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Tesla Coil Help!! Got only 3 days left to complete my project, plsss help

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ElectricalEngg.

Tue Mar 17 2009, 01:36PM

Registered Member #1946 Joined: Sat Jan 31 2009, 11:37AM
Location: India
Posts: 43

friends I only have 3 days left help :(
any suggestions on mmc capacitor bank will be very helpful thx again ^_^

Sulaiman

Tue Mar 17 2009, 06:13PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

You can use almost ANY kind of non-polarised capacitors to make your MMC
Some types are excellent, some are really poor.
Provided the overall capacitance and voltage ratings are ok it will work.
A quick guide, best to worst for commonly found types;

KP Polypropylene foil/film
KP/MMKP Polypropylene foil/film and double metalised film internally in series
MKP Polypropylene metalised film
MKT Polyester/plastic/mylar/PET metalised film
Ceramic, first letter X, Y, Z.

You must run at home for longer than the time you intend to demonstrate the coil
to ensure the capacitors don't overheat or EXPLODE during your demo .... not good.

Blowing air through the spark gap makes a HUGE performance difference,
use a small fan/blower etc. or a vacuum cleaner on 'blow'. (or 'suck' even)

You really should have a safety gap to protect the transformer in case of
failure or wrong setting of the main spark gap.
It doesn't need to be efficient, just present.
With just the transformer and safety spark gap connected, adjust the gap so that it just fires with full ac input voltage.
For the main and safety spark gaps don't use sharp points,
the larger and smoother the surfaces the better.

Plasma Lover

Wed Mar 18 2009, 12:23AM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

kashish0711 wrote ...

friends I only have 3 days left help :(
any suggestions on mmc capacitor bank will be very helpful thx again ^_^

Please trust me, the capacitor you made is rated at 1.05nF, if the 1.05 part is right, at all. Unless, of course, the bottle you're using is one of those little bottles you get on airlines, in which case, it would be in the order of from one to fifty picofarad.

If you are planning on making an MMC and only have a few days left, just make more beer bottle caps. They're easy to make and cost almost nothing. They aren't very efficient, but, then again, neither is your secondary coil. The beer bottle caps can be put in parallel, as explained later in this post.

The reason the high capacitance capacitors work well for TC caps is that, when put in series, a capacitor's voltage rating will go up (because of the new voltage rating of the one before it, plus it, when wired in series) and put in parallel the capacitance goes up (because they share current).

When put in parallel, a capacitor's voltage remains the same, and its capacitance doubles as the number of capacitors doubles. If you have three 2ÂµF caps in parallel, you will have a 6ÂµF capacitor when ran in a tank circuit.

Just keep these things in mind. My recommendation is to put fifteen of the bottle caps in parallel and try that, then adjust it for best performance, tuning for best performance in between capacitor changes.

By the way, people have used bottle caps with 15KV transformers and had no problems...just make sure you don't seal the bottle like so many people foolishly recommend. If you do seal the bottle, it may explode due to internal heating. Also, don't quite fill it to the top, or the oil will spill over due to thermal expansion.

Good luck!

ElectricalEngg.

Wed Mar 18 2009, 02:42PM

Registered Member #1946 Joined: Sat Jan 31 2009, 11:37AM
Location: India
Posts: 43

@Sulaiman, I got this ceramic capacitor
rated 8200 pF (8.2nF) and 2000 Volts

11ilocz

would they be good enough?
or do I need to buy any other one?

and I wanna know how to add resistors I mean what quantity and hot to connect them I mean in series caps and in parallel caps

and should I operate them inside some oil
coz I heard that they only have half their rated voltage when operated in open air, but full when operated in oil having a good dielectric strength. but I am not 100% sure abt it

and ok Ill make sure that I run it more than demo time at home first thx

and I am using a computer fan attached to a heat sink for the spark gap :)

and is the spark gap as given in the diagram above be good enough?

@PlasmaLover: Yeah I checked that today it was the one you told

bottle cpas are not looking good enough to me as I will not be able to know what is the voltage rating of them :(
and in case they fail, I mean they get damaged while demo or just before it, I wont have another way :(

but if I am able to successfully make MMC, I can make 2 of them before I go to the tech fest for showing demo and I can replace in case it gets any problem :)

and I got the calculation system thx

and can you tell how will the resistors go in the circuit, they stable the circuit right? and they also discharge cap when switched off :)

thx for your help guys, can you guyst confirm me if the capacitors I am using top build the tank circuit are Ok??

