Cessna 210 charging problem

I am now able to reproduce my charging problem.

Engine off, Bat and Alt on:
Bus voltage: 24.8
Supply to Voltage Regulator: 22.6
Voltage Regulator Output to Alt Field: 21.6

I'm thinking maybe I should rig a jumper from Bus to the Voltage regulator
to see if the problem has to do with that 2.2v drop through the "Alt/Reg" 5A
circuit breaker, the Alt side of the master switch, and the Overvoltage
relay.

Any comments from you electrical gurus out there?

Can anyone tell me WHERE the overvoltage relay is mounted in my Cessna 210M
(1978)?

Thanks!
John Clonts
Temple, Texas
N7NZ

Most of the 24 volt Cessna's have the over voltage relay built into
the regulator. The over voltage protection has two stages. The first
stage turns off the field pass transistor. If the voltage still goes
higher the second stage turns on a crowbar SCR that blows an internal
5A fuse in the regulator.

From what you describe the alternator has field voltage (21.6) so it
should be generating current. With power off the field should measure
15-25 ohms. Your brushes may be worn out.

I had a problem a few years back where new brushes would not last 50
hours. I finally found that all of the replacement brush springs
were too stiff. There is two ways to fix this. Get the springs out
of a "OLD" junkyard alternator or cut a 1/4 inch off of the new
stiffer springs. I have no idea why the spring stiffness changed but
it is noticeable and measurable.

John

On Thu, 08 Jul 2004 03:53:23 GMT, "John Clonts"
wrote:

I am now able to reproduce my charging problem.

Engine off, Bat and Alt on:
Bus voltage: 24.8
Supply to Voltage Regulator: 22.6
Voltage Regulator Output to Alt Field: 21.6

I'm thinking maybe I should rig a jumper from Bus to the Voltage regulator
to see if the problem has to do with that 2.2v drop through the "Alt/Reg" 5A
circuit breaker, the Alt side of the master switch, and the Overvoltage
relay.

Any comments from you electrical gurus out there?

Can anyone tell me WHERE the overvoltage relay is mounted in my Cessna 210M
(1978)?

Thanks!
John Clonts
Temple, Texas
N7NZ

On Thu, 08 Jul 2004 03:53:23 GMT, "John Clonts"
wrote:

I am now able to reproduce my charging problem.

Engine off, Bat and Alt on:
Bus voltage: 24.8
Supply to Voltage Regulator: 22.6
Voltage Regulator Output to Alt Field: 21.6

I'm thinking maybe I should rig a jumper from Bus to the Voltage regulator
to see if the problem has to do with that 2.2v drop through the "Alt/Reg" 5A
circuit breaker, the Alt side of the master switch, and the Overvoltage
relay.

John, I didn't see your original charging problem, so cannot comment
on that, but will make a few general comments on this post.

21.6 Volts seems like a high field voltage to drive the alternator.
What kind of load was on the system during this measurement? I'm not
certain, but believe wih minimal load, the field voltage on my 14V
system was around 6-7V.

The 2.2V drop between the master bus and VR is not good and can lead
to several problems in the electrical system. I would fix this before
doing anything else.

#1. The bus voltage will be high. The VR will crank up the field
voltage until its input 'sees' 24V. Given a constant drop of 2.2V
between bus and VR, the bus will be at 26.2.

#2. If the resistance causing the 2.2V drop is caused by a bad CB,
switch, or loose/corroded connection before the OVR, the resistance
will vary depending on temperature and turbulence knocking the system
around. This will cause OVR cutouts as the OVR will occasionally see
the full bus voltage which is 24V + the voltage drop from a second ago
(26.2V or higher).

#3. Resistance between the master bus and the VR input sets up an RC
circuit which (when extreme) can cause charging system oscillation.

I like your idea of trying to eliminate the drop between the bus and
the VR input by direct connecting it to the bus. (Make sure to have
your avionics master OFF when doing this kind of troubleshooting!).

