I will go through and check everything as you recommend to verify. 

[Ragsf15e]

18 minutes ago, Bryan G said:

I’ve read through your previous electrical issue, definitely helped cage my brain and get moving in the right direction. Once I get it back together, I will go through and check everything as you recommend to verify. 

Hopefully yours is fixed with the new part.  If not, take your time.  
Good luck!

[Shadrach]

On 6/13/2022 at 10:15 PM, Bryan G said:

I’ve read through your previous electrical issue, definitely helped cage my brain and get moving in the right direction. Once I get it back together, I will go through and check everything as you recommend to verify. 

Just noticed your bird is 50 N Numbers and 50 serial numbers younger than mine. Your airworthiness certificate is dated just 31 day after mine. It’s incredible how many airplanes they were building in ‘67.

[Bryan G]

15 minutes ago, Shadrach said:

Just noticed your bird is 50 N Numbers (N6339Q) and 50 serial numbers younger than mine. Your airworthiness certificate is dated just 31 day after mine. It’s incredible how many airplanes they were building in ‘67.

So cool. What color? I feel like every Quebec is the same color as mine, there might be a correlation I’m unaware of. 

[Shadrach]

On 6/13/2022 at 11:41 PM, Bryan G said:

So cool. What color? I feel like every Quebec is the same color as mine, there might be a correlation I’m unaware of. 

Still original.

 

[Browncbr1]

19 hours ago, Ragsf15e said:

I don’t have the same take on voltage.  However, I’m no EE either…

your alternator should sit at 14+\-.1 regardless of if your battery is fully charged.  Your vr should keep the electrical system at that same 14+/-.1.  Mine definitely does on my edm930.  While the battery is charging, the amps indication on the 930 indicates higher amperage to the battery - which is all the amp meter measures for most of us, current to/from the battery.  However, the voltage doesn’t change when the battery is “topped off”.  The VR keeps it at 14.

If you’re showing 13.6 or so in flight, you’ve got some resistance somewhere in your system.  Probably a corroded connection and easy to fix once found.  I had similar and traced voltage back from the alternator until I found it (couple years ago).  Sanded the connectors, 14v steady ever since.  

I bet if you start the engine and let it idle but then check the output from the alternator with a dvm and alligator clip wires, you’ll see the alternator is putting out 14v.  Your system is losing it somewhere along the way.

zephtronics has a low voltage troubleshooting guide for less than 13.9V.

Iirc, the installation manual for the plane power stc says to adjust the voltage regulator with the meter clips directly on the VR.   It says set it to 13.8.   When we did that about 7 years ago, the jpi showed 13.6 ..   that is when I knew for sure there is some drop or calibration thing going on between the jpi volt signal wire and what reads on the screen.   When the engine is not running, the jpi reads lower than actual voltage at the battery.   
 

in any case, I’m not EE and I think you’re probably right too.   But, I was just sharing what has always been normal for my installation for years.   I recently put in new brushes, and the 2nd market rectifier is still in there.   

Edited June 14, 2022 by Browncbr1

[Ragsf15e]

4 hours ago, Browncbr1 said:

Iirc, the installation manual for the plane power stc says to adjust the voltage regulator with the meter clips directly on the VR.   It says set it to 13.8.   When we did that about 7 years ago, the jpi showed 13.6 ..   that is when I knew for sure there is some drop or calibration thing going on between the jpi volt signal wire and what reads on the screen.   When the engine is not running, the jpi reads lower than actual voltage at the battery.   
 

in any case, I’m not EE and I think you’re probably right too.   But, I was just sharing what has always been normal for my installation for years.   I recently put in new brushes, and the 2nd market rectifier is still in there.   

From what you’re saying, I think your alternator and VR are probably fine.  However, you have a corroded connection or some other resistance between the alternator and where the jpi picks up the voltage.  On a properly functioning system, there’s no voltage drop between the alternator, power bus, avionics bus, aux bus and all the way back to the battery.  However, after 55+ years it’s easy to get a little corrosion and that’s enough to increase resistance.  
It probably won’t hurt anything but keep an eye on it to catch it if it falls further.

[carusoam]

If you hear an rpm dependent whine in the audio system…

This is a sign of the diode bridge missing a diode….

See Byron’s post above about swapping in a new rectifier/diode bridge…

Tell us more about the odd tone you heard in your headset?

Best regards,

-a-

[Bryan G]

@jetdriven $35 Rectifier fixed the problem, back to 14.0 volts again. Thanks everyone for the input and helping me save my money for more fun Mooney things!