CJT ) writes:
NSM wrote:
"geoff smith" wrote in message
.uk...

I have seen an advert for an L.E.D flashlight that is activated by shaking
it,there are no batteries.
How does it work ?

It's like a reverse vibrator.

N


I think it would have to be a solar powered vibrator to make the analogy
work.

Actually, the vibrators I've taken apart have a cheap DC motor in them,
and then a weight on the shaft that is asymmetrical. So when the motor
turns, there is an imbalance, hence the vibrations.

The concept of a reverse vibrator is that if you shake it, you get power,
while a vibrator shakes when you apply power.

But since there is a motor in there, it's not a great analogy. Everyone
knows that an electrical motor can generate power if you turn the shaft.
You aren't likely to be able to rotate the shaft of the vibrator motor
by shaking it, so it's not a reversible concept.

Let's not forget those cheap DC motors have magnets in them, and
a winding. Not really different from the concept of those flashlights.
The difference being the mechanical arrangement. Instead of turning
the shaft to get voltage, there is a more free-form generator that
works when you shake it.

Indeed, I have a windup LED flashlight, and I assume the only real
difference is that I crank it to charge it, rather than shake it.

Michael