While at it, I made the mod to my Mitsubishi alternator per Paul
Messinger's article in Contact! Issue 46. I took the simpler route;
use
the built in voltage regulator, but break the connection to the
internal
field supply so I can use external over-voltage protection. I'm sure
the external, linear regulator with OV protection is the ultimate, but
at $228 (Aeroelectric Connection) not worth it. Main issue is to
remove
the potential for runaway voltage failure (however remote) that could
do
serious damage to the electrical system. The surgery on the
alternator
was relatively simple - I'd be happy to detail the experience further
for anyone interested. alventures@msn.com
Al Gietzen
I am interested Al
Paul Lamar
Ed Andersen wrote:
Al, I would be interested in the how you modified your internal voltage
regulator. While I have a Bosch remanufacture alternator, I think they
are similar in that aspect. I had long thought that pulling my 5 amp
field coil CB would kill the voltage, but found out it only prevents the
alternator from functioning if pulled before start up. Once started,
pulling the circuit breaker did not kill the output.
Ed
I'll refer you first to Paul M's article- Contact!, Issue #46 Sept-Oct
1998. He goes into much more detail and covers both Nippon Denso and
Mitsubishi alternators. I can Fax a copy to you if you'd like to give
me a fax number. The procedure below should get you through the mod I
made.
In summary - Auto alternators with internal voltage regulators generally
provide power to the regulator and the field coil internally from the
rectified output from the alternator. These are square-wave switching
type regulators that regulate required current output by high frequency
on-off switching of the current to the field windings. Potential
regulator failures can result in reduced voltage output, no output, or
full rated current output from the alternator, and potentially high
voltage. The first two types have us flying to a nearby airport (or
home) on battery power to make repairs. Although rare, the third type
of failure can have serious consequences to electrical system components
within seconds of the failure; too soon for pilot action.
The way to prevent this over voltage (OV) possibility is to provide an
external source of regulator and field power, generally switched by your
alternator switch, and which includes a so-called "crow-bar" OV
protection circuit which immediately opens the circuit to the regulator
and field coils. Of course you then have to disconnect the internal
source.
I did this on my Mitsubishi alternator; a 65 or 70 amp rated Bosch
rebuild. It is externally different than the 50-55 amp units that P.M.
discusses because the mounting points are in a different rotational
position, and the Battery "B" terminal comes directly out of the
rectifier bank; but they are otherwise the same.
The procedure is to remove the pulley, remove the three bolts that hold
the case together, and slip the front half of the case off the shaft.
Leave the field windings in the rear half, and remove the armature. The
slip-rings and back bearing come out with it, and it may take a little
persuasion, but proceed with some care. Slight prying with a screwdriver
carefully inserted through the slots in the case should do it.
When you look into the back of the case you will see the carbon brushes
now protruding into the space where the slip rings were. These are
spring loaded and will obviously have to be held back in place if you
are going to get this back together. Don't worry, simple means are
provided. If you'll orient the case so the brushes are protruding from
the top; the regulator unit is at the top right, and the bank of output
rectifiers are at the bottom. The connection that you want to sever is
the one just above the screw on the bottom right.
It is a soldered connection. The connection hiding in the solder is a
small tab extending down from the regulator that nests into a wider
"dished" tab extending from the rectifier bank. Use any method you want
to cut the connection without damaging anything. What worked well for
me was to loosen the screws a few turns that hold the brushes/regulator
unit (depending on the model, one of these may be the B terminal bolt
that extends out the back of the case). This allows some movement of
the regulator so you can apply some pressure to it through the slot in
the back of the case while you place the tip of your soldering iron on
the soldered connection. As soon as the solder melts, the connection
will pop apart. You don't want to apply too much heat for too long near
the rectifiers.
Now take the loosened screws completely out and remove the
brushes/regulator unit. Snip off the connecting tab. Now is a good
time to retract the brushes for reassembly. You'll notice there is a
small hole through the brushes, and through their holder, and through
the back of the case. Retract the brushes and put short length of stiff
wire (a 1/16 drill bit worked nicely) through the hole, extending out
the back of the brush holder. Re-install the brush/regulator unit
carefully placing the wire (drill bit) through the hole in the case.
Put the armature back in place, remove the wire (drill bit), re-assemble
the case; etc, etc..
The two spade terminals on the back (which may or may not be labeled "L"
and "IG" for idiot light and ignition switch) will now be connected in
common to your OV protected +12 power circuit, which will come off about
a 10 amp breaker, and through your ""alternator" switch. This will
power the regulator and the field windings. You will no longer have an
idiot light connection so have some other means for detecting low
voltage. Have a large (100 amp) fuse in the battery "B" terminal
circuit, and make sure that the alternator case is well grounded to the
negative side of the battery because it is the other side of this
potentially high current circuit. Bob Nuckols (Aeroelectric Connection)
sells an OV protection circuit for $35.
If you want to go a step further to an external, linear (non-switching)
regulator, some further modification can be done when you have the
regulator removed. Refer to P.M.'s article for that.
Sorry, I didn't take any photos, and the ones in the Contact! Article
are very poor quality.
Al Gietzen