[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: need help/capacitors and AC



Original poster: "Scott Bogard" <teslas-intern@xxxxxxxxxxx>

Matthew
I don't think you pay attention to the AC rating, because the cap charges and discharges several times (depending on your spark gap) during the 60 Hz AC cycle (so if you are using 400 bps, it is as if it is seeing DC for 3.something firings). Use the DC rating, but make sure you use peak voltage (NSTvoltage/.707), so if you are using a 15kV, string your caps until you have at least 21216.4 volts (a little extra won't hurt a bit, and is reccommended).
Scott


From: "Tesla list" <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: RE: need help/capacitors and AC
Date: Thu, 03 May 2007 22:54:17 -0600

Original poster: "Matthew Boddicker" <shmerpleton_town@xxxxxxxxxxx>

This is Matthew,
On the cornell-dubilier web page it said that the model 942C caps went to 2000dc or 500ac. Do I pay attention to the dc or ac rating?
thanks Scott,
Matthew


From: "Tesla list" <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: RE: need help/capacitors and AC
Date: Thu, 03 May 2007 00:18:03 -0600

Original poster: "Scott Bogard" <teslas-intern@xxxxxxxxxxx>

Matthew,
I have never built an MMC, but I researched them, as I was going to build one. What is the voltage rating on your caps? 1200 seems like an awful lot of caps for an MMC (to me at least), especially considering you are using an NST, which probably has fairly low current (30, 60, or 90, mA). Re-run your calculations, {V=V1+V2+Vn..., and C=1/((1/C1)+(1/C2)+(1/Cn)...)} and if you get the same results, consider using different MMC caps (like the 942C rated at 1500 or 2000 volts). I would say, using the 2kV, you would need about 20 some, for a small 3 in. coil, and maybe a little more for a bigger coil, or a higher current supply (not 1200 capacitors). Plus remember, one can generally push the operating voltage of the caps a little beyond what they are rated (if you don't mind replacing one once in a while), but be careful, use peak voltage (15kV/.707) to calculate the necessary voltage rating of the capacitor!

Anyway, to answer your second question, I believe it works like this, as your frequency increases, your maximum current must go down (that is how it works with Maxwell caps, or so says the company that makes them).
Voltage breakdown is irrelevant (not really, but for your purposes it is).

To answer your third question, generally NSTs are 15kV from terminal to terminal (one is +7.5 kV, the other is -7.5 kV, and then they switch as the AC cycle progresses). Remember this is RMS voltage, use peak for calculating you capacitor voltage (RMS/.707). I hope this helps.
Scott Bogard.


From: "Tesla list" <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: need help/capacitors and AC
Date: Wed, 02 May 2007 18:40:07 -0600

Original poster: "Matthew Boddicker" <shmerpleton_town@xxxxxxxxxxx>

This is Matthew Boddicker

I am currently designing a MMC, but I need the right capacitor for the job. I am going with cornell-dubilier caps, but my recent calculations said that I would require around 1200 caps for a MMC.

My question is how does a capacitor react to different frequencies of current? the cornell-dubilier web page says that the cap can handle 500Vac at 60Hz. if my circuit for my coil operates on a much higher frequency will I require a higher ac voltage rating or a lower one?

last question but equally relevant. My NST's output is 15,000 volts, is that the voltage between both output nodes or is 15,000 the voltage between one node and ground?

Thanks,
Matthew Boddicker

_________________________________________________________________
Download Messenger. Join the i'm Initiative. Help make a difference today. http://im.live.com/messenger/im/home/?source=TAGHM_APR07


_________________________________________________________________
Watch free concerts with Pink, Rod Stewart, Oasis and more. Visit MSN In Concert today. http://music.msn.com/presents?icid=ncmsnpresentstagline



_________________________________________________________________
Watch free concerts with Pink, Rod Stewart, Oasis and more. Visit MSN In Concert today. http://music.msn.com/presents?icid=ncmsnpresentstagline




_________________________________________________________________
Download Messenger. Join the i'm Initiative. Help make a difference today. http://im.live.com/messenger/im/home/?source=TAGHM_APR07