Electrical issue

[Airstevo]

Hi, hoping for a little help. Have a new to me k model and have only had a few flights in it. Last flight, any rpm below about 1200 would cause the audio panel to start flashing, radios would cut in and out, and high/low volts would be on. Even powering up to 2000, the audio panel would be steady, but transmitting would still cut out, ammeter showed 0, but charging on the jpi would show 12.5 and sometimes 13 then back down. Mechanic tested everything and said it seemed to be charging, but was possibly some slippage in the alternator drive from the engine so replaced that. Mechanic said it was all fixed and tested and it all works now but when I went to taxi out to fly, it’s all the same issues. I spent 15 minutes trying to put a load on it by running flaps and transmitting and same issues. Low volts stayed in no matter what rpm, radios cutting in and out, and trouble transmitting. Over time I noticed system voltage dropping towards 10. So I went back to the hangar. The alternator was replaced by the last owner a year ago with and overhauled unit. If you know about electrical things, would you mind weighing in on what this could be?  A bad battery?  Connection from alternator, or just a failing alternator already?   Thank you very much. 

[PT20J]

 Could be lots of things. I’d check connections to the alternator first. Here’s a troubleshooting guide that might help.
https://planepower.aero/wp-content/uploads/2018/02/Troubleshooting-Single-Engine-Externally-Regulated-Alternators.pdf

Radio shops are sometimes better at troubleshooting electrical issues than A&Ps if you need hands on help.

Skip

[Ragsf15e]

2 hours ago, Airstevo said:

Hi, hoping for a little help. Have a new to me k model and have only had a few flights in it. Last flight, any rpm below about 1200 would cause the audio panel to start flashing, radios would cut in and out, and high/low volts would be on. Even powering up to 2000, the audio panel would be steady, but transmitting would still cut out, ammeter showed 0, but charging on the jpi would show 12.5 and sometimes 13 then back down. Mechanic tested everything and said it seemed to be charging, but was possibly some slippage in the alternator drive from the engine so replaced that. Mechanic said it was all fixed and tested and it all works now but when I went to taxi out to fly, it’s all the same issues. I spent 15 minutes trying to put a load on it by running flaps and transmitting and same issues. Low volts stayed in no matter what rpm, radios cutting in and out, and trouble transmitting. Over time I noticed system voltage dropping towards 10. So I went back to the hangar. The alternator was replaced by the last owner a year ago with and overhauled unit. If you know about electrical things, would you mind weighing in on what this could be?  A bad battery?  Connection from alternator, or just a failing alternator already?   Thank you very much. 

What Skip said is an understatement.  Many (but not all @M20Doc) A&Ps aren’t great at electrical troubleshooting.  They are however good at replacing lots of stuff which becomes expensive.  You can carefully troubleshoot your problem with a knowledgeable person and a voltmeter.  
 

If you’re showing 12.5 or 13v on a 14v system, there’s a problem.  At 12.5, that’s basically battery voltage, so your alternator may be totally off line.  In addition to skips troubleshooting guide, common things to check (and easy) are battery ground, engine to airframe ground, and the field wire attached at the alternator. 
 

You need basic electrical skills/knowledge and a digital voltmeter. Troubleshoot 3 times before throwing parts at it (kind of like measure twice, cut once).

[khedrei]

You said they replaced the drive coupler (gear that connects the alternator to the accessory case). That thing runs close to 1 AMU USD i think. Mine was no good on my K. Easy to check. With the top cowling off, put your finger inside the fan of the alternator and gently try to turn the prop. Do it yourself or your friend might chop the tip of your finger off. Wear thin work gloves to minimize pressure. If you can turn the prop in either direction without chopping off your finger the coupler is bad. Is it possible they simply tried to repair it? New ones run 2k or more. The ones they sell at Spruce are refurbished. Perhaps you got a dud? Check it first cause its easy.

 

Otherwise check voltage regulator? Connections as mentioned above. 

