Hi Greg,

On 27-Sep-03, Greg Mayman wrote to Roy J. Tellason:

 RJT>> Before the vehicles I had that had this solid-state stuff I had
 RJT>> one that used a single-coil relay.  It was apparently supposed
 RJT>> to operate at a fairly high rate,  between two sets of contacts
 RJT>> or in between.

 GM> Yes, I still have one of those regulators. It was used on most DC
 GM> generators. An early form of pulse width modulation of the
 GM> generator field. I don't recall ever seeing it on alternators, but
 GM> it could have been used -- it would work just as well on a
 GM> rotating field as on a fixed one.

The early alternators all used vibrating contact regulators.
Electronics was just comeing in then, and rectifiers were one of the
first parts able to cope with the automotive environment.

 RJT>> The damn thing let my battery keep on running down until I bent
 RJT>> the tab that held the spring for that contact a bit,  forcing
 RJT>> the issue somewhat.  I can also remember earlier stuff yet,
 RJT>> going back to the sixties or thereabouts,  that had three coils
 RJT>> in there.

 GM> Yes, there was the "cutout" that connected the output of the
 GM> generator to the battery once the generator had reached a high
 GM> enough voltage. It had a second winding in series with the output
 GM> that was supposed to cancel out the field of the voltage winding
 GM> when the generator stopped and current flowed back into it. When
 GM> you think about it, a heavy duty diode would have done the job
 GM> almost as well, and a lot more reliably.

That was before diodes were reliable enough. The three coil systems
were for dynamos (you only need two on an alternator). They were:-
1) an isolator relay, to cut the dynamo off untill it produced
enough output.
2) a voltage regulator trembler relay.
3) a current limiter trembler relay.

Two coil regulators for dynamos used a current bucking coil on the
voltage regulator coil to limit the output current.

One thing to remember is that _all_ dynamos needed a current limiter
as they are not intrinisically self limiting.
Most alternators intrinsically self limit the current output, so all
that is needed is a voltage control. The only automotive alternators
that we built (I worked for CAV) that had current limiting in the
regulator were sealed marine and military versions where there was
none of the usual air cooling of the windings.


 GM> There was the second relay that was the voltage regulator that
 GM> "buzzed" at a fairly high rate to control the current in the
 GM> field. Sometimes this had a second current winding to limit the
 GM> output current, sometimes this was done with a third relay.

See above...



 RJT>> I don't think it's much heavier than that,  though I could find
 RJT>> out when I get my hands on those wiring diagrams.  And it's not
 RJT>> like it's carrying that current continuously.  The ammeter in
 RJT>> the truck is actually marked with a "40" at each
end,  and it's
 RJT>> *very* seldom I've ever seen it go the whole way over,  and then
 RJT>> only for a fairly short period of time.

 GM> Yes, that's right. The leads usually aren't very long as the
 GM> battery is usually near the alternator. And 5000A/squ.inch isn't
 GM> all that heavy, certainly not when that is only reached
 GM> occasionally.

The duty on most car batteries and the rating of the alternators is
such that for most people by the time they've pulled out the drive,
and certainly by the time they've reached the end of the street all
the power taken from the battery to start the engine has been
replaced, and that is about the only time the full alernator current
can go to the battery. In a modern car the alternator has a high
current rating to drive all the extra things in the car (windscreen
wipers, lights, heater/air conditoning fans, engine cooling fan,
heated screens, heated mirrors, heated seats, in car entertainment,
etc...), most of which only work when the enging is running anyway.

George

--- Terminate 5.00/Pro