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SSTC bridge blew up

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Sigurthr

Wed Apr 03 2013, 05:49AM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

For the ground wire as thick as possible. Flat copper strap works even better but is expensive.

You can't solder to aluminium with regular 63/37 solder, it takes special aluminium solder to work. Your bridgework looked fine though, but if you do want to change things up see if you can get thin copper strips. They are less inductance than wire and are easier to solder.

Too bad you don't have a scope; I could show you via pictures on how to check the GDT phasing.

Atomic

Sat Apr 06 2013, 08:55PM

Registered Member #8743 Joined: Thu Dec 13 2012, 04:18PM
Location:
Posts: 12

Found a store that has 2m rods but I'm quite sure I won't be able to get them 2m deep. Is there any problem if I leave a lot of rod over the ground?

How many rods do I need at least?

I think I'll try with stranded copper wires on the bridge, should be easier to solder. Unless those aren't indicated..
I'm pretty sure I won't be able to buy copper strips here. Might be easier to get some raw copper PCB and etch it, just for the bridge work...

Hope I'll buy a scope someday :)

Physics Junkie

Sat Apr 06 2013, 09:23PM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

Atomic wrote ...

Found a store that has 2m rods but I'm quite sure I won't be able to get them 2m deep. Is there any problem if I leave a lot of rod over the ground?

How many rods do I need at least?

no problem with it sticking out of the ground. If this was a high power sstc or drsstc then I would say do it properly. but you will be just fine. the more rods the better but theres really no reason to use more than two. I'd say use two, that way the amount of rod sticking out of the ground would be somewhat negligable. if the rods are 2m long, then bury them about 2m apart.

Sigurthr

Sat Apr 06 2013, 09:25PM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

For Rf work it doesn't matter if you use stranded or solid copper wire as the skin effect constricts the current to the surface either way. If the strands are individually insulated then it works better than solid core of the same diameter, this is called Litz wire.

Get the rods as deep as you can, length exposed above the ground does nothing. Think of it like the current x voltage = power equasion; 10 rods at 1ft or 1 rod at 10ft deep same effect. (In practice there may be some increased performance with the 10 1ft rods as the soil may not be homogenously conductive and you'd have better luck hitting a conductive spot with more rods - but the analogy still stands).

I wouldn't stress over the bridge construction, what you had before looked fine honestly, and I've built far more inductive bridges that still survive to this day under heavier loads. Do what you did before and it should be fine.

Atomic

Mon Apr 15 2013, 10:01PM

Registered Member #8743 Joined: Thu Dec 13 2012, 04:18PM
Location:
Posts: 12

Finally had some time to rebuild the bridge and got first light yesterday!
The streamers are small (0.5 to 1") but the field seems to radiate a lot, it could light up a CFL easily from a foot away.

The sound it made was quite weird, it had a beating like an out of tune instrument. Sometimes it took a few seconds to start sparking as well.

Got about 5 runs of up to 30s before the bridge blew up again. The heatsink got somewhat hot after 30s. This time I'm quite sure the high side gate resistor shorted to Vbus+ and the source pin of the MOSFET exploded (again). The rest of the bridge suffered minor damage and I think I'll be able to fix without rebuilding.

Didn't have time to ground the rod so I just used a bigger counterpoise. Also increased the antenna, shortened the primary GDT wire and the coil primary wire and placed everything closer together.

Videos (including the explosion!):

I'll only try to run it again with a proper ground and a new table (setting it up on the ground sucks big time).

Any tips are appreciated, speacially to get bigger streamers!

Thomas W

Tue Apr 16 2013, 05:25PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

i believe not only would a ground will keep you safer, but it can help with the streamers.

Kizmo

Tue Apr 16 2013, 06:14PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

Atomic wrote ...

You are asking for trouble with this kind of build style.

1. Get rid of those breadboards
2. SMPS + sstc is never a good idea. Get iron core transformer for your controller.
3. Driver boards should be in grounded metal boxes

It is more than likely that all RF crap gets to the feedback loop of your SMPS and makes it shut down or do other weird things. I have seen this happening several times before.

Sigurthr

Tue Apr 16 2013, 08:12PM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

I've found that grounded logic boards and supplies are only needed when using a counterpoise. This is not a rule but merely an observation based on my own findings.

The above posters are right though, and I did warn you about breadboard drivers a month or so ago =P. Also I wrote a full reply to your identical post on LPF =).

As I said on LPF, cheep on chuggin, you're making great progress!

Atomic

Wed Apr 17 2013, 10:00PM

Registered Member #8743 Joined: Thu Dec 13 2012, 04:18PM
Location:
Posts: 12

Thanks for the tips, guys!

I'll try and get a ground rod before I run it again. The only problem is the wire, no local stores have 6AWG and all of the sellers say the standard for grounding is 2.5mm^2 (which is just below 13AWG). Do you guys think that'll work?

As for the breadboards, I have several reasons not to drop them:
-I'm not great with soldering, which will mean lots of dead parts
-I'd like to experiment with the driver and specially with the interrupter to get the best results possible before etching a board
-I intend to change the antenna to CT feedback on the near future
-I'd like to add sound modulation
-I've seen a video of a very good SSTC with a breadboard driver

Bought a 15V 1A transformer today and will try it on the next run. Hope it improves things.

As for grounded metal boxes I'm pretty sure that's not really needed... I've seen way too many videos of great coils with plastic boxes or no box at all.

zzz_julian_zzz

Wed Apr 17 2013, 11:50PM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

Atomic wrote ...

Thanks for the tips, guys!

I'll try and get a ground rod before I run it again. The only problem is the wire, no local stores have 6AWG and all of the sellers say the standard for grounding is 2.5mm^2 (which is just below 13AWG). Do you guys think that'll work?

Sir, you might consider to connect the wires in parallel for lower impedance wiring..

And, ground metal box is important. this will make your brain circuitry invulnerable to unwanted noise, signals, etc, that will cause glitches to the system and explosions.
Thanks.

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