Mooney Low Voltage

Can anybody help me diagnose this problem? Just bought my new (to me)
1978 Mooney 201, flew it back from Kansas City to Atlanta, no problem.
Flew to Richmond, VA - again no problem. Leaving RIC for Atlanta, the
low voltage light started flashing. Didn't want to carry on IFR so
stopped into Danville. Left the plane there, and the mechanic removed
the altinator and tested it (all ok) and replaced the voltage regulator
with a new one. All ok (charging 13.9 volts). Started the plane, the
altinator gauge was showing a charge, and took off. About 30 mins into
the flight again the low voltage started flashing. By the time I had
checked all the CB's it stopped. Then about an hour later it started
again. I tried pulling the Alt Field CB and resetting, no joy. It
continued to flash untill I was in the pattern at LZU.
So, now - what next? Bad Diodes on the Altinator breaking down at
altitude?(I was at 8000'), loose altinator belt? (unlikely - it had
just been reinstalled). Over voltage on the Altinator causing the
Voltage reg to drop off line, and I didn't wait long enough when I
reset the Alt-Field circuit breaker? Bad ground straps??
Any and all thoughts welcomed at this point - this is the worst kind of
problem to hunt down.
Thanks
Ian

wrote:

Any and all thoughts welcomed at this point - this is the worst kind of
problem to hunt down.

How old is the battery and is it marginal? ie. can you crank and crank
or do you have to get it right the first time...

Check all of your ground connections first. Disconnect them all and
clean them.
Diodes do not break down with altitude. They are sealed. They will break
down with heat. Once they break down they are dead. The do not fail
intermittently. The brushes may be an issue though. Is the Alternator
getting enough air? Mine overheated until I installed a blast tube.
Michelle

wrote:

Can anybody help me diagnose this problem? Just bought my new (to me)
1978 Mooney 201, flew it back from Kansas City to Atlanta, no problem.
Flew to Richmond, VA - again no problem. Leaving RIC for Atlanta, the
low voltage light started flashing. Didn't want to carry on IFR so
stopped into Danville. Left the plane there, and the mechanic removed
the altinator and tested it (all ok) and replaced the voltage regulator
with a new one. All ok (charging 13.9 volts). Started the plane, the
altinator gauge was showing a charge, and took off. About 30 mins into
the flight again the low voltage started flashing. By the time I had
checked all the CB's it stopped. Then about an hour later it started
again. I tried pulling the Alt Field CB and resetting, no joy. It
continued to flash untill I was in the pattern at LZU.
So, now - what next? Bad Diodes on the Altinator breaking down at
altitude?(I was at 8000'), loose altinator belt? (unlikely - it had
just been reinstalled). Over voltage on the Altinator causing the
Voltage reg to drop off line, and I didn't wait long enough when I
reset the Alt-Field circuit breaker? Bad ground straps??
Any and all thoughts welcomed at this point - this is the worst kind of
problem to hunt down.
Thanks
Ian

Battery is almost new (I believe it was replaced last year, or the year
before). It cranks just fine - I have never had any feeling that I was
running out of juice. Of course, the plane is starting first time!
According to the manual, the low volage would flash if the altinator is
not delivering a charge. That is what is leading me in that direction.

Battery is almost new (I believe it was replaced last year, or the year
before). It cranks just fine - I have never had any feeling that I was
running out of juice. Of course, the plane is starting first time!
According to the manual, the low volage would flash if the altinator is
not delivering a charge. That is what is leading me in that direction.

Thanks for that. Heat might be an issue - I had to crack the cowl flaps
open to keep the cyl head temps down yesterday - it was 10C at 8000'!
How did you install a blast tube?

wrote:

Any and all thoughts welcomed at this point - this is the worst kind of
problem to hunt down.

A few months ago the low voltage light started intermittently illuminating
on my Bonanza. Since the alternator was newly rebuilt and the battery new,
we suspected that the low voltage sensor itself was having a problem.

The mechanic found that the wire leading to the low voltage sensor (don't
recall which end of the wire, however) was loose.

--
Peter
























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Thanks! That was one possibilty I had not thought of.

Ian

SInce you mentioned an alternator belt. I am assuming it is a Lycoming
with the alternator up front.
My new alternator came with the blast attachment on the back of the
unit. We ran a 1" hose to the front of the cowling. A flange may be
necessary for your installation. Mine is attached under the air filter
housing. Just under the engine air intake.

Michelle

wrote:

Thanks for that. Heat might be an issue - I had to crack the cowl flaps
open to keep the cyl head temps down yesterday - it was 10C at 8000'!
How did you install a blast tube?

Michelle P writes:

Check all of your ground connections first. Disconnect them all and
clean them.

What the woman said. Grounds are the #1 cause of intermittent problems.

Also, how do you KNOW you have a problem; besides, that is. a flakey
LV warning? Put a DVM on the bus for a flight.



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