Small motors can make a perfectly adequate
alternator - ideally you want a brushless DC motor (or an AC alternator) to
avoid any brushes and mechanical drag and wear.
I don't know the details of your anemometer but if its
producing an AC voltage now which you measure the frequency of then it may be
entirely suited.
As a guide, an alternator can run at very high efficiencies if
properly designed. With a brushless alternator (magnet rotor, coil stator),
apart from the losses due to drag and friction you will have ohmic (I squared R)
losses in the stator coil. For small units efficiencies of 80% plus should be
easily achievable.
It may be that for a modest power requirement you could use
the anemometer rotor to deliver power a substantial part of the time (say 50%)
and then unload it to take readings. The unloaded time would need to be long
enough for it to settle into its steady state condition. If you want to measure
sudden gusts this method may not be adequate. You may also be able to calibrate
its rotational speed relative to wind speed WHILE LOADED so that it serves both
purposes at once. If doing this you would probably want a regulator which always
had the same load at given input voltage (ie appears to be eg pure fixed
resistive) BECAUSE if the load varies then anemometer speed could vary with load
for a given wind speed.
> Presumably to get the same drive V & I out
> of a motor you would have to turn it
at its
> (normally) driven speed and lesser V
& I
> would be had at lower speeds.
Simplistic comparison of motor and alternator:
Y'All feel free to critique this description AND
provide a more understandable one:-)
A unit with winding resistance R operated as a
motor at a given current IN and speed and field must have a voltage equal to the
generated voltage (called back emf in this application) PLUS I squared R losses
applied for a given speed. For the same unit run as an
alternator at the same current OUT and speed and field the GENERATED voltage
will be the same but the OUTPUT voltage will be I squared R less than this. By
this analysis, all things being equal, the motor will need 2 x Isquared x R more
voltage applied to its terminals to run at the same speed as the same unit when
operated as an alternator. (
regards
Russell
McMahon
_____________________________
(* - or woman, child or internet enabled
intelligent entity :-))
-----Original Message-----
I'm investigating a weather station / data-logging project
using an
F84 or 508 plus RAM or EEPROM. The
components and mechanics
aren't a problem,
but looking at the cup anemometer prototype I wondered
if a second one could be used for
turning a small motor to top up the
battery. Is this a viable method ?
How efficient is a motor when it's used as a generator
or are the two
merely the same device ? Presumably to
get the same drive V & I out
of a motor you would have to turn it
at its (normally) driven speed and
lesser V & I would be had at lower
speeds.
Usually I'd use an el cheapo solar cell but in this app
there's the little
added challenge of perhaps using something else. Has
anyone tried
this method of small battery charging ?
Jinx