Voltage regulator contacts

I have a problem. Both of my voltage regulators seem to have failed
in an identical manner.

I have old-style three-relay regulators - one overvolt cutout, one
overamp cutout, and one contactor to connect the armature lead to the
bus. I can't replace these with solid state because none is available
- these are paralelling regulators, with a fourth tab that hooks into
a paralelling relay. I can't use them, either.

Seems that the contacts on the overvolt cutout have become degraded in
some way. Instead of essentially zero resistance (with closed
contacts) I'm seeing about 30 ohms. Cleaning the contacts with some
1000-grit sandpaper restores the zero resistance - and fixes the
generator problem, for a few minutes. Then the generators go offline
again, and upon testing, the resistance is back to where it was.

Anyone know a fix and/or the reason this happens?

Michael

(Michael) wrote in message . com...
I have a problem. Both of my voltage regulators seem to have failed
in an identical manner.

I have old-style three-relay regulators - one overvolt cutout, one
overamp cutout, and one contactor to connect the armature lead to the
bus. I can't replace these with solid state because none is available
- these are paralelling regulators, with a fourth tab that hooks into
a paralelling relay. I can't use them, either.

Seems that the contacts on the overvolt cutout have become degraded in
some way. Instead of essentially zero resistance (with closed
contacts) I'm seeing about 30 ohms. Cleaning the contacts with some
1000-grit sandpaper restores the zero resistance - and fixes the
generator problem, for a few minutes. Then the generators go offline
again, and upon testing, the resistance is back to where it was.

Anyone know a fix and/or the reason this happens?

Sounds like the silver is gone off the contacts. I wonder if a
bit of silver solder was applied and filed for contact profile?

Dan
Michael

Michael,

I had a problem on a 56 172 where the regulator went out after three months.
We found that on the master, there were a set of contacts for the field
circuit that were bad. Replaced the master switch and no more problems. May
or my not apply to you plane.

On my '65 Skyhawk, I was having lots of problems with regulator/alt. The
Cessna designed switch is terrible. Contact resistance is too high and
if you look at the switch inside you can see wear and contamination. A
good military DPST toggle would be a good choice.

Larryskydives wrote:

Michael,

I had a problem on a 56 172 where the regulator went out after three months.
We found that on the master, there were a set of contacts for the field
circuit that were bad. Replaced the master switch and no more problems. May
or my not apply to you plane.

--
Regards, Ross
C-172F 180HP

On a possibly related subject, the load meter on our '74 Archer develops St.
Vitus dance about 25% of the time. Battery seems to charge fine, and you
can't hear any noise in the headphones, but the meter just jumps up and down
a couple of time a second. No one can figure out what the problem is. The
shop boys say that they see it a lot in Cherokees, and that they have seen
replacing the master switch cure it. Any other ideas?

--
Bob (Chief Pilot, White Knuckle Airways)


"Ross Richardson" wrote in message
...
On my '65 Skyhawk, I was having lots of problems with regulator/alt. The
Cessna designed switch is terrible. Contact resistance is too high and
if you look at the switch inside you can see wear and contamination. A
good military DPST toggle would be a good choice.

Larryskydives wrote:

Michael,

I had a problem on a 56 172 where the regulator went out after three
months.
We found that on the master, there were a set of contacts for the field
circuit that were bad. Replaced the master switch and no more problems.
May
or my not apply to you plane.

--
Regards, Ross
C-172F 180HP

The master switch has two poles, one for the contactor which handles about a
quarter amp, and one for the alternator field circuit, which has to handle a
couple of amperes. The switch is not really suitable for high DC current
applications, so the contacts tend to burn with time. When they get old, you can
get fluctuations on the field circuit, which in turn causes the output current to
fluctuate. The ammeter in a cherokee is in-line with the alternator output.
Check your master switch's alternator side connection. It should be less than a
tenth of an ohm or so when closed. A bad ground on the regulator can also cause
similar problems. Check the ground path from the regulator case to the battery.
Be especially vigilant checking the riveted pieces, as oxidation under a rivet in
the ground path can cause the alternator output to fluctuate. You might try
running a separate ground wire from the regulator directly to the battery to see
if it eliminates it (use 16 ga or bigger). I'd bet it is one of the two. If
not, then check the circuit breaker to make sure it has low resistance. If not
there, then it could be the diode that is in series with the alternator on later
model Cherokees.

wrote:

On Tue, 3 Feb 2004 16:29:09 -0500, "Bob Chilcoat"
wrote:

On a possibly related subject, the load meter on our '74 Archer develops St.
Vitus dance about 25% of the time. Battery seems to charge fine, and you
can't hear any noise in the headphones, but the meter just jumps up and down
a couple of time a second. No one can figure out what the problem is. The
shop boys say that they see it a lot in Cherokees, and that they have seen
replacing the master switch cure it. Any other ideas?

I don't suppose you have Strobes or Beacon that flashes at twice per
second. Just a daft thought!

