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

[verpies]

C2 is 100uF, so ½C*( (15V)2 - (4V)2 ) =  ½ 100 * 209 = 10450 (uJ?) which is way to low i think

½ * 0.0001 * (225 - 16) = ½ * 0.0001 * 209 = 0.01045 J = 10.45mJ

(see also http://www.calctool.org/CALC/eng/electronics/capacitor_energy)

The disparity comes from the fact that (15² - 4²)  <> (15 - 4)²

L = 38mH, so ½L*(1.1A)² = 19 * 1,21 = 22.99 (mJ?)

That's correct
So at switch off you have 22.99mJ of energy stored in the coil, but after recovery you have only 10.45mJ of energy stored in the capacitor, which constitutes 45% recovery efficiency.

If you use a smaller C2 capacitor (e.g. 10μF 100V) and start the recovery from an empty capacitor and delete R2, then this efficiency number will increase a lot.

Cheers

P.S.
I have a 10μF 400V polypropylene cap sitting in front of my keyboard now, that would be ideal for this purpose because it is almost a lossless pulse cap.  I wish I could teleport it to you.

[itsu]

Verpies,   

thanks,  i have some 10uF 630V poly caps here which i can use.

Itsu

[woopy]

Hi all

Just to add to my video , i placed a drum with winglets  on my rotor to create an aerodynamic torque.

Pic 1 is the rotor with the  drum and winglets

Pic 2 is the scope shot when the coil is at 20 mm distance from the rotor magnets

Pic 3 is the scope shot when the coil is at 4 mm at the better timing i could get.

It seems clearly that at 20 mm distance the rotor spins slowly but draws a lot of current. And there is a nice flyback spike.

At 4 mm distance the rotor spins  faster (which means more torque for higher speed) and draws much less current. And there is also a nice flyback spike to recover.

With the aerodynamic load i can no more  get the sweet spot where i got the current smoothing down to zero and no flyback spike as per the video with no load. And the best power is got when the current trace is as per Pic 3.

Food for thought

Laurent

[MileHigh]

With the aerodynamic load i can no more  get the sweet spot where i got the current smoothing down to zero and no flyback spike as per the video with no load. And the best power is got when the current trace is as per Pic 3.

Food for thought

Laurent

Excellent observation Laurent.  I can share some additional thoughts.  You clearly showed how with the aerodynamic load, even for a pulse motor, there is a price to pay for driving that load.  As the aerodynamic load gets smaller and smaller, it gets more and more difficult to measure the decreasing amount of extra power consumption required to drive that load.  There may be other secondary effects that mask that increased power consumption, especially if those secondary effects reduce the power consumption.

Now, it's possible to start making your measurements where the load is already quite small, and the secondary effects are already present.  In that case, it becomes very difficult to figure out what is going on.

[gotoluc]

Hi Luc and all

Yes i have made a small rotor with 2 neomag oriented sideways.

After 2 days of playing with , i have stumbled upon some interesting things.

https://youtu.be/N7S_cbAYp6c

It seems that the timing is very important as well as the distance between the rotor and the core of the coil.

At some "sweet" point the current trace goes smoothly to zero at the end of the voltage pulse and so it seems that the flyback spike disappears completely.

I don't know if it helps, but this is very interesting

Laurent

Merci Laurent for taking the time to test and make a video of this interesting pulse motor magnet configuration.

You are right, at a certain timing you can eliminate flyback.
What I also found is if your pulse on time is centered in the induced EMF the input is the less and RPM the most with the coil at a certain distance from the magnets (sweet spot).
Hopefully you will find other interesting things to do with it.

Thanks for sharing

Luc