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No limits to DRSSTC

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LAN_403

HV Enthusiast

Thu Mar 16 2006, 02:12PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Why are you using all those MMCs. You clearly have the dough, so why not just get a custom pulse capacitor built. It will really simplify things and probably cost about the same.

Dr. Drone

Thu Mar 16 2006, 03:19PM

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Steve Conner

Thu Mar 16 2006, 03:51PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
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I see you have a friend at the local power company, that will come in handy later on

I think it's great that you're using MMCs as it's probably the biggest MMC installation ever. Doing something nobody has ever done before gives us more experimental data.

The MMC I'm building here is a measly 16 strings of 10 0.47uF 1kV caps

Dr. Drone

Thu Mar 16 2006, 05:41PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
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HV Enthusiast

Thu Mar 16 2006, 06:06PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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wrote ...

The more I get input on you can not do that, it just makes me want to do it even more.

I don't think anyone is saying you can't use an MMC. But soldering 847 capacitors together in an MMC is no small labor task especially considering that for the same price you can get a single pulse cap to do the same job. I have no doubt in my mind that your 847 cap MMC will work as planned. But i kind of look at it in the way that someone would solder 400 1/4W resistors together to get a 100W rated resistor when that person can just go out and get a 100W resistor.

Also, not sure how it about how it will affect you system-wise, but that MMC you propose will have considerable inductance. Remember - parallel conductors (multiple strings) which have current going in the same direction just adds inductance. Of course, this inductance being part of the tuned primary circuit might not affect you either way . . .

Steve Conner

Thu Mar 16 2006, 06:46PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I always think that MMCs dissipate heat better than commercial pulse capacitors, because they have a bigger surface area for a given rating of capacitor. You can also blow air in between the strings which I think would be a good idea on high powered DRSSTCs. You can't blow air through the guts of a commercial cap, and the worry is that a physically large cap will melt in the middle while still feeling cool on the outside. Sure the oil does help in an oil-filled capacitor, but given that it's trapped in between the plates and can't convect, I think the MMC may still win.

I have a few 10kV 0.05uF pulse capacitors, they stay cool on my spark-gap coil but get worryingly hot on the DRSSTC. I bought them second-hand for about the price of an equivalent sized MMC, plus a bit to cover the assembly labour I wouldn't have to do. I'll try one against a 10kV 0.05uF MMC one day and see what difference there is.

Inductance isn't a problem as long as it's small compared to the primary inductance. If it's not, you can take extra steps like reversing the direction of current flow in every alternate string (but being extra careful to leave enough clearance to prevent flashovers)

GimpyJoe

Thu Mar 16 2006, 06:55PM

Registered Member #316 Joined: Mon Mar 13 2006, 01:30PM
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I really can't think of what to say... Wow! I've seen pictures and videos of Greg Leyh's 40kva coil and that was amazing. I can't wait to see what a nice efficient DRSSTC could do with several tens of kva! I really hope I can see it in person when it's finished. Good luck!

Dr. Drone

Thu Mar 16 2006, 07:11PM

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teravolt

Thu Mar 16 2006, 08:50PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
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single biult pulse capaitors of 14kv may less internal inductiance than a series paralell and might be smaller. What you got should work good. can't wate to see

HV Enthusiast

Thu Mar 16 2006, 10:36PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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wrote ...

Yes, inductance is a concern; I am going to use 1/16 inch copper bus about 1.5 inches wide between strings of caps to help with inductance. Actually I did get input from DC that this will not work, can not handler the power and will be choking on RF. I did get some good input too go for it by others on the Tesla list. 10 years ago if you told me about MMCâ€™s, I would have thought this was not a good idea; however, after using them on the last few coils, I am a firm believer of MMCâ€™s.

One way to decrease inductance is to possibly divide your MMC in half into two separate MMCs, one on each side of the primary coil. This way you can build each MMC and put them either on top of each other (opposing directions to cancel inductance) Not as good as alternating each string with different current directions, but should help.

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