"Martin Riddle" wrote in message
...

"Ian Field" wrote in message
...
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.


It doesn't matter what the Voltage/current ratio is, but all you'll get
out of it is 3W.
If you step it up to 12v you loose some efficiency in the conversion, so
you'll get ~85% of 3W.

FYI: I'm already getting more than 3W by using a voltage doubling bridge
rectifier, the 6V SLA prevents it from actually doubling the voltage but in
trying to do so it pushes a little more current than it was designed to.

You seem to have not understood what I meant by letting the generator output
voltage stretch its legs - I'm not talking about using a boost converter to
increase the voltage, I'm talking about reducing the current draw with a
buck converter so the output voltage rises due to less current draw.