Another approach would be to measure the voltage after each of the
field CB, field switch, OVR, and VR input. This will probably tell
you where the drop is, and you can do this without the plane running.

BE EXTRA CAREFUL when probing around under the panel, it is easy to
short things with voltmeter probes.

-Nathan

(John) wrote in message ...
Most of the 24 volt Cessna's have the over voltage relay built into
the regulator. The over voltage protection has two stages. The first
stage turns off the field pass transistor. If the voltage still goes
higher the second stage turns on a crowbar SCR that blows an internal
5A fuse in the regulator.


I think mine is separate, per my comparison with the docs at
www.zeftronics.com. ("Type B" system using R25101 or R25102, not sure
which yet).

BUT I have not been able to find the OVR yet I assume its up under
the panel somewhere, but in that rats nest I can't find it. Can
anyone tell me which side? or high/low? Mounted or just hanging?
There are a few barrel-like connectors hanging around in there that
look about the same size is what I imagine the OVR to be.

From what you describe the alternator has field voltage (21.6) so it
should be generating current. With power off the field should measure
15-25 ohms. Your brushes may be worn out.

The field resistance was 18 ohms. I didn't try moving the prop to see
if it varied though-- I'll try that.


I had a problem a few years back where new brushes would not last 50
hours. I finally found that all of the replacement brush springs
were too stiff. There is two ways to fix this. Get the springs out
of a "OLD" junkyard alternator or cut a 1/4 inch off of the new
stiffer springs. I have no idea why the spring stiffness changed but
it is noticeable and measurable.


Wow. We DID replace our alternator just last August at annual time,
and it has about 50-75 hours on it since then...

Thanks for your input!

Cheers,
John Clonts
Temple, Texas
N7NZ

Nathan Young wrote in message . ..
On Thu, 08 Jul 2004 03:53:23 GMT, "John Clonts"
wrote:

I am now able to reproduce my charging problem.

Engine off, Bat and Alt on:
Bus voltage: 24.8
Supply to Voltage Regulator: 22.6
Voltage Regulator Output to Alt Field: 21.6

I'm thinking maybe I should rig a jumper from Bus to the Voltage regulator
to see if the problem has to do with that 2.2v drop through the "Alt/Reg" 5A
circuit breaker, the Alt side of the master switch, and the Overvoltage
relay.

John, I didn't see your original charging problem, so cannot comment
on that, but will make a few general comments on this post.

21.6 Volts seems like a high field voltage to drive the alternator.
What kind of load was on the system during this measurement? I'm not
certain, but believe wih minimal load, the field voltage on my 14V
system was around 6-7V.

This was with the engine off and no load to speak of. Maybe I will
try monitoring it as I add load, and see what it does.

The documents at www.zeftronics.com suggested that the VR field output
of "0.5-2.0v less than the VR input" was acceptable (22.6 - 21.6 =
1.0v)


The 2.2V drop between the master bus and VR is not good and can lead
to several problems in the electrical system. I would fix this before
doing anything else.

#1. The bus voltage will be high. The VR will crank up the field
voltage until its input 'sees' 24V. Given a constant drop of 2.2V
between bus and VR, the bus will be at 26.2.


Per your logic I think I would be seeing 30.2 instead of nominal 28.0
when the engine is running? I will check that.

#2. If the resistance causing the 2.2V drop is caused by a bad CB,
switch, or loose/corroded connection before the OVR, the resistance
will vary depending on temperature and turbulence knocking the system
around. This will cause OVR cutouts as the OVR will occasionally see
the full bus voltage which is 24V + the voltage drop from a second ago
(26.2V or higher).

#3. Resistance between the master bus and the VR input sets up an RC
circuit which (when extreme) can cause charging system oscillation.


I have noticed the ammeter bouncing slightly at about 4 per second
(when in the VR "control region") ever since we have owned the plane.
Maybe that was not acceptable?

I like your idea of trying to eliminate the drop between the bus and
the VR input by direct connecting it to the bus. (Make sure to have
your avionics master OFF when doing this kind of troubleshooting!).


