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Solid States Devices => solid state devices => Topic started by: TommeyLReed on May 31, 2014, 11:29:10 AM

Title: Making a back emf motor generator and load testing.
Post by: TommeyLReed on May 31, 2014, 11:29:10 AM
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 (https://www.youtube.com/watch?v=ZrNpWRZIdco)

Title: Re: Making a back emf motor generator and load testing.
Post by: Farmhand on May 31, 2014, 01:59:02 PM
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
Title: Re: Making a back emf motor generator and load testing.
Post by: Dave45 on May 31, 2014, 03:45:52 PM
Excellent work, have you crunched the numbers?


Title: Re: Making a back emf motor generator and load testing.
Post by: TommeyLReed on May 31, 2014, 04:21:15 PM
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.
Title: Re: Making a back emf motor generator and load testing.
Post by: TommeyLReed on May 31, 2014, 04:29:24 PM
This is the motor test with oscilloscope readings.

https://www.youtube.com/watch?v=C2as5sZCdn4 (https://www.youtube.com/watch?v=C2as5sZCdn4)
Title: Re: Making a back emf motor generator and load testing.
Post by: Farmhand on June 01, 2014, 06:48:25 AM
Hi Tommy, I'll watch the video now, maybe a misunderstanding, I don't think I said the motor coils would show a transformer effect to the generator coil, I said an oscillator with the third winding can output a (Edit: Transformer) effect voltage and a flyback voltage. I was saying that maybe the generator coil could collect the "back emf" from the motor coil magnetic field collapse without the "back emf"collection arrangement in use because the core is shared.


You would need to disconnect the back emf collection arrangement and scope the generator output before the bridge rectifier and remove the load resistor from the generator output capacitor so the voltage can climb from the spikes.  We should be seeing the sine wave and spikes. If the cap is climbing above the normal generator voltage then there is spikes doing it most likely.

Another way without scope is to get the motor running with back emf collection in place separate to the generator as you did and get a stable generator voltage on the generator cap with no load resistors, then remove the back emf collection arrangement and see if the generator cap voltage rises.

 I can see spikes, are the spikes on the generator output when the back emf collection is in place ?

I think any spikes you see above the generator voltage on the generator output are "back emf"/magnetic field collapse spikes from the motor coils, which could be a problem if you want a stable generator output voltage. The capacitor will collect them if in place and they probably would not be seen if there is a load o the caps.

If the gen cap climbs up to a voltage the generator sine wave cannot charge the cap to then it must be spikes doing it.

Edited: I mistakenly wrote generator effect when I meant transformer effect above. I changed it.
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