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.

<Snip>
Check out the web page http://www.geocities.com/TimRV6A/alternator.htm which
contains photographs that show the entire process of modifying the
alternator

 
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