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Salt water bottle capacitor

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Tigeris

Sat Oct 25 2008, 04:09AM

Registered Member #1656 Joined: Wed Aug 27 2008, 03:28PM
Location: Pittsburgh PA
Posts: 53

I have about 20 12oz. beer bottles to use, (brown). I just need to know is there any ratio of salt and water to use? Is there any type of salt i should use? Should they be parallel or series?

I have a 12kv 30ma Xformer and just want to make sure i do this right so i dont mess anything up.

Arcstarter

Sat Oct 25 2008, 04:54AM

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

Just add tons of salt :P. Add salt until it will not dissolve anymore. Just regular table salt works. And they should be in parallel until you have the capacitance that you want. You will need a capacitance meter to measure it though.

Brad

Sat Oct 25 2008, 02:42PM

Registered Member #1632 Joined: Mon Aug 11 2008, 08:53PM
Location: Plainfield, IL
Posts: 12

I do not want to discourage, but the first capacitors I used while building my SGTCs were bottle caps. There were very poor performers. The worst part is disposal, I just did it a month ago and I regretted ever making them! They never worked well for me, and the money I spent on bolts, oil, foil, insulating materials, could have gone toward making a nice MMC. Once I finally went to a MMC I started seeing real Tesla coil performance! They are very easy to make, even for the beginner, and work superbly! I'm sure others may have had good experiences, maybe they will share.

Brad

Here is a picture of my 15kv/30ma coil running - the discharge is ~ 32" from point to lawn chair.

Mads Barnkob

Sat Oct 25 2008, 09:38PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

I had great experience with my first salt water capacitors, and I also got a few good surprises with them.

I made them from 2x 1.5L plastic coca-cola bottles, wrapped them in aluminumpaper, put some wire on it and wound it all in tape to get it tight, into the water i just had a piece of cobber busbar.

They seemed to have same capacitance with light as dense salt resolution, the real difference was getting the aluminum paper tighter to the plastic bottle, that increased capacitance a great deal.

A single bottle had around 2.5nF capacitance and after maybe 3-4 hours total runtime only had little damage to the aluminumpaper, very little. I used them at 20kV with low current.
After 2 months they still had the same capacitance despite the water was all green from dissoluted cobber.

These costed me nothing to build as I had everything in the house and its all dirt cheap in the first place, but they really are poor performes, BUT will do you great till you can afford industrial equipment.

Nik

Sun Oct 26 2008, 04:23AM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

I made foil/plastic sheet caps that worked a lot better then my salt water ones. Foil/plastic caps can be folded up to fit in smaller spaces and are a lot lighter to carry BUT they tend to have a shorter life and break down easily if they get over volted.

TravisD

Sun Oct 26 2008, 11:08AM

Registered Member #1658 Joined: Thu Aug 28 2008, 11:27AM
Location: Yungaburra Qld Australia
Posts: 8

Beer bottle caps i found were ok but there are others caps out there, doorknob caps are great!!!, but beer bottle ones can do, there cheap and easy as to make, mine cost nothing and i have an odd few around the place, some get a capacitance of around 1.4nf or so, i didnt use any thing fancy just bottle and clothes hangers and yea just stuff lying around, i belive even nikla tesla used salt watter caps in his experiments...

Arcstarter

Sun Oct 26 2008, 04:58PM

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

Actually i think he used Leyden jars, which are essentially the same think but they where with metal plates, not salt plates.

Anyway, i do not think that you should use most doorknob capacitors because they are just not suitable. Some might be alright but i would not trust them for reliability.

Hazmatt_(The Underdog)

Sun Oct 26 2008, 06:30PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Mica transmitting caps and Mica doorknob caps are great for continuous wave, but don't even consider them for pulse, they die and kill your transformer fast! (box cap shown )

Ceramic SrTiO TDK UHV series caps are beautiful for SGTC pulse duty. The 9 in my SG bank don't even break a sweat. (1kW charging )

Tigeris

Mon Oct 27 2008, 01:06AM

Registered Member #1656 Joined: Wed Aug 27 2008, 03:28PM
Location: Pittsburgh PA
Posts: 53

Alright! Thanks every one for all your help. I got the bottles set up and my spark gap makes nice bright white sparks. I haven't gotten the primary coil set up yet. But here are a couple pics of the cap bank, spark gap and details of my Xformer.

8 Bottles, with about 1" of oil on the top. 4 in series, 2 sets in parallel. The square things are peices of PCB, with a vent hole. 12 ga. copper wire in the bottles.

Let me know what you guys think :)

Cap Bank

Spark Gap

Xformer details

Mads Barnkob

Mon Oct 27 2008, 05:47AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Looks nice, you have managed to keep it simple, thats a good thing for a first :)

Your paralled caps will stress the first in the chain, since you tap it there, alternative solution is to pull a wire from each and connect all 8 in the same junction, or move your connection in the middel so you have 4 on each side, this should make the stress abit more even.

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