[Bolter]

I also believe in trouble shooting and not wasting money, like the others.  That said, the original vintage voltage regulators are prone to failure and worth upgrading.  I would replace that, if you have an original 1960's technology type, as an upgrade as well as possibly fixing the problem.  Zeftronics R15300 is listed for the M20K (12V).

[Airstevo]

1 hour ago, khedrei said:

You said they replaced the drive coupler (gear that connects the alternator to the accessory case). That thing runs close to 1 AMU USD i think. Mine was no good on my K. Easy to check. With the top cowling off, put your finger inside the fan of the alternator and gently try to turn the prop. Do it yourself or your friend might chop the tip of your finger off. Wear thin work gloves to minimize pressure. If you can turn the prop in either direction without chopping off your finger the coupler is bad. Is it possible they simply tried to repair it? New ones run 2k or more. The ones they sell at Spruce are refurbished. Perhaps you got a dud? Check it first cause its easy.

 

Otherwise check voltage regulator? Connections as mentioned above. 

Yeah that’s what they did and how much it cost but didn’t change the problem at all. That’s frustrating. It happened immediately so I’m unsure what they saw after they “fixed” it then tested it. 
they said they tested the voltage regulator, power output of the alternator and all seemed good. Good ok electrical gremlins 

[Airstevo]

23 minutes ago, Bolter said:

I also believe in trouble shooting and not wasting money, like the others.  That said, the original vintage voltage regulators are prone to failure and worth upgrading.  I would replace that, if you have an original 1960's technology type, as an upgrade as well as possibly fixing the problem.  Zeftronics R15300 is listed for the M20K (12V).

I’ll take a look at those thanks! 

[Airstevo]

3 hours ago, Ragsf15e said:

What Skip said is an understatement.  Many (but not all @M20Doc) A&Ps aren’t great at electrical troubleshooting.  They are however good at replacing lots of stuff which becomes expensive.  You can carefully troubleshoot your problem with a knowledgeable person and a voltmeter.  
 

If you’re showing 12.5 or 13v on a 14v system, there’s a problem.  At 12.5, that’s basically battery voltage, so your alternator may be totally off line.  In addition to skips troubleshooting guide, common things to check (and easy) are battery ground, engine to airframe ground, and the field wire attached at the alternator. 
 

You need basic electrical skills/knowledge and a digital voltmeter. Troubleshoot 3 times before throwing parts at it (kind of like measure twice, cut once).

Thank you. I will check that stuff. I think they did just throw parts at it. I’m not sure how to handle the cost of their “repair” since it didn’t fix anything 

[Airstevo]

5 hours ago, PT20J said:

 Could be lots of things. I’d check connections to the alternator first. Here’s a troubleshooting guide that might help.
https://planepower.aero/wp-content/uploads/2018/02/Troubleshooting-Single-Engine-Externally-Regulated-Alternators.pdf

Radio shops are sometimes better at troubleshooting electrical issues than A&Ps if you need hands on help.

Skip

Thank you for the guide. I’ll go through it and see what I can figure out. 

[Will.iam]

Might be the avionics relay going bad?

had my whole dash go out and back on multiple times in one flight. Found out avionics relay is a common thing to go out when your craft was built in the 80’s. 
after replacing that didn’t have a glitch since. 

[Ragsf15e]

9 hours ago, Airstevo said:

Thank you. I will check that stuff. I think they did just throw parts at it. I’m not sure how to handle the cost of their “repair” since it didn’t fix anything 

I learned that the hard way after letting/helping my mechanic throw parts at an electrical problem for ~2 years. Alternator, voltage reg, master switch, and field wire.  Ouch, expensive. Talked to a EE friend who had built a plane.  Took him 5 minutes to tell me how to troubleshoot my problem.  Turned out it was a slightly corroded connection to my power bus.  Took a piece of sandpaper and 10 cents of elbow grease to fix.  Got some good life lessons there though.

The big stuff can break (alternator, voltage reg), but you just want to narrow it down first.

