Hi Gang! Here's my small spark gap Tesla coil,
so called because there's this spark gap here, as opposed to a solid state circuit.
This one is also tunable, for best results, to some extent.
In this video I'll show you step-by-step how to make it and tune it.
Note that this is my first Tesla coil, even though it's around version 5 of it,
so I'm giving you what I've learned up to this point.
Check the video comments for any corrections or useful suggestions from others.
Also note that though tuning is done, it's done in a limited way and so resonance
cannot be gauranteed.
One key part, and the hardest to make part, is this power supply here.
I'm using my Cube high voltage, DC power supply. I won't go into detail on how to make it here.
I have this other video explaining how to do that instead.
Click on this annotation or the link in the video description.
The rest is fairly easy to make and consists of two resonant circuits.
The first is called the primary circuit and consists of these capacitors,
this spark gap, and this primary coil.
The second is called the secondary circuit and is just this much taller coil
and this ball on top covered in almuminum foil,
which is called a topload.
Note that I called them resonant circuits. They both resonate on their own, at some frequency,
moving energy around between their capacitors and their coils.
The capacitor in the secondary circuit is the capacitance within the tall coil itself,
and in the ball and the surroundings.
The details of how it works would take a whole other video
but for here what's important to know is that you want the resonant frequency of
the primary circuit to be as close as possible to the resonant
frequency of the secondary circuit.
One approach to getting the frequencies the same
is to start by designing your Tesla coil using an online Tesla coil calculator,
then making it, and then tuning it
since what you make won't exactly match what you calculated.
The online calculator I used is this very popular one called JavaTC.
I didn't use all the features of this calculator. Just the things in the top section.
What I was shooting for was that when I click on its RUN JAVATC button,
the two frequencies it gave me here would be close to the same.
This is the resonant frequency for the secondary circuit
and this is the resonant frequency for the primary circuit.
Doing these calculations is an iterative process. You try some values for what you think you
can make, then click on the RUN JAVATC button
to see if you get frequencies that are close together.
If they're not then you try new values, and keep doing that until you come up with
something you can make. I try to get a primary resonant frequency
that is a little less, at most 10% less,
than the secondary resonant frequency. That's a rule of thumb that's intended to
account for the fact that the spark gap will heat up over time,
affecting the actual frequency.
For the units I chose cm, or centimeters, or the metric system since it makes things
easier. But I'll give dimenstions in inches too.
Before going further, I fill in the dimensions for the room the
Tesla coil will be in.
Now to start making it.
First, the secondary coil.
Since they're easy to find, I decided to use a paper towel tube
and a toilet paper tube taped together. The top and bottom radius are both 2.2 centimeters,
and that goes in the calculator here.
I'm using 26 gauge, enamel coated wire. This is available in electronics stores
and can be salvaged from old motors and electronics. I'm putting on 750 turns, which works out
to a 34.425cm long coil. I used another online calculator to get the
total wire length needed, which is 103 meters,
but make sure to have a little extra for the two ends
for connecting to things. That's all in the calculator here.
Rather than count turns while winding it, I just mark the length on the tubes.
I poke holes at either end, and push one end of the wire through one hole,
securing it with tape. I start winding.
There are faster ways of doing that that take some set up,
but I can do it while a good science documentary, so I continue by hand.
In the end it takes only around two hours. Notice that then ends don't have to be very
long, and shorter is better.
I trim the top end of the tube, and carefully strip off the insulation.
Some tape on the inside, and/or some glue,
like this super glue from a hobby store, will help keep it in place.
For the topload, I'm using this 8 centimeter in diameter Christmas
tree ornament from a craft store.
Pretty much any round ball will work. A rule of thumbs is that
it should have a larger diameter than the secondary coil.
But make sure you include its dimensions in the online Tesla coil calculator
like I did. The Sphere Center Height is from the bottom
of the Tesla coil to the center of the sphere.
Once you've filled it all in and selected topload,
click on add to add it to the list of Sphere Objects.
The outer surface has to be electrically conductive, so I wrap it in kitchen aluminum foil,
trying to make it as smooth as I can. After triming it inside,
I tape the two halves together, making sure that the foil on one touches the
foil on the other. Next, I tape the wire from the coil to the
topload. And then I hot glue the topload to the end
of the tube. Tape also works.
Next I need to make the primary coil. I made two of them.
At first I made one using 12 gauge insulated wire
and then to try tuning it better I made another with 16 gauge bare wire.
The resulting output is around the same so I'll show making the 12 gauge insulated
wire one, since it's easiest.
From playing around with the calculator I found that
a 4 centimeter radius with 7 turns of wire
gives me the needed resonant frequency. I calculate the height of the coil
by measuring the diameter of the wire and multiplying it by 7,
which gives me around 2.5 centimeters.
Before winding the coil I need to make the cylinder that it's wrapped
on. So to make the cylinder
I need a piece of cardboard that's 2.5 centimeters high
by 23.5 centimeters long, but after adding extra for playing around
with any overlap, I decide on 4.5 centimeters by 30 centimeters.
I cut it out, and then I make a mark at 23.5 centimeters.
I wrap it around a can to make it roundish, and tape it such that one end stops at the
23.5 centimeter mark, with the overlap on the inside.
But I also want to be able to move this up and down for tuning purposes.
So I cut another piece of carboard that's one centimeter taller,
but when I tape it, I size it to fit snuggly inside the first
one. Now the first one can slide along that one.
Time to wrap the wire onto it. I start by putting two pieces of tape beside
each other that span the height of the cylinder.
I also put another piece on the opposite side. Near the bottom of one tape, I tape the wire
in place, and start coiling it around.
