On 16 May 2006 15:33:00 GMT, Jim Yanik wrote:

Mark Lloyd wrote in
:

On 15 May 2006 13:33:39 GMT, Jim Yanik wrote:

Richard J Kinch wrote in
31:

Don Klipstein writes:

A younger adult biker in good shape can crank out 1/4 horsepower
- about
185 watts.

You mean for long periods, right? Simply climbing stairs is a lot
more power than that.

Meanwhile, I don't think it takes that much effort to lift a 5
pound
dumbbell 1 foot and put it back down once every five seconds.
That's one foot pound per second.

Still too optimistic.

At least half of shaking is wasted right off (having to muscle the
inertia to a stop). And you are shaking mostly dead weight of the
flashlight *and* your arm, not just the magnet or whatever is the
magnetic flux item (starting to sound like Doc in _Back to the
Future_).

It's not meant to be efficient,it's meant to be reliable;the light is
"supposed" to never need batteries and always be ready for use.

Most people would be quite uncomfortable just holding a forearm out
steady for more than a few minutes. They used to punish us in grade
school with that.

Shaking is a truly dismal generator principle. It just seems clever
to a casual, first impression.

Unless you use a bridge rectifier,the return stroke of the magnet
induces current in the opposite direction,and you would need a diode
to block the reverse current,the diode has a forward voltage drop
(~0.4v if you use a Schottky diode),and you lose the energy from the
reverse current with a single diode.


FYI,I took apart my $3 "shaker" LED light,and the "magnet" was just a
piece of unmagnetized plain steel rod,the coil wires were tucked under
the lower battery terminal,*not soldered to anything*,and the
batteries were a CR2032 and a thinner CR2025,for a total of 6
volts.They evidently use the (CR2025?)cell's internal resistance to
limit LED current.

A LED is supposed to need SOME series resistance to work properly.

Many of the tiny keychain lights use the battery's -internal resistance- to
limit LED current.Some of those button cells cannot supply much current at
all.(high internal resistance)

The light I looked at recently had no electrical components other than
a blue LED, 2 CR2032 batteries held between the leads, and a bit of
springy material that kept the circuit open except when squeezed.
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

Don Klipstein wrote:

Didn't you ever have one of those generators on your bicycle as a kid?
What a chore to crank, and you had the advantage of using your legs on
pedals.

I had those. They put out 3 watts, and were said to be 30% efficient,
with the biggest loss being in the area where the tire contacts the part
that the tire turns.

We used to hook them up to waterwheel type gadgets and spin them with
the spray from a faucet and see how much voltage we could get. In the
most impressive display, we got a dim glow out of a low wattage 110 v
bulb.

Richard J Kinch wrote:
Don Klipstein writes:

A younger adult biker in good shape can crank out 1/4 horsepower -
about
185 watts.

You mean for long periods, right? Simply climbing stairs is a lot more
power than that.

Meanwhile, I don't think it takes that much effort to lift a 5 pound
dumbbell 1 foot and put it back down once every five seconds. That's
one foot pound per second.

Still too optimistic.

At least half of shaking is wasted right off (having to muscle the
inertia to a stop). And you are shaking mostly dead weight of the
flashlight *and* your arm, not just the magnet or whatever is the
magnetic flux item (starting to sound like Doc in _Back to the Future_).

Most people would be quite uncomfortable just holding a forearm out
steady for more than a few minutes. They used to punish us in grade
school with that.

Shaking is a truly dismal generator principle. It just seems clever to
a casual, first impression.

I can't help feeling that the whole thing is just some huge
masturbation joke that will be exposed on a future episode of Punk'd.