Electrical gremlins

4RNB

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4RNB
C172M, new avionics and engine in past year or two. Alternator replaced before leaving the shop. I still get irregular low volt and amp alarms. Normally goes away within minutes.

A week or two ago my paint shop did a test flight and took a look at this with an avionics company. On the ground the problem seemed to go away, but the avionics guy said that the voltage monitor was on the avionics bus bar and should be switched to the battery bus bar. He had what seemed to be a page from a G3x install manual saying that is where it should go. I spoke to my avionics installer who seemed to not think it was that big of a deal, still willing to take a look at it. Annual appointment set for June.


Yesterday I went out to get current for passengers, had low alarms for a few minutes when at 2300 RPM, increased to 2500 RPM and went away.

Today, the darn thing alarmed the whole flight with my wife on board! Turning AP off did not help. Increasing power did not help. Lights on/off had minimal impact (all LED). Back up G5 did not help when turned off.

I'm the guy that gets so frustrated with these things that at times it could be easy to just sell the darn thing and be done with it...aka bipolar owner. But interested enough to apply to AP school this past week.

So we landed today with low amp readings, volts in the 11s and a message on the GPS/Com that said "Com overtime overtime or under voltage. Reducing transmitter power".

I am now worried about cranking power, want to get the plane somewhere to get examined. Perhaps a second shop? Perhaps all my avionics are just overtaxing the alternator and it needs to be upped in size? OR is my battery getting old? Concord RG-25XC 105% capacity when installed 11/20.

I'm willing to fly with irregular alarms, perhaps from oversensitive settings, but the radio alarm was new and concerning. This tells me there legit is another issue to be fixed.

What would you do and what does the troubleshooting also look like?

Kind of tough to plan for a run to Florida or other XC.
IMG_5385.jpegIMG_5385.jpeg
 
Very frustrating, especially after dropping a lot of cash. But you have to fix it. Otherwise, long XCs will be worrisome instead of enjoyable. Best wishes.
 
Poke around to check for loose or warm wires or switches right after flying.
Time to get a AP mechanic to trouble shoot it if you don't find anything obvious.
It is all part of sorting out a new to you plane that is 45 years old.
Don't ask me how I know.
 
If you don't know what stuff looks like under the panel and in the engine compartment, there isn't much we can say to help you find the problem.

I will say that it is most likely a problem with a loose or corroded connection at the alternator or regulator or ALT switch or its breaker.

Electrical troubleshooting is the weakest skill among a majority of mechanics. They tend to just start replacing stuff because they don't understand electricity or how the various components work. It's all a guessing-game to them.
 
What would you do and what does the troubleshooting also look like?
To clarify... all the voltage/amp readings are solely based on the avionics displays?
And nobody has verified any of those readings with a VOM or performed any type of basic troubleshooting?
 
Back of alternator. I saw the orange cap partial wore out, touched it, seemed to be attached by rust dust.
Now, what is this wire called so I can order one for whoever I can find to replace?
 

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Back of alternator. I saw the orange cap partial wore out, touched it, seemed to be attached by rust dust.
Now, what is this wire called so I can order one for whoever I can find to replace?
That sure as heck looks like the output terminal. If it's completely disconnected like it appears, you're not charging the battery and if the field is energized (different wire) possibly damaging the alternator. An intermittent output connection might cause something like the symptoms you describe, assuming the alternator functions normally when connected.

Nauga,
the alter nator
 
That sure as heck looks like the output terminal. If it's completely disconnected like it appears, you're not charging the battery and if the field is energized (different wire) possibly damaging the alternator. An intermittent output connection might cause something like the symptoms you describe, assuming the alternator functions normally when connected.

Nauga,
the alter nator
It was sort of on, but no resistance to pulling apart. Pretty clear to me it was what has caused my issues for a while now.
Best I can guess it is 10awg? A decent shop might be able to make one and install?
 
"Alternator replaced before leaving the shop".
Glad you found something.
That connection looks to be on an older alternator? But I really can't tell from the picture.
 
