ENERGY AMPLIFICATION

[forest]

Ok, some more info on coil. Inductance is 335uH, resistance of circuit is mostly on this coil and I can measure it only approximately to be 0.3 ohm , (plush resistance of mosfet only 5 mohm as stated in datasheet). I cannot attach scopeshot as I have very very old analog one, but without any snubber it is a not much distorted square wave but with additional 60-70V peak when mosfet is turned off, gradually dimisnishind to around 12V or the voltage of the power supply (which is SLA battery 12V/7Ah)
I think such super simple circuit has nice potential for testing so called BEMF (or kickback pulse rather).
More later...

[Magluvin]

Ok, some more info on coil. Inductance is 335uH, resistance of circuit is mostly on this coil and I can measure it only approximately to be 0.3 ohm , (plush resistance of mosfet only 5 mohm as stated in datasheet). I cannot attach scopeshot as I have very very old analog one, but without any snubber it is a not much distorted square wave but with additional 60-70V peak when mosfet is turned off, gradually dimisnishind to around 12V or the voltage of the power supply (which is SLA battery 12V/7Ah)
I think such super simple circuit has nice potential for testing so called BEMF (or kickback pulse rather).
More later...

.3ohm(approximately. possibly lower or a bit higher) 12v in.  Even at 50% duty cycle could draw nearly 20A(near 40a with constant 12v).

This is why I had leaned toward the function of the diode and coil freewheeling causing 4A instead of the diode being reversed, and now as it shows, I leaned 'right'.

Forest, is there a reason for the 15us?  Is that what the secondary reacts to best(resonant?) ?  That was the reason why I suggested lower freq, like half or 1/4 the original freq and adjust the on duty cycle to 15u, where the longer off time possibly gives the coil more time to collapse before the next turn on.  But if the sec is still ringing, it could induce the primary to produce ac currents, more likely not 70 to 90v as there should not be spikes after the primary produces a spike when the trans is turned off till the next turn off.

mags

[MarkE]

Ok, some more info on coil. Inductance is 335uH, resistance of circuit is mostly on this coil and I can measure it only approximately to be 0.3 ohm , (plush resistance of mosfet only 5 mohm as stated in datasheet). I cannot attach scopeshot as I have very very old analog one, but without any snubber it is a not much distorted square wave but with additional 60-70V peak when mosfet is turned off, gradually dimisnishind to around 12V or the voltage of the power supply (which is SLA battery 12V/7Ah)
I think such super simple circuit has nice potential for testing so called BEMF (or kickback pulse rather).
More later...

You are driving this thing with 15us pulses, but at what repetition rate?  From the schematic you have shown so far you pump energy into the coil that has nowhere to go.

[Magluvin]

True. He did say 15us pulses square wave, and that doesnt mean 50% duty cycles necessarily.

Mags

[TinselKoala]

If you have a camera you can easily make a very acceptable scopeshot of your old old analog scope. I do it all the time with my Tek 2213a and HP180a scopes. Annotations can be added with a simple graphics editor like my favorite mtPaint. It might take a few practice shots before you get your exposure set properly for the job, but it's very valuable to be able to do it. I usually use my Canon DSLR in manual mode, no flash, 1/30 or 1/15 sec, f/5.6, ISO800. You could probably also get an acceptable shot with a cellphone camera, although I haven't tried it yet.

I still haven't seen the part number of the diode in question. It can make a huge difference. The diode could be leaky, blown completely, too slow to be of much benefit, or simply in backwards.

The diode should be a high current, ultrafast type. I use MUR1560 (600V, 15A, 55 ns)  for rectification in my wireless system receivers which operate at around 800 kHz or a period of around 1.25 microseconds. My electromagnetic levitator performance was greatly increased by using a RL3A type from an old TV chassis, 50 ns recovery, 400 V 3A.
You could try something like UF4007 (1 kV 1A 75 ns) or the similar BYV26E but that would be kind of underrated for the task, I think.  The FR60x series are readily available but not really "ultrafast", with recovery times of 150-500 ns. Still, I've used them with success in slower circuits like bipolar transistor-based coil drivers.
The recent coildrivers I've made use MUR480ES also from old CRT monitor chassis (very good, 800V 4A 75 ns) or BYV26E (barely adequate but working OK).