Intermittent Alternator

Still didn't see anything starting with a "6" on that chart. When I 1st moved south I would be in shorts and T-shirts when it was 40s. 40+ years later I got a jacket on when it gets below 70 and looking to put the flannel sheets on my water bed when it gets below 60.... just saying.
I start sweating in the 60s. I prefer shivering over sweating.

I will try to do another ground run tomorrow at lunch. I don't think I have a lot of meetings on the schedule at work.

Meanwhile, my mechanic thought of another diagnostic to try. Something about a diode.
 
Since this ground attempt with a full electric load didn't get the same result as your 2nd graph above, maybe try it again with your normal elec load for flying along with a similar throttle movement as though you're taking off? Be interesting to see if the alternator drops off like graph B with throttle increase and recovers when throttle pulled back. It should the way I see it.

New data today:

JPI alternator 3.JPG

2100 rpm seems to be where it starts to struggle. In that first run above, it was fine going through 2000 and then I saw the amp meter start to wobble at 2100. Brought it back to 2000 and it was fine again. Took it back to 2100 and above and the needle went to zero. However, the ALT light did not come on and the JPI didn't flash VOLTS at me. Looks like it was dipping to 12.5 volts but not worse. Then did another run and went up to 2300 rpm. Same thing. Starts wobbling at 2100 and then dies. This time at 2300 the JPI captured 12.1 volts. Again, the ALT light did not come on and the VOLTS didn't flash at me. Third run was just me playing around to see when the wobble would happen, plus I took a video of the voltage regulator (which has a light on it for status). The light stayed green the whole time. I took a video of the middle run (or maybe it was the last run??) that I can post for you @Bell206 if you'd like to see the behavior.

I have a non-aviation friend who thinks this is the behavior of a bearing going bad in the alternator. I know these remans have a history of being over greased and causing issues. Unless someone has a different epiphany, I think we're going to yank the alternator off and open it up and see what we see.
 
FWIW, I recently had my alternator IRANed for about $250 by Aero Accessories. New bearings and brushes, cleaned, bench-tested. 8130 issued. www.aeroacc-vny.com
 
Not a mechanic, but I have seen a similar issue. Our plane has the Voltage Regulator and a an overvoltage regulator/Breaker (whatever the term for it is), Had a similar issue where the Overvoltage protection was failing and shutting the charging off when it shouldn't. Our looked like a smaller voltage regulator, or similar to some automatic resetting breakers I have seen.

Might have looked something like this. But has been more than 10 years since we replaced it. I was thinking it had a 3rd terminal on it.
1707175214549.png
Have no idea is your plane as something similar.

Brian
 
the ALT light did not come on and the JPI didn't flash VOLTS at me.
And these lights were on during the flying failures?

Given you can duplicate it on the ground I'd verify your voltages to and from the alternator before pulling it. My concern is to make sure there is not an underlying wire/signal issue.

While its RPM sensitive its also load and time sensitive as it didn't drop off during last full load run and the drop off didn't happen immediately as shown in graph B above.

Check the static voltages listed in post #22 with a VOM plus you still need to verify with a VOM what your JPI is telling you since the lights didn't come one... but that could just be a trigger setting.

If it were me I'd run it and check things till you can put the fault solely on the alternator since there still is variations to the failure mode. Perhaps PM Dan T and see if he has something more to add?
 
Check the static voltages listed in post #22 with a VOM plus you still need to verify with a VOM what your JPI is telling you since the lights didn't come one... but that could just be a trigger setting.
I'm not really sure how to do that. This is the VR (conceniently located under the panel behind the rudder pedals). Where would I put the leads?

20240205_160019.jpg
 
Not a mechanic, but I have seen a similar issue. Our plane has the Voltage Regulator and a an overvoltage regulator/Breaker (whatever the term for it is), Had a similar issue where the Overvoltage protection was failing and shutting the charging off when it shouldn't. Our looked like a smaller voltage regulator, or similar to some automatic resetting breakers I have seen.

Might have looked something like this. But has been more than 10 years since we replaced it. I was thinking it had a 3rd terminal on it.
View attachment 125101
Have no idea is your plane as something similar.

Brian
That was the first thing we replaced. Didn't help.
 
Where would I put the leads?
Let's start with the static voltages I listed in Post 22. This will give us a baseline. I need to think about how best for you to check things with aircraft running.

Unless you have a terminal strip somewhere you'll need some small/thin "probes" to check at the splices. A "T" pin works.