[Airstevo]

thank you all for the input.  this is a great source.  I went out this morning to talk to the mechanic, and he suggested we run it again with him putting his voltmeter on everything to see what was going on.  Of course the problem couldn't be replicated, things worked pretty much how they were supposed to, he showed 14 volts at the alternator, but inside on the jpi and aspen efis, both showed the volts moving around a little bit.  but charging this time, from about 13.5-14.  but moving constantly.  he thought that was odd, so shut down, checked circuit breakers, then found some metal shavings on some breakers, tightened up a few things, then ran it again but tried to put as much load on it as possible, running trim, flaps, all lights on, transmitting at the same time.  after this started seeing voltage drop below 12, ammeter showed drain.  he took voltage at the alternator and confirmed dropping there too, then got to 11 volts as i continued.  all of this done with running RPM anywhere from 1200 to 2000.  same result. He believes it's the alternator.  any other ideas before I pull the trigger on that?

 

[EricJ]

1 hour ago, Airstevo said:

thank you all for the input.  this is a great source.  I went out this morning to talk to the mechanic, and he suggested we run it again with him putting his voltmeter on everything to see what was going on.  Of course the problem couldn't be replicated, things worked pretty much how they were supposed to, he showed 14 volts at the alternator, but inside on the jpi and aspen efis, both showed the volts moving around a little bit.  but charging this time, from about 13.5-14.  but moving constantly.  he thought that was odd, so shut down, checked circuit breakers, then found some metal shavings on some breakers, tightened up a few things, then ran it again but tried to put as much load on it as possible, running trim, flaps, all lights on, transmitting at the same time.  after this started seeing voltage drop below 12, ammeter showed drain.  he took voltage at the alternator and confirmed dropping there too, then got to 11 volts as i continued.  all of this done with running RPM anywhere from 1200 to 2000.  same result. He believes it's the alternator.  any other ideas before I pull the trigger on that?

I don't suppose he was watching the field voltage input to the alternator during all this?    That could have been revealing whether it was the alternator or potentially the regulator.

 

[carusoam]

How many connections do you think your Mooney has between your volt meter and the alternator?

Starting at the battery…

Alternator switch…

Master relay…

Avionics master relay…

Voltage regulator…

Alternator…

Grounds…

Some mechanics are really good with electrical challenges…. Including the drawings they need on hand….

 

Some mechanics know where the big issues are often found…

Around here… the field wire is always suspect… They break most often….

They also control what the alternator is doing…

If the field wire breaks… the alternator stops working… loose connection is similar…

 

How old is the battery, has it had a capacity check? 
 

Nice clean connections can always be helpful…

Don’t replace anything until it’s connections have been tested, cleaned, or determined how old the things are…

PP thoughts only, not a mechanic…

Best regards,

-a-

[Bolter]

14 minutes ago, EricJ said:

I don't suppose he was watching the field voltage input to the alternator during all this?    That could have been revealing whether it was the alternator or potentially the regulator.

 

As a more crude test done without the A&P, could you pull the field breaker and observe the level of voltage change on the JPI?   In the extreme, you would see no change, indicating the alternator was doing nothing at all.  Of course, it could then still be a connection.  Lots of people have reported fatigued connections at the alternator. 

[carusoam]

The JPI is nice… it has a digital volt meter right in it… 

The alternator switch, is the on/off source for the field wire…

Soooo…. If you suspect the alternator of not working… flip its switch to see what changes… and how it behaves…

There are also digital volt meters that plug right in the cigarette lighter for ease of use…

 

Unfortunately… the wire connections at the back of the alternator switch could be the source of the challenge… as well as the 30 other connections…

1) What alternator do you have…

2) What voltage regulator do you have…

M20Ks probably didn’t get the sticks and stones and springs voltage regulator…  if for some reason it did… you are free to get a Zeftronics device instead…

PP thoughts only, not a mechanic…

Best regards,

-a-

[Ragsf15e]

