On 3 Nov, 23:31, Andy Wade wrote:
Fred wrote:
If the unit is as you say a brushless unit it's unlikely to be self exciting
and therefore unlikely that any residual magnetism will be sufficient to for
the rotor voltage to overcome the forward diode drops. *If it's brushed then
it is more likely since brushes have very little forward drop.

The one I looked after was definitely self-excited. *The only battery
involved was for the engine starter motor.

I would have thought the AVR would have terminals for a battery for the
initial excitation? *Given that this is a 1980's alternator I doubt the
electronics at the time would have stretched to supplying 71V and 18A.

Did you read my description properly? *That level of voltage and current
are for the main alternator and the only 'electronics' involved is the
rectifier diodes built into the rotor. *The PWM o/p from the AVR was in
the same 16 V, 1.8 A range mentioned by the OP, and was handled by a
single TO3 power transistor - possibly an OC35(!) although I can't
remember for sure.

--
Andy

Hi there,

In fact I was not expecting so much information, having searched all
over for several months. I posted first in alt.electrical engineering.
I have not been back there either as I was disappointed by the lack of
interest.

Having read all these posts I am very motivated now. However this is a
big machine and I was planning to build it all on two heavy bits of
channel and make up the drive coupling to one of two Perkins P3
engines I have - or even sacrifice the 1.9 litre engine out of an old
Mondeo I am still using, but which has a limited expected life. This
is pretty efficient and most of all, - quiet, at this sort of speed.
However it is not something I can just Hook Up. I wanted to be fairly
sure that it could be made to work and was very disappointed when
Mawdsley told me that they had ditched all their historical data
during past reorganisations.

The technology is actually 1970,s but it is way ahead of the old car
regulator. I shall remove the covers to the exciter and take some
pictures. but it will take a few days. Watch this space. The
alternator was driven in line by a similar sized 3 phase motor
continuously, to provide a smooth supply to a medium sized ICL
computer installation. A Quick Start diesel Generator came up in a few
seconds in the event of a complete mains failure, but this set could
spin on with little drop in speed for this time. There was a lot of
rotating mass. It certainly worked, but the next generation was a big
UPS. Although I was the resident ICL Rep. I was the only one with
any technical training and so everything of this nature fell in my lap
by default. Even the old equipment that was taken out!

My sincere thanks to those who have helped, it has given me a whole
lot to investigate and the will to get started.

Many thanks, George Bell.