With BATT and ALT switches on...

Measure/record battery voltage at the battery.
Then, measure V at the red wire splice.
Then, measure V at the blue wire splice.
Then, measure V at the F1 post on the ALT an not the ring terminal.
Turn power off.
Then, with VOM on ohms, measure resistance from black wire screw at regulator to F2 on ALT.

1707179515156.png
 
With the output falling off at 2100, I would suspect that the slip rings were cleaned up in a lathe, but the rotor wasn't tracking on center too well. That makes the slip rings eccentric, and the brushes can start bouncing. at some resonant RPM. That weakens the field current and the output falls off. I've seen it exactly once.

I have a special high-tech alternator testing device. It is a piece of half-inch plywood about ten inches long, with four screws in it. Each screw has a long wire soldered to it. One goes to ground, usually under a regulator mounting bolt at the firewall. Another gets attached to the battery or bus. A third goes to the field terminal on the alternator, and the last goes to the field terminal on the regulator. Sometimes you have to get creative in accessing test points, but the time spent can save a lot of money.

You sit in the airplane with this thing in your lap. You connect your voltmeter between the ground screw and the others while running the engine and seeing what the voltages do. The bus or battery should show a higher voltage when the engine is running that when it's not. As the RPM goes up and down, it should remain rock-steady. Adding or subtracting loads shouldn't change it much. at all. As the RPM goes up, the field voltage should decrease, and reducing RPM should raise it. Adding loads should raise the field voltage, turning stuff off should reduce it. All that proves that the regulator is working as it should. The field voltages at the alternator and regulator should always match. If they don't, you have a wire going bad, or a failing crimp terminal, or there might be a noise filter in the field wire circuit that's acting up.

If the battery/bus voltage jumps around or falls at 2100, it's likely eccentric slip rings, or something loose in or related to the alternator. Bad bearing, maybe, too. Overtightening the belt can wreck that tiny rear bearing. And check that big ground cable from the alternator to what appears to be a lug on the starter. It might be loose, or have loose crimp terminals, or have corrosion inside the terminals between the terminal and the cable wires, or the starter might be loose, or even the alternator might be loose. That ground cable would be much better attached to the firewall rather than the starter. There has to be another cable or strap grounding the engine to the firewall, or maybe to the engine mount, and it might have the same sort of problems as I've noted. Loose, dirty, oily, corroded, engine torque or thrust yanking on it. Or maybe it's missing altogether, and the starter and charging currents are grounding though your engine control cables. Ugh. That wrecks them real quick.

Hard to diagnose this sort of thing at a distance. Experienced eyeballs right there, having a good look, might turn up the problem real quick. But experienced eyeballs seem to be getting scarce. Too many retirements, too few replacements.
 
I'm not really sure how to do that. This is the VR (conceniently located under the panel behind the rudder pedals). Where would I put the leads?
This is your regulator (ACU, actually):

1707186373672.png

Red should have bus voltage on it. White should be connected to the overvolt light, but yours is capped off. Blue is the field wire to the alternator, meaning that it was spliced to the original white wire that goes to the alternator. Check that splice for security. It's the red butt connector in your picture, and it wasn't done with the proper ratchet crimper. Black goes to the second, grounded field terminal on the alternator. I don't see it at the alternator, so they might have grounded it to the panel. If everything else is OK, it should work. IF.

There is a diode shown in the alternator's output to the bus. That maybe be the problem, as well as a suspect breaker there. Diodes get hot and can open up.
 
Since this is an ACU we're talking about here, it might be useful to cover a weakness with these modern devices.

The old electromechanical regulator took a significant fraction of an amp to actuate its voltage regulator relay. When the voltage got too high, the relay was pulled open by its coil, which was fed from the bus or alternator output, and the alternator's field collapsed, basically turning the alternator off. As soon as the voltage fell below the setting, the relay closed and reenergized the field and up went the output again. This sounds pretty crude, and it was, but the induction of the field coil made the square wave thus formed in the field coil into a much-smoothed sine wave, and a filter capacitor on the alternator (sometimes inside it) or on the field wire at the firewall, levelled it even more. That little regulator relay basically buzzed all the time, staying closed microseconds longer when demand was high, and open microseconds longer when demand was low.