2 hours ago, Airstevo said:

thank you all for the input.  this is a great source.  I went out this morning to talk to the mechanic, and he suggested we run it again with him putting his voltmeter on everything to see what was going on.  Of course the problem couldn't be replicated, things worked pretty much how they were supposed to, he showed 14 volts at the alternator, but inside on the jpi and aspen efis, both showed the volts moving around a little bit.  but charging this time, from about 13.5-14.  but moving constantly.  he thought that was odd, so shut down, checked circuit breakers, then found some metal shavings on some breakers, tightened up a few things, then ran it again but tried to put as much load on it as possible, running trim, flaps, all lights on, transmitting at the same time.  after this started seeing voltage drop below 12, ammeter showed drain.  he took voltage at the alternator and confirmed dropping there too, then got to 11 volts as i continued.  all of this done with running RPM anywhere from 1200 to 2000.  same result. He believes it's the alternator.  any other ideas before I pull the trigger on that?

 

I agree with @ericj that you need to check the field voltage, however… if the alternator is showing 14v output on a voltmeter and your jpi is showing 13.5 or less, there’s a problem.  You want to follow the wire from the alternator through the noise filter, through the 70amp (or similar) main alt breaker (this is a big sealed one), and finally into the power bus.  Use the dvm voltage probes to check voltage at each place and find where it’s dropping.  You may just have a corroded connection.  You can reach under the panel on the circuit breaker bus to measure voltage there.  It should be exactly the same as alternator output.

[khedrei]

I would still encourage you to check for a slipping drive coupler if you haven't already.  When under heavier load it has a better chance of slipping.  The rubber coupler is simply pressed into the cup so temperature will also affect it.  They are refurbs an if you got a dud, it would be covered under warranty.  I have heard of a few people who have.

[carusoam]

Just now, khedrei said:

I would still encourage you to check for a slipping drive coupler if you haven't already.  When under heavier load it has a better chance of slipping.  The rubber coupler is simply pressed into the cup so temperature will also affect it.  They are refurbs an if you got a dud, it would be covered under warranty.  I have heard of a few people who have.

This is the important one…

The other possible issues are fifty cent items… up to a couple of hundred bucks…

But, a slipping drive coupler can get really expensive extra fast…

Soooo…. At least find the problem first…

Before it gets expensive…

Best regards,

-a-

[Airstevo]

should the drive coupler move at all?  they said it was moving after they grabbed it with a wrench on it so initially figured that was the problem.  so they replaced that already.   also added 30% to the part cost which i'm not a fan of.  they did check the field voltage and it was reading only slightly less than the alternator output.  I don't think they checked the buss connections yet.  They did check voltage at the battery and it was showing close to what the voltage on the jpi and aspen efis were showing.  I don't know if they systematically have checked each section from the alternator to the the point where the jpi was reading it, but they did a bunch.  eventually, the alternator output started dropping to well below 12v and I think thats when they started pointing fingers and deciding it was the alternator now.  So now my problem is, they installed a new coupler, that didnt fix it but are charging me $1000 for the part and whatever labor that involved, and still didn't fix the issue.  I have the price of the alx-9525B alternator overhaul cost, and it seems about half that of a new one, so if they try to get me again for another 30% for these parts, they've lost a customer.  It seems like they like to throw parts and labor at it, until they find it.  Frustrating

[khedrei]

The drive coupling should not move under normal load.  It is designed to fail if something seizes to prevent damage.  How much load does that take.... ? I don't know.  I am not a mechanic.  If they reefed on it with a wrech its possible they broke it loose and it wasnt the issue hence why you are still having a problem.  If it was the issue, there is a slim possibility your new one was a dud.  I was under the impression you had the plane back and thats why I gave you some instructions on how to check it.  It takes 2 minutes to check and can easily rule it out.

As far as the situation you are in, I would be fighting them for sure.  They diagnosed the fix, and it was wrong.  If they are decent people they would waive the labor to install the coupling, wave the 30% mark up.  I was able to re-re that part in less than 2 hours, so it shouldn't be a huge lose for them.  If I were you, I would offer to pay dead cost for the part, and allow them to continue troubleshooting.  You stay a customer, and keep relations good.  If they aren't willing to agree on that I would find another mechanic.

