Capacitors in Series
As soon as someone admits to being foggy on series-connected
capacitors an automatic caution flag needs to come up. Anytime
caps go in series, and especially if you're about to throw a
'megavolt' across it a set of parallel resistors needs to be
provided. This equalises the voltage across each capacitor, and
consists simply of a resistor across each cap of the series
combination...looks like a ladder network. Unless this is done
the cap string will not act as a voltage divider, and one or
more caps may end up with a voltage across them that exceeds
their working voltage rating. At least this is the practice
with capacitor banks that are expected to have dc voltages
across them. If run off ac only the caps will voltage divide,
but the resistors still sound like a good precaution to me.
> From grendel!grendel.objinc-dot-com!tesla-at-csn-dot-net Mon Jan 30 15:08:23 1995
> Date: Mon, 30 Jan 1995 12:57:18 +0700
> From: tesla-at-grendel.objinc-dot-com (Nikola Tesla aka Chip Atkinson)
> To: EDHARRIS-at-MPS.OHIO-STATE.EDU, GCerny-at-ix-dot-netcom-dot-com, chip-at-grendel.objinc-dot-com,
> kdg128-at-batoche.usask.ca, kukkonen-at-alpha.hut.fi,
> mconway-at-deepthnk.kiwi.gen.nz, nvv-at-mlb.semi.harris-dot-com,
> richard.quick-at-slug-dot-org, steve.greenfield-at-rook.wa-dot-com,
> Subject: RE: TESLA VIDEO
> Content-Length: 6338
> >From richard.quick-at-slug-dot-org Mon Jan 30 01:14 MST 1995
> >Received: from uustar.starnet-dot-net by csn-dot-net with SMTP id AA00593
> (5.65c/IDA-1.4.4 for <tesla-at-grendel.objinc-dot-com>); Sun, 29 Jan 1995 21:58:15 -0700
> From: richard.quick-at-slug-dot-org (Richard Quick)
> Subject: RE: TESLA VIDEO
> Date: Mon, 30 Jan 1995 03:11:00 GMT
> To: tesla-at-grendel.objinc-dot-com
> * Original msg to: Lisanap-at-cats.ucsc.edu
> MN> The DC transformer I mentioned in my previous post is rated
> MN> at 1.5 MA. It is set up with a complete control circuit,
> MN> including a switch, a small variac, a meter, and RF chokes and
> MN> bypass caps across the primary and ground lugs. The primary is
> MN> 118 VAC, 50-500 CPS. I can make a Jacob's ladder from this?
> MN> One side + and the other - ? If that works I expect it would
> MN> require a dedicated ground or could it be filtered back into
> MN> the house ground?
> Oh, you did not mention before that this was a DC power supply.
> While it is possible to make a Jacob's Ladder from this, I doubt
> if the secondary amperage is sufficient to make it decent. I wonder
> if there are ideas from anybody else on what this might have been, or
> what it can be used for?
> MN> What I have:
> MN> Power supplies - 15/60 (1), 12/60 (1), 12/30 (2). Right now
> MN> I have the 15/60 hooked up to the tank that isn't working. Think
> MN> I'll swap it for the 12/60 to keep from taxing the Caps - six
> MN> Sprague hockey pucks, .004, 30KV. Using 4 of these in parallel
> MN> in the current tank.
> These are really very poor tank circuit capacitors. They get hot,
> they are low Q, and they fail under pulse excitation. They are the
> best bypassing capacitors I have ever used when placed in series.
> MN> I am a little cloudy on how these operate in series. If caps are
> MN> in series do you get more voltage rating with the same capaci-
> MN> tance as a single, (I'm assuming identical caps)?
> No, voltage rating goes up, capacitance goes down. Two of these
> .004 uF -at- 30 kVDC caps in series will withstand 60kVDC with a com-
> bined capacitance (in series) of .002 uF. Three in series will
> withstand 90kVDC with a capacitance of .0013 uF, four in series
> = .0009 uF -at- 120kVDC, five in series = .0007 uF -at- 150kVDC, six
> in series = .0005 uF -at- 180kVDC.
