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Teodor Zafiroski

Sun Apr 12 2015, 07:30PM

Registered Member #48007 Joined: Wed Jun 18 2014, 01:00PM
Location: Prilep, Republic of Macedonia
Posts: 33

I was able to fire up this circuit today, and got some incredibly small output, the circuit draws just over 500mA at 12V, I think that's because of the 3.5+3.5 turns on the primary, I need to reduce it to about 1.5+1.5 when I connect all of the caps in parallel, that should give me a greater power draw... Here's the schematic:

And here's a video of it in operation:

When I get my hand closer to the coil, the extra capacitance pulls it in tune and the tube lights up, the spark to my fingers is so hot that my fingers began smoking, the burns don't hurt though...

I need to reduce the primary turns, connect the tank caps in parallel instead of series, and that should result in larger sparks, and hopefully- streamers!
P.S. When I place the link to the youtube video in a youtube tag, the video won't load.

hen918

Sun Apr 12 2015, 07:33PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

I think it would be a good idea to use a chicken stick and not put your fingers that close...

Teodor Zafiroski

Sun Apr 12 2015, 07:35PM

Registered Member #48007 Joined: Wed Jun 18 2014, 01:00PM
Location: Prilep, Republic of Macedonia
Posts: 33

We're talking about really low powers here... I use a chicken stick whenever I work with higher powers...

dexter

Mon Apr 13 2015, 10:23AM

Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195

i tried this setup too but 2+2 turns and at 36V from a 150-200VA transformer and got 10mm streamers output
the primary was not in tune with the secondary ~200KHz primary 250KHz secondary
the mosfets got wery hot after a few second of operation

Teodor Zafiroski

Mon Apr 13 2015, 11:44AM

Registered Member #48007 Joined: Wed Jun 18 2014, 01:00PM
Location: Prilep, Republic of Macedonia
Posts: 33

2+2 turns at 36V? That explains a good part of the heating, and at that frequency with that much turns and at that voltage I expect the current draw to be large, have you measured it?

dexter

Mon Apr 13 2015, 03:28PM

Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195

did no current measurements because i just slapped the parts together to see how it performs....

i used the same Royer to overdrive flybacks at 36V about 30A without much heating of the mosfets but the frequency was much lower 30-40KHz

Sigurthr

Mon Apr 13 2015, 10:25PM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

Unexpected or excessive FET heating almost always comes down to one or more of three causes:

1) Running in the Linear region from insufficient or incorrect gate drive.

2) Shoot Through / Crossconduction from inadequate gate drive dead time.

3) Avalanche Conduction from exceeding BVds. Inductive kicks on turn off of each leg can cause massive heating effects without instantly destroying the device. As such it often gets ruled out as a culprit unless measurements are done to watch the Vds and ensure no spikes are seen.

hen918

Tue Apr 14 2015, 04:49PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

Sigurthr wrote ...

Unexpected or excessive FET heating almost always comes down to one or more of three causes:

1) Running in the Linear region from insufficient or incorrect gate drive.

2) Shoot Through / Crossconduction from inadequate gate drive dead time.

3) Avalanche Conduction from exceeding BVds. Inductive kicks on turn off of each leg can cause massive heating effects without instantly destroying the device. As such it often gets ruled out as a culprit unless measurements are done to watch the Vds and ensure no spikes are seen.

Or it could be due to the MOSFET being a re-named cheaper, bad quality or otherwise fake Chinese copy.
but, if bought from a reputable supplier, it is usually safe to assume that this is not the problem.

dexter

Tue Apr 14 2015, 05:10PM

Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195

hen918 wrote ...

Or it could be due to the MOSFET being a re-named cheaper, bad quality or otherwise fake Chinese copy.
but, if bought from a reputable supplier, it is usually safe to assume that this is not the problem.

is not a fake mosfet i used the same setup (see picture few posts above) at 36V ~30A on a flyback, the power resistors and the windings got hot before the mosfets :)
IRFP260M's bought from a respected site

Teodor Zafiroski

Wed Apr 22 2015, 05:36PM

Registered Member #48007 Joined: Wed Jun 18 2014, 01:00PM
Location: Prilep, Republic of Macedonia
Posts: 33

I calculated the number of turns of the primary for the capacitance that I had, and tested it today. I got a small brush discharge, followed by a click when I made an arc to ground and the arc was gone. The breaker turned off, and when I turned it on again it immediately turned off every time. The MOSFET's were warm to the touch, and the inductor and tank caps as well. When I removed the MOSFET's from the circuit, the measurement had shown that they had failed all pins shorted. (one of them had 500 Ohm resistance gate to source, the other one had zero resistance gate to source, but they both were shorted drain to source)
I guess they became another addition to my silicon graveyard...
What may have blown them?

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