The ACU uses pulse-width modulation of the field current. This is also crude, but accepted as effective because it doesn't generate the heat that a transistorized resistance circuit would make inside the ACU. Regulating the field current using variable resistance will generate heat, see? Smooth, but hard on stuff. Really old regulators (like, much older than me, and that's old) used a stack of carbon discs that were compressed together by a spring, and the compression was relieved by a solenoid that forced the spring back. When voltage fell, the spring was able to compress the discs, lowering the stack's resistance and increasing field current, If voltage rose too much, the solenoid removed some of the spring force, relaxing the pressure on the discs. Smooth, but big and heavy and dirty and subject to heat and vibration damage. Too crude.

The electronic circuitry in that ACU needs only microamps from the alternator's output or the bus to change the field current. Really, really sensitive, and therein lies a problem. Any disturbance to the aircraft's electrical system can fool that ACU into thinking the voltage has risen, and the overvolt function within it will shut the alternator off. And what can disturb the airplane's system to that degree? A leaking COM antenna cable connector. RF (radio-frequency) radiation gets out and cuts through wiring and generates sharp little voltage spikes in it. The ACU mistakes this for an overvolt condition. The old electromechanical regulators were immune to this. Those sharp little spikes generated far too little current in the sensor circuit to cause trouble.

We had that problem in a late-model 185. The alternator kept going offline, but only when flying, it seemed. Couldn't find anything wrong anywhere, but I finally (finally) read the service manual, and buried in a little paragraph there was the stuff about corroded antenna cable connectors. I found it in the ceiling of the airplane. People in the airplane breathe, and in that breath is moisture. That air finds its way past the headliner and condenses on the inside of the top skins in cooler weather, and gets the antenna cable bayonet connectors wet, starting corrosion that interferes with the grounding of the cable shield. RF gets out and causes the mayhem described. I took the airplane out, started it up, hit the PTT, and bang! there was the overvolt light. At our uncontrolled field we made a radio call on takeoff, but didn't notice the light until farther along. The other end of that cable under the panel, or any splice along the way, also needs checking, as it can also get dirty/loose, corroded. I cleaned that antenna connection and the problem went away.
 
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Put the parts shotgun down... I had an intermittent alternator issue that turned out to be a loose field wire. Could be different harmonics at different RPMs rather than high power vs low power.
Wow, this is insightful! I've been debugging an intermittent alternator for a while now and after reading this checked my monitor logs. All failures occured at 2500RPM. Going to have the shop check connections more carefully.
 
Since this is an ACU we're talking about here, it might be useful to cover a weakness with these modern devices.

The old electromechanical regulator took a significant fraction of an amp to actuate its voltage regulator relay. When the voltage got too high, the relay was pulled open by its coil, which was fed from the bus or alternator output, and the alternator's field collapsed, basically turning the alternator off. As soon as the voltage fell below the setting, the relay closed and reenergized the field and up went the output again. This sounds pretty crude, and it was, but the induction of the field coil made the square wave thus formed in the field coil into a much-smoothed sine wave, and a filter capacitor on the alternator (sometimes inside it) or on the field wire at the firewall, levelled it even more. That little regulator relay basically buzzed all the time, staying closed microseconds longer when demand was high, and open microseconds longer when demand was low.

The ACU uses pulse-width modulation of the field current. This is also crude, but accepted as effective because it doesn't generate the heat that a transistorized resistance circuit would make inside the ACU. Regulating the field current using variable resistance will generate heat, see? Smooth, but hard on stuff. Really old regulators (like, much older than me, and that's old) used a stack of carbon discs that were compressed together by a spring, and the compression was relieved by a solenoid that forced the spring back. When voltage fell, the spring was able to compress the discs, lowering the stack's resistance and increasing field current, If voltage rose too much, the solenoid removed some of the spring force, relaxing the pressure on the discs. Smooth, but big and heavy and dirty and subject to heat and vibration damage. Too crude.

The electronic circuitry in that ACU needs only microamps from the alternator's output or the bus to change the field current. Really, really sensitive, and therein lies a problem. Any disturbance to the aircraft's electrical system can fool that ACU into thinking the voltage has risen, and the overvolt function within it will shut the alternator off. And what can disturb the airplane's system to that degree? A leaking COM antenna cable connector. RF (radio-frequency) radiation gets out and cuts through wiring and generates sharp little voltage spikes in it. The ACU mistakes this for an overvolt condition. The old electromechanical regulators were immune to this. Those sharp little spikes generated far too little current in the sensor circuit to cause trouble.

