The Master Of Magnetics "Steven Mark"

[bob.rennips]

Sulake,
People have been at this for some time doing their best within their financial means and abilities to interpret what they find.
Please do not complain or be demanding, just accept what people can do and have done both in testing and contributing.
Best to break out our own test gear and try to replicate and contribute ourselves than try to apply pressure to those like OTTO already doing the hard yards here.

Smoky

On the contrary, Sulake IS contributing much to the discussion.

He's pointing out that the results do not appear anomalous. He's asked for a clarification of the circuit. He's redrawn the circuit. He's also pointed out that the MOSFET as drawn by OTTO, IS acting as a switch. He's provided (I believe) what looks like a simulated out, based on traditional electrical theory, from something like SPICE.

I've tried the circuit but don't see anything in the high voltages that I wouldn't expect in standard theory. Further more as any experimentor should be doing I've devised a simple further experiment to confirm whether your conclusions are correct.

Your theory is that the collector going through the center of coil is somehow adding to the voltage spike and/or current. To test this theory of yours a simple experiment is to have EXACTLY the same wire and components and connections but NOT have the collector going through the coil.

My results stay EXACTLY the same; QED the theory of the collector in the coil is INCORRECT OR the circuit I'm using is WRONG.

It is either one or the other. Given that OTTO has now posted the defintive circuit and components I believe my circuirt is identical to those being used by others.

So what's left is for YOU ALL to do this further test and let us know if you get any difference in results. If you do then we have to start looking at what other factor makes my circuit different from yours.

[otto]

Hello,

@Bob

YOU ARE NOT USING A IRF 840 MOSFET or you are using a oridinary transistor!!!!

Otto

[bob.rennips]

Hello all,

@Bob

ok, you tried the test. What transistor have you used???

What do you see on your scope??

Please, let us know.

Otto

IRF840 by ST (Thompson)
http://www.futurlec.com/Transistors/IRF840.shtml

I note that it has a reverse voltage diode built in. I can't imagine other manufacturers wouldn't have the reverse voltage diode.

Who makes your 840 ? I'll look up the datasheet to see if there are any differences - shouldn't be.

I get a standard decay pulse after the pulse turns OFF.

As I manually move through the frequencies on my function generator, the maximum voltage of the decay pulse, goes to a maximum (about 50V) and then reduces, continuing up the frequencies the voltage rises again and surpasses the previous high voltage (about 110V). Expanding the timeline on the scope and it may be going as high as 200V but the rise and fall of the first pulse is very steep so it's hard to tell what the maximum is on the scope.

My interpretation is the first peak is a harmonic of the second actual resonant frequency of the circuit.

What are you seeing  on your scope ?

[otto]

Hello,

tomorrow you will se photos of  almost ideal kicks. Depending on used frequencies from nothing to over 400V.

I used almost all IRFs. In this moment I have at home 15 - 20 of them. I think from 2, maybe 3 various manufacturers, there is NO diffrernce.

We will see tomorrow.

Otto

[MeggerMan]

Hi Otto,
Are you using a bench power supply or battery?
I was wondering if the spikes you are seeing may have come from a secondary winding of your PSU. You need to scope your supply possibly.

Are you getting any kind of current to go with these 400V spikes?
Is the 400V measured across the lamp?
What frequency and duty cycle?

I am amazed you can get such a large back emf with so few turns, no ferrous core and only 12v.
Look forward to seeing your scope shots.

Regards
Rob