Just a few questions on tesla coils

[illconductor]

Hi. im wondering why the secondary is an aircore coil. why not just use a standard iron core one?

and in the tank circuit, i think you need an inductor, a capacitor and a supply. So the inductor is the primary of the air coil?

does the secondary of the supply play any part in the LC cirucit.. that is would i include this in calculation of L and C value.

.. and finally, would you make Xc and XL of cap and air core sec equal?

 

[BrownOut]

1) IMO, an iron core would be damn heavy and inefficient.

2) That sounds right. Also need a spark gap

3) Probably. You need to be able to determine the frequency of the primary by measurement. There will always be some parasitic component you won't include in your calculation.

4 ) Yeah, that's the whole point. The main reason a telsa coil works is because it operated an resonance, which builds up the voltage much higher than it would otherwise be. The primary need to be tuned to the resonance of the secondary, after that has been measured. There is a good you-tube video on how to measure the resonate frquency and tune the primary. Sorry, I don't have the link; you'll have to search for it. Also, it's my understanding that there is significant inter-coil capacitance, so your calculation using a lumped cap. as the top cap will by off by a little. It's very important that you measure the resonant frequency.

 

[Sceadwian]

The frequency of a tesla coil is moderately high you'd lose a lot in the core, especially a solid iron core.

 

[illconductor]

aha thanks

 

[Frosty_47]

Tesla Coil is not going to work with iron core as it will quickly get saturated.

There is a program out there (WinTesla I think) that can aid in all of your calculations and give you a spark length estimate as well.

Good luck and try not to fry the neighborhood transformer...

 

[illconductor]

yeah youd be in deep sh-- if you fryed the tranny hey
i was thinking of powering it from 12 lead acid as to get around that problem, plus big sparks from 12v is much more impressive

 

[BrownOut]

How are you going to generate the HV for the primary spark gap? That's often done with a big transformer, like an oil heater ingnition transformer. It requires a KV or so, I think.

 

[illconductor]

well i could use one of those i suppose

 

[BrownOut]

well i could use one of those i suppose

Except they don't work from a 12V battery. You'll have to use an invertor or something. Post some pics when you finish

 

[crutschow]

Another reason to use an air core it to insulate the very high voltages generated in the secondary.

 

[RCinFLA]

Spark gap is the impulse stimulator. Part of frequency multiplication.

In the 'old days' I used 60 Hz, 12 kV neon sign transformer to do the first boost. It drove the spark gap to the resonate primary side tank circuit on the Tesla coil. Would light a 40W florescent bulb 15 feet away.

The spark gap impulses the primary side resonant tank which was tuned to several hundred kilohertz. I used about a 2 foot by 2 foot glass plate with aluminum foil stuck on both sides. First glass was about 1/8 inch thick which I blew a hole in so went to 3/16 inch thick glass. The Q of this cap is critical otherwise the 'ringing' disipates too quickly. The air coupled HV secondary winding relies on high frequency to couple enough energy to it. If primary tank Q is too low there will not be enough high frequency current component to effectly couple to secondary HV winding of Testa coil. (6 MHz seems a bit much)

The 'ripping loud' noise of the spark gap only happens when load is resonant. Too close spacing on gap and you will catch return jumps on the high freq ringing which will de-Q the tank. Too far apart and it won't spark. Proper point is as far apart as possible to start the spark jumps. The tank resonance must be much higher frequency then primary source frequency otherwise you will get too much of tank ringing jumping back across the spark gap lowering the tank Q.

This is how the 'wireless' transmitter worked on the Titanic. In its case the interrupter was a magnetic switch vibrator to generate the low frequency stimulator to the spark gap. (and NO, I was not born at that time)

 

[BrownOut]

Here is a design using a switching power supply that incorporates an automobile high voltage ignition coil for the primary HV. This can be operated from a 12V battery. I've made HV power supplies similar to these, and they work well. I can tell you, however, that you need more protection for your timer and transistors. Use transorbs and/or MOVs to prevent kickback voltages from the automobile coil from frying your electronics.

**broken link removed**

 

[illconductor]

hmm very interesting, so you tune your tank circuit to 20khs or something like that, based on the secondary?. and to tune the tank would you have xc =xl or does the spark gap and secondary play a part in it

 

[BrownOut]

As I understant it, you figure out the frequency of the secondary, and tune the primary. One connection to the primary is made with a clip, which can be moved to different coils to change the frequency.

But I never made one; just read about it.