Steve Ward's Mini SSTC problem / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

Steve Ward's Mini SSTC problem

1 2 3 next

Move Thread

LAN_403

Brad

Sun Oct 05 2008, 03:30PM

Registered Member #1632 Joined: Mon Aug 11 2008, 08:53PM
Location: Plainfield, IL
Posts: 12

Hello all,

I have constructed several SGTCs in the past with some great results, but now I have decided to start exploring the world of SSTCs. I decided to build Steve Ward's mini SSTC to get an education in SSTCs since it seemed like a nice simple design. My question is this. Right now I have UCC37322 and UCC37321 removed, only the sockets are left on the board, and I am looking at the logic signals coming from the 555 and 74hc14. I have no power to my mosfets, just +12 and +5 for my timer and 74hc14. I can see my logic signals, and they look good, but while looking at the logic signals, my 1uf tantalum caps across the +12vdc supply in the socket for the gate drivers keep overheating and dying. Is this a result of not having the gate drive chips in place, or just possibly a bad batch of caps? All of my ic's have sockets on the board, so I can test small sections of the board with the delicate chips removed that are not in use, to prevent unnecessary death in the testing phase. I am using 1uf 35vdc tantalum caps. Looking at my +12vdc on my scope, it appears very smooth, and I have verified that the caps are only getting +12vdc. Any input would be greatly appreciated.

Thank you,
Brad

Dr. Drone

Sun Oct 05 2008, 04:04PM

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

Brad

Sun Oct 05 2008, 04:22PM

Registered Member #1632 Joined: Mon Aug 11 2008, 08:53PM
Location: Plainfield, IL
Posts: 12

Thank you!! I am new to a lot of this, I knew electrolytic caps were polarized, but I didn't know that Ta caps were until now. I checked my board and looked at the tiny printing on my caps, and sure enough I wired them up backwards! I'm glad this will be an easy fix.

Thanks again for your help!

Brad

Dylan

Mon Oct 06 2008, 03:21AM

Registered Member #1024 Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95

Most SMD tantalums are marked with a stripe like a diode, only the stripe indicates the positive terminal.
For some reason I constantly put them in back to front, my brain sees the stripe and says 'negative'.

aonomus

Mon Oct 06 2008, 03:54AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

Tantalums are known to not respond well to reverse polarization (ie: explode, sometimes with fire). I just finished building Steve Ward's mini SSTC and I used unpolarized 1uF caps and placed them as close as possible to the UCC's. Good luck on your project!

Brad

Mon Oct 06 2008, 09:12PM

Registered Member #1632 Joined: Mon Aug 11 2008, 08:53PM
Location: Plainfield, IL
Posts: 12

I just found some replacement caps for these at work, although they are 4.7uf instead of 1.0uf, I can't see any reason why these will not work in place of the 1uf caps. Thanks for the help and encouragement guys!

Brad

Brad

Thu Oct 23 2008, 06:39PM

Registered Member #1632 Joined: Mon Aug 11 2008, 08:53PM
Location: Plainfield, IL
Posts: 12

Thanks to your help, I got this coil running last night, and boy was I surprised that is fired up right up! I ran it on and off for about an hour. Eventually my curiosity got the best of me and I turned my duty cycle all the way up and my pulse width all the way up. (I'm new to this, I think that is the right description for my on signal as long as possible and my off signal as short as possible) Needless to say something blew. At first I thought it was a MOSFET, but upon closer inspection it looks like one of my fast diodes across my MOSFETs blew(D1 and D2 on the schematic), as it is the only thing on the board with scorch marks. First I would like to thank Steve, I am amazed how well it worked right off the bat. Second, on his final schematic D1 and D2 are listed as items that can likely be omitted, I am thinking about doing that, but is it a good idea since I blew one? Is that maybe a sign that it blew instead of my MOSFET? Any input would be greatly appreciated.

Thanks!

Brad

Bamacoiler

Thu Oct 23 2008, 09:23PM

Registered Member #1628 Joined: Wed Aug 06 2008, 08:48PM
Location: Huntsville, AL USA
Posts: 95

No experience on the subject but decent with electronics I guess...

Did you ever think he said they could be omitted because they blew easily?
May be a dumb statement but it makes sense to me.

101111

Fri Oct 24 2008, 06:25AM

Registered Member #575 Joined: Sun Mar 11 2007, 04:00AM
Location: Norway
Posts: 263

Well, evidently there seems like there would be a quite large pulse coming back in the same direction as the diode is connected.. So something seems to be wrong. But there are others that might explain this better then me.

Brad

Fri Oct 24 2008, 02:45PM

Registered Member #1632 Joined: Mon Aug 11 2008, 08:53PM
Location: Plainfield, IL
Posts: 12

Aesthetically, the coil operates well, ~ 8 in discharges to air. But I noticed that one MOSFET gets much warmer than the other. I'm tempted to just cut the diodes out like Bamacoiler suggested and see what happens, but that solution is not very satisfying. Also, I left out the 5ohm resistors on the gate drive, Steve mentioned something on his site that this may be able to be done, but could it have some negative effects?

Thanks for the help,

Brad

1 2 3 next

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