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Re: Salt Water Cap?????
Original poster: "Christopher Boden by way of Terry Fritz <twftesla-at-uswest-dot-net>" <chrisboden-at-hotmail-dot-com>
Go to http://www.thegeekgroup-dot-org/Projects/Tesla/capacitors.htm
The Geek Group Bucket Cap:
Though terribly lossy, a decent cap can be made for tesla coil service for
under $50 in about an hour that is easily repaired and ill give you years of
service if properly maintained. Tesla himself used SW (Saltwater) caps, but
Cap technology has progressed a bit in the past hundred years and the
current choice is Metalised film polypropylene. But if cost is a serious
issue, and performance isn't, SW caps are the way to go.
1 clean new 5 gallon bucket. This should be made from HDPE and MUST NOT BE
1 well sealing lid (preferably airtight) for the bucket
12 longneck beer bottles, preferably Corona brand, these must be washed and
3 quarts of new synthetic motor oil
25' of 10AWG bare solid copper wire
1 rubber stopper, about .5" or so, no smaller than .25"
2 "5-Way" binding posts (these must be separate, not the kind that come as
an attached pair) panel-mount.
2 of the 5"dia X 7" tall cardboard containers of Morton's Salt (or
equivalent). ANY salt will do, iodized or not, even Epsom salts would work.
1 glass pitcher with a good pour lip. You must be able to pour from this
into a bottle without spilling everything all over. It must be glass if you
ever plan on using it again, plastic is OK but getting the salt taste out is
rather difficult. 2 quarts is the best size.
1. Fill the pitcher about 75% full of the hottest water you can stand. Add
one container of salt and stir for a full 2 minutes. There will be a LOT of
salt on the bottom, this is alright. Let it sit for about 5 minutes.
2. Fill as many bottles as you can to the base of the neck with the salt
water from the pitcher. Be careful not to pour out all the water. Do NOT
POUR OUT THE SALT IN the bottom of the pitcher. When the pitcher starts
getting low just add more hot water and stir. When the salt in the bottom
starts to get low, add another container of salt. It's alright if you get a
little salt in the bottles, it won't hurt anything. It just wastes salt.
Fill all the bottles to the same level, where the base of the neck just
starts. If you have an extra, fill a 13th glass bottle and set it aside.
3. Place all 12 bottles in the bucket, they will *just* fit. Fill the area
around the bottles with Saltwater to the same level as the bottles are
4. Now you have to make the jumper wires to connect the bottles. You want
to cut and bend piece of copper wire so that they form an inverted "U"
shape. Each wire should go from inside 1 bottle, about 1" from the bottom,
out, over, and into the bottle next to it down to the same level in the
second bottle. This is a LOT easier than it sounds. Connect each bottle to
the one next to it, most bottle will have 2 or 3 wires going into them.
Just make sure they are all connected.
5. Mount one of the Binding posts in the center of the lid. And another one
as high up on the side of the bucket as you can without interfering with the
lid. These will be your terminals.
6. Connect a piece of wire from the side terminal (on the inside) extending
down into the water jacket around the bottles. This wire should go straight
down and stop about an inch from the bottom of the bucket.
7. Connect a piece of wire about 1' long to the inside of the top terminal.
This will be threaded into a bottle (any one should work) when you put the
top on. You may have to trim it a bit, but make the wire as long as you can
without it hitting the bottom of a bottle.
8. Fill each bottle all the way up with motor oil, don't worry about
spilling any into the water jacket. Once all the bottles are filled, pour
the remainder of the oil into the water jacket, this is your corona
suppression. It should take about 1 quart to fill the bottles.
9. Check your connections, make sure everything is tight. Before mounting
the top onto the bucket, drill a hole for your stopper. Plug the hole TIGHT
with the stopper. You might even want to use a mallet to hammer it in. If it
leaks you have a mess you won't soon forget.
10. Mount the lid, and seal everything tight. You now have a .0125uF 80KV
Check everything with a meter to make sure. The value of the cap will take a
week to finally settle as the oil absorbs a LOT of water. If you look at the
extra bottle you made, you will see salt settle on the bottom. This is fine,
and actually helps to make sure that the SW is as concentrated as it can be.
If the salt content were to lower it would just absorb salt from the bottom.
Remember to short out your cap after use and during storage. It will kill
you in short order if you don't respect the power it can hold. As will ANY
cap of serious size.
1 Bucket cap is perfect for a 15/60 NST, if you have more NST's, just add
more buckets. We have 4. If you are running 15/30NST's then just use 2 NST's
to a bucket. For a single 15/30 NST, just open it and only connect 6
bottles. (you can actually add another binding post on top and have 2 caps
in one with 2 groups of 6 bottles wired separately, one to each binding
post. The side terminal is the negative for both.
Christopher A. Boden Geek#1
President / C.E.O. / Alpha Geek
The Geek Group
Because the Geek shall inherit the Earth!
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