Thanks again :)

Plasma Lover

Wed Mar 18 2009, 06:23PM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

Well, i suppose it would be completely possible to make it using those capacitors, but then you would need to have at least five in series to get you a voltage rating of 10KV which would be suitable for your transformer, and then you would need to get enough rows of these to make 15nF.... That would be 10KV at 15nF, or a total of 0.75 J. That means that, since each capacitor is rated at 0.0164J, you would need 46 caps, at least to get 0.75J; you would use five in series and, since that would decrease capacitance, you can measure that by taking the total energy in J per cap and multiplying it by the number of capacitors, then figuring out the needed capacitance by squaring the capacitors' rated voltage (after putting them in series) and then dividing the J expected by the voltage rating. The equation would be -

0.0164J*5(caps in series)=0.0825J; 0.0825J/10,000V^2 = capacitance = 0.000000000825F = .825nF

To make .825nF into 15nF, you need to divide 15 by .825 to get 18.18, or, in other words, to get a near-resonant capacitor (as my own estimate) you would need eighteen rows in parallel of five caps in series, which equates to 90 capacitors. Better buy 100 in order to be on the safe side, if you're only going to make one MMC.

On the other hand, the voltage rating of bottle caps are actually quite high. You can make extras and switch them out much more easily than you can an MMC's caps, as well. It would be a much more simple design, even if not as pretty. Just keep them in some kind of dish to contain any spilt liquid, just in case. Really, i advise bottle caps, having done those equations.

Good luck,

Christopher

(fifteen years old and fighting myself for life and happiness)

Arcstarter

Wed Mar 18 2009, 08:33PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Actually, for a lond lasting capacitor, i would go with at least 15-20kv rating. CDE capacitors for example are only 500vac rated, yet we abuse them with around 2 times that voltage.

Basically, for a dc rated capacitor, you want 2 times there rated voltage, plus a few kv for a safety margin. The cap bank voltage on my 12kv 60ma NST is going to be rated 32-36kv for example.

I would suggest you spend some real money, and buy some of the .15uf 2000vdc CDE capacitors, and use a larger than resonant value. In other words, just put 8 of them in series, for 18.7nf and a 16kvdc rating (this is absolutely perfect for a 6kv 30ma nst).

ElectricalEngg.

Wed Mar 18 2009, 09:51PM

Registered Member #1946 Joined: Sat Jan 31 2009, 11:37AM
Location: India
Posts: 43

omg 100 caps hm.. 1200 rs., I can manage that :)
and well still havnt got the bottle cap out of mind due to some of the positivie comments :)

I wanna know if I could use less mmc caps and keep the capacitance less and instead increase the capacitance through the torroidal and spark gap?

our main motive is to use the resonance for that we can adjust Xc from capacitor, spark gap, torroidal.
what you say would it be possible?

say I use 6 in series and 6 in parallel

and for bottle capacitor, as per my calculations, 15 bottles should give a capacitance of around 0.0285 micro farads

what should I do?? :(

Fraggle

Thu Mar 19 2009, 02:34AM

Registered Member #1526 Joined: Mon Jun 09 2008, 12:56AM
Location: UK
Posts: 216

All of the information you could possibly need is available from Google, I think you ought to spend a few hours reading and you`ll be sorted.

Plasma Lover

Thu Mar 19 2009, 04:29AM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

kashish0711 wrote ...

omg 100 caps hm.. 1200 rs., I can manage that :)
and well still havnt got the bottle cap out of mind due to some of the positivie comments :)

I wanna know if I could use less mmc caps and keep the capacitance less and instead increase the capacitance through the torroidal and spark gap?

our main motive is to use the resonance for that we can adjust Xc from capacitor, spark gap, torroidal.
what you say would it be possible?

say I use 6 in series and 6 in parallel

and for bottle capacitor, as per my calculations, 15 bottles should give a capacitance of around 0.0285 micro farads

what should I do?? :(

.0285ÂµF? That doesn't work out right. Are you thinking that each bottle is 2nF? It seems that you are, since you said yourself that your one cap is about 1nF. So, if you have 1nF and you put fifteen in series, you get 15nF. But, if you're making the caps yourself, I suggest you test them with a meter (if you have one on-hand) in order to make sure that they capacitance is right. The meter on a multimeter will work fine, just get wires small enough to stick into the holes on the meter. That's the tough part! =) It takes a little while to get it all set up.

Keep us updated!

By the way, in the future, I recommend using the CDE caps, as well, but since you don't have much time, that wouldn't work well.

LithiumLord

Thu Mar 19 2009, 12:32PM

Registered Member #1739 Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261

Well, in fact a bottle is around 1-2nF, however I don't like bottle MMCs due to higher loss factor and really heavy weight.

>fifteen in series
In parallel (I know this was a typo as I kept sometimes mixing words myself like this - but just to make it more clear)

>and the small cap across output you said, whats that for? pf improv?
Nope, I mean one between the neutral terminals - it will exclude the chance that some ground faults would cause RF to form up against the coils of the NST, eventually heating it or causing a damage or internal flashover.

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