Making a back emf motor generator and load testing.

[TommeyLReed]

This is a simple project to take any type of electric motors and convert the back emf to add efficiency to input of power.

I show how to use a hall effect for a three phase printer motor to produce a motor/generator effect and also collecting BEMF to add to the efficiency.

I also just got my Rigol DS1102E in a few weeks ago for better accuracy.



https://www.youtube.com/watch?v=ZrNpWRZIdco

[Farmhand]

I think if your generator coil is on the same core piece as the motor coil then if the "back emf" has no where else to go it will discharge the motor coils "discharge"/"back emf" on switch off through the generator coil to the load. This is what happens when we wind an oscillator like a joule thief with a third winding and use it to collect the voltage spikes produced when the coil is opened/switched off. This produces both a transformer effect when the coil is on and collects the discharge when the coil is turned off.

So I think even without your "back emf" collection arrangement the back emf is still collected via the generator coil.

Scoping the generator output with and without the back emf collection arrangement might see if it does or not. Might depend on the load.

I find it best to discharge coils on switch off to a voltage of double the supply voltage.

I'm not a fan of clamping the coil discharge/back emf to the supply + rail either.

Cheers

[Dave45]

Excellent work, have you crunched the numbers?

[TommeyLReed]

Hello FarmHand,

I am uploading the oscilloscope so you can see the output, I don't see any transformer effect due to the pulse to drive the motor. You would have a 180 deg reading on the sine wave.

These are some of the test readings and efficiency:

1) Input 5v@.37a=1.85w
Generator output (4.71v/98ohms)*4.70v = 0.2263w
BEMF output (1.71v/98ohms)*1.71v = 0.0298w
Total watts output (0.2263w+0.0298w) = 0.2561w
100% / (1.85w/0.2561w) = 13.8% efficiency

2) Input 9v@.59a=5.31w
Generator output (10.95v/98ohms)*10.95 = 1.2234w
BEMF output (5.60v/98ohms)*5.60v = 0.32
Total watts output (1.2234w+0.32w) = 1.5434w
100% / (5.31w/1.5434w) = 29.06% efficiency

3) Input 12v@.73a=8.76w
Generator output (15.53v/98ohms)*15.53 = 2.4610w
BEMF output (8.65v/98ohms)*8.65v = 0.7482
Total watts output (2.461w+0.7482w) = 3.2092
100% / (8.76w/3.2092w) = 36.6% efficiency

4) Input 15v@.85a=12.75
Generator output (19.77v/98ohms)*19.77v = 3.9085w
BEMF output (11.35v/98ohms)*11.35v = 1.2882w
Total watts output (3.9085w+1.2882w) = 5.1967
100% / (12.75w/5.1967w) = 40.8% efficiency

5)Input 19v@.99a=18.81w
Generator output (24.97v/98ohms)*24.97v = 6.2350w
BEMF output (14.70v/98ohms)*14.70v = 2.1609w
Total watts output (6.2350w+2.1609w) = 8.3959
100% / (18.81w/8.3959w) = 44.64% efficiency

Seems like the more power the greater the efficiency.

[TommeyLReed]

This is the motor test with oscilloscope readings.

https://www.youtube.com/watch?v=C2as5sZCdn4