As my TL494 board seems to be working now, I connected up two new fets to it, but find that they still heat up, as they had done previously with the now burnt out fets.

Are you still using this circuit ?

I had only 10 ohm resistors going to the drivers, previously, and 460ohm to ground.

That would have given you faster rise and fall times.

If the TL494.pin13 has 5V on it and you are taking the outputs from pins 9&10, then it means the TL494 is operating in push-pull mode with active-high pulses out of emitter follower outputs (pins 9&10 are emitters). 
The TC4420 is a non-inverting driver and the IRFP250P is an N-Ch enhancement mode MOSFET so their polarities are matching with active-high pulses.

I am afraid it will be difficult to help you without a scopeshot of drain currents and drain-source voltages.

It sounds like they are overheating due to overlapping of the triggering pulses or they are not turning off fast enough (my guess is they are not turning off fast enough before the other FET is energizing).

Hi all,

While trying out Sergey grenade mod in the lab I had to calculate wire lengths/etc. So I made calculator script (Python) which may be useful for others as well:


$ ./grenade_calc.py
Grenade configuration - alexewsergey mod.
Coil wire length: 37.50m
Tesla Coil(CCW) aluminum wire length: 37.50m
Copper strip(CW) (after Tesla Coil) wire length: 0.94m
Ground wire length: 25.00m
Inductor Coil(CW) length: 12.50m


Coil length: 22.00cm
        L0(CW): 22.00cm, Wire Length: 9.42m                 
        L1/L2(CW): 22.00cm, L1 turns: 60, L2 turns: 60        2.68 x 4  per layer
        L3/L4(CCW): 11.00cm, L3 turns: 30, L4 turns: 30       '' ''   x 2    ''    ''
        L5/L6(CCW): 5.50cm, L5 turns: 15, L6 turns: 15         '' ''   x1     ''    ''
                                                                                  37.5m /14 = 1/4 wave in this case


P.S> Please see akula explanation diagram about where extra energy comes from and what to aim for:


http://i.imgur.com/BHKqosd.jpg

Cheers!

test 1

winding the grenade with a 37.5m length please note I don't think winding 60 t + 60t and 30 t + 30 t and 15 t +15 is going to work I just tried it I ran out or wire at L4 !!! and it's not tuned to anything at all on our test equipment.

test 2

Two of us also tried winding a 'none inductive wind' of 2 layers, that gives you nothing at all in volts just current.

Fun ain it ! 

I note the thread has many readers but no one is sharing, if you want to keep it going please share !

  TK and All:
  I will upload some scope shots when I can. The circuit was working just like I showed in my last video. But, it was still overheating the new IRFP250N mosfets, and producing very little light at the bulbs.  However, right now the TL board is not working at all, so I replaced the TL494 chip, to another new one, but it still won't fire up. So, I'm working on it, and will upload the scope shots when I get it working again.
  I have not forgotten about the scope shots. "They will come",  like Geo says...  or built it,  and,  IT will come.

  I want to replace the driver chips to the bigger through hole ones mounted on some sockets, when my order of the bigger TC4420 drivers gets here. I have the IC sockets, but not the drivers for them. As I was sent the wrong size ones previously, and I have not received the new through hole bigger size drivers, yet.
 In any case, I'm still working on all of this, to the degree that I can work on the circuit, even though I was sent the wrong P250N fets also, instead of the P260N.
   Might be a lot easier just to buy the TL494 board for $7, like Itsu had bought and tested on his push-pull set up, at one time.
Also, a cheap and more efficient DC to DC converter, like Stalker is using on his last videos.

   
 

   Verpies:
   I did some more testing last night to see what is causing the TL board to not fire up.
   From my 24v, 10A PS, through the 12v voltage regulators to the TL494 IC, is exactly 12v,  to pins 11, 12, and 8. I also get 5v from pins 13, 14, and 15, which are bridged together.

That's OK.
What waveform do you have on TL494.pin5 ?

But, no voltage is coming out of the IC output pins 9 and 10, at all. I've tried three new TL494 ICs, but get no output to the drivers.
Disconnecting the 1000ohm resistor to the fet drivers so there won't be any interference if there is something wrong there, makes no difference.

That's a bad test because disconnecting R3 or R4 also disconnects R6 & R?, which are pull-down resistors (resistors connected to ground), which are needed for a varying signals to appear at TL494.pin9 & pin10.

For this test, it's better to pull out the FET drivers from their sockets than disconnecting R3 or R4.

  OK,  I think that I found the problem,  a possibly faulty electrolytic capacitor C2, a small 4.7uf cap on pin 2 of the TL494. I'll replace it out tomorrow, and see if that takes care of it, as it's late here tonight. Thought I'd let you know, but, in any case I'll know more tomorrow night.

Nick Zec is your Left big capacitor defect ?