We had that problem in a late-model 185. The alternator kept going offline, but only when flying, it seemed. Couldn't find anything wrong anywhere, but I finally (finally) read the service manual, and buried in a little paragraph there was the stuff about corroded antenna cable connectors. I found it in the ceiling of the airplane. People in the airplane breathe, and in that breath is moisture. That air finds its way past the headliner and condenses on the inside of the top skins in cooler weather, and gets the antenna cable bayonet connectors wet, starting corrosion that interferes with the grounding of the cable shield. RF gets out and causes the mayhem described. I took the airplane out, started it up, hit the PTT, and bang! there was the overvolt light. At our uncontrolled field we made a radio call on takeoff, but didn't notice the light until farther along. The other end of that cable under the panel, or any splice along the way, also needs checking, as it can also get dirty/loose, corroded. I cleaned that antenna connection and the problem went away.
This ACU has a status light. If it were throwing an over voltage indicator, wouldn't the light turn red? During my test yesterday the light stayed green the whole time. I did notice in the video playback that at one point the green light flickered off then back on (a quick micro second; almost didn't even see the flicker) when I pulled the throttle back.
 
This ACU has a status light. If it were throwing an over voltage indicator, wouldn't the light turn red? During my test yesterday the light stayed green the whole time. I did notice in the video playback that at one point the green light flickered off then back on (a quick micro second; almost didn't even see the flicker) when I pulled the throttle back.
I only mentioned the RF/ACU interference problem because someone is probably fighting it right now. May not be the case with your airplane. With the problem being specific to one RPM, it sounds to me like something loose shaking enough to cause alternator output to fall off.
 
What's always bugged me about these intricate diagnosis on airplane charging systems is that in the automotive world nobody would put this much time and effort into it. A 60-amp Chrysler alternator for a car can be had for under $100, last I looked an external voltage regulator can be had for maybe $20. Obviously the certified aviation versions of these parts cost an order of magnitude more and that's why we do all the testing.

But this gives me an idea. Considering we're paying an A&P quite a bit for diagnosis is there a shortcut? What if we temporarily swapped out our aviation 60-amp Chrysler alternator for a $60 automotive unit to see if the problem goes away? Could that potentially save an aircraft owner hours of diagnostic time and potentially weeks of downtime waiting for the problem to be identified? Any chance the FAA would field-approve a test flight with something like this as a diagnostic method? I can't think of a reason you couldn't use it for testing on the ground at least.
 
What's always bugged me about these intricate diagnosis on airplane charging systems is that in the automotive world nobody would put this much time and effort into it. A 60-amp Chrysler alternator for a car can be had for under $100, last I looked an external voltage regulator can be had for maybe $20. Obviously the certified aviation versions of these parts cost an order of magnitude more and that's why we do all the testing.
Yes. In the automotive world a lot of "repairs" are done the same way as in the airplane world. Replace stuff until the problem goes away. Sometimes one will replace that $100 alternator two or three times until some brighter mechanic points out that the cheap fuseblock for the alternator is burnt or corroded. Sometimes the regulator gets replaced until the same sort of thinking mechanic suggests checking for a shorted field in the alternator, or worn brushes in it, or a loose "S" wire between the alternator's stator terminal and the S terminal on the regulator. In a car, that stator generates a bit of electricity when the car is started, due to residual magnetism in the rotor, and that current turns the regulator on. In the airplane, that S terminal on the regulator gets fired by the ALT switch. Done that way so we can turn off a rogue alternator in flight.

The OP's airplane has an ACU. Alternator Control Unit. It is entirely electronic, no mechanical relays, and has overvolt protection built into it. Cars didn't get those. They got alternators with built-in regulation.

This sort of non-thinking, non-troubleshooting applies to an awful lot of stuff. Many batteries get replaced because the $40 master or starter contactors are shot, offering resistance to the massive current flows. Ohm's Law tells us that with large amperage, even a tiny resistance causes a big voltage drop. $500 strobe powerpacks that don't work get replaced when their $25 40-year-old breakers, or $15 ancient switches, have oxidized or burned contacts. Flap motors get replaced because of a gummed-up $8 microswitch. It goes on and on. Electrical knowledge is easily the most common weak point for most mechanics.

