StepperMotor used as a electric generator

Hi
I have build a wind-turbine or windmill don't know the different of these 2 words !
and the generator is made of an small stepper motor like this stepper-motor.jpg.
like configurations drawings and method with load and instruments if.

thanks in advance

A stepper motor has a magnetic field which is on a armature which is like a long cog, so it has lots of bars running down it, each bar is a north pole or a south pole. The windings are sets of fixed coils again with lots of " teeth" pointing inwards. The armature aligns the teeth, then when the coils are pulsed, the field moves one tooth around , so the armature, "steps" one tooth around to follow it. The effect is that the position of the rotor can be accurately controlled by altering the number of pulses applied. Typically, there will be 100 -> 200 steps per revolution. So to make it spin like a typical motor you need to have a pulse generator continuously supplying pulses to the coils in the right order.
In your application, I would think that a bridge rectifier across each set of windings and connect the DC outputs to gather is the best you can do.
Frank

chuckey said:

A stepper motor has a magnetic field which is on a armature which is like a long cog, so it has lots of bars running down it, each bar is a north pole or a south pole. The windings are sets of fixed coils again with lots of " teeth" pointing inwards. The armature aligns the teeth, then when the coils are pulsed, the field moves one tooth around , so the armature, "steps" one tooth around to follow it. The effect is that the position of the rotor can be accurately controlled by altering the number of pulses applied. Typically, there will be 100 -> 200 steps per revolution. So to make it spin like a typical motor you need to have a pulse generator continuously supplying pulses to the coils in the right order.
In your application, I would think that a bridge rectifier across each set of windings and connect the DC outputs to gather is the best you can do.
Frank

Click to expand...

thanks for the info
but I mean in a practical method to measure the Power with current meter and volt meter, if I shot-cut the output I will get some current spikes but not voltage. and opposite if no load I get some voltage spikes but non current.
so how do I measure ? and calculate it ?... is it the same method we use to measure internal resistance in a battery ?

So you want to measure the output of the motor then? First of all you must set up some arrangement to rotate it. Then measure the voltage into a load, change the load and measure the voltage again. So you have now two voltages and you can calculate two currents. Now work out (V1 - V2) / (I1 - I2) this will give you the output impedance of the machine at the rotational speed. So you can work out Volts per RPM. What else would you want know - perhaps the overload current? , Look up on google motors of this size and the amount of current they take, assume your one is the same, now you can work out for any given load the maximum voltage and hence the rotational speed.
Wind turbines should rotate at 2/3 the wind speed based on the blades mean pitch for maximum extraction of power from the wind.
Frank

Since you have an inductive generator with an unknown ESR and capacitive load (battery) with ESR, you need a 2 ch. DSO to multiply V*I to get in-phase real power vs. VA Reactive power which is just resonant and not real power. ie. if current is out of phase with current it is AC resonance and not real RSM power.

YOu can monitor current with series resistor similar to low ESR of battery on ground side and attach grounded probe for current and use 2nd probe for Voltage. If scope does not have true multiply function, then simply add low ESR Cap (1mΩ polyurethane) across battery to get DC after schottky bridge. Ensure you have reverse diode clamp to protect bridge so as not to exceed Vr rating.

Power is non-linear with angle of rotation due to position of coils w.r.t. built in magnets. Low ESR bridge rated for much higher current than expected is better. eg. 10A here for say 2Amp motor or use Quadrature MOSFET bridge driver with sensor to commutate bridge may give lower ESR or voltage drop than 1V bridge (0.5V pk from ESR of 0.2V threshold Schottky diode bridge with 2 active in series on each winding.) bigger bridge is better but more $.

Since motor also acts as a brake (load) you may need PWM controlled MOSFET bridge to raise ESR of load by duty cycle in order to keep above stall speed or simply use on/off regulator after bridge with hi-power PNP transistor rated with current gain > 10 in saturation. THen run driver to power switch with Enhancement mode MOSFET or consider a " High Side electronic Switch after bridge.

Let us know your results. with table of results and photos.