Message-Id: <5.1.1.5.2.20040615135400.02454890@localhost>
Date: Tue, 15 Jun 2004 14:04:07 -0500
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
From: Mark Steitle <msteitle@mail.utexas.edu>
Subject: Re: [FlyRotary] Re: Small alternator?
In-Reply-To: <list-163663@logan.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 11:34 AM 6/15/2004 -0700, you wrote:

>Hi Mark;
>   I'm looking for an alternator also. would appreciate
>your external alternator wiring info.
>                      Thanks John Overman
>                             Velocity RG
>                             13B Turbo
>                             Washington State
John,
Here you go...

=============================================
Bob N. strongly recommends using externally regulated alternators only, or
modifying the internal regulator models so as to allow it to be shut down
if necessary. (Supposedly, a voltage run-away can happen in a few seconds.)
Problem is that the articles I read explaining how to convert the
internally regulated alternators to external regulation didn't work. (Did I
do something wrong?) I think I have worked out a simpler solution. The
objective here is to isolate the field windings from the diode bridge so
that the alternator can then be externally controlled.

This is how I went about converting my alternators. First I removed the
back cover, exposing the diode bridge, regulator assy. and brush holder.
Then removed the regulator and brush holder and threw the regulator assy in
the trash.

Next I removed the brush holder and shaped a little brace from
1/8" phenolic that will support one side of the brush holder and isolate it
from the diode bridge. This piece will be about 7/8" x 1/4" with a #8 hole
in each end. Do not make this piece out of metal or it will short out the
diode bridge. Also make up a jumper wire about three inches long with a
ring terminal on each end. One end will attach to the right terminal on the
brush holder and the other will attach to the alternator case (gnd.).
The other terminal on the brush holder will need a spacer under it to keep
everything aligned properly.

The left brush will need to have the lead wire
un-soldered from the brush holder. The wire comes through the back of the
brush holder. Unsolder it there and drill out the hole just a bit to allow
a #20 wire with shrink tube to fit snugly through the hole. Solder the #20
wire to the end of the braided wire on the brush.

Now we're ready to reassemble the whole thing. Pass the #20 wire through
the hole drilled in the brush holder and reinsert the spring and brush.
Screw the brush holder back into place, with a spacer washer under the left
terminal. The ground wire goes on the opposite terminal. Feed the wire
soldered to the brush through a hole in the alternator cover, with a
grommet to prevent chaffing. This wire will go to the "F" terminal of the
external voltage regulator. I used a generic Ford unit from a mid-seventies
model (approx. $10/ea from Auto Zone). The S & A terminals of the regulator
tie together and get fed from the alt. switch & 5 amp breaker. The "B"
terminal on the alternator goes to the battery contactor. The other
terminal on the regulator isn't used.

I modified two ND alternators using this method and they both work great.
It takes about 30 minutes to do the modifications. All I need to do now is
add a crowbar over-voltage protector to each regulator and I'm set to go.
Or you can use a B&C voltage regulator with built-in OVP and low-voltage
warning.

_-========================================================================