I was in the air brake component remanufacturing industry for more than 12 years. I once tested a whole bunch of the common control, relay valve and compressor governor cores that came in for exchange, and found about 80% of them working just fine. The mechanics didn't know how the systems worked, nor where the weak points were usually found, and so they would replace a valve three or four times before they finally realized that the fault must lie elsewhere. We started putting a fluorescent red card in every box, with our 800 number, telling them to call if they were flummoxed. I gave a lot of advice to mechanics that way.
 
Not a mechanic, but I have seen a similar issue. Our plane has the Voltage Regulator and a an overvoltage regulator/Breaker (whatever the term for it is), Had a similar issue where the Overvoltage protection was failing and shutting the charging off when it shouldn't. Our looked like a smaller voltage regulator, or similar to some automatic resetting breakers I have seen.
...

That was the first thing we replaced. Didn't help.
Your Zeftronics R15VOL has built-in overvoltage protection.
 
Must be something in the central Illinois air. My alternator just went off line over Peoria but I opted for the main airport and they’ve already pulled it in to diagnose. I’m sure this prompt service at a Mooney Service Center will be very economical.
 
Too much resistance on the brushes and they should have the parts in stock. Here’s hoping I can be back in the air today.
 
28 minutes to diagnose? They got a NASCAR pit crew in there or what?
 
Must be something in the central Illinois air. My alternator just went off line over Peoria but I opted for the main airport and they’ve already pulled it in to diagnose. I’m sure this prompt service at a Mooney Service Center will be very economical.
You were wise to go to the main airport. :)
 
Too much resistance on the brushes and they should have the parts in stock. Here’s hoping I can be back in the air today.
Just remember to drop @Ted 's name to the owner so you can get the family mark-up. Err, discount. The owner is Ted's old CFI
 
28 minutes to diagnose? They got a NASCAR pit crew in there or what?
Cowling is going back on now. I can not complain about the speed.

Just remember to drop @Ted 's name to the owner so you can get the family mark-up. Err, discount. The owner is Ted's old CFI

I think I got the president, who is directing 3 techs, and was reminiscing about the heyday of Mooney J models. I reckon he’s the kind of guy that has forgotten more about aviation maintenance than I can ever hope to know.
 
Correction, I got the owner Scott Welch.
 
Were you able to at least finish lunch? Damn.
 
Just remember to drop @Ted 's name to the owner so you can get the family mark-up. Err, discount. The owner is Ted's old CFI

Correction, I got the owner Scott Welch.

Indeed, my old CFI and boss while I flew for him. You can thank/blame him for me being on PoA, at least partly. Missa (hasn't been on here in a long time) got me started on this place. But Scott's responsible for most of my ratings.

And at the very least, tell him hi for me. :)
 
Must be something in the central Illinois air. My alternator just went off line over Peoria but I opted for the main airport and they’ve already pulled it in to diagnose. I’m sure this prompt service at a Mooney Service Center will be very economical.
You showed up in a Mooney, right? Had it been another type, maybe they would have told you to pound sand ;)
 
Fix failed. Scott’s been great the whole time and they were able to scrounge up an overhauled one and get it shipped here overnight. Hopefully back in the air tomorrow. And I’ve already talked @Jim K into a ride. Not the OG plan but getting some fun in that wouldn’t have happened is damn cool.

And at the very least, tell him hi for me. :)
Consider it done. :)
 
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Fix failed. Scott’s been great the whole time and they were able to scrounge up an overhauled one and get it shipped here overnight. Hopefully back in the air tomorrow. And I’ve already talked @Jim K into a ride. Not the OG plan but getting some fun in that wouldn’t have happened is damn cool.


Consider it done. :)
Sorry I'm out of town or else I could've taken care of you.
 
Final diagnosis, a wire to the alternator was too short and caused the stud to break free from the alternator. New alternator installed next day, along with a point out of other sub-par work in a few spots, and I was back in the air. Added a few knots with a much lighter wallet.
 
You can remove it in 15 or 20 minutes and take it to auto zone they will test it for you tell them it’s off of your tractor
 
Final diagnosis, a wire to the alternator was too short and caused the stud to break free from the alternator. New alternator installed next day, along with a point out of other sub-par work in a few spots, and I was back in the air. Added a few knots with a much lighter wallet.
And the appropriate fix was replacing the entire alternator?
 
And the appropriate fix was replacing the entire alternator?
Yep. I think the stud sheared off inside. I bought an overhauled one ($1400 in case anyone wants to experience the Hartzell sell out joy with me) so I could depart ASAP. Or I could wait a week for mine to be overhauled.
 
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