Thanks for your replies.
The Midget is a '72 (chrome bumper, 1275cc) - I think they changed to
alternators within several months of my machine. The short term answer seems
to be avoiding traffic jams which allows me to keep the engine speed up and
hence the dynamo.
I found an article in Practical classics (March '93) which
described the dynamo/alternator swap for an A series engine so I'll probably
have a go over the Christmas break. The main problem is the difference in
shape between the two components, the alternator being a lot shorter and
slightly wider. The article solves this by using a long length of nut stock
between the dynamo mountings threading through the alternator mounting.
The smaller pulley wheel requires a smaller fan-belt and the higher current
output requires higher grade wire at the other end. Wiring changes are very
straightforward.
Fortunately, its easily reversible if originality becomes a concern (or the
alternator fails).
> Is there someone out there who can explain in layman's terms why an
> alternator is better than a generator for the battery? I have heard this
> stated before, and couldn't think of any reason... Thanks!! sf
A friend at work passed me a book explaining in great detail the workings
of alternators and dynamos. I won't go into the electrics but basically the
dynamo has a rotating inner core with windings in which current is generated.
This current is fed out as d.c. through brushes at the commutator. The friction
of the brushes and the weight of the inner core limit the maximum speed of the
generator. A consequence is that the generator speed at idle is insufficient to
drive many electrical devices.
An alternator has it windings in an outer fixed ring (stator) and the current
is generated in this stator. The internal core comprises magnets which rotate
to set up the fields. The a.c. current is rectified to d.c. through diodes.
The lighter weight of the internal core and the lack of brushes for
rectification allow the alternator to rotate up to three times faster than a
dynamo. Thus a smaller pulley wheel is used and it generates plenty of current
at idle speeds.
The dynamo also requires an external control box to regulate the voltage
output, while most alternators have internal regulation control.
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