Class E SSTC thread / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

Class E SSTC thread

first previous 3 4 5 6 next last

Move Thread

LAN_403

Marko

Sat Jul 08 2006, 11:40PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Yeah, and it is many times worse if ball burns under the foil with weak presence of oxygen.
Stink/smoke bombs are made like that :p

Poliester ball I made dried out.
I simply brought it outside and ignited ping-pong ball mold. It didn't smoke much since it had enough air to burn.
Then I just sanded the remaining carbon off the poliester ball.
I also had to repair some 'imperfections' additionally so it's drying now =)

And yes, I definitely need to fnd a better tank cap for this coil...

hehe

PS. thanks, Steve, for info..

ragnar

Sun Jul 09 2006, 06:35AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

You'll either think this is some kind of sick joke, or that I'm a masochist, or that I'm bored. Either way, it's too late. Here's the gatedriver: =P

Let's see if I can get a little less dissipation in ze FET now.. ^^

Marko

Sun Jul 09 2006, 02:05PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

What would be the real use of such a 'full bridge' of tiny FET's?

Steve Conner

Sun Jul 09 2006, 02:30PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Maybe he tried it just to see if it would work. I think it's pretty cool actually, whether it's any use or not. I guess it's some sort of gate driver for a larger FET.

Marko

Sun Jul 09 2006, 03:39PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I sanded away remaining carbon from the poliester ball, and prepared t to be taped...

Coil worked like nuts now, topload doesn't look good like before but it's functional at least.
Another great news is that I managed to overheat the mosfet.

I blame the poor ceramic cap I tortured over there, I definitely need replacement (it is just wonderful that 100V cap survived 200V peaks, probably he healed due to enormous currents after each breech).

What I seek now is to get 15cm sparks (and hopefully best Steve Ward's coil finally

)

I replaced the mosfet and got better cap. This time it is 10nF 2kV, I hope it won't trouble me anymore.

The biggest problem that terrors me now is that peak tank voltage swings up to some 430-450V, with only 50 input; I'm definitely running away there.maybe I should try to lower the number of primary turns to 2. I don't know if it is best matching foor primary but I hope to reduce peak voltage and spare mosfet's from dying.

Maybe I should even consider richie burnett's approach, wich means separating class E amp from the primary. This way I could make the amp work reliably and hopefully find best impedance match for secondary (?).

ragnar

Sun Jul 09 2006, 11:03PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

When running 50Vin I get peaks up to about 180V... if the amp is not well loaded you'll get very high drain voltage spikes. What's your coupling like?

Marko

Sun Jul 09 2006, 11:32PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

After some studying I realized that my tank voltage also hangs about 200 (and even less) volts in the beggining, and then climbs as mosfet and capacitor heat up (this new cap is even hotter than last one, I should find some MKP cap for this but I don't have any at hand

)
Even massive HV ceramics don't behave too good..
I need to get sleep and research this tomorrow

My coupling is pretty high, too high acually (?).

Also, If I remove any breakout point and not let the coil break out from topload tank voltage also stays at some 190 - 180 V.

When huge arcs detune the coil it suddenly jumps to 'hot' 400 volts.

BP, what heatsink are you using and how hot does it get over etc. one minute with etc. 100W input power?
And what spark length you get, ofcourse?

ragnar

Mon Jul 10 2006, 04:02AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Play with the coupling to see how it affects the spark loading and the class-E damping, you'll have to retune frequency as you go, but it'll help you optimize the dissipation in the FET.

On mine, the tank voltage rings up about twice as high when there's no breakout. As soon as breakout occurs, the Q goes down enough for critical damping at just ~200V with 50V in.

The heatsink I'm using is the same shiny aluminium stock seen in previous photos. He gets very warm after 30secs of operation, but the coil is always sputtering and I worry about shoot-through in the FET --- I need to shield the driver circuitry.

The max sparklength I can get is about 6cm, but whenever I do this the coil tends to breakout at the edge, burning the former, and the Q goes down too much that I lose the critical damping condition on the FET.

Speaking of FETs, stuff the 2N7000 fullbridge -- my IRFP460 is now driven as a matched resonant circuit with more UCCs. When I shield the driver electronics now, I think it'll be totally stable.

You like? =-)

rev

Mon Jul 10 2006, 05:05AM

Registered Member #112 Joined: Fri Feb 10 2006, 01:19AM
Location:
Posts: 48

i've though of "stacking" ucc's but never literaly stacking them mostly for issues of the ones to the center most over heating. seems to not be a problem.

...

Mon Jul 10 2006, 05:57AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

it is somewhat common in the hifi cominuty to stack dac chips on top of eachother, but they are one step ahead of us... They put a little piece of copper/aluminum between each chip and then attach that to a heatsink on the side of the chips...

@BP as far as your problem with the coil breaking out at the top of the former... You can solve this by unwrapping a few turns at the top, then rewapping them in a loose spiral to the top of the former and then set a nice fat washer on top of that. Then stick a breakout point on top of that... If you don't want to retune with the extra topload you can omit the washer and just stick the breakout point on the side of the coil where the wire ends...

oh, and 6cm

Somewhere I lost a sense of scale in your pics, I was thinking more like 2cm You are certinly beating my vttc efficiency (as close as I can come you your solid state leetness) of 12cm at 1.8kw

first previous 3 4 5 6 next last

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob