On Wed, 18 Jan 2012 15:45:52 -0500, "P E Schoen"
wrote:
"Tom Del Rosso" wrote in message ...
Oh, and I'm curious about this dynamo vs alternator issue. Some people
have said these things generate AC. If none of us have tested one,
maybe we should assume the worst.
Is that the only reason you oppose the use of a transformer? You might
have said so with less fuss.
Assuming the worst, I'd think to use a full wave bridge and no
transformer.
I, too, am unsure whether hub dynamos produce AC or DC. Larkin's design with
the transformer assumes AC, while Thompson's assumes DC.
Dynamo outputs AC, DC is required to charge a battery.
If his "model"
includes diodes, then their specifications become very important to overall
efficiency, since two diode drops may constitute 1/4 of the voltage. If the
hub dynamo is a true alternator, then AFAIK it would contain diodes (as in
an automotive alternator), and would very likely use three (or six) phase.
But according to the following, the output IS AC, and it must be single
phase if there are only two terminals:
http://www.nscl.msu.edu/~daniel/sreg.htm
As I've already stated, the CONCEPT works, efficiency can be brought
up in several ways.
Perhaps even greater efficiency may be obtained by using a voltage doubler
consisting of two Schottky diodes and two capacitors. If the dynamo outputs
6 VAC then the doubler should produce about 16 VDC. However, the performance
at low speeds would depend on the frequency of the AC and the size of the
capacitors. The autotransformer is also subject to low frequency limitation,
and in fact may present a heavy load when it saturates at low frequency,
although not if the AC output is proportional to speed.
The limitation is the dynamo characteristics. I tried
auto-transformers up to 100H inductance.
Besides, the output, according to Larkin is a CURRENT... not quite,
but almost.
[snip]
...Jim Thompson
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