Anomalous Ammeter Readings + Loss of Alternator

ArrowFlyer86 said:
I didn't know you would physically open up a breaker or switch to examine the contacts. That's not something I'd do on my own, I'll have to ask my A&P to look at those.
Click to expand...
You don't open them to inspect them if you want to use them again. Opening them destroys them, but there's an education in doing so.
 
ArrowFlyer86 said:
Thanks, I thought something looked a little strange there.
View attachment 130651

The purple arrow points to the other end of the jumper line and it's a fairly new addition to the plane (a G5 installed by an avionics shop).
For whatever reason it looks like the breaker the avionics shop used does not fit neatly in that slot the purple arrow points to, so they ran a jumper line from it's terminal there over to piggyback on the same bus connection with the field wire?

Here's the front view of the panel. The red line indicating where I believe the jumper is linking.
View attachment 130652
Click to expand...
Ugh. Looks like the mismatched breaker came from a junk box. Electrically OK but not quality workmanship.
 
3393RP said:
Ugh. Looks like the mismatched breaker came from a junk box. Electrically OK but not quality workmanship.
Click to expand...
Agreed. Not sure why they didn't match the same form-factor/size as the existing breakers. It's an eye sore. I also do not appreciate how it seems to push the rail in on the back. Seems totally avoidable if you just use the right size breaker.
But... that's the quality I get for paying $5k to an avionics shop for a G5 AI install lol.
 
The G5 STC install manual requires a pullable breaker, which is likely why that was done. Personally I like to change all those breakers over to modern pullable breakers.
 
3393RP said:
Ugh. Looks like the mismatched breaker came from a junk box. Electrically OK but not quality workmanship.
Click to expand...

As Ryan pointed out, that is not always the case. Some items have very specific installation requirements if you’re going to actually install the item in accordance with an STC.

And, I’d argue that all the non pullable breakers that Piper installed 50 years ago should be the ones in the junk box.
 
Here's some alternator photos... Just took it apart for fun to see what condition it'd be in after being in service so long.

1719541739803.png

1719541187097.png




1719541136625.png
1719541260039.png
1719541111114.png

This one seemed like its spring had lost all resistance and it freely fell out of its housing.
1719541022372.png

The was a more intact.
1719541064086.png

I don't know why, but I expected those to be much bigger.
 
I see what appears to be some grease on the slip rings. That's from overgreasing the rear bearing. That makes resistive sludge on the slip rings and limits the field current and therefore the alternator's total output.

I'm wondering what round brushes are doing in square brush holders.

And yes, that spring wasn't keeping the brush firmly against the slip rings. Could cause intermittent failure.
 
Dan Thomas said:
I see what appears to be some grease on the slip rings. That's from overgreasing the rear bearing. That makes resistive sludge on the slip rings and limits the field current and therefore the alternator's total output.

I'm wondering what round brushes are doing in square brush holders.

And yes, that spring wasn't keeping the brush firmly against the slip rings. Could cause intermittent failure.
Click to expand...
No question there was a lot of crap built up on it. Went through many a paper towel wiping it down. And yeah, the housings for the springs were definitely square. One of them seemed firmly attached, the other seemed connected to nothing and just fell out.

Also I saw your post here with TS steps (a bit late). This is after the alternator was off the plane but still fully assembled... with my digital multimeter connected to field terminal and a ground spot the readings were all over the place as I slowly rotated the pulley apparatus.
From a minimum of about ~24 Ohms to a maximum of about ~150 Ohms as I rotated the alternator. It was never less than 24.
 
@Dan Thomas
Dan Thomas said:
Yup. Most likely the field brushes are shot.

I'm not convinced that your alternator is the source of all your problems, though. I think there will be more to the story.
Click to expand...
You're like an Oracle.

So the A&Ps wire up the new alternator, right? Getting ready to pick up the airplane. Guess what happens next... The VR no longer has any voltage at its field wire terminal. Best they can tell it's kaput. But they DO confirm the OV unit is behaving fine.

Fun fact... The field wire *DID* have voltage going to it the last time the plane was used (when I taxi'd over to the shop with the dead alternator, I still had the test leads hooked up showing field wire voltage).. Lo-and-behold, we install the new alternator and now the VR doesn't work lol.

600+ hours using the plane without a single electrical issue and then these two fail at the same time? Gotta be a correlation there lol.

Regardless, I'm glad it's Friday because I need a beer after all this.
 
If you decide to replace the VR, replace it and the OV relay with an all inclusive Zeftronics unit.

Aviation devices, sensors, alternators & regulators | Zeftronics

Zeftronics designs and builds protective sensors, alternators, regulators & general controllers for safer & more efficient aircrafts. Learn more here!
zeftronics.com zeftronics.com
 
Replaced alternator and voltage regulator, since both failed at around the same time, and haven't had an issue since.
 
ArrowFlyer86 said:
Back again to learn from the PoA brain trust :)

First, here's my ammeter gauge:
View attachment 129936

Normally it's at 35A upon start and fades to ~10A after <1min. Yesterday it stayed at 35A after startup; first time I've seen that. I decided to stay in the pattern and keep a close eye on it. After retracting gear on initial takeoff it settled back to 35A. Sometime in the next 60 seconds it dropped to zero. No breakers blown. I verified it wasn't a low reading: it was 0. Adding load did nothing to the instrument. Landed, taxi'd it back, stayed at 0 the whole time.