Best I can guess it is 10awg? A decent shop might be able to make one and install?
I couldn't say. In my case it's 6awg and making a replacement is trivial with a heavy-duty crimping tool. Rerouting and fastening it is a whole 'nuther matter - fairly straightforward but a lot of clamps and supports to get it through. :cool:

Nauga,
free floating
 
I couldn't say. In my case it's 6awg and making a replacement is trivial with a heavy-duty crimping tool. Rerouting and fastening it is a whole 'nuther matter - fairly straightforward but a lot of clamps and supports to get it through. :cool:

Nauga,
free floating

As said, you (or mechanic) really want the proper crimp tool for the ring terminal, mashing with a hammer just doesn't cut it. If you think more cables are old and need replacing, Bogert sells cable kits, but more expensive than making one new cable: https://bogertaviation.com/
 
What brand and model of regulator is installed? I'm guessing you have a modern regulator with integral over voltage (OV) protection... but someone may have overlooked the factory OV relay buried in the wires behind the circuit breakers. This intermittent action is how they fail. Could be field breaker, or alternator half of master switch. Are you cycling the alternator switch to bring it back on line?

Then... a bad piece of wire or connection. You can wire a light or meter to the various way stations between the field breaker and the F terminal in the alternator to figure out where the voltage is disappearing.

Paul
 
#1 mentioned overtaxing the Alternator.

Many 337’s include an Electrical Load Analysis which would state the amperage draw.

Another thought is to use an inductive ammeter to check the draw.

Repetitive short flights may not allow the battery to regain a full charge as well.

It is not unusual for folks to cut wire strands during the stripping process.

This little issue or a poorly crimped termination can cause big issues later.

Many Techs lack proper tooling for some sizes.

Using a vise or hammer can make an expensive installation fail to operate properly.

A bigger Alternator would be on hold until these points are resolved.
 
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Shop was able to look at it today. Battery wire on alternator too short to work with, needs replacement. They have the wire, not sure about the fittings. Post on alternator needs replacement, they think they can handle that also. A few parts might need to be ordered. They are very behind on work, I got lucky getting any attention. It likely helped that they were able to get in my hangar and leave the plane there. Fitting likely was too large for the post, caused some wallering (?sp), hence the post damage. Color might be from it being a brass post.

Prior upgrades had a load analysis performed. Plane power regulator.
 
If you landed, and it was at 11 volts, like really at 11 volts, checked with a simple hand held volt meter… you’re not charging.

1. Battery going bad.
2. Alternator not doing its job
A. It’s bad
B. Voltage regulator bad
C. Wiring

That’s about it. If it is indeed at 11v, put a battery charger on it and see if you can get it to nominal 12.6 or whatever. If it never really gets there, start with a bad battery presumption.

As your voltage gets low, EVERYTHING will act wonky. Like it’s possessed by demons wonky. Throws off your troubleshooting.
 
I think to replace the terminal lug on your alternator will require a overhaul which I thought you said was done in the recent past?
Good luck with it.

My alternator was replaced with a rebuilt alternator 2.5 years ago when my original quit working. In 30 hours it will have 500 hours on it and I debating whether I take it back to Aerotech of Louisville Ky or inspect the brushes myself first at that time. Time and hours fly by! I am not waiting for it to quit again.
 
I think to replace the terminal lug on your alternator will require a overhaul which I thought you said was done in the recent past?
Good luck with it.

My alternator was replaced with a rebuilt alternator 2.5 years ago when my original quit working. In 30 hours it will have 500 hours on it and I debating whether I take it back to Aerotech of Louisville Ky or inspect the brushes myself first at that time. Time and hours fly by! I am not waiting for it to quit again.

The shop owner made it sound like he thought he could just replace the post in house, but it would void any remaining factory warranty if there were any left. He thought this would get me back in the air sooner.
 
If you landed, and it was at 11 volts, like really at 11 volts, checked with a simple hand held volt meter… you’re not charging.

1. Battery going bad.
2. Alternator not doing its job
A. It’s bad
B. Voltage regulator bad
C. Wiring

That’s about it. If it is indeed at 11v, put a battery charger on it and see if you can get it to nominal 12.6 or whatever. If it never really gets there, start with a bad battery presumption.

