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A feasible goal for a Miniature SSTC?

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LAN_403

Reaching

Thu Feb 09 2006, 09:46PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

my micro drsstc works at around 300khz and i get very good performance out of it. i cannot agree with the argument, igbts cannot switch faster than 100khz, thats definately wrong. there are igbts which can switch up to 500khz without many problems, see the FGAF40n60UFD from fairchild for example. you even can switch them with 1mhz but the max switchable current decreases dramatically, but for a micro coil who cares? its definately possible.

a 1" x 4" coil wound with 0,1mm wire has a resonant fres from around 1,5mhz. when you put a 1,5" x5" toroid on it you are at around 720khz. so whats the problem?

heres a pic of the smallest drsstc ever isnt it?

Dr. Shark

Thu Feb 09 2006, 09:49PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

A lot of people are suggesting to use very fine wire to get the fres down, but I was hoping that there are other ways. By using thin wire, you end up with much less copper on the coil, so the total power handling will go down considerably, which is not going to help bis sparks. Richie Burnetts Class E TC actually uses fairly thick wire, so he can push 500W through it, and that makes for some very impressive (if not long) arcs.
Of course for a high voltage the ratio of inductance/turns/whatever needs to be large, but using a higher primary voltage or less turns will probably have the same effect.

I dont really see the problem of the driver being bigger than the coil that serious: The brains can be done in SMD if one really wanted to push the limits, and a fullbrigde of 40n60 miniblocs, hell, is not that big, is it?

EVR, I have read all the old threads, but the point for me really was to get the longest sparks out of a small coil, and IIRC the coils there hardly produced any sparks at all.

Reaching

Thu Feb 09 2006, 09:56PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

look at this coil, arent that big sparks for the coilsize?

this coil is only slightly bigger than you wrote above. 2"x6" :D

Extreme Electronics

Thu Feb 09 2006, 10:16PM

Registered Member #74 Joined: Thu Feb 09 2006, 09:17AM
Location: Nottingham UK
Posts: 99

Im impressed with your coil, Reaching, thas some acheivement
Ok 100Khz, was a little low.. I have had IGBT's running faster than this, but as you state their max current drops considerably.

I realise that there are IGBT's that will switch up to 500Khz but at that frequency with the current limitations are they any better than mosfets ? according to the data sheet a FGAF40n60UFD at 500Khz is limited to about 10A.

What is the primary current on your small DRSSTC ?

I dont see any problems with flashover being the limiting factor 3-4X the secondary length is regularly acheived with good field control and a breakout

Derek

Marko

Thu Feb 09 2006, 10:23PM

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

I saw reaching's coil before and it looks even impossible how it doesn't arc to primary, with that streamer. :D
But this is rather too big for real mini-coil, i would put a line at C- vitamine (1 inch) for that... ?!
What im talking about are really miniature coils.

For driving coils like that IGBTs are really not needed, they could be replaced easily with bipolars or mosfets, modifying ZVS driver for higher freq. could be good idea.

I saw lots of small coils without toploads, but they are important here as with big coils, and also lowers resonant frequency (ping pong ball is ideal :D)

Dr. Shark

Thu Feb 09 2006, 10:26PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Hey Reaching, that is definitely a great coil, is it the DRSSTC5 with 280kHz on your homepage? I might actually look into building something like that, but I would really like to go even smaller

Did you not test this coil with MOSFETs too, I think you were talking about that on the old board?

Marko

Thu Feb 09 2006, 10:36PM

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

I am now building a bit larger drsstc, secondary may even be over-sized (but its good, low frequency), lol its all off the topic..

!dodge

Reaching

Thu Feb 09 2006, 10:53PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

yeah, its the drsstc5 on my site.
i tested it with mosfets but they popped all the time due to the high switching losses and i gave up.now i use a fullbridge of irg4pc50ud igbts.

yeah and i had many prim sec arch overs at the testing phase and wracked around 6 igbts until i got it. now i have a strikerail but i can only go up to 200ys on time, with more i have primary arch overs all the time.

i havent measured the primary current so i dont know but i think it will be around 200A or so

i welcome competition of course, its a real challenge

Jim

Thu Feb 09 2006, 11:25PM

Dunce.
Registered Member #28 Joined: Fri Feb 03 2006, 03:29AM
Location:
Posts: 76

Derek and I had a bit of a friendly competition a while back, as to who could create the smallest SSTC. I believe I still hold the winner title... haha... but we won't get into that, will we. I had one that was, if I can remember clearly, about 1 dia X 1.3 cm long, and made a spark length of ***5mm***!

JimG

Fri Feb 10 2006, 01:51AM

Registered Member #52 Joined: Thu Feb 09 2006, 04:22AM
Location: Austin TX
Posts: 57

I recently built this 1.1 Mhz DRSSTC that has a 1x3.5" secondary. I've been able to get 5.5" ground strikes with it.

I had considered running it as a class E, but went with a full bridge of SMD IGBTs instead.

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