Sudden low voltage indication

Morgan3820

Morgan3820

En-Route
Joined
Jun 29, 2013
Messages
4,792
Location
New Bern, NC
Display Name
El Conquistador
Home Airfield
KEWN
Noticed taxiing for take off. 12.2v with no change in rpm. Along with RF buzzing in headset.
Ideas?
Hoping alternator brushes as that would be easy and cheap.
 
May be a failed diode, the battery will be in trouble soon.

See an A&P before there is harm to the battery.

If possible, connect a portable charger to the battery to bring it back up to normal charge, leaving partly discharged for days is very harmful.
 
Sudden? I'm not betting on alternator brushes. ACU / voltage regulator is my guess, but I'm just a knuckle dragger whose first thought is how big of a hammer to use on it.
 
sudden buzz in headset, points to diode failure in the bridge. 12.2v is indication of no alternator output. time for an overhaul im betting, but some investigation is in order before replacing parts.
 
I immediately put a charger on the battery.
Piper Arrow II fwiw
I had not thought of diodes.
I am glad this happened at home base.
 
For what it’s worth, I just replaced a set of brushes in an alternator that manifested itself in the exact same way you describe. I would not rule it out.

Regardless of the cause, you’re going to need to see a mechanic and let them diagnose the problem.
 
Dan Thomas said:
That alternator doesn't look good. Loose laminations in the core imply that the whole thing is falling apart. Black dust might be aluminum oxide from case fretting, or could be brush dust.
Click to expand...

... and the word CHRYSLER on it! :D
 
Dan Thomas said:
That alternator doesn't look good. Loose laminations in the core imply that the whole thing is falling apart. Black dust might be aluminum oxide from case fretting, or could be brush dust.
Click to expand...
Then, In for overhaul it is!
 
My ford alternator quit working last year on a Fri night about a 1/2 hour after dark. Luckily I was 15 miles from my home airport when I noticed it.
I called Aerotech Sat morning and they(man, don't remember his name, sorry) answered. Asked if he had rebuilt ones on the shelve, he said no but could rebuild one from a core that he had on the shelve Monday morning. I said great but had my doubts that he would do it Monday morning. I called again Monday 8;30 morning and talked with a lady who said he was in the back working on it. My wife was in Louisville antique shopping anticipating picking it up for me. I gave her our core. Aerotech called at 11 am saying it was ready for pickup! My wife was there by 11:30 and I had it bolted on our plane by 4:30 pm after work and flew it. Has been on the plane for over 300 hrs now has worked flawless so far. I plan to to have it checked out by them again at 500 hrs. It was less than 300 bucks, got to love 172s, so cheap to keep in the air.

MY AP lives 2 miles from the airport and is at my hangar whenever I call him for this kind of work. We work together regularly.

Aerotech was great to me as I was a nobody.
Old one.
(edited)_IMG_0191.JPG

Fresh one,
IMG_1110.JPG
 
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Also, while you're at it, have a look at your battery box and cables. The original setup used a flat braided ground and positive strap, less than robust when new, and can be problematic in a 40 year old bird. Bogert Aviation has cable replacements, mod kits, etc. if needed.
 
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