As your voltage gets low, EVERYTHING will act wonky. Like it’s possessed by demons wonky. Throws off your troubleshooting.
The flight where the alarm persisted as the voltage drop was a hoot! She was sitting in the plane with me, very calm and trusting, but hyper focused on the red alarms instead of enjoying the scenery. I did a bit of trouble shooting in the air turning things on and off sure that did not help. On the ground she said she knew the engine would not quit and it was a clear enough VFR day in familiar ground she knew I'd land safely at home if everything died.

At this point, we know it was the battery wire on the alternator.

I'm just a bit embarrassed to have been so focused on this being an avionics issue as there have been irregular alarms since the upgrades. In hindsight, all of this is consistent with an oversized fitting rattling around on a post, coming and going until no more fitting existed to hold on.
 
The ring terminal didn’t wear out from “rattling” around on a stud.
IMO corrosion caused the damage.
It seems like one of the shops would have seen that except for the paint shop, they have no reason to look there.

Didn’t you say you had a new engine installed?
 
The ring terminal didn’t wear out from “rattling” around on a stud.
IMO corrosion caused the damage.
It seems like one of the shops would have seen that except for the paint shop, they have no reason to look there.

Didn’t you say you had a new engine installed?
Yes new engine, 2nd alternator as first wasn’t making enough power.

There is so much for me to be negative about in aviation I have to be careful searching out blame for a shop that reused 50 yr old corroded wires. I’ll go cra cray trying to blame others. The big picture answer for me is to reach a point of DIY by going to ap school.

Shop helping me says they take pictures, will share when I get the disc.
 
Well I hope your luck will change and you can get some hours in your new aircraft.
Can you find one mechanic that will look after your aircraft and mentor you?
 
I'm not sure on mentor. I've tried.
 
That crimp terminal broke because the mechanic put stress on it when he attached it to the stud. The alternator that came out of the 172M would have been a Ford, with its output terminal on the back of the alternator, and the cable tied up with the ground cable and field wire. To get the output wire terminal father out board, the cable bundle should have been cut apart and stuff moved around so the cable could reach the new location with no stress, and if the cable was too short, a new one should have been made and installed.

Stress, plus vibration, likely busted that terminal. It might have already been work-hardened with age and flexing and prone to cracking. Corrosion in that location is seldom a problem; the terminal is tinned copper, and unless it was around the battery, it won't be rotten.

As far as wire size, we just open the 172M service manual and look at the alternator wiring diagram:

1712080932385.png
So that wire part number is 8-PB36. Over in the lower right corner of that diagram we have a chart:

1712081056505.png

The -8 in that part number means it's an 8-gauge wire. The wiring diagram also tells us it's shielded, which is a separate part. Cut to length and slide it over the wire, comb out the strands from the braid at each end and twist them together, and crimp short lengths of wire and appropriate terminals to them for grounding to the alternator case and airframe near the breaker at the other end.

The old service manuals. Answer books. Get them and use them. These diagrams are from a free online copy.
 
A concern is many folks do not have proper tooling for what many consider a “ simple task”.

Terminals are often improperly installed as I said earlier.

A bud was in charge of many of the AMP products.

He has thousands of dollars worth of install tools.

He said currently it is difficult to get the proper terminations and tooling

from outlets such as Grainger and others.

Tooling is terrible and $$$.

He was astonished to find Harbor Freight has improved their installation tools

and still has a very cheap price. This was not the case a few years back.

I’ll see him tonight and try to get a p/ n.
 
I recently spent a day troubleshooting a 172K that had a history of "electrical gremlins". The A&Ps had replaced the alternator and voltage regulator and that only seemed to make the problems worse.

After futzing around most of the day, I noticed that the Voltage on the Alternator B lead was 3.5 volts higher than volts on the bus bar. I found that Alt field wire was connected to the bus via a thermal breaker that is behind the panel and not easily accesible. That old thermal breaker was breaking down and had a high internal resistance responsible for the 3.5 volt drop.

I'm not saying that specifically is you're problem. I think the 172M voltage regulator wiring is different than the 172K. But, it'll probably be something like that. So, find someone who know how to troubleshoot electrical circuits, instead of just throwing parts at the airplane and hoping that fixes it.
 
