I have a PVC tube half an inch wide, 18 1/2 inches long that wound with copper wire before reasearching it. I want to know if I could make a small tesla coil with it with out seeting the frequency impossibly high. I calculated it to have about 1628 coils of wire on it. Once I had wound the wire it seemed incredibly skiny. Ihave also already made a homemade capacitor that personal tests have rated at 15 kv, and about
14 nf. Can anyone tell me if it would work, or how to make it work?
I have a PVC tube half an inch wide, 18 1/2 inches long that wound with copper wire before reasearching it. I want to know if I could make a small tesla coil with it with out seeting the frequency impossibly high. I calculated it to have about 1628 coils of wire on it. Once I had wound the wire it seemed incredibly skiny. Ihave also already made a homemade capacitor that personal tests have rated at 15 kv, and about
14 nf. I also have several flyback transformers from old tv sets I could use as a power supply and if that work I have an old 7 volt transformer I could always wire backwards. Can anyone tell me if it would work, or how to make it work?
I don't mind telling you that I am 14 years old and the only "electrician" (I prefer to call it electrical engineer) in my family. My parents are understandably terrified of wall voltage, so I plan to run it off of a 24 volt scooter battery I have. If i waited for the roll of paper towels in My kitchen to run out, would the cardboard tube make a better SECONDARY coil? Don't know what I was thinking when I said primary.
40ish (a little less) years ago, I used a knife-switch for the spark gap and a 6" paper cylinder about four feet long (wound with 34GA wire) and fired it with an oil ignition transformer (10kV @10ma). They wouldn't let me have power at the school science fair. :-(
Back when tubes were new, someone did microwaves with a spark gap so don't worry too much about the frequency. You won't be able to get all that high of a voltage though.
Most Tesla coils use something like a neon sign transformer to drive the spark gap.
I think a paper towel roll will make a better secondary than one of any length and half an inch wide. For a diameter this small, I think a good wire size is about 30-32 AWG - 34 is not that far off.
I do advise getting PVC pipe bigger than this and winding with wire of size about 28-30 AWG. Get some at Home Depot or keep an eye on where such pipe could end up in the trash.
I do advise against cardboard carpet roll tubes, cardboard salt containers, or any cardboard that is not especially favorable in having high resistance. I have had bad results here! Paper towel tubes may be OK and will probably outperform plastic ones of less than half their diameter, and I have gotten good results with larger tubular cardboard oatmeal boxes. A largish oatmeal box does well with 31-32 AWG wire in a solid state Tesla coil, resonating around 250 KHz, and may want more like
28-30 AWG wire in a Tesla coil system with a spark gap.
If you use 4 inch inside diameter PVC pipe, I advise no thinner than 32 AWG wire, preferably 30 for a solid astate Tesla coil and 28 for a spark gap one. I also advise to not use more than 16 inches of 4 inch PVC pipe
- it appears to me that optimum length for this diameter is usually around
12-16 inches.
And I do believe that my 6 inch diameter 24 inch long secondary wound with 27 AWG wire has the wire size slightly thinner than optimum - I would recommend AWG 26, and to prefer 24 over 30.
Also, longer length usually does not help when beyond both about 4 times the diameter and much longer than your expected spark length, unless necessary to get the frequency workably low in a solid state Tesla coil. And then, I advise to increase the diameter of the secondary. And to have turns count a bit below 1,000 turns if possible with wire AWG 30 or a bit thicker, and also with achieving an adequately low resonant frequency (typically near or below 400 KHz). If 30 AWG wire has length less than about 190 meters (quarter wavelength of a bit more than 400 KHz), I recommend to upsize the secondary more than to downsize the wire. And to have secondary upsizing having enough upsizing in diameter to have diameter at least 20-25% of the length.
A possible source of good winding forms: Plastic shops whose customers are mainly artists and advertising display creators. Look for clear acrylic tubing. But after that, settle for PVC pipe at a home center. Get thinner wall versions in the unlikely event you have a choice.
1628 turns seems like more of a secondary than a primary.
Back in the days of, I used first a 211A, then a 304TL as power oscillator in a Telsa coil. The secondary was about 4 feet long, but the wire was wound with a goodly space between each turn (lathe with leadscrew).
The primary had about 8 turns. The plate supply was about
1300 volts DC (mercury rectifiers). Primary probably had
3-400 high frequency vac across it. The turns ratio was in excess of 1:400, so the theoretical output would have been about 120,000 volts. It would pull 6" arcs no sweat. There was plenty of punch behind those 120,000 volts. It would burn through light bulbs, the paint on the masonry basement wall, etc.
That will depend on the amount of power you put in and the flash-over point of your windings.
The voltage on a Tesla coil secondard increases until it finds a path to start losing energy as fast as it is being put in. The Q of the coil should be quite high so ordinary resistive losses would require quite a high voltage to start eating up the energy.
To put a lot of power into the secondary, the primary must be tuned to very near the same frequency and also have a high Q. You need to use very heavy wire for the primary. The capacitor just before the spark gap, the gap, the tuning capacitor and the primary are all carrying high RF currents. All of this wiring needs to be kept short. You want to keep the area enclosed by the wiring to an absolute minimum.
Probably you can get decent sparks with a tuned solid-state oscillator even from the 24 V battery. (*I* would not like my 14-year-old to do the same stunts that I did when I was 14).
There is lots on Google:
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but, many of the designs are, IMO, overcomplicated.
I would try a single-ended MOSFET oscillator first, using a High-Voltage MOSFET, heat sink and remember to clamp the gates with tranzorbs. Maybe based on a Colpitts Oscillator with MOSFET driver and feedback taken from the primary coil. Something on Oscillators here:
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Maybe you can be really crude and use CMOS gates to build a ring oscillator (three inverters in series with feedback) and "close the ring" by having the last inverter stage being the MOSFET Driver stage. Should run at whatever resonant frequency your coil is at.
The whole idea being that a tesla coil is a resonant transformer and it works best at the resonance frequency, the simplest way to hit/find that is to build an oscillator around it.
Cardboard should be better than PVC because it will have lower dielectric losses (it still might catch fire if there is some conductive crap in the paper; its maybe recycled stuf). Test is and see.
PS:
2N3055's commonly seen in "on-the-net-designs"are outdated IMO, the max voltage is 80V so they die real easy im most inverter designs; if you want cheap transistors for high voltage use TV Line Output types instead.
No - it's a string of an uneven number of inverters where the output is fed back to the input so - doing nothing else - it oscillates at some frequency determined by the propagation delay in the chain.
In our case the resonant frequency of the tesla coil should set the frequency by acting as a low-pass filter in the feedback chain.
ala this:
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or
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(& other stuff, which may be fun)
If the first inverter is a comparator the second a MOSFET driver IC and the last an output stage driving the tesla coil primary it *should* be possible to pick up feedback from the secondary in some way; maybe with a capacitive probe or with a winding on the secondary and get the loop to close.
Maybe some light DC feedback is needed to kick it off too. It is a *good idea* to protect the input of the oscillator from overvoltage!!
PS:
I might, just might get some time to play with this next month when I am not travelling.
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