Thanks, I thought of it myself but have since read of it elsewhere

Another approach would be to measure the voltage after each of the
field CB, field switch, OVR, and VR input. This will probably tell
you where the drop is, and you can do this without the plane running.


Yeah but aren't those buggers hard to get to? At least I have never
attempted it.

BE EXTRA CAREFUL when probing around under the panel, it is easy to
short things with voltmeter probes.


Ok, thanks for all the info!

Cheers,
John Clonts
Temple, Texas
N7NZ

If your regulator case is about 3" wide by 5" tall and 1" thick and
has a round plastic plug then it has a built in over voltage relay
function. This regulator also has remote voltage sensing for both the
positive and the ground. You need to check the resistance for both of
these sense wires.


I almost died once when a Cessna with this type of regulator developed
a high resistance ground fault. If I had pulled up the electric gear
before I sucked up the electric flaps I most likely would not be here
today. The NTSB report would have said "Pilot Error". There was not
enough juice left in the battery to suck up the gear and there was
not enough power to fly level with 30 degrees of flaps on the go
around. The regulator thought the battery was charged but the battery
was slowly discharging and the under voltage light was not on nor was
the amp meter showing a discharge either.

I would look to see where the excessive voltage drop is on the
regulator power. Measure across each connection with a DVM.
You also need to check the fat ground braid between the engine case
and the motor mount frame for high resistance.
0.05 ohms will give you a 2.5 volt drop at 50 amps.
You need to get the service manual for the aircraft to check the
wiring correctly. Cessna sells the manuals for about the cost of one
gas tank fill up.

John

On 8 Jul 2004 11:54:28 -0700, (John Clonts) wrote:

(John) wrote in message ...
Most of the 24 volt Cessna's have the over voltage relay built into
the regulator. The over voltage protection has two stages. The first
stage turns off the field pass transistor. If the voltage still goes
higher the second stage turns on a crowbar SCR that blows an internal
5A fuse in the regulator.


I think mine is separate, per my comparison with the docs at
www.zeftronics.com. ("Type B" system using R25101 or R25102, not sure
which yet).

BUT I have not been able to find the OVR yet I assume its up under
the panel somewhere, but in that rats nest I can't find it. Can
anyone tell me which side? or high/low? Mounted or just hanging?
There are a few barrel-like connectors hanging around in there that
look about the same size is what I imagine the OVR to be.

From what you describe the alternator has field voltage (21.6) so it
should be generating current. With power off the field should measure
15-25 ohms. Your brushes may be worn out.

The field resistance was 18 ohms. I didn't try moving the prop to see
if it varied though-- I'll try that.


I had a problem a few years back where new brushes would not last 50
hours. I finally found that all of the replacement brush springs
were too stiff. There is two ways to fix this. Get the springs out
of a "OLD" junkyard alternator or cut a 1/4 inch off of the new
stiffer springs. I have no idea why the spring stiffness changed but
it is noticeable and measurable.


Wow. We DID replace our alternator just last August at annual time,
and it has about 50-75 hours on it since then...

Thanks for your input!

Cheers,
John Clonts
Temple, Texas
N7NZ

On 8 Jul 2004 12:06:26 -0700, (John Clonts) wrote:

Nathan Young wrote in message . ..
On Thu, 08 Jul 2004 03:53:23 GMT, "John Clonts"
wrote:

I am now able to reproduce my charging problem.

Engine off, Bat and Alt on:
Bus voltage: 24.8
Supply to Voltage Regulator: 22.6
Voltage Regulator Output to Alt Field: 21.6

I'm thinking maybe I should rig a jumper from Bus to the Voltage regulator
to see if the problem has to do with that 2.2v drop through the "Alt/Reg" 5A
circuit breaker, the Alt side of the master switch, and the Overvoltage
relay.

John, I didn't see your original charging problem, so cannot comment
on that, but will make a few general comments on this post.

