On Sun, 04 Dec 2011 09:23:12 -0700, Jim Thompson
wrote:

On Wed, 30 Nov 2011 13:09:54 -0700, Jim Thompson
wrote:

On Sun, 27 Nov 2011 14:56:00 -0000, "Ian Field"
wrote:

Tinkering with the old Sturmey archer bicycle dynamo, I was wondering
whether it would charge a 1.2Ah SLA any better if the loading was modified.

The generator is rated 6V/3W, but off load at a decent rate of knots it can
produce over a couple of hundred volts.

What I was wondering was whether its possible to get more energy into the
battery by letting the generator output voltage stretch its legs so to speak
and convert the excessive voltage down with a buck converter.

Can anyone advise on the practicality of this please?

Thanks.


Bwahahahahaha! So this was the original post? Bwahahahahaha!

...Jim Thompson

Perhaps Larkin would be happy to address Ian's question, "What I was
wondering was whether its possible to get more energy into the battery
by letting the generator output voltage stretch its legs so to speak
and convert the excessive voltage down with a buck converter"?


Very likely so. It's a simple impedance matching issue. The alternator
was designed to power an incandescent load at roughly constant
current, so will probably generate more that its rated 3 watts into a
higher impedance load, certainly into a conjugate load. A source that
has a loaded output voltage of 6, and an open-circuit voltage in the
hundreds, is not operating at its maximum-power-transfer point/

A transformer+rectifier would probably work, too. What Ian should do
is chuck the alternator into a vise, spin it with a drill motor, and
measure the voltage and impedance at various speeds. That would be
interesting. Of course, extracting more power will require more
mechanical input, ie pedaling harder. It would be interesting to
measure torque, too. All that could be done in an hour or so, and
would be fun.

But don't let me disturb your clucking with electrical theory.


I'm in need of another laugh.

On a more serious note, would some young buck (that excludes us
venerable professor-level types :-)

Of course you exclude yourself. If you ever understood this stuff,
you've clearly forgotten it.

care to analyze the problem with
Ian's proposition?

Extra brownie points if you can make Larkin froth incoherent ;-)


Say something substantive. The only things you have suggested in this
thread so far have been off-topic or flat wrong. Silly old hen.

John