I'm not a mechanic, but those are my 2 cents.

Aside from checking all the wiring, grouds, voltage regulator and alternator field, there isn't much more that can go wrong with the system.  if you have a short in one of your pieces of equipment it should show a heavy current draw on the JPI.  If that's not showing, and it's just low voltage, the only thing left is the alternator.  Hell, at this point you could put your alternator on a friends plane to rule out wiring issues and confirm the bad alternator.

Good luck to you.

Edited September 27, 2022 by khedrei

[Ragsf15e]

Throwing parts at these issues is rarely successful without solid troubleshooting.  A bad alternator isn’t out of the question, but I’d want to be sure before replacing it… that being said, I got to be the chump who paid for a new alternator and install only to find out that wasn’t the problem (3 years ago).  

It wasn’t worth destroying the relationship with my maintainer over it.  I counted it as education and I studied the electrical system myself, talked to some really sharp EE types and troubleshot/fixed it myself.  Now if I have another electrical problem, you can bet I won’t just drop off the keys and checkbook for maintenance.  But my mechanic is great with airframe and engine.

[Pinecone]

The good news is, if you replace a part, and it is not the problem, you can put the removed part on the shelf as a spare for when that part actually fails.

 

Making lemonade out of lemons.

[GeeBee]

On 9/26/2022 at 10:48 PM, Airstevo said:

should the drive coupler move at all?  they said it was moving after they grabbed it with a wrench on it so initially figured that was the problem.  so they replaced that already.   also added 30% to the part cost which i'm not a fan of.  they did check the field voltage and it was reading only slightly less than the alternator output.  I don't think they checked the buss connections yet.  They did check voltage at the battery and it was showing close to what the voltage on the jpi and aspen efis were showing.  I don't know if they systematically have checked each section from the alternator to the the point where the jpi was reading it, but they did a bunch.  eventually, the alternator output started dropping to well below 12v and I think thats when they started pointing fingers and deciding it was the alternator now.  So now my problem is, they installed a new coupler, that didnt fix it but are charging me $1000 for the part and whatever labor that involved, and still didn't fix the issue.  I have the price of the alx-9525B alternator overhaul cost, and it seems about half that of a new one, so if they try to get me again for another 30% for these parts, they've lost a customer.  It seems like they like to throw parts and labor at it, until they find it.  Frustrating

I replace my drive coupler every 500 hours with new (most people do rebuilt). You can test them with a tool and torque wrench. I don't mess around with them because a bad one can mess up your engine and maybe your day really bad. Anyway if your coupler has over 500 hours on it, let it go. You needed a new one anyway.

https://www.aircraftspruce.com/catalog/topages/approach_adckit1.php

[EricJ]

20 hours ago, Ragsf15e said:

Throwing parts at these issues is rarely successful without solid troubleshooting.  A bad alternator isn’t out of the question, but I’d want to be sure before replacing it… that being said, I got to be the chump who paid for a new alternator and install only to find out that wasn’t the problem (3 years ago).  

It wasn’t worth destroying the relationship with my maintainer over it.  I counted it as education and I studied the electrical system myself, talked to some really sharp EE types and troubleshot/fixed it myself.  Now if I have another electrical problem, you can bet I won’t just drop off the keys and checkbook for maintenance.  But my mechanic is great with airframe and engine.

Well, I'm an EE and an A&P and replaced my alternator about a year ago after a failure on a trip.   I did a field repair to the field wire, which seemed to be loose, but it didn't fix it, so when I got home I started debugging.   The zeftronics LEDs said the field was shorted, which I confirmed with a multimeter (displaying voltage), so I replaced the alternator.

The new one didn't work, either, and I discovered that when I did the field repair I'd shorted a stray strand of the shield of the field wire to the wire when I recrimped it.   D'oh. 

So my field repair would have worked just fine and cured the problem except I snagged that strand of the shield in the crimp.   

Anyway, now I have a spare alternator.