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Registered Member #52
Joined: Thu Feb 09 2006, 04:22AM
Location: Austin TX
Posts: 57
To be fair, it peaks at 30W after a burst and drops to 8W before a burst. The 6" strike was after it had charged for 2.5 seconds. The rate is currently set to 1 burst per second with 5" strikes. I think if I had a better primary that I could get more efficiency.
This is the schematic as it currently stands. The bad thing about it is that the power supply isn't regulated.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Yea, at over 1MHz too! I think the coolest thing is that it's actually powered off a wall wart and still manages 5-6" sparks. Way to go JimG!
BTW: Pulsed SSTCs can give a very high "Efficiency" in terms of inches of spark out per watt in, just by operating at a very low breakrate. In the limit, you could make a giant DRSSTC, spend a whole afternoon charging its DC bus cap bank off a 9v battery with a tiny DC-DC converter (even a small battery contains hundreds of joules) and then release all the energy in a few milliseconds to produce a giant 10 foot arc. Then you could truthfully claim you got a 10 foot arc out of a 9v battery and a 3 watt DC-DC converter.
This is considered cheating though: if you want to play at high efficiency, you have to measure it in the steady state at 100-120 discharges per second. The reason for choosing this breakrate is that John Freau used 120 in his original experiments on efficiency.
Registered Member #52
Joined: Thu Feb 09 2006, 04:22AM
Location: Austin TX
Posts: 57
Steve Conner wrote ...
This is considered cheating though: if you want to play at high efficiency, you have to measure it in the steady state at 100-120 discharges per second. The reason for choosing this breakrate is that John Freau used 120 in his original experiments on efficiency.
I didn't want to boast about the power usage too much because when running at 100 bps it only produces 1/2" streamers and 1" sparks.
When doing the longer sparks the cap drains within a few bursts. The mosfet drivers will almost completely drain my supply capacitors and it could take about a quarter second before the switch mode power supply starts fully working again. It's an issue with using a single 12VA wall wart to power both sections of the circuit.
Omicron wrote ...
Are the computer caps the same one sold at the electronics gold mine?
No, I got the cap from a local electronics parts surplus store.
I've started winding a lower frequency secondary and figured I could cut my circuit board length in half by going with a two layer bridge. The EG cap may be a good fit to make a smaller controller.
Registered Member #358
Joined: Sat Apr 01 2006, 06:13AM
Location: UCSB
Posts: 28
First of all, I must say that I am impressed. The first time I saw it, I thought it was bigger than that, and just another 'little' DRSSTC.
There are a few things I don't get though. The most important one, is why did you step the voltage down to 12v with a wall wart, and then step it back up for the IGBTs, instead of just rectifying mains? A single diode could easily supply more power at 170v. Then you could turn up the break rate a bit, and make it even cooler.
You said that you learned that tuning the primary low, you could get the same results with IGBTs as with MOSFETs (detuning is a cool trick, huh?). How much lower are you talking about? What is the driving frequency vs the secondary resonance frequency?
I think you can push this thing harder! Step up the voltage more, and see what it's capable of!
Registered Member #52
Joined: Thu Feb 09 2006, 04:22AM
Location: Austin TX
Posts: 57
JimmyH wrote ...
There are a few things I don't get though. The most important one, is why did you step the voltage down to 12v with a wall wart, and then step it back up for the IGBTs, instead of just rectifying mains? A single diode could easily supply more power at 170v. Then you could turn up the break rate a bit, and make it even cooler.
I went with the wall wart because I wanted to be in close proximity to the coil while I poked around with it and not have live mains. It would have been a better accomplishment if I didn't have to sacrifice a fast break rate for long streamers. The next coil I build will definitely not be powered this way.
JimmyH wrote ...
You said that you learned that tuning the primary low, you could get the same results with IGBTs as with MOSFETs (detuning is a cool trick, huh?). How much lower are you talking about? What is the driving frequency vs the secondary resonance frequency?
The drop in fequency wasn't much, ~1.4Mhz down to ~1.3Mhz. I not sure of the exact frequency since I eyeballed it with a scope. With the new top load the caculated resonance is 1.17Mhz, but I'm running closer to 1.10 Mhz.
I've noticed that I'm getting no notches in my waveform off of the primary coil, my larger DRSSTC would get them after 10 to 15 cycles. Is this common with de-tuning, or is a symptom of low coupling?
JimmyH wrote ...
I think you can push this thing harder! Step up the voltage more, and see what it's capable of!
I have a lower frequency coil wound and I've started designing a new circuit with better gate drivers. The coil I have now has an unloaded frequency frequency of 1.98 Mhz and the new one is 1.55Mhz and is a half inch shorter. I've decided to leave the current coil as a show piece and really push it with the new coil.
Registered Member #358
Joined: Sat Apr 01 2006, 06:13AM
Location: UCSB
Posts: 28
I went with the wall wart because I wanted to be in close proximity to the coil while I poked around with it and not have live mains. It would have been a better accomplishment if I didn't have to sacrifice a fast break rate for long streamers. The next coil I build will definitely not be powered this way.
Well, if you're gonna do another one, putting a fat 10kohm resistor in series could give you the same effect while you test it out.
The drop in fequency wasn't much, ~1.4Mhz down to ~1.3Mhz. I not sure of the exact frequency since I eyeballed it with a scope. With the new top load the caculated resonance is 1.17Mhz, but I'm running closer to 1.10 Mhz.
Ok, I wasnt sure if you were just driving the crap out of it at 500khz, or something rediculously low.
I've noticed that I'm getting no notches in my waveform off of the primary coil, my larger DRSSTC would get them after 10 to 15 cycles. Is this common with de-tuning, or is a symptom of low coupling?
Yeah, that tends to come with detuning, but low coupling would also reduce the notching. If you're worried about coupling, javatc can probably give you a better number than you can measure :P
I have a lower frequency coil wound and I've started designing a new circuit with better gate drivers. The coil I have now has an unloaded frequency frequency of 1.98 Mhz and the new one is 1.55Mhz and is a half inch shorter. I've decided to leave the current coil as a show piece and really push it with the new coil.
Ok, cool. As long as you push the new one . Steve Ward and I are thinking of making tiny (DR)SSTCs, so if you want to keep your recognition of owning "the most badass tiny SSTC", then don't slack on the new one!
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JimG's Smaller DRSSTC
I think the coolest thing is that it's actually powered off a wall wart and still manages 5-6" sparks. Way to go JimG!
. Steve Ward and I are thinking of making tiny (DR)SSTCs, so if you want to keep your recognition of owning "the most badass tiny SSTC", then don't slack on the new one! 