21.6 Volts seems like a high field voltage to drive the alternator.
What kind of load was on the system during this measurement? I'm not
certain, but believe wih minimal load, the field voltage on my 14V
system was around 6-7V.

This was with the engine off and no load to speak of. Maybe I will
try monitoring it as I add load, and see what it does.

The documents at www.zeftronics.com suggested that the VR field output
of "0.5-2.0v less than the VR input" was acceptable (22.6 - 21.6 =
1.0v)


The 2.2V drop between the master bus and VR is not good and can lead
to several problems in the electrical system. I would fix this before
doing anything else.

#1. The bus voltage will be high. The VR will crank up the field
voltage until its input 'sees' 24V. Given a constant drop of 2.2V
between bus and VR, the bus will be at 26.2.


Per your logic I think I would be seeing 30.2 instead of nominal 28.0
when the engine is running? I will check that.

Crap. My bad John, 30.2 is correct. I was thinking nominal voltage
of 24, not 28.

Based upon this...

I suspect the 210 has 2 problems.

#1. You probably have a bad alternator. As long as the pulley isn't
slipping, I believe 21V field voltage would be sufficient to drive 28V
output.

#2. You still need to resolve the 2.2V drop between the bus and the
VR input. The aforementioned RC behavior could definitely cause the
pulsating ammeter you've seen. Also another cause for pulsating
ammeter is a faulty field master switch. The contacts heat up,
expand, break contact, cool down, make contact and start the cycle
over again.

-Nathan

"John Clonts" writes:

I am now able to reproduce my charging problem.

Engine off, Bat and Alt on:
Bus voltage: 24.8
Supply to Voltage Regulator: 22.6
Voltage Regulator Output to Alt Field: 21.6

I'm thinking maybe I should rig a jumper from Bus to the Voltage regulator
to see if the problem has to do with that 2.2v drop through the "Alt/Reg" 5A
circuit breaker, the Alt side of the master switch, and the Overvoltage
relay.

Any comments from you electrical gurus out there?

Those readings sounds almost OK to me....

a) I'm assuming the bottom end of the field is grounded.

b) With the engine NOT running, the voltage regulator keeps
thinking "More power, Scotty" and raises the field voltage
as far as it can. The 1 v. drop across the VR sounds fine
to me.

c) The 2v drop from the bus to the VR-in is bothersome. You can
find such 2 or 3 ways. [Or rather, if it was legal for you to...]

1) Using a DVM, put one probe on the bus, and the other on the VR
input. Set to 2v fullscale. Still see a drop that big? Leave the
one probe on the bus, and move the other one one step upstream. Is
that a fuse/breaker? Iterate until you see what point has the drop.

2) Leave it on for a while and then FEEL for the hot connection.
But see 3)....

3) If the other poster is correct, the field resistance is ~~15 ohms,
vs the ~3 ohms of an auto 50A/13.8 volt alternator. That means the
max field current is ~1.8 amps. That feels low, but I've not worked
on a 28VDC system in decades, and then it was not the alternator..





--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

Filter/Condenser/Capacitor screw had come loose and was bouncing around
inside of alternator (Electrosystems 3eff10300aa, less than a year old!).
Unfortunately it took some diodes and the stator coil with it. Replaced
alternator. Bus voltage was somewhat high. Cleaned connectors on master
switch and plug to voltage regulator, which solved the high bus voltage AND
the "bouncing ammeter needle/flickering panel lighting" problems.

Thanks to Pete Weston at Gatesville (KGOP) for the assistance!

Cheers,
John Clonts
Temple, Texas
N7NZ


"John" wrote in message
.
Most of the 24 volt Cessna's have the over voltage relay built into
the regulator. The over voltage protection has two stages. The first
stage turns off the field pass transistor. If the voltage still goes
higher the second stage turns on a crowbar SCR that blows an internal
5A fuse in the regulator.

From what you describe the alternator has field voltage (21.6) so it
should be generating current. With power off the field should measure
15-25 ohms. Your brushes may be worn out.

