C182 - Intermittent Alternator

I have a 1978 C182 Q. I recently experienced my alternator turning off and the
high voltage light coming on. I cycled the switch (1/2 master) and got it to
reset every time, however, the interval between episodes varied. I had the
Voltage Regulator and the Alternator replaced (new) and flew a couple of
flights since with no problem... until my last flight. Last flight it happened
again. The Alternator switched off and the high voltage light came on. I
cycled the switch and it reset.

What else is causing this? Is it a bad switch? Loose connection at the bus?

Has anyone else experienced this and what was your solution?

Any feedback is appreciated.

K C
PP ASEL IA
N759JB

WinstonCup wrote:

I have a 1978 C182 Q. I recently experienced my alternator turning off and the
high voltage light coming on. I cycled the switch (1/2 master) and got it to
reset every time, however, the interval between episodes varied. I had the
Voltage Regulator and the Alternator replaced (new) and flew a couple of
flights since with no problem... until my last flight. Last flight it happened
again. The Alternator switched off and the high voltage light came on. I
cycled the switch and it reset.

What else is causing this? Is it a bad switch? Loose connection at the bus?

I had loose ground connections under the panel and on the breaker buss...

Has anyone else experienced this and what was your solution?

Tighened the above and replaced the battery - it was weak and wouldn't
turn over the engine if it didn't crank almost immediately...

Any feedback is appreciated.

I'm good at that...

I have found several cases where the 60 amp alt breaker would get old
and tired and not "trip" but would cause an intermittent open. This
will spike the electrical system and cause a over voltage trip. Also
an old electrolytic cap across the over voltage relay input will not
filter out the normal buss spikes and cause a false trip.

Here are the top problem areas that I have seen:
#1 Bonding ground strap from the engine case to the airframe ,or
engine mount, has high resistance due to corrosion. (This one almost
killed me one day, and would have too if I had pulled the gear up
before the flaps on a go around.)
#2 Intermittent master switch or alternator switch half on
Cessna’s.
#3 Old dried out voltage spike suppresser capacitor across the over
voltage relay on Cessna’s.
#4 Stainless steel washer between the battery cable terminal and
the battery post. It is OK if it is under the wing nut but is not OK
if it is between the terminal and the battery post.
#5 Worn out high resistance 60 amp alternator circuit breaker.
#6 Loose connections to the amp meter or inside the amp meter or
both. Generally tightening the terminals will fix the problem.
#7 Worn out master relay.

There is a quick safe way to test the resistance of each connection
without the engine running and it only requires a 12 or 24 ohm 50 watt
or bigger power resistor and a digital volt meter. The method used is
called "Kelvin 4 wire resistance measurement" By using an
independent current source and voltmeter that can read voltages to at
least one millivolt , you can measure the milliohms in each connection
while you bang on , tap or move the wiring or part. This will
uncover many vibration induced problems in a controlled method. You
are now looking for millivolt CHANGES in voltage across the part as
the part is moved or the wiring is moved. What you do is induce
about a one amp current in the wiring chain that you want to test with
the aircraft’s battery and the 12 ohm (24 ohm for 24 volts) resistor.
One amp is used because it makes the math easy, one millivolt drop is
equal to one milliohm of resistance (V=IR). With the one amp
flowing through what you want to measure use the voltmeter to measure
the voltage across the part or wire segment. In this way you can
measure directly the resistance of each crimp connection for each
terminal and each connection of the terminal to the stud and also the
resistance of each wire segment or you can read the resistance or the
whole circuit that may contain several items in series. As an example
connect the resistor between the battery terminal of the alternator
and the alternator case and turn on the aircraft master power relay.
Measure the voltage from the alternator case to the engine, from the
engine to the airframe and from the airframe to the battery negative
terminal. Remember whatever voltage that you measure will be 50
times greater if you have a 50 amp alternator while the alternator is
fully charging. The power dissipated in each connection is the
resistance times the current squared. For 0.1 ohms at 50 amps the
power in the 0.1 ohm resistance would be 250 watts and the voltage
drop would be 5 volts.

As strange as it appears I found one cessna that kept tripping the
over voltage that was caused by someone who had clear coated the
alternator rear case half and the ground stud did not make good
contact from the alternator diode stack to the case at all times.
This allowed the suppression cap to charge up to 90 volts or more then
discharge to ground which induced a big voltage spike on the
alternator wiring.


John


On 10 Nov 2004 22:18:14 GMT, (WinstonCup) wrote:

I have a 1978 C182 Q. I recently experienced my alternator turning off and the
high voltage light coming on. I cycled the switch (1/2 master) and got it to
reset every time, however, the interval between episodes varied. I had the
Voltage Regulator and the Alternator replaced (new) and flew a couple of
flights since with no problem... until my last flight. Last flight it happened
again. The Alternator switched off and the high voltage light came on. I
cycled the switch and it reset.

What else is causing this? Is it a bad switch? Loose connection at the bus?

Has anyone else experienced this and what was your solution?

Any feedback is appreciated.

K C
PP ASEL IA
N759JB

Well, I can tell you what it usually is. I use to have a Cessna shop back
in Michigan and most of the time this was cause by the failure of the
overvoltage protection relay. In fact Cessna has a service letter on it
that requires you to place a capacitor in line with it because this relay
has a tendency to kick off too easily as it gets older. I don't recall what
year Cessna incorporated it into manufacturing but it was in the early 70's.

It shows up the way you described, occasionally at first and then more often
until finally you won't be able to recycle it back on. I had to replace one
on my 172 last year, same symptoms. It's located in the wire bundle behind
the CB panel on the pilots side on most models. A cylinder about 3-4 inches
long, 1 inch in diameter with 3 wires.