David

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email
http://www.andraka.com

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759

That is exactly what my ammeter was doing. Then one day, while the
engine was running, I reached to turn the master off. I noticed when I
touched it and rotated slightle side to side that I could make the
ammeter rock solid or dance, as you say. I had already cleaned every
point of contact that I could get to in the electrical circuit.

Bob Chilcoat wrote:

On a possibly related subject, the load meter on our '74 Archer develops St.
Vitus dance about 25% of the time. Battery seems to charge fine, and you
can't hear any noise in the headphones, but the meter just jumps up and down
a couple of time a second. No one can figure out what the problem is. The
shop boys say that they see it a lot in Cherokees, and that they have seen
replacing the master switch cure it. Any other ideas?

--
Bob (Chief Pilot, White Knuckle Airways)

"Ross Richardson" wrote in message
...
On my '65 Skyhawk, I was having lots of problems with regulator/alt. The
Cessna designed switch is terrible. Contact resistance is too high and
if you look at the switch inside you can see wear and contamination. A
good military DPST toggle would be a good choice.

Larryskydives wrote:

Michael,

I had a problem on a 56 172 where the regulator went out after three
months.
We found that on the master, there were a set of contacts for the field
circuit that were bad. Replaced the master switch and no more problems.
May
or my not apply to you plane.

--
Regards, Ross
C-172F 180HP

--
Regards, Ross
C-172F 180HP

On Tue, 3 Feb 2004 16:29:09 -0500, "Bob Chilcoat"
wrote:

On a possibly related subject, the load meter on our '74 Archer develops St.
Vitus dance about 25% of the time. Battery seems to charge fine, and you
can't hear any noise in the headphones, but the meter just jumps up and down
a couple of time a second. No one can figure out what the problem is. The
shop boys say that they see it a lot in Cherokees, and that they have seen
replacing the master switch cure it. Any other ideas?

Have you connected a to the bus while this is occuring? I bet the bus
voltage is oscillating too.

As others have suggested, a bad master switch can cause this problem.
Current flowing through the master switch cause it to heat. This
causes the contacts to deform, which breaks contact, which allows the
switch to cool, which then allows it to conduct again. Over and over
and over again.

You should get this fixed ASAP, it is definitely not good for the
charging or electrical system.

You might want to try pushing on master switch or on the panel cover
near the master switch to see if it 'amplifies' or fixes the problem.
This would confirm the need for replacement of the switch.

-Nathan

On Mon, 09 Feb 2004 23:53:10 GMT, Nathan Young
wrote:

On Tue, 3 Feb 2004 16:29:09 -0500, "Bob Chilcoat"
wrote:

On a possibly related subject, the load meter on our '74 Archer develops St.
Vitus dance about 25% of the time. Battery seems to charge fine, and you
can't hear any noise in the headphones, but the meter just jumps up and down
a couple of time a second. No one can figure out what the problem is. The
shop boys say that they see it a lot in Cherokees, and that they have seen
replacing the master switch cure it. Any other ideas?

Have you connected a to the bus while this is occuring? I bet the bus

^^^^^^^^^ Previous post should have said 'voltmeter'.

Ray Andraka wrote in message ...
The master switch has two poles, one for the contactor which handles about a
quarter amp, and one for the alternator field circuit, which has to handle a
couple of amperes. The switch is not really suitable for high DC current
applications, so the contacts tend to burn with time. When they get old, you can
get fluctuations on the field circuit, which in turn causes the output current to
fluctuate.

In most airplanes the alternator switch controls only a relay in the
regulator, not the field current itself. The relay connects the
voltage regulator relay to the "A" line, which runs to the alternator
output which in turn is connected to the aircraft's electrical system.
The small current required to run the relay might not be enough to
keep the master/field switch contacts burned clean, and the relay
contacts themselves can get worn.
The voltage regulator contacts can burn and start cutting out or
sticking shut intermittently, too.

A bad ground on the regulator can also cause
similar problems. Check the ground path from the regulator case to the battery.
Be especially vigilant checking the riveted pieces, as oxidation under a rivet in
the ground path can cause the alternator output to fluctuate. You might try
running a separate ground wire from the regulator directly to the battery to see
if it eliminates it (use 16 ga or bigger). I'd bet it is one of the two. If
not, then check the circuit breaker to make sure it has low resistance.

Bad grounds are certainly most likely. As our airplanes get older
and older, the oxidation begins to provide many hours of
entertainment.

Dan

wrote:

On Tue, 3 Feb 2004 16:29:09 -0500, "Bob Chilcoat"
wrote:

On a possibly related subject, the load meter on our '74 Archer develops St.
Vitus dance about 25% of the time. Battery seems to charge fine, and you
can't hear any noise in the headphones, but the meter just jumps up and down
a couple of time a second. No one can figure out what the problem is. The
shop boys say that they see it a lot in Cherokees, and that they have seen
replacing the master switch cure it. Any other ideas?

I don't suppose you have Strobes or Beacon that flashes at twice per
second. Just a daft thought!

David

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email
http://www.andraka.com

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759