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Adam Munich

Sat Jul 09 2011, 04:18AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

After 5 hours of wasted life I've given up on a full bridge with gate drive ICs. Those things are now obviously too fragile for the powers I'm trying to push, so I've thought of a new design with the parts I have. Basically it's two 3525 controllers with their oscillator caps in //. That'd sync them up, and I can use one to drive a GDT and the other will drive the low side fets directly. I really can't think of a more robust way to do it than that, so I'll try that tomorrow. If it doesn't work I'm blowing the damn bridge to bits with some ETN and buying a variac.

@nah I need some more info on that.

Arcstarter

Sat Jul 09 2011, 06:26AM

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

Nah wrote ...

Adam, can you help me figure out how to create a trigger?

I'm doing a EMP based project using 2 kjoules, and I don't know how to set it off.

I was thinking of using a trigger transformer and a xeon flash tube....

A xenon tube would be a bad idea, unless you like picking glass out of your face. 2kj would probably explode with such current. Not to mention, it would be incredibly lossy, turning a lot of energy into light and heat.

You guys, SCRs are not that expensive

Those are 1200v, and halfbridge modules (so if ya kill one ya got another one), and 2000 amps ITSM for 10ms, and 20ka i2t (IE point at which the die melts, or fusing current i believe). Im not sure what that means for it's max current for such a short pulse, though.

That is more expensive, but the datasheet says the maximum permissible energy is 349KA2s, but im not so sure what that even means.

Forty

Sat Jul 09 2011, 04:13PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

i've done the xenon tube thing for one of my earlier coilguns. just a couple hundred joules was enough to scorch the inside of a cardboard shield i put around it (with >1cm spacing on all sides.) the bulb was about 1.5 inches long and from a large camera flash unit. Although, if it's for an emp device, you might be able to use the exploding bulb as your emp spark.
But this is supposed to be about grenadier's bank.
have you thought about building a voltage multiplier to charge it? with a little care in building it, you could power it from mains. i'd definitely include some inductors and a resistive load like light bulbs, or else the initial current draw would trip your breaker in a heartbeat. you could use the mot as an inductor, your extra caps for the multiplier, and then all you'd need are the diodes.

that's the sort of setup i'm referring to.
for triggering it, if you didn't already have the pneumatic piston thing half ready then i'd say get an scr, but you might as well try it now. it's going to be loud, and might explode, so be careful.

Nah

Sat Jul 09 2011, 04:14PM

Registered Member #3567 Joined: Mon Jan 03 2011, 10:49PM
Location: USA, 1960s
Posts: 260

Do you think that the current is constant?

So 20,000 amps for 1ms?

Adam Munich

Sat Jul 09 2011, 04:39PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I think I might do that multiplier, considering my half bridge didn't work. The ICs synced up well enough, but as soon as I put a load on the bridge things died. To hell with bridges!

I'd like to get mazilli's driver working, but it refuses to work unless there is a huge air gap. If there isn't a huge gap, or half the core missing the thing squeals like mad and the fets heat up, and I really can't figure out a way to stop that. Replacing the gate driv resistors with an lm7812 did nothing.

I just want something that works, without having to put 1500 turns on that broken xrt. Although, that xrt makes a perfect isolation transformer for the voltage multiplier, and rate of charge could be changed with different lightbulbs, and 120*4 / .707 = 680 volts which is perfect for my cap bank... hmm...

pauleddy

Sun Jul 10 2011, 02:48AM

Registered Member #2909 Joined: Wed Jun 09 2010, 12:31AM
Location: fort belvoir, Va USA ( south of DC)
Posts: 145

for my bank i just have 2 480/240-120 50kva stepdown transformers run in reverse, and in series, limeted by 2 250W 7ohm resitors, and 1kv 30A brige rectifier that puts out about 780-800v dc. for safty of the charger i have a charge relay to diconnect the bank from the charge system and a large diode to prevent voltage reverse. for swithing i was lucky to find a big heavyduty 3 phase power swith for a sewage pump, 400V 800A, and has a solidnoid to switch it. it works for me, i personly like the simplicty of it, solidstate drivers are cool and all but i like the good old hum of 60hz and a 168000uf bank chargh to 750v in 1 1/2 minuts

Adam Munich

Sun Jul 10 2011, 02:30PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Well here is what I have so far.

*Transformer is held down to the board with epoxy, the caps with hot glue. Seems to work well.
*Diodes are what I had to use, 8A 1000V ultrafasts that can handle 120A repeated surges.
Caps, 2200uF 350V. Overkill but it's what I had.
*Switching for the low voltage side will be a 10A ssr, for the HV side a 75A 1200V IGBT will be used. Once again overkill, but what I had to use.

Now it's time for current limiting. I could use an mot but it's bulky, heavy and because of the high flux density, wasteful. I could also use a halogen lamp but that would likely melt everything. My third option is capacitive current limiting, and with a 110uF cap at 60hz XC= 24 ohms, which would limit power to 600W. The issue is finding a suitable capacitor.

Think lytics would work if put back-2-back to make a non-polar cap? Most likely they'd just explode...

Dr. ISOTOP

Sun Jul 10 2011, 02:36PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

If you use a TL494/<insert favorite PWM IC here> you can just turn down the duty cycle.

Adam Munich

Sun Jul 10 2011, 02:48PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Duty cycle of a 60hz transformer? Or do you mean switching the output IGBT? Hmm, that could possibly work, though there'd still be a big inrush current when the multiplier is first plugged in.

Inducktion

Sun Jul 10 2011, 07:15PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

You can get some reasonably high uF MKP caps from wima.

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