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Mini SSTC runs funny. Few issues!

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Killa-X

Mon Oct 26 2009, 04:08AM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

Hello all. I recently had my frat test of my mini SSTC today. The first test was bad. Nothing worked at all! After time of looking around, I nearly gaved up. Myfirst MOSFET, that gets the first voltage, always gets hot. Eventually one of my uccs died. And when I put my 555 interupter to the ciruit, and share grounds, it doesn't work! Arcstarter looked over my diagrams and said they are all good. More messing, I pliged te interupter right in the antenna of the 46hc hex inverter. I ended up getting 2" streamers on 56v. After time, the one fet heats up, and I saw this orange glow. It was my GDT wound with twisted magnet wire. Someow it cooked it self and melted by shorting. Tisktisk.

So here's my questions.
1: what causes a MOSFET to get hot? The first one gets hot, te 2nd one stays cool.
2: why is it when I share the ground from my 555 to ucc board, things don't work. It's just power supply grounds!
3: I noticed since the first time, my 400, 560 bank on the 120vac to dc, a buzz emits from there. With my interupter to the hex inverter, the buzz I'm hearing from that board matches the same frequency. What's weird is it almost sounds like it's coming from the capacitors. Either that or mY e there's a bad solder connection buzzing? What!

I got time for help. Ldoking for CAT5 cable to strip and make a new GDT out of something else besides 3 strands of twisted 24awg. Thanks!

raff

Mon Oct 26 2009, 04:31AM

Registered Member #2315 Joined: Tue Aug 25 2009, 02:35AM
Location: Leyte, PH
Posts: 161

try this:

wound 15Turns on your GDT and MEASURE with an LC meter... what is the inductance value?

Arcstarter

Mon Oct 26 2009, 05:20PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

About the heating... That is why i told you i wanted to see the gate waveforms :P. I know you showed me, but that was with the interrupter, and before you really had time to change it, the GDT went up in smoke... After you fix the GDT, run around 30 volts or something to the bridge, with pin 3 of the UCCs to +12v, and scope the gates. Let me see it on webcam when you do :P.

It could be too much dead-time on one, causing shoot-through, it could be bad waveforms (the leads on your GDT where very friggen long), tuning could help, adjusting coupling, maybe more topload to lower the freq could help...

The 555 has to be grounded. Common negative. The whole circuit uses common negative, meaning the 5v, 12v, and 9v (the battery for the interrupter) are all the same ground, so you can use the same ground for all the ICs. All of the ICs need reference voltage and all that great stuff.

The filter caps are buzzing when the bridge starts pulling current. When the interrupter is off, there is nothing being pulled from the caps. When it is on, the caps are filtering/supply more current. Maybe electro-magnetic repulsion or attraction. I am sure not all caps would do that. Not to mention, i used alot more than 1,000uf on my bank to make the hum in the sparks go away (in CW mode). The general rule of thumb is around 1,000uf per amp, i usually double that, because i like the almost silent sparks. Just a slight hiss

.

Like i said before, your GDT was fine. I think you are putting too much current into the primary, somehow. 24 gauge is good for 3.5 amps. Your supply is not made for more than an amp. Im not sure, someone else may be able to tell us what is wrong

StevenCaton

Mon Oct 26 2009, 05:54PM

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

Your buzzing is probably coming from your gate drive transformer itself. Its called lamination rattle.

When I built that coil, the GDT would make a buzzing noise that would change frequency with the interruptors frequency.

Killa-X

Mon Oct 26 2009, 06:58PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

SteveC wrote ...

Your buzzing is probably coming from your gate drive transformer itself. Its called lamination rattle.

When I built that coil, the GDT would make a buzzing noise that would change frequency with the interruptors frequency.

isnt. The GDT isnt anywhere near the 120V bridge...I used a straw to pin the location and its from the PCB board with 120V to DC, and 2 capacitors..that buz IS the capacitors cihp.

Arcstarter

Mon Oct 26 2009, 08:11PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Just the plates rattling im sure, due to the load. No matter what it is, don't worry too much. Just be sure to shield yourself from anything if it explodes. I have had many diodes explode and draw blood. If it will draw blood, it could damage your eye.

Be careful...

brtaman

Mon Oct 26 2009, 09:13PM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Arcstarter wrote ...

Just the plates rattling im sure, due to the load. No matter what it is, don't worry too much. Just be sure to shield yourself from anything if it explodes. I have had many diodes explode and draw blood. If it will draw blood, it could damage your eye.

Be careful...

Yes, definitely wear eye protection! I have had FET shrapnel come within inches of my eyes at great speed. Needless to say the sharp hot plastic will do extensive damage to an eye.

What sort of power supply are you using to supply the driver board? I an enormous ammount of trouble due to nasty ripples in my power supply of the time. One of the results of it was extreme heating and failure of initial mosfet on the bridge, leading of course to explosions.

Killa-X

Tue Oct 27 2009, 03:48AM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

Unny all my posts have been done on my iPod. I type fast. :). Anyways. I did some more messing today. Made a new GDT out of a 12ft serial cable. Over 15 wires in it, I can make over 21 GDT with that!! Anyways. Today the GDT and UCCs never got warm. I also replaced my fÃªte seeing t was shorting my transformer. I need to get 12v zeners on the gate I'm sure, but I ran new fets, no heat sinks, and was getting small hf 1cm steamers. Not near as good as befor. Yet somehow my 555 connected to the antenna made that go. I'm thinking the antenna was too close making it high frequency. It even caused some lights up stairs to flicker, going to take it off mains ground and move the tesla ground to my old earth ground that my sgtc used.

To your question, I'm using a 198W stereo transformer. Today, only 38 volts. It's the same transformer I use for anything HV with flybacks. As I mention ealier, I have more tests to try out. Seeing it runs for 10 secs without my fets getting warm (no heatsink) means I'm getting somewhere! I can even finally run my 555 WITH it's ground connected unlike last time!

Tomorrow is another day. Moving to new ground rod. And taking any suggestions from here. Also going to pop 56v in (had 2" streamers) and mess. As arcstarter saw, those 2 inch streamers were exactly correct. Sounded very good.

Thanks all! iPod heh :D

Dr. Dark Current

Tue Oct 27 2009, 03:43PM

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

Sorry for not reading the whole thread, but problems like this are often caused by bad feedback phasing or insufficient feedback. Try swapping your SSTC primary connections, if this doesnt help then swap your GDT primary, if still nothing swap the primary once more.
(IIRC only one out of 4 combinations is right?)

Killa-X

Wed Oct 28 2009, 12:39AM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

Well, tomorrow or so ill have to get you a picture of my messed up wave forms im picking off my scope. I'm able to interupt it, but it seems to stay at a high frequency. The scope also doesnt even show any sign of a visable square wave...It's really messed up...I didnt get much testing done today when i made a new GDT, with much closer windings and better twistings.

The only thing im stuck on, is when my coil is on, i get messy waves on my scope. When i turn it off, i get a blip (Small time frame) of a decent looking square wave, then it goes off. It seems like when i turn off ONLY my power supply to the fet board (58V) while it discharges it shows a square wave...Any reason why?

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