A concern is many folks do not have proper tooling for what many consider a “ simple task”.

Terminals are often improperly installed as I said earlier.

A bud was in charge of many of the AMP products.

He has thousands of dollars worth of install tools.

He said currently it is difficult to get the proper terminations and tooling

from outlets such as Grainger and others.

Tooling is terrible and $$$.

He was astonished to find Harbor Freight has improved their installation tools

and still has a very cheap price. This was not the case a few years back.

I’ll see him tonight and try to get a p/ n.

Thanks for the offer, think we will be good.
 
I recently spent a day troubleshooting a 172K that had a history of "electrical gremlins". The A&Ps had replaced the alternator and voltage regulator and that only seemed to make the problems worse.
Yeah, the old parts cannon. An expensive way to fix an inexpensive problem.
That old thermal breaker was breaking down and had a high internal resistance responsible for the 3.5 volt drop.
Oxide forms on the silver contacts in the breakers, introducing a resistance that can cause all sorts of weird stuff. Too many years on these old airplanes. With that resistance, the breaker will heat up faster and trip sooner, and the mechanic will spend many hours look for the short in the circuit that isn't there.

The same thing happens to master and starter contactors (solenoids). Their contacts are copper, and they not only get burned from arcing when they're shut off, but oxide forms on the copper as well. With massive starting currents running through both the master and starter contactors, any resistance at all introduces a large voltage drop. Ohm's Law tells us that. A fiftieth of an ohm in just one of those will cause a five-volt drop with 250 amps running through it, and you can't afford a 5-volt drop there. The engine won't crank much, if at all. So mechanics start replacing the battery, then the starter, then the alternator, on and on, when the problem was one or both $40 contactors.
I think the 172M voltage regulator wiring is different than the 172K.
Not much at all.
 
How easy is it to change a post, the battery post, on a plane power alternator?
 
How easy is it to change a post, the battery post, on a plane power alternator?
You'd have to buy the part from them (they might not sell parts) then take it apart and fix it. Might be a lot better to send it back to them for repair. A newbie could mess the whole thing up otherwise.

That post goes into the diode plate. If it has been stressed bad enough, the plate might be damaged.
 
Alternator is off
 

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Alternator is off
As you can see from the significant distance between the base nut and securing nut on the post, the connection was not properly tightened when the alternator was installed during your alternator work or engine change long ago.

It also appears, from what's left of the wire terminal, that as you observed the ring may not have been the proper size. That, and the loose nut, allowed the connection to arc repeatedly under load, which eroded the post and ultimately vaporized the ring terminal.

That the issue wasn't discovered by annual inspections and other access to the engine during "the past year or two" doesn't speak well of the maintenance personnel that worked on your aircraft. A thorough examination of the charging system components during annuals is required, but in this case was obviously not performed.
 
Alternator is off
Yup. Arced to death. There should also be another wire on that same terminal, the 18 gauge sense wire that goes to the A terminal on the regulator. 8-PB35 is the number, on that wiring diagram I posted in post 25. Where is it? Without that, the regulator has no source of field current, for one thing, and has no idea what the voltage is. Is that terminal also burnt off and hanging somewhere? Find the wire on the A terminal (the second of the four terminals on the underside of the regulator) and trace it back to the alternator.

The four terminals are I-A-S-F. I = Indicator (overvolt or low volt light on the panel), A = armature (a carryover term from the generator days when the armature was the output), S = stator, which goes to the ALT switch on the panel to turn the regulator on, and which used to connect to the stator terminal in the car's system; and F = field.
 
New alternator came today, hoping the shop can get a wired made for me. I feel a bit foolish after a chance encounter. I was looking for the wire to go directly to the battery proper, not anywhere else. The route looked like it would be convoluted and difficult so I did not look very hard. Guy in the hangar working on his plane was an AP, we talked for a bit, I saw where he was looking, and saw the real path. Darn, I could have changed that. He will help, showed me what parts to order. Should be here Tuesday and he is willing to help or sign off.

What a great number to have!
 
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