OK, Thinking-Cap Time...

Jay Honeck wrote:
Of course, we have a new squawk shortly after coming out of the shop.
Perhaps someone here can point me in the right direction?

Alternator problem. Possibly a filter, but my guess is a diode is going bad.

3) The noise slows down -- or speeds up -- in synch with the prop RPM. At
2300 RPM, it's going a bit faster than once per second -- maybe around three
times every two seconds.

Alternator speed depends on engine speed.

5) Adding load to the system (landing lights, fuel pump, etc.) makes the
noise louder. Adding load to the system and then suddenly turning
everything off makes the noise and amperage oscillation go away -- for about
30 seconds. It then returns.

Adding load makes the alternator work harder. Cutting it all out lets it loaf
until the battery charge drops a bit, then the alternator has to work again.

George Patterson
If a tank is out of ammunition, what you have is a sixty ton portable
radio.

I'd say George is dead on. I also thought filter, but the fact that the
amps oscillate makes me think diode. I've never heard of a bad filter
causing an ammeter oscillation, the filters that have failed for me just
complain loudly.
Jim

Could it be a very loose alternator belt ? The symptoms don't all jib
though.

I third the thought. I have a capacitor filter across the output of the
alternator and ground. I have also cooked an alternator in the summer .
The fan on the back was not enough forced air for a high load when it is
hot. I added a blast tube form the front of the cowling to the "Blast
adapter" on the back on the Alternator. The hole in my cowling just
below the engine air intake is for the alternator. Works great. No more
over heating problems.
Michelle

George Patterson wrote:

Jay Honeck wrote:

Of course, we have a new squawk shortly after coming out of the shop.
Perhaps someone here can point me in the right direction?


Alternator problem. Possibly a filter, but my guess is a diode is
going bad.

3) The noise slows down -- or speeds up -- in synch with the prop
RPM. At 2300 RPM, it's going a bit faster than once per second --
maybe around three times every two seconds.


Alternator speed depends on engine speed.

5) Adding load to the system (landing lights, fuel pump, etc.) makes
the noise louder. Adding load to the system and then suddenly
turning everything off makes the noise and amperage oscillation go
away -- for about 30 seconds. It then returns.


Adding load makes the alternator work harder. Cutting it all out lets
it loaf until the battery charge drops a bit, then the alternator has
to work again.

George Patterson
If a tank is out of ammunition, what you have is a sixty ton
portable
radio.

"George Patterson" wrote in message
news:Q%7ff.60$N44.3@trndny08...
snip
Alternator problem. Possibly a filter, but my guess is a diode is going
bad.
snip

Diodes are solid state devices which either work, are open (most common
failure), or are shorted out (less common failure). They don't suffer from
"going bad" or "getting weak". They either work or they don't. If they are
intermittant, it's a connection, not the diode itself.

DB
(Many years of Electronics experience)

"Doodybutch" writes:



Diodes are solid state devices which either work, are open (most common
failure), or are shorted out (less common failure). They don't suffer from
"going bad" or "getting weak". They either work or they don't. If they are
intermittant, it's a connection, not the diode itself.


Well, maybe... I have had some larger power diodes whose *internal*
bonds would open when the diode got hot. When it cooled again, guess
what.

I also had a matrix of small-signal glass diodes that tested just
fine with an ohmmeter, but in operation.... turns out some would
"zener" when tested with the 12v that was used in the circuit.

But I really doubt that Jay's issue is alternator diodes....


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