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

[verpies]

Is this the kind of signal you would expect for the yellow one?

Almost.
Notice that C2 is not discharging all the way down to 0V.

To discharge C2 all the way down to 0V:
- start discharging C2 sooner
or
- discharge C2 longer. (if I knew Q3's gate waveform then I could decide whether increasing L2's inductance is necessary for this).
or
- discharge C2 faster by decreasing R2 (Warning: don't decrease R2 so much that Q3's maximum pulsed drain current is exceeded)
or
...all of the above or combination thereof

Also, put some small but good bypass caps to ground on the source of Q3 and on cathode of D2, because there is an unwanted voltage spike on the purple trace. While you are at it, decrease the inductance of the entire drain circuit of Q3 including C2 (short leads, small loop area, etc...)

Below is a revised schematic with the correct probe placement and countermeasures against the voltage spike form L2.
If C3 and C4 do not help, then adding R4 will slow down the closing of Q3 and its drain current spike that gets converted to a voltage spike by stray inductances in the drain circuit.  For R4 try anything between 0Ω to 1K.

What are you using for U2 ?  Do you use its inverting input or non-inverting?

[tinman]

@Verpies, Tinman and Milehigh:

Luc has a scope shot above labeled "Reverse direction Flyback". How does this equate with your "Same direction" theory for BEMF?

Because you need to understand the circuit,scope probe placement,and the way the two inductors are coupled to each other.


Brad

[gotoluc]

It would be a violation with one coil, but with two coils one can push flux and current into the other coil.
Without seeing two gate waveforms (or d-s) on the same scopeshot, it is difficult to conclude much more.

Loosely coupled inductors ( a transformer with low k coupling coefficient ) are notoriously hard to analyze when they have capacitors across these inductors on both sides.  Without the diodes in series they behave like a tuned transformer.

Good point verpies!... I can confirm even thought both E cores are very close to being identical I noticed one is using a little more current then the other and I'm quite sure it's the one I didn't provide the scope shots.

Luc

[sm0ky2]

I'm a little confused about the premise here....

We are trying to improve efficiency of an electric motor,... by adding losses to the system adding a transformer???

my experience with this matter has led me to believe the "most efficient" motor that mankind has so far created
is the one we use in nearly every electric device that has a motor in it....
like a stand-alone fan, or a vaporizer, im sure you've seen these things, they are brushless A/C motors, just an inductor, with two large copper links,
and an aluminum rotor with arc-shaped grooves in it.

when these are operated at a frequency that is compatible (multiple, divisor, or octave of) with the self resonant frequency of the inductive core.
they run at 95+ % efficiency. That means if you have a supercapacitor storing an hours worth of run-energy,
you can cycle back and forth a "q-Mogen" of two of these motors for 54 minutes, (minus heat losses in your circuit)
before the energy is depleted.

We have no better motor than that.(except some magnetically suspended stuff NASA did in space...)
So it seems like a good place to start.
What I don't get, is how adding something that increases losses is supposed to raise efficiency?? like a flyback transformer?

Flybacks are notoriously sources of system losses. They are discontinuous by nature, and generally over-tax the maximum frequency of the inductor.
This is because of the high conversion ratio, I.E. # of turns on the primary compared to secondary. The voltage has to step-up faster than the induction time factor.
When the timing of the inductive core is faster than the time it takes for the signal to circle around all those turns in the secondary coil,
it has to "skip a beat" to re-synch. That sounds weired, but that's what happens inside the inductor. When the flux is saturated, and has not gone down yet, and it switches again, the inductor can't keep up. so lets say you run a fly-back for 100 cycles.
there will be a number of these cycles where the energy is unrecoverable, because it switched faster than the secondary coil could dump its energy.
it will depend of course on the ratio of turns, and the operating frequency, but lets just for example assume it's 3 out of 100.
so you're flyback runs at 97% efficiency before you attach it to the motor. that's - 3% just by adding a flyback
This effect is well known in the television industry, and is calculated into the total energy consumption of devices, as displayed on the FCC tag.

if you have a flyback of X ratio, operating at frequency Y, you will have Z losses.

[verpies]

We are trying to improve efficiency of an electric motor,... by adding losses to the system adding a transformer???

No, I think this is an experimental tangent that investigates the simulation of a rotor by a transformer

Flybacks are notoriously sources of system losses. They are discontinuous by nature, and generally over-tax the maximum frequency of the inductor.

No, "flybacks" last as long as the engineer wants. Precisely t=½π(LC)^½
In circuits like this the "flyback" current is not discontinuous but quarter-sinusoidal.

What is the maximum frequency of the inductor, anyway ?