nuckolls.bob(at)aeroelect
Guest
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 Posted: Sat Nov 15, 2014 8:06 am Post subject: Charging system problem - please help troubleshoot |
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At 00:21 2014-11-15, you wrote:
| Quote: |
Cessna 182J with 60A alternator, mechanical regulator, no overvoltage circuit.
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1966 straight-tail 14V?
Really? I wasn't aware that any Cessna S.E. aircraft
were not fitted with ov protection in the field
relay excitation lead.
| Quote: | Alternator quit charging - shop found brushes totally worn, slip
rings out of round, and rear bearing noisy. Slip rings trued,
brushes replaced, bearing replaced. Bench and flight tested
OK. But on subsequent trip from Calif. to OSH, following problem
occured: about an hour into each leg static would appear in VHF and
ammeter would flicker rapidly between charge and discharge. Turned
off the alternator field with the split master switch, waited a few
minutes, then turned it back on. System resumed charging normally.
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This kinda smells like a worn-out switch on the
alternator-side of your split rocker. Has that
switch ever been replaced that you know of?
| Quote: | Replaced the regulator at OSH with a solid state unit by
Zeftronics. On way back to Calif. had similar problem, only this
time the system would simply stop charging, as evidenced by an alert
on the JPI engine analyzer that the system voltage had fallen into
the 12 volt range. As before, I could turn off the field, wait a
few minutes and then restore normal operation (13.9 volts) by
turning the field back on. It would seem something is
overheating. Diodes in alternator? Bad field switch contact? Bad
breaker? Bad capacitor?
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Assuming the alternator and regulator are
golden, then all you have left are the field
breaker, master switch, or intermediate wiring.
If the split-rocker has never been replace, I'd
put a new one in just on principal. Even if this
switch has not been stressed hard electrically,
A switch that is nearly 50 years old is a high
order suspect. Plus, it's an easy replacement
given its location in the airplane.
I'm curious as to the absence of o.v. protection.
I was working at Cessna Pawnee plant the year that
airplane was built and we were just starting to
understand this new-kid-on-the-block alternator.
It was just about that time that we experienced
a rash of mechanical regulator failures that
created some rather harsh ov conditions. I did
a design for the 'fire-cracker' ov protection
module that was added to the field control relay
on electro-mechanical regulators. These were not
'stock' until about 1970 but I was under the
impression that they go added to older models
as a service bulletin. I've got a meeting at
Textron next week, I'll get with my favorite
archivist and research the history of that mod.
In any case, I'd bet the odds are better than
50-50 that the split rocker is the problem.
If not, then ALL other wiring and joints are
not totally innocent until proven . . . field
circuit breaker too. Those were the lowest cost
device we could lay our hands on . . . and given
that the breaker has probalby not tripped even
once in 50 years gives rise to visions of corroded
contacts.
Just for grins, it might be useful to rig a
'heavy load' of a 20' or so of 20AWG wire.
Use this length to dead short that field
breaker and cause it to trip a half dozen
times or so . . . this might 'burn' off
corrosion and set things right in the universe.
Bob . . .
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