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

[gotoluc]

Hi Luc!

May be you have misunderstood my circuit.
The drive coil has 90 Ohm DC resistance (a 12 V relays coil).
"high voltage coil" has a DC resistance of 3000 Ohm

That is how I understood it.

Of course I could use a drive coil with only about 1 Ohm DC resistance (instead of my drive coil with 90 Ohm DC resistance).

Yes, that's what I was recommending and for your drive coil to be even lower than 1 Ohm will be better.
The flyback coil also should be as low resistance as possible but 5 to 10 time the inductance of the drive coil.

Still looking forward to your new test

Luc

[conradelektro]

That is how I understood it.

Yes, that's what I was recommending and for your drive coil to be even lower than 1 Ohm will be better.
The flyback coil also should be as low resistance as possible but 5 to 10 time the inductance of the drive coil.

Still looking forward to your new test

Luc

I got these two FEROXCUBE transformer cores (see the attached photo) and I can rewind them according to your specifications.

One will be the drive coil with about 0.5 Ohm DC and about 20 mH.

And the fly back coil (in my case the primary of a step down transformer) will have about 200 mH (and about 5 Ohm DC). The secondary will step down 10:1, just to have a low Voltage output (because the fly back spike will have several hundred Volts).

It will take some time.

To be honest, I do not expect a big difference. The input will be several Watts and the output again about 2% of the input power. Just to play with higher power does not necessarily give a a higher relative output.

Many people underestimate what a power input of e.g. 50 Watt can produce. 2% of 50 Watt will be 1 Watt, which looks like a lot if taken by it self. But in comparison to the 50 Watt spent, it is not really a big deal. Electric motors have a loss of up to 40%, really good ones loose 20% of the input power.
So, a loss of 2% in the fly back spikes is not much in reality.

Greetings, Conrad

[verpies]

This test shows, that there is very little energy in the fly back spike. May be one has to use a better technique (not a transformer) to get more energy out of the fly back spike.

Yes, you can disconnect the transformer altogether and measure the voltage to which the capacitor gets charged. The recovered energy will be E=½CV²
The only caveat is that you need to empty the capacitor before each flyback pulse.

The capacitor should be able to withstand the voltage V = i_L*(L / C)^½,  where i_L is the current flowing through the coil when the MOSFET opens.
...and this voltage should not be higher than the blocking voltage of the MOSFET and the reverse breakdown voltage of the diode (non-SiC Schottky preferable)

[itsu]

And with "non-SiC Schottky" you mean something like this:

Gallium Arsenide Schottky Rectifier   http://pdf1.alldatasheet.com/datasheet-pdf/view/166395/IXYS/DGS20-025A.html (250V)?

or this:  http://ixdev.ixys.com/DataSheet/L652.pdf (600V)?

Thanks,  itsu

[conradelektro]

Yes, you can disconnect the transformer altogether and measure the voltage to which the capacitor gets charged. The recovered energy will be E=½CV²
The only caveat is that you need to empty the capacitor before each flyback pulse.

The capacitor should be able to withstand the voltage V = i_L*(L / C)^½,  where i_L is the current flowing through the coil when the MOSFET opens.
...and this voltage should not be higher than the blocking voltage of the MOSFET and the reverse breakdown voltage of the diode (non-SiC Schottky preferable)

The "capacitor alone" is a better and cleaner approach for a theoretical power calculation in the spikes. Practically it will be difficult to empty the capacitor after each spike in a clean way (without effecting the storage of the spike energy).

I like the idea of harvesting the spike energy with a coil. After all we are dealing with a magnetic effect and why not try to get back a magnetic force. Putting a coil in the fly back path is a new idea, which I have not seen before (or which I have not recognised before). Whenever I tried to measure the energy which is fed back to the power supply with a diode alone, I failed. It never seemed that less power had to be supplied to a pulse motor with a fly back diode in place than without it. May be I am to stupid to measure that, but I also never saw a convincing measurement.

And the next step for me is to see the spike coil as the primary of a step down transformer, because the spikes have very high Voltage and one wants a low Voltage output (for practical use). The capacitor and the hysteresis of the step down transformer "transform" the very narrow fly back spike into a more sine wave like signal, which is more useful than a spike.

But I doubt that there is much energy in the spikes. And the energy seen as "magnetic force" or seen as "electricity" will be about the same. So, either to speed up the rotor (magnetic force) or to gain some electricity (which could be fed back to the power supply as an output from the spikes), it will not be much (only in the order of a few percent of the input power to the circuit or motor).

May be Luc could tell us where exactly he is looking for "more energy"? I tried to measure the energy in the spikes (more an estimate than an exact measurement, but it gives an order of magnitude) and it was not much.

I am not criticising Luc, I just want to understand and to measure the energy in the fly back spikes. Where is the magic? Or better said, where does Luc hope to find the magic? Any speculation is accepted and I will try to measure it in an "equivalent circuit". It can not be, that a motor is absolutely necessary? Or does it have to be a motor? I also accept that the magic is in the motor, but where in the motor, for sure not in the spikes.

Greetings, Conrad