Sharing ideas on how to make a more efficent motor using Flyback (MODERATED)

[verpies]

I've attached another scope pix taken from the same test but with the cursors re-positioned to show the mean of CH2 which is 234.8mv but also notice the Math mean of -82mvv.

Show me the cursors re-positioned in such manner, that they encompass only the positive excursion of the red Math waveform and you will make a believer out of me if the Math Mean becomes all positive.

[verpies]

@Gotoluc

In case your scope cannot do a Mean of a Math channel that multiplies 2 other channels (a current and a voltage), here is how to eyeball the power contained in the pulse created by a switched constant voltage source, just by looking at its current waveform:

The real current pulse is blue in all four scopeshots below:
1) The area of the red triangle is much larger than the area of the blue pulse, thus the red triangle overestimates the energy of the blue pulse.
2) The area of the yellow triangle is much smaller than the area of the blue pulse, thus the yellow triangle underestimates the energy of the blue pulse.
3) The area of the green triangle is the same as the area of the blue pulse, thus the green triangle approximates the energy of the blue pulse, the best.

The image in the lower-right corner shows how to eyeball and draw this green triangle that approximates the blue pulse well - Namely, as you draw it, make sure that the orange area and the purple area are equal.

Once you have that green triangle drawn, its height will give you the interpolated peak current. Let's call it i_PEAK
The width of the triangle is the period of the ON-pulse. Let's call it t_ON
If you multiply the constant supply Voltage * i_PEAK *  t_ON * 0.5 then the result will be the energy contained in this pulse expressed in Joules.

P.S.
If you want your result in Joules, then:
The Voltage must be expressed in Volts (e.g.: mV are not allowed) and must be constant during the entire ON-pulse.
The I_PEAK must be expressed in Amps (e.g.: mA are not allowed)
The t_ON must be expressed in seconds (e.g.: ms or μs or ns are not allowed)

The t_ON is a little narrower than the blue pulse, because the remainder of the blue pulse's width is the short energy recovery period, when the energy is transferred from the coil to the cap.

[Yttrium]

Nice work Luc, others have investigated this area and probably still are, the infamous Romero diverted the spike into motoring coils, lots of info on his site, i can't remember the address.

I'll look for some example threads and remind myself of what's already been looked at in this area.


Y.

[Magluvin]

I have 2 of the below outrunner motors. Do you think a circuit could be built to power it and collect the flyback to power the second one which would be attached to the same shaft?

Thanks for your time and help

Luc

My electric bike uses a 3 phase hub motor.  I had posted about it in the rotating thread.  I hooked up my scope to just 2 of the 3 wires going to the coils just to see if there is anything to grab when it comes to bemf.  Surprisingly there doesnt seem to be much. When the motor is WOT wide open throttle, there is no pwm pulses. Just acts similar to a pulse motor. And when I throttle down some to where there is pulsing, im not seeing any great spikes. Like the whole pwm 3phase process is clamping the spikes.  So the motor may have to be driven another way, possibly by even separating the windings and having individual drive circuits for each in order to avoid the clamping, or what ever is happening.

It is a 48v system. Scope seems to be showing more. Not sure what is up with that yet. Probably the little bit there is of spiking. I kinda expected some big spiking. Maybe the diodes on the fets putting out the flames.  Was thinking to put a bridge rectifier across the coils in pairs where there would be 3 bridges to collect from.  The bridge diodes would have to be lower conducting voltage than the fets diodes in order to get output, if the diodes in the fets are what is clamping the spikes.

The scope shots were of the hub motor wheel off the ground free wheeling.  The pyramid shape of the trace turns into a clean sine when the throttle is turned to off showing the motor generating near what the wave forms show and dies out as the wheel slows to a stop.

Not trying to distract. Just noticed your 3 phase motor and posted this. Be nice if we could figure this out. Will be playing with this more.

Mags

[itsu]

Itsu,

OK, I may be misunderstanding you but the measurement shown on the previous scope shot is the mean or average of the Math waveform between the vertical cursors and not the full screen width. I've attached another scope pix taken from the same test but with the cursors re-positioned to show the mean of CH2 which is 234.8mv but also notice the Math mean of -82mvv.

You can use the vertical cursors to define any measurement window in time that you desire with any of the available measurement resources on your scope. It is really powerful IMO!

partzman

Partzman,

ok, i see what you mean, i will make some further tests and see if it is useable, i would be indeed a powerfull function.

Thanks,  itsu