> MN> And in a balanced tank config do I use 2 in parallel on each
> MN> side of the primary or do I need 4 on each side? My guess is 4
> MN> on each side. This would maintain the original capacitance of
> MN> the "unbalanced" circuit. It would balance the circuit and also
> MN> increase the voltage capacity of the caps (tank) as a whole.
> MN> (I hope you can understand this what I'm trying to get across.
> MN> I haven't figured out how to edit this yet).
> Not to worry about the computer skills, they will come, and so will
> the coiling skills. But you don't want to start out with the balanced
> circuit right out of the gatehouse. The kickback from the balanced
> circuit will eat those DC rated Sprague doorknobs for breakfast.
> Besides, you will need all of those doorknobs to bypass some of that
> kickback to protect your neons, so you won't have any main tank
> circuit capacitors...
> MN> Gaps - 4 tungsten-faced gaps from arc welders. They are mounted
> MN> in Al clamps with lots of cooling fins. The faces are 3/8" dia.
> MN> They are in series and set at .03" right now.
> These are really excellent electrodes for main system spark gaps, and
> are readily available. They are manufactured commercially for arc
> initiators in TIG welders I believe. They are flat tungsten plates a
> couple of mm thick that are bonded to a heavy steel slug which really
> sinks the heat. I see you have also mounted the electrodes in finned
> heat sinks for long run times. How about giving us a brand name,
> address and part number for these? This would be a good addition for
> my Tesla References file.
> MN> Primary - 8 turns of 1/8" copper tubing in a flat spiral. I take
> MN> it this is too small? I plan to upgrade this.
> Yeah I would do some more work here. The conductor is too small in
> diameter and too short. Try 60 feet of 3/8 inch soft copper tubing
> on a new saucer type coil form.
> MN> Secondary - 2" by 15" of #22 magnet wire (Belden), which comes
> MN> out to 550 turns. The ratio is way off and the wire length too
> MN> short, I think.
> Yeah, this secondary is a little messed up. Way too skinny and long,
> with dimensions similar to a paper towel center tube :-( Not enough
> turns, not enough diameter, the only thing really correct was the
> proper gauge of wire was used... Not that that helps much.
> MN> I have a 4" diameter lexan tube standing by that I would like to
> MN> start from on this next attempt. My existing secondary has a 1
> MN> 3/4" by 7" Al toroid.
> Lexan (polycarbonate) puts PVC drain pipe to shame when it comes to
> RF losses. This is pretty good coil form material here. Give us
> some thoughts on the planned coil specs for this form.
> MN> My goals are to start a larger coil with higher Q, and rework the
> MN> existing one to see what I can get out of it. If I beef up the
> MN> primary and change to a saucer config? Or is the secondary size
> MN> ratio too far out?
> You need to retire the previous coil systems, and build these new
> barn burners from scratch.
> MN> I noticed all the toys you have in your garage. I hope you did not
> MN> lose anything in the flooding.
> I was within a matter of weeks of having ground broken for the new lab.
> Plans were drawn up at a reputable architect, land was picked out with
> options to purchase pending bank loans, bank was ready with the cash,
> my 20% was in hand, and it began to rain, and rain, and rain. Then
> the levy broke near the land where I was looking to build, next all
> new construction was banned, then the building codes and insurance
> requirements were changed.... I lived on high ground, it was just the
> lab that would have been endangered.
> MN> I'll be sure to get some specs on the coil that I saw the other
> MN> day and let you know. I should have posted this to the mailing
> MN> list also, but I keep hitting the reply command straight back to
> MN> you. Mark R. Napier lisanap-at-cats.ucsc.edu
> Oh, it will all get forwarded to the group. You should see it all
> over again Monday or Tuesday.
> Richard Quick
> ... If all else fails... Throw another megavolt across it!
> ___ Blue Wave/QWK v2.12