Hand-cranked stepper motor as a generator

[ALVARO_CS]

thanks TK
(to say the truth I was expecting your opinion as well as MH´s one)
Lots to learn yet, that´s why I posted my question.

[mscoffman]

hello Conrad
(or anyone with knowledge enough in measurements)

I made a simple setup with a small bipolar stepper motor driven as generator by a DC motor.
I need your help in an explanation of a behavior I do not understand.

the DC motor is feed via a PC power supply (modified with a  voltage regulator)

The input to it is 9V  (not changed in the following tests)

The output from the stepped m. is via two BR made out of 4 4007 diodes in paralel buffered with electrolytic cap 120uF 400V (see schematic)
Output measurements made at the cap terminals

The tests show the following data:
----------------

input: 9V at 400mA (with no load)
out: 18V

input:9V at 450mA loaded with a 100 Ohm/4W resistor after the cap.
out: 7.5 V
------------------
input: 9V at 350 mA with out terminals shorted (max load ?)
out: no V (as expected). . .speed of motor notoriously /noticeably/ increased
------------------
May someone explain this motor speed up and lowering of input ?
any help greatly appreciated
cheers
Alvaro

These measurements are indeed within theoretical expectations.

1) Generator is unloaded - high voltage output due to lack of electrical load on generator ("LENZ LAW GENERATOR" electrical load acts
as mechanical brake), No power is being produced, as there is zero current in the load => low mechanical load on motor => high RPM's

2) Generator is loaded - generator acts as brake - motor input current rises due to mechanical load on motor - generator output voltage
is lower due to Ohms law in resistance of coil versus resistance of load. Real world motor(s) automatically adjust their operating current to
their mechanical load to some extent. This saves energy on average - causes the motor to "lug" under appropriate conditions.

3) Unique condition in Generator - shorting output coil collapses internal magnetic field - zero driver voltage => zero current (in a generator
circuit only). No power being generated <=> no mechanical braking force. In a generator circuit some driver voltage is required to cause
some current flow in load - if the generator doesn't supply this driver voltage where does it comes from? - it doesn't. Voltage is what
causes the electron Current to flow in a circuit.

One could use Ohms law math to calculate approximate generator output coil impedance(resistance) of generator coil.

This is a good experiment showing several unique and somewhat surprising conditions in a real world motor/generator set. Congrats.
Instrumentation readings helps one to understand what is occurring in the circuit.

:S:MarkSCoffman

[mscoffman]

If magnetic cogging force is to extract energy then there must be an integration time frame. If rotation is sufficiently fast then the
integration time frame is violated and less net energy will be extracted. This is a consequence of unusually rapid radius squared
interaction in magnetic fields. (you might want to consider the fast HHO interaction rates if you need to outrun magnetic interactions)

:S:MarkSCoffman

[ALVARO_CS]

Thanks again for all the kind explanations.
reading on the subject, I found this quote:

" Efficiency also approaches 100% if the source resistance approaches zero, and 0% if the load resistance approaches zero. In the latter case, all the power is consumed inside the source (unless the source also has no resistance), so the power dissipated in a short circuit is zero."

I found in the forums, that there is a common misunderstanding between efficiency and power transfer

[meiji_jap]

By chance I found this web page depicting a hand-cranked stepper motor http://bjblaster.homedns.org/projects/renewable/hand_power/index.html and I decided to try it myself.

My video http://www.youtube.com/watch?v=qec_qsDseCY shows a hand-cranked stepper motor, a rectifier circuit and a Joule Thief circuit.

The stepper-motor is more than 20 years old and I bought it some time ago for very little money from a surplus dealer in Germany. The face plate of the stepper motor has a side length of 80 mm. A heavy and sturdy stepper motor with six wires. The axle has a diameter of 10 mm.

The hand-cranked stepper motor first drives eight white LEDs which seem to get too much power. A rectifier circuit allows to measure the output power (at about 60 rpm or one crank turn per second) which amounts to approximately 0.8 Watt. It does not help to turn the crank much faster as shown in the video, the output will not rise much.

The hand cranked-stepper motor and the rectifier circuit first drive a radio and then a Joule Thief which lights a 200 Volt / 1 Watt Led-lamp and alternatively a gutted CFL (compact fluorescent lamp, spiral shaped gas discharge tube, ignites at ~800 Volt).

Unless you find a person who is willing to crank the stepper-motor, this idea will not be very useful. But it is an interesting experiment.

Greetings, Conrad

I like the idea how you made the crank handle to grip the motor -- anyway would you mind to explain as in your video why when you turn whether clockwise or otherwise it still generate energy because i have a motor...12  volt DC when i turn it only generate electricity when the connection is correct. -- it generate around 0.8 volt to highest around 5 volt