21 watts from a hand cranked generator

[Gotwind Ben]

This surprised me.
The Freeplay alternator produces more power than I first thought.
Here you can see me hand cranking 4 amps into a 3.6v NimH battery pack. (not advised for long periods of time).
That's 21 watts of power - according to the watts up meter, I have no reason to doubt it.
How come ohms law states
3.6v x 4A = 14.4 watts, thats a third less than actual power generated?
I suspect it is something to do with efficiency.





Most of the hand cranked competition you would be lucky to get 0.5A before the handle broke or gears shear.
Buy Freeplay gear if they are still trading

I expect it has to do with RMS vs Peak of the rectified single phase AC.

Watt's Law is generally considered to use the RMS value, which would be about 16.7W.
Peak (simplified) would be 23.5W.
The remaining 12% error could easily be from a spiky and very non sinusoidal wave form.

Those little PMAs have a lot of frequency related issues when it comes to accurate measurements.
It would be interesting to see what happens with a 1000uF 16V cap in the circuit, between the clips.
I expect it would get things into more DC oriented results.

Geeze. I was charging a 12V battery with a filtered peak open voltage considerably below the battery voltage.
That's like water flowing up hill! :o
Never did get that one figured out...
G-

Why not 100'ish watts? ;)



The details, 180v Leeson geared 19:1 motor, 120vac 100W bulb, will start to burn at 90vdc, but only popeye could keep it lit for any length of time.

Fun stuff,
Tim

[Gotwind Ben]

Nice.
It would make a decent pedal generator :?:

sorry Ben, wasn't trying to hijack your thread.

There is a little electrickery happening, the geared motor is indeed coming very close to 100 watts of generation, but at a high voltage low current, might not be the best choice for a 12v pedal gen (it certainly would work though), but a whole lot less watts.

Snapped an open voltage video, watch what happens right about 230vdc



Fun stuff,
Tim

Hi Ben

In the video.... the load on the dynamo does seem abit less hard to turn than connecting directly to a device, perhaps, just difficult to keep up the at that pace...

I have tested resistors acting as load, I can reach 10-11v 2a / 20+watts also
Im going to go back and try to replicate that again...
Maybe the watts meter is acting as load :?:

Here is my electric bike version 8-)