You can get them from Cessna or for less money under STC from Chief and
other suppliers. They're listed on their web site.

"WinstonCup" wrote in message
...
I have a 1978 C182 Q. I recently experienced my alternator turning off and
the
high voltage light coming on. I cycled the switch (1/2 master) and got it
to
reset every time, however, the interval between episodes varied. I had
the
Voltage Regulator and the Alternator replaced (new) and flew a couple of
flights since with no problem... until my last flight. Last flight it
happened
again. The Alternator switched off and the high voltage light came on. I
cycled the switch and it reset.

What else is causing this? Is it a bad switch? Loose connection at the
bus?

Has anyone else experienced this and what was your solution?

Any feedback is appreciated.

K C
PP ASEL IA
N759JB

"bill" wrote in message . com...
Well, I can tell you what it usually is. I use to have a Cessna shop back
in Michigan and most of the time this was cause by the failure of the
overvoltage protection relay. In fact Cessna has a service letter on it
that requires you to place a capacitor in line with it because this relay
has a tendency to kick off too easily as it gets older. I don't recall what
year Cessna incorporated it into manufacturing but it was in the early 70's.

It shows up the way you described, occasionally at first and then more often
until finally you won't be able to recycle it back on. I had to replace one
on my 172 last year, same symptoms. It's located in the wire bundle behind
the CB panel on the pilots side on most models. A cylinder about 3-4 inches
long, 1 inch in diameter with 3 wires.

You can get them from Cessna or for less money under STC from Chief and
other suppliers. They're listed on their web site.

A bad grounding of the ground lead from the overvoltage relay
can cause the same problem. They're often connected to the park brake
bracket, which gets pulled and flexed and thngs eventually come loose.

Dan

"WinstonCup" wrote in message
...
I have a 1978 C182 Q. I recently experienced my alternator turning off
and the
high voltage light coming on. I cycled the switch (1/2 master) and got it
to
reset every time, however, the interval between episodes varied. I had
the
Voltage Regulator and the Alternator replaced (new) and flew a couple of
flights since with no problem... until my last flight. Last flight it
happened
again. The Alternator switched off and the high voltage light came on. I
cycled the switch and it reset.

What else is causing this? Is it a bad switch? Loose connection at the
bus?

Has anyone else experienced this and what was your solution?

Any feedback is appreciated.


We had some problems in this area with our C210. There is EXCELLENT
diagnostic information readily available at www.zeftronics.com. (once you
figure out exactly which "type" you have). Our "main problem" was a failed
alternator (capacitor flopping around inside), but in the process we got rid
of a voltage drop across a circuit breaker connection and/or master switch
which had been causing our ammeter to "pulse" for as long as we've owned the
plane...

Good luck!
John Clonts
Temple, Texas
N7NZ

I, too, have just had the high voltage light coming on on my 1973 Cessna
172. Recycling the Batt half switch didn't reset the light.
So a mechanic is coming Saturday to check it out. I got my service manual
out and it said that the causes could be a defective overvoltage sensor, a
defective regulator, defective master switch, or associated wiring.
Doesn't necessarily mean the alternator is bad.
This happened to my C-182 back in the early 80s and it was due to a
defective stator wire in the alternator.
Tom Cummings
"John Clonts" wrote in message
...

"WinstonCup" wrote in message
...
I have a 1978 C182 Q. I recently experienced my alternator turning off
and the
high voltage light coming on. I cycled the switch (1/2 master) and got
it
to
reset every time, however, the interval between episodes varied. I had
the
Voltage Regulator and the Alternator replaced (new) and flew a couple of
flights since with no problem... until my last flight. Last flight it
happened
again. The Alternator switched off and the high voltage light came on.
I
cycled the switch and it reset.

What else is causing this? Is it a bad switch? Loose connection at the
bus?

Has anyone else experienced this and what was your solution?

Any feedback is appreciated.


We had some problems in this area with our C210. There is EXCELLENT
diagnostic information readily available at www.zeftronics.com. (once you
figure out exactly which "type" you have). Our "main problem" was a
failed
alternator (capacitor flopping around inside), but in the process we got
rid
of a voltage drop across a circuit breaker connection and/or master switch
which had been causing our ammeter to "pulse" for as long as we've owned
the
plane...

Good luck!
John Clonts
Temple, Texas
N7NZ

(WinstonCup) wrote in message ...
I have a 1978 C182 Q. I recently experienced my alternator turning off and the
high voltage light coming on. I cycled the switch (1/2 master) and got it to
reset every time, however, the interval between episodes varied. I had the

Sounds like it might be an overvoltage. The overvoltage spike will trigger
the OV protection locking the alternator off line till you cycle the switch.

Most common cause for ov is low battery water and corrosion in battery c
connections... ie, something that keeps the battery from holding the bus
against current spikes.

Bill Hale

"bill" wrote in message . com...
Well, I can tell you what it usually is. I use to have a Cessna shop back
in Michigan and most of the time this was cause by the failure of the
overvoltage protection relay. In fact Cessna has a service letter on it
that requires you to place a capacitor in line with it because this relay
has a tendency to kick off too easily as it gets older. I don't recall what
year Cessna incorporated it into manufacturing but it was in the early 70's.

............................................


I had the same thing happen on my C172M. Replaced the OV sensor with
a Zeftronics unit. The old one was tripping out at very little
overvoltage - like 15.5 V as I recall. I had to use a scope to figure
out what was happening.

John F (earlier post) is your next approach. He knows what he is
talking about.

THANKS TO ALL THAT POSTED!!!

I have printed each response and will take this with me to the service shop.

K C