This morning I start it up - surprisingly it reads 35A and then fades to about 25-30A on my taxi over to the A&P. Better than yday but still high. I add/subtract load to verify the gauge is actually responding to load.

I explain the issue to my A&P before heading back to work. They started it then sent me a picture showing it's at normal levels.
View attachment 129937

The current working thesis by the A&P is that a stuck starter could be the cause. My starter is a freshly overhauled unit purchased 2 months ago. I believe my starter solenoid is factory original from 52y ago. A grounding issue is also flagged a potential culprit. We're checking the wiring to rule that out.

My questions to the electro-mechanically inclined:
(1) A stuck starter explains the high current draw, but I don't understand how that would cause the alternator to stop generating any power in flight without blowing a breaker?
(2) If it's a grounding issue, same question. I can see how it'd have a high current draw but I don't see how that could cause the alternator to stop generating any power in flight without blowing any breakers?
(3) Since no breakers popped during y'days flight. What could cause the alternator to start generating power again today? I know "turning it off then back on again" is a common fix for electronics.. But given the wiring diagram I'm not sure what would have "reset" btw yday and today?
Click to expand...
Is the battery more than 4yrs old? Test it for a shorted cell. Replace the starter solenoid, cheap and easy. How old is the voltage regulator? It controls the field circuit in the alternator.
 
I didn't really go through the entire thread but to me it sounds like wiring. I'd check all wiring and connections. I'd be sure ammeter, alternator and voltage regulator all have the same good ground reference if they need one. If there is a high resistance ground on any one of them, the voltage it outputs, regulates or monitors could be higher than the the others with weird results. Terminal connections that look normal that are poorly crimped and possibly filled with corrosion could do it too. Make sure there are no poorly done splices in the mix.
 
ArrowFlyer86 said:
Replaced alternator and voltage regulator, since both failed at around the same time, and haven't had an issue since.
Click to expand...
The above was posted BEFORE these two:
sansoneservices said:
Is the battery more than 4yrs old? Test it for a shorted cell. Replace the starter solenoid, cheap and easy. How old is the voltage regulator? It controls the field circuit in the alternator.
Click to expand...

kontiki said:
I didn't really go through the entire thread but to me it sounds like wiring. I'd check all wiring and connections. I'd be sure ammeter, alternator and voltage regulator all have the same good ground reference if they need one. If there is a high resistance ground on any one of them, the voltage it outputs, regulates or monitors could be higher than the the others with weird results. Terminal connections that look normal that are poorly crimped and possibly filled with corrosion could do it too. Make sure there are no poorly done splices in the mix.
Click to expand...
You really should read the thread.
 
Dan Thomas said:
The above was posted BEFORE these two:



You really should read the thread.
Click to expand...
Good point. Better answer is probably to pass by troubleshooting threads. I respond to technical support requests at an airline in my day job. Sometimes they are for troubleshooting. The system at work has a status field that lets everyone know if a matter is resolved or not.

Sometimes we see requests no one can figure out, and we have all the correct data and diagrams published for that aircraft. When I say no one, I mean Mx, Engineering, Airframe OEM and maybe even device manufacturer can't see it. So it becomes a long trial and error process with pages and pages of history in the request tool, airplane mx log, etc. On a Monday, I'll typically only look at a resolved issue if there is something unusual about it that might indicate a fleet wide issue or if it's good lessons learned subject matter.

There is a lot of good info in some of these threads on other types of questions. Troubleshooting without good diagrams for the subject airplane is rarely effective, even on a good day. Participation without knowing if it's been resolved is probably pointless.
 
Last edited:
kontiki said:
Troubleshooting without good diagrams for the subject airplane is rarely effective, even on a good day.
Click to expand...
I keep saying something similar. Look up the wiring diagram, understand it, and pinpoint the most likely problems that fit the symptoms. Most manuals even have troubleshooting charts to get you started, but of course they cannot cover every possible factor.

Too many folks just suggest replacing stuff. We already have too many mechanics who practice such methods, and it's expensive, ineffective and inefficient. The OEMs publish service manuals for our enlightenment.
 
Dan Thomas said:
I keep saying something similar. Look up the wiring diagram, understand it, and pinpoint the most likely problems that fit the symptoms. Most manuals even have troubleshooting charts to get you started, but of course they cannot cover every possible factor.

Too many folks just suggest replacing stuff. We already have too many mechanics who practice such methods, and it's expensive, ineffective and inefficient. The OEMs publish service manuals for our enlightenment.
Click to expand...
IMO there is no substitute for a trained eye just looking the aircraft over as a first step.

Walk into any bar and mention your car has low power and you will get 25 R&R and engine additive recommendations without anyone even looking under the hood and seeing that a connector came loose from a do-hickey on the engine.

I've seen pseudo logic schematics that describe the operation of a system at a very high level, for a black box generally as powerful as a desktop Mac. The whole team then goes down the rabbit hole, 3 shifts for a week before someone finds the real problem, completely unrelated to the type of fault suggested by the schematic.

I bet some AI tool given the right prompt could have come up with the majority of the suggestions in this thread.
 
You must log in or register to reply here.
Back
Top