I also tape the first turn on the other side. And then I keep coiling until I get to the
last turn. I tape that one on the other side,
and finish it by taping it beside where the first one started.
The two ends sticking out are called the leads, and are represented in the calculator here.
As I said I made another primary coil using 16 gauge bare wire,
with the same dimensions, to try some additional tuning.
But once I'd tuned it, it gave comparable results,
meaning my 12 gauge insulated one was already well tuned.
For the spark gap, I cut the top off a plastic soda bottle
and I make two holes on either side, being very careful not to stab myself.
I'll be fitting some nails in and I want the fit to be fairly tight.
Then I cut slots down the side. That's so that I can put the nails in
with their flat heads facing each other. Notice that the gap between them is easily
adjustable. You want the spark gap to be in air as much
as possible like this so that the surrounding air can help keep
it cool.
And the last part is the primary circuit's capacitor,
or capacitors in this case. From playing with the calculator,
I know I need 0.004 microfarads, or 4 nanofarads, of capacitance.
To get that I'm using four of these ceramic capacitors,
1 nanofarad each and rated for 20,000 volts. I bought them from amazing1.com
but you can find them on ebay and other places for low prices.
Having four 1 nanofarad ones allows me to try different combinations.
To connect them together I have this terminal strip,
or terminal block. There are holes on both sides and these holes
are connected together, these holes are connected together and so
on. You can solder the the capacitors together
if you prefer or use some other method.
I prepare these wires and put them in these holes
along with two capacitors and that connects them both in parallel.
It doesn't matter which way they go, there's no plus or minus to the capacitor
legs. The screws on top hold them in place.
I insert two more capacitors on the other side.
Make sure they're all in tight. When it's all finished,
this wire and all these legs of the capacitors are connected
together. And this wire
and all these legs are connected together. All the capacitors are now in parallel,
causing their capacitances to add up for a total of 4 nanofarads.
Finally I can cut the terminals from the rest of the strip.
I need a base and some way to hold the secondary coil up.
For that I cut a piece of paper towel roll, and cut a section out along its length.
That gets hot glued to one end of a board. That's so that it'll fit snugly inside the
secondary tube with enough of a gap for the wire to fit through.
It fits on nicely.
Time to put the whole Tesla coil together.
I start by removing the secondary coil from the base
and slipping the primary coil over it. Then it's just a matter of putting the secondary
back in place, and lowering the primary.
The nice thing about this design is that it's easy to try different primary
coils.
This wire coming from the bottom of the secondary coil
needs to be connected to ground. For that I have this standalone plug
which I bought from a hardware store, and inside it I've connected just one wire
to this long prong, In North America, that's ground.
After plugging that into a wall socket, I connect the other end of that wire
to the wire coming from the primary. A more premanent connection can be done by
soldering it or you could put some sort of spade or butt
connectors on the wires.
Then I connect one end of the primary coil to the wire coming from the high voltage power
supply. That's also connected to one side of the capacitors.
The other side of the capacitors goes to one side of the spark gap,
but notice that connection is made using an alligator clip
that's part of a wire going to the power supply's negative.
And lastly, the other end of the spark gap goes to the
other end of the primary coil. Done!
Check that there's a gap in the spark gap, and that the primary coil is centered around
the secondary coil. Turn on the power supply and turn it up.
The loudness depends on the size of the spark gap,
a bigger gap is louder, and less frequent,
but more powerful each time. So you can play with that.
To tune it, get a long plastic stick, perhaps even a ruler,
and tape a wire to one end of it. I'm using a clamp to hold the stick vertical.
At the top, attach a needle. The other end of the wire can just hang down.
Turn on the power supply. Then slowly adjust the distance between the
tip of the needle and the topload such that you get a non-continuous
spark. Slowly move the needle closer until the spark
starts being continuous. Your body can interfere with all this,
so you can step away a meter, or a yard, after each time you move the needle.
Next, turn off the power supply. Make a discharge stick by taping a wire to
the end of a stick, with perhaps another of those plugs on the
other end of the wire. With it plugged into ground, discharge the
spark gap, and the topload.
Be careful not to move the topload when you do this,
since that will interfere with the distance to the needle.
Now that everything's safe, raise or lower the primary coil.
This changes the coupling between the two circuits.
Turn the Tesla coil back on. Move the needle closer or farther
until you get a non-continuous spark again, and then closer until you start getting continuous
sparks again. If the distance between the topload and the
needle is farther than before then you're moving the primary coil in the right
direction, otherwise try the other direction.
Keep doing this until you get the longest continuous sparks.
Another form of tuning involves changing the number of turns on the
primary coil. Here's another primary coil I made.
The main difference is that it uses bare 16 gauge wire,
the key being that it's bare wire. It has the one extra turn for extra adjustability.
Since there's no insulation, there's a gap between each turn.
Just like the other primary coil, this one has one end connected to the high
voltage power supply. But the other end goes nowhere.
Instead, one end of the spark gap is connected to the coil
via this wire with alligator clips. By moving this alligator clip elsewhere on
the coil I can change the number of turns,
and therefore the frequency more directly.
But after doing that, I find that I still get the longest sparks
between the topload and the needle when I have around 7 turns,
just as calculated. So using this easier to make coil is just
fine.
And that's one way to make a small spark gap Tesla coil.
Well, thanks for watching!
See my youtube channel, rimstarorg for more interesting videos like this.
That includes one with more demonstrations of this Tesla coil in action.
Also, the one I mentioned about how to make the Cube power supply.
And for variety, one on how to do wireless transmission of
electricity using a joule thief circuit.
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See you soon!