Re: Help my neighbour's kid with his school project...

In <80a29458-5186-404c-b275-3f6347ef9d42@xxxxxxxxxxxxxxxxxxxxxxxxxxx>,
J.A. Legris wrote:
On Feb 17, 1:34 pm, _ <jtayNOSPAM...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx wrote:
On Sat, 16 Feb 2008 18:27:57 -0800 (PST), J.A. Legris wrote:
On 2/13 8:50 pm, _ <jtayNOSPAM...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx wrote:
He's making a model of a tidal generation plant.  The crucial bit
for which he asked me for help is this:

<<In short, makes 300 millivolts from a PM motor being used as a
generator>>

Sadly, output from a PM motor being used as a generator is DC. 300
millivolts DC has low opportunities for doing much of anything with
electronics.

If whoever needs to make use of such low voltage DC has access to
germanium transistors, then I would advise doing web searching (Google or
the like) for boost converters used with solar cells and using germanium
transistors. Sadly here, geranium semiconductors are a lot more obsolete
than putting solar cells in series for more voltage.

If the PM motor has its DC output unsteady enough, then it could be fed
into a neon sign transformer, and the output from the neon sign
transformer can go through a bridge rectifier (maybe preferably made of
Schottky diodes) to feed an LED that is efficient at low currents - such
as many blue, blue-green and non-yellowish-green ones with nominal
wavelength 468 to 529 nm and nominal voltage drop 3.1 to 3.6 volts.
Also with characterizing current (current used for most data***
figures) no more than 20 mA!

Beyond that, can any way of periodically mechanically interrupting the
current be worked in? If so, then it gets easier for a step-up
transformer that this current goes through to produce something that is
useful to power a higher-efficiency LED (through a bridge rectifier).
Transformers should be smaller here - maybe run backwards a 6.3V 300 mA
"filament transformer".

Other than that, how about upscaling the project to put 10 or 16 of
these PM motors in series? That may not only provide sufficient voltage
after a bridge rectifier with Schottky diodes (such as 30V 1 amp rectifier
duty ones) but maybe also so much current as to consider "high power" LEDs
with ratings and characterization currents around 350 mA to an amp. Those
actually do well at 50 mA! When current is around or under 50 mA, don't
worry about heatsinking! If current is near or over 40 mA, use high power
LEDs rather than low power ones - my favorite most-efficient non-red
non-orange "low power" LEDs have efficiency maximized at 2-6 mA or so!

- Don Klipstein (don@xxxxxxxxx)
.

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