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