Greg Mayman wrote in a message to Roy J. Tellason:

 RJT> It would seem to me that at the high current levels (tens of amps)
 RJT> they're wasting a bunch of power as heat,  and the voltage being
 RJT> dropped a bit is also going to cause the charging rate to be just a
 RJT> little slower. 

 GM> I have seen these things in the past, but I can't remember what the
 GM> heatsinks were like, probably they were pretty big.

Last one I remember seeing (taken out of a vehicle -- it was defective) was
maybe 4 inches square,  3 inches high,  pretty big for just a couple of
diodes being on there.

 GM> Yes, I guess the charging rate would be slower.

 GM> And I've also wondered what the drop across the diode would do to
 GM> the regulator. Should it be set a bit higher than normal? No-one
 GM> I've spoken to about this seems to think it is necessary.

Actually I'd think it would.

 GM> OTOH someone once said the regulator should be connected to one of
 GM> the batteries AFTER the isolator diode.

Yes.  The regulator I'm familiar with (Mopar stuff) is grounded,  and only
has two other terminals,  one of which goes to the field winding.  I forget
if the other end is grounded or tied to ignition,  and where the other wire
from the regulator goes,  but it's pretty simple,  really.  Except for if
you get a bad ground,  which I had happen to me one time and which boild
out the battery in my truck,  before I caught it and cleaned things up.

The other terminal on the alternator is the output,  and that's where you'd
connect the isolator.  #10 wire,  as I recall.  So you'd need to insulate
that ring terminal somehow,  run a wire from it to one of the isolator's
outputs,  and run another one from the isolator to the stud terminal on the
alternator.

 RJT> I used to be able to acquire the occasional data book here and there, 
 RJT> but haven't in years now.  It's probably a good thing,  as the ones I
 RJT> do have take up a bunch of space now!  :-)  This stuff is also coming
 RJT> out on cdrom,  and may be downloadable as pdf files,  I haven't looked
 RJT> yet.

 GM> Theree is a lot of stuff on the 'net, but only very rarely do you 
 GM> find data for outdated devices. I suspect the same would apply to
 GM> CD-ROMs :-(

Oh,  I expect the data is out there somewhere...   :-)

 RJT> I'm thinking those part numbers are actually "2SK707"
and "2SK799", 
 RJT> that sound any better?

 GM> Could be. It sounds logical.

 GM> But I still don't have any data for those either.

 RJT> There were some of those parts that also seemed to have diodes across
 RJT> the gate-source connection,  though not all of them.  I've seen some of
 RJT> those parts that seem to have something of the sort built in,  too, 
 RJT> though I can't recall just why.  Maybe to prevent breakdown at the
 RJT> gate? 

 GM> Could be. Offhand I can't think of another reason. Were they zeners
 GM> or just ordinary diodes?

I don't know yet.  :-)

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