alternator output

hi, all -

I'm working on a project... I've taken a '73 Honda CB350 and built a bit
of a cafe racer. I'd like to fit it with a modern headlight, with a
modern bulb... However, the alternator is only rated to output 100W max,
which I don't think will do it.

I'll want to ride with the headlight on all the time. And I'm not using a
battery.... kick or bump start only, using a "Bat-pac" which is basically
another regulator to give a nice steady voltage output.

So, here's the question: Is there any way I can get more power out of
this alternator? Could I rewind the stator? Replace the rotor with a
stronger magnet? Run a modern, external alternator off the front of the
engine where the starter was originally mounted?

Thanks for the ideas.

-Sean

 

I think Krusty alreay made the most fundamental point; you'll work hard
and pay dearly for any gains

The power obtainable from an electromagnetic machine is proportional
(roughly) to the amount of iron in the magnetic circuit and the freqency
of operation. Of course, it depends heavily on _how_well_ the iron and
speed are used, but they're the essential limits.

The first thing to do is look at the stator; if it's a multipole
ring like the one illustrated here:
http://www.electrexusa.com/electrex_stators.html
there won't be a huge amount of room for improvement.
If on the other hand the stator looks like the _lower_
illustration on this page:
http://www.electrexusa.com/electrex_LC_ENTER.html
you have considerable room for improvement.

To get more power out of an existing (well-designed) stator the steps
would be:

1. replace the windings with fewer turns of heavier wire. That will
give you more current, but require higher rpm to get usable voltage.
Tricks like using rectangular wire the packs tight in the stator
slots are helpful.

2. Increase the strength of the magnets. That will bring the rpm for
minimum usable voltage back down. There's only so much headroom here,
iron saturates. On a bike that old modern magnets might be an improvement,
however.

The notion of mounting a small automotive alternator (Nippondenso
makes a nice one) is appealing, but the mechanical problems look
intractable; the starter geartrain is not sized for continuous
operation, and you'll likely want the alternator to run at close
to crankshaft speed, not several times higher as the starer does.
It's a serious mechanical engineering project.

You're up against a tough problem.

If you're getting 100 watts out of a two-phase stator putting the
headlight on the AC side will help some, with a shut RR downstream
for regulation and battery charging. That will avoid some diode losses.

Good luck!

bob prohaska