I had a problem a few years back where new brushes would not last 50
hours. I finally found that all of the replacement brush springs
were too stiff. There is two ways to fix this. Get the springs out
of a "OLD" junkyard alternator or cut a 1/4 inch off of the new
stiffer springs. I have no idea why the spring stiffness changed but
it is noticeable and measurable.

John

On Thu, 08 Jul 2004 03:53:23 GMT, "John Clonts"
wrote:

I am now able to reproduce my charging problem.

Engine off, Bat and Alt on:
Bus voltage: 24.8
Supply to Voltage Regulator: 22.6
Voltage Regulator Output to Alt Field: 21.6

I'm thinking maybe I should rig a jumper from Bus to the Voltage
regulator
to see if the problem has to do with that 2.2v drop through the "Alt/Reg"
5A
circuit breaker, the Alt side of the master switch, and the Overvoltage
relay.

Any comments from you electrical gurus out there?

Can anyone tell me WHERE the overvoltage relay is mounted in my Cessna
210M
(1978)?

Thanks!
John Clonts
Temple, Texas
N7NZ

Nathan Young wrote in message . ..
On Thu, 08 Jul 2004 03:53:23 GMT, "John Clonts"
wrote:

I am now able to reproduce my charging problem.

Engine off, Bat and Alt on:
Bus voltage: 24.8
Supply to Voltage Regulator: 22.6
Voltage Regulator Output to Alt Field: 21.6

I'm thinking maybe I should rig a jumper from Bus to the Voltage regulator
to see if the problem has to do with that 2.2v drop through the "Alt/Reg" 5A
circuit breaker, the Alt side of the master switch, and the Overvoltage
relay.

John, I didn't see your original charging problem, so cannot comment
on that, but will make a few general comments on this post.

21.6 Volts seems like a high field voltage to drive the alternator.
What kind of load was on the system during this measurement? I'm not
certain, but believe wih minimal load, the field voltage on my 14V
system was around 6-7V.

The 2.2V drop between the master bus and VR is not good and can lead
to several problems in the electrical system. I would fix this before
doing anything else.

#1. The bus voltage will be high. The VR will crank up the field
voltage until its input 'sees' 24V. Given a constant drop of 2.2V
between bus and VR, the bus will be at 26.2.

#2. If the resistance causing the 2.2V drop is caused by a bad CB,
switch, or loose/corroded connection before the OVR, the resistance
will vary depending on temperature and turbulence knocking the system
around. This will cause OVR cutouts as the OVR will occasionally see
the full bus voltage which is 24V + the voltage drop from a second ago
(26.2V or higher).

#3. Resistance between the master bus and the VR input sets up an RC
circuit which (when extreme) can cause charging system oscillation.

I like your idea of trying to eliminate the drop between the bus and
the VR input by direct connecting it to the bus. (Make sure to have
your avionics master OFF when doing this kind of troubleshooting!).

Another approach would be to measure the voltage after each of the
field CB, field switch, OVR, and VR input. This will probably tell
you where the drop is, and you can do this without the plane running.

BE EXTRA CAREFUL when probing around under the panel, it is easy to
short things with voltmeter probes.

-Nathan


Nathan,

As posted elsewhere I did finally solve the problem. The main problem
was the filter capacitor inside the alternator had come loose and was
bouncing around in there. Explained my intermittent charging, and
then eventually it wiped out the alternator completely.

After replacing the alternator the bus voltage was higher than
desired, but we were expecting this. We jumpered from +bat to the VR
input as described above, and the voltage came down-- confirming the
resistance problem. We cleaned the connections on the master switch
and on a connector to the VR itself. That solved the high bus voltage
problem.

It also eliminated my "bouncing ammeter/flickering panel lights",
which had been that way ever since we got the plane so I didn't even
think it WAS a problem!

Thanks for everyone's input-- it's been a great learning experience!

Cheers,
John Clonts
Temple, Texas
N7NZ