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Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
Goodchild wrote ...
And yes I would make your tank impedance much higher, Not just for a lower tank voltage put also the fact that you will have less primary current for a longer period of time.
A higher tank impedance results in a higher tank voltage for a given primary current.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
This is true but.. you also run a longer burst meaning you will have a lower peak current. Take the QCW for example you can usually get away with only a 4Kv cap for 4 or 5 feet of output.
zzz_julian_zzz, don't mix capacitors that is a no no. I would however suggest using some 0.47u at 2Kv 940C they seem to be a good price for there ratings vs the others in the line up. I understand cap are expensive but if you can't build the right bank your better off saving and buying the right kind.
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
Goodchild wrote ...
This is true but.. you also run a longer burst meaning you will have a lower peak current. Take the QCW for example you can usually get away with only a 4Kv cap for 4 or 5 feet of output.
I see what you're saying, but QCWs are different enough that comparing spark length and primary currents to a pulsed DRSSTC is a bit unfair. With a certain (relatively big) DRSSTC system with a given bridge voltage and spark length target, the tank voltage will generally rise as you increase the tank impedance. Higher primary impedance also means a more expensive tank cap, at least if you try to stay close to the datasheet max rating of the caps.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
My approach is to use an OCD that limits the current instead of ending the burst outright, and a PLL with a limited lock range. With these two adjustments I can set it up so that the tank cap voltage rating is never exceeded.
If this results in unsatisfactory spark length, that's a separate issue.
My experience is with smaller tank capacitors like 0.05 or 0.1uF, with about 400A of tank current at 220kHz. I designed for a 300us burst, but I've been running it up to 1 or 2ms with the 400A limit.
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
I'll post up the output, once the DRSSTC has been powered. Thanks for the inputs, please wait for the output.. I'll go first on the high impedance primary with a capacitor (not poly prop but tested with my other DRs works just fine w/ tolerable heating) capacitors of (0.15/2kv) 4 in series / paralleled by 5 = 187.5 nf /8kV ..
If not satisfied with the output, I'll change the capacitors to CDE (.15 /2kV) arranged to make total capacitance of 0.255uf / 4kV
If IGBT popped due to prim current I'll change it from mg150qy2s51(150A/1200v - fullbrdge) to mg400q2ys60 (400A/1200v -halfbridge) since my coil runs at 90KHZ sec and primary runs at 70KHZ.. Am I gonna face another issue due to phase lead???
Thanks!
EDIT: @ Eric, I noticed that in your DRSSTC 2 & 5 you used system voltage of 680V,. The question is, If the current in the primary is in SAME level with both 680v (of course with shorter on time) and 330v (longer) and Also the Voltage in the primary is the same, Would it produce the same spark length output??? Thanks..
My experience is with smaller tank capacitors like 0.05 or 0.1uF, with about 400A of tank current at 220kHz. I designed for a 300us burst, but I've been running it up to 1 or 2ms with the 400A limit.
Did these long bursts improve spark length? Or just thickness?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
It improved both length and girth. The coil was hitting the walls of the Faraday cage and arcing down to its own strike rail, which it didn't do before with shorter bursts at a higher repetition rate.
However, current draw from the mains was stupendous, so I'm not sure if it made an improvement in terms of spark length per watt.
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
Hey, Just uploading the pics of my LTSPICE computed Set up.. =),. Please comment on my primary =) a little trash-rush set up =) but hopefully this will suffice my requirement parameters =D
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LTSPICE Top load Voltage output
The coil was hitting the walls of the Faraday cage and arcing down to its own strike rail, which it didn't do before with shorter bursts at a higher repetition rate.
