Anomalous Ammeter Readings + Loss of Alternator

[Dan Thomas]

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.

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]

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.

Understood! And good to know...

 

[3393RP]

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

Ugh. Looks like the mismatched breaker came from a junk box. Electrically OK but not quality workmanship.

 

[ArrowFlyer86]

Ugh. Looks like the mismatched breaker came from a junk box. Electrically OK but not quality workmanship.

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.

 

[Ryan Klems]

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.

 

[mondtster]

Ugh. Looks like the mismatched breaker came from a junk box. Electrically OK but not quality workmanship.

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.

 

[ArrowFlyer86]

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.












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


The was a more intact.


I don't know why, but I expected those to be much bigger.

 

[Dan Thomas]

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.

 

[ArrowFlyer86]

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.

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.

 

[mondtster]

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

As far as I know, that’s the standard Chrysler brush setup.

 

[ArrowFlyer86]

@Dan Thomas

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.

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.

 

[Dan Thomas]

Regardless, I'm glad it's Friday because I need a beer after all this.

With your luck, there might be something wrong with the beer, too.

 

[Domenick]

If you decide to replace the VR, replace it and the OV relay with an all inclusive Zeftronics unit.

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