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coillah

Fri Jun 19 2009, 02:39AM

Registered Member #1517 Joined: Wed Jun 04 2008, 06:55AM
Location: Chico CA
Posts: 304

This will be the fourth time I have replaced my bridge components for the Mini SSTC. I would like to know if anyone else has had trouble in the past getting the SSTC5 to cooperate. The behavior of the circuit seems very erratic, and unreliable.

After replacing all of the components I am assured at least one good fire up. I can crank my power up to 100%. After a few runs, the bridge breaks again. I have absolutely no idea why it breaks down, and I am at the end of my patience. I would write with a more positive tone if it was not such a pain to replace blown parts (bad design on my part XD ).

Some things I have noticed, the bridge seems to break when I am turning off the circuit, slowly? Is it possible that the circuit is susceptible to variations in power input such as those seen when turning the device on or off? I have a video of operation on youtube:
Vid

I am sure someone here has some advice or thoughts, please! I am on my last set of mosfets and diodes, I would really like to not have to order more.

Another note, I have no idea if the fets are really the thing that is dying... The coil usually ceases functioning without any noise at all.

Dr. Drone

Fri Jun 19 2009, 04:02AM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673

semiconductor

Fri Jun 19 2009, 06:01AM

Registered Member #1989 Joined: Fri Feb 20 2009, 05:28AM
Location: Edmonton Alberta, Canada
Posts: 17

I am having the same problems with my SSTC5. I keep blowing my bridge. sometimes when I turn the bridge on I get a short 1" blip of corona on my breakout point and thats it... I have ran out of silicon and have givin up for now... unless anyone has any suggestions???

Dr. Dark Current

Fri Jun 19 2009, 08:05AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Maybe you guys need to use more primary turns and tighter coupling?

plazmatron

Fri Jun 19 2009, 03:45PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

I had a similar problem, with the SSTC5 that was eating silicon like no tomorrow.
There are a number of things to check.
First off are you using an SMPS to provide your 12v? These can behave in unpredictable ways in even modest RF fields. Use a linear supply.

Are there enough decoupling caps on all the chips, the UCC`s, the 555 and the hex inverter? Its a good idea to have a high value electrolytic for each chip as well as the tantalums. This is especially important, if you are running unenclosed boards all over the worktop!

I found antenna feedback to be a pain in the ass, and replaced it with a 100:1 current transformer, I found feedback to be a lot more stable after that, as well as resulting in a more compact coil.

As Dr.Spark says, start with a low bridge voltage to iron out SSTC issues.

Post some pics of your setup.

Les

teravolt

Fri Jun 19 2009, 07:35PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

this circuit has no syncronization of duration and pulse train. with this design the bridge can be interruped at any time during the primary oscillation and can alow high voltage to come back to the fets when they are turned off at the wrong time. Steve Wards universal driver is far more sapirior and you could inject a frequency into the feed back input to create a sstc

Nicko

Fri Jun 19 2009, 08:28PM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

I've built one of these and its rock solid - I run it at a max of about 210VAC in (its slightly upgraded for UK 230VAC mains).

It barely gets warm and is highly reliable...

Son #2 playing with SSTC5 fire...

Not very pretty, but it works...

Not being an ACC, I really & truely have something new for the upcoming Cambridge TeslaThon

vasil

Fri Jun 19 2009, 10:10PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

The problem can be indeed a small number of primary turns.
Also, the distance between the antenna and the coil is very small. Just keep a safely distance and bend the top of the antenna away from the coil.

http://www.geocities.com/livvasil/Mini8.jpg

Also, it seems to be CW, not interrupted. Maibe your FETs are low current, bad design of the bridge, no filter caps on the logic chips, primary cap near the resonance, etc.

StevenCaton

Fri Jun 19 2009, 11:38PM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

Colliah, try putting the electronics in an aluminum project box to shield them from the resonator. You can definitely run into RF problems running your circuit board out in the open. I have a hunch that RF will eventually kill the mini sstc with no shielding of the electronics. Also, I still have a hunch that a toroid isn't neccesary for a half bridge of p260's, as it loads down the bridge too much.

"Insanity: doing the same thing over and over again and expecting different results." - Albert Einstein

I'm definitely not saying that you are insane, but some serious changes are probably in need for your circuit to work well. I went through the exact same thing as you, so I feel your pain. Change those variables, such as number of primary turns, coupling, etc. I want you to have that coil working.

Proud Mary

Sat Jun 20 2009, 12:08AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I'm sure that a lot of circuits made by members fail because of inadequate shielding.

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