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is there any electrical connection between toroid and the secondary winding in Tesla Coil? Answered

i have secondary on a 2.5 inch PVC and my toroid is made of aluminum duct .  now i want to know whether there is any electrical connection between these 2 ?


Every design I have seen has the top of the secondary connected to the torroid (or whatever kind of "top load" you are using). I have them connected that way on my coil. They need to be connected, as the torroid provides most of the capacitance in the secondary resonant circuit.

When I built my secondary, I left extra wire on one end, so that I would have enough to connect to the secondary. I have a plastic post on the top of my secondary with a metal screw in the center. The wire from the secondary connects to this screw, and the torroid connects there as well.

so it is safe to connect the toroid with the secondary , assuming the the voltage across secondary would be something like 10k ??

I have one end of the secondary connected to the torroid, and the bottom end connected to a good earth ground. I actually have a dedicated ground rod for mine.
I have always read that using the third (safety ground) prong of an electrial outlet for the ground of a Tesla coil is not a good idea, as the inductance of the wiring in the house back to the actual earth ground is high enough to develop a significant voltage across it.

I don't know theoverall size of your coil, but most develop a secondary voltage much greater than 10kV. Even for medium size coils, much larger secondary voltages should be normal. There are rules of thumb for approximating the voltage by the maximum arc length from the top load terminal to ground, based on the fact that air breaks down at about 10kV per centimeter.

hii .... actually this is my first attempt to tesla coil ... i m doing it for my college project ... i use a secondary coil 63mm in dia , with wire .3mm thick and 1000 turns... my primary is made of 10 SWG wire with 6 turns with first dia being 160 mm and consequent turns 5mm apart .. i had ordered a transformer 220/4000V and 35mA ... i dont noe whether it is current limiting or not ... i made toroid using a 4inches aluminium duct .. 22 inches in circumference ... now a few questions :-
1) can i use a series of 400V capacitance for primary ?
2) what should be the value and current rating of my bleeder resistance ( connected accross capacitance)
3) how do i limit the current ; provided i dont noe whether my transformer can limit the current or not ... ?? if using a choke what would be a good value of the choke and its rating ??
4) can i wind primary on a wooden structure or do i need acrylic sheet or Bakelite ???
5) how do i tune my tesla coil ... i have no access to occilioscope :( :(

thanx alot BTW for sharing your experience !!!

1) A capacitor with a 400V rating will not nearly be sufficient.
The primary capacitor must have a voltage rating of at least the maximum output voltage of the transformer, multiplied by 1.4. The 1.4 factor is due to the fact that the voltage rating of the transformer will be specified as RMS, but the maximum voltage seen by the capacitor will be the sine waves peak voltage. In practice, the capacitor rating should be somewhat greater than 1.4 times the tranformer output voltage rating, to allow for some safety margin to prevent the capacitor from being damaged.

2) I don't think it is necessary to have a built in bleeder resistor. I just make shure that I short the capacitor with a probe which has a long nonconductive handle.

3) Determine your choke as follows:

Choke Impedance = Transfomer output voltage / max desired current
Choke Inductance = Choke Impedance / (2 * pi * line voltage frequency )

I'm assuming the line frequency where you are is either 60 or 50 Hz.

4) Wood should be ok. Most flat primaries just use wooden or plastic supports. If it is a cylindrical primary, plastic pipe like PVC is commonly used.

5) The seondary coil and top load should be chosen to resonate at or near the frequency of the primary.

Tuning the primary and secondary to the same frequency is generally accomplished by means of an adjustable tap on the primary. This allows the user to change the inductance of the primary by using more turns or fewer turns, based on where the tap is connected. The inductance and capacitance of the primary circuit determine the frequency that it will oscillate at when the spark gap fires.

There are numerous tesla coil designs on the web, often with much more thorough answers to these type of questions. Seek out as much information as you can, and err on the side of caution.

Good Luck!!

hii ... i got the ans ... i was connecting the choke on the secondary ...so the value was comin out to be too high

thanx for the help

hi ... thanx alot ... it was helpful ... just 1 doubt remain though ..... the choke from this formula coms out to be 364 H ...... isnt it too high ??? my trf is designed to handle 35mA in the secondary so i took that as max current !!!

BTW again thanx alot !!!

Yeah, that is too high of an inductance. I wasn't thinking straight on that one.

Your transformer secondary will have some resistance, which will limit the short circuit current, so a choke would not need to be as large. The resistance of the secdondary windings on neon sign transformers can be many kilo ohms.

I would add additional resistance instead of a choke. Determine the resistance value you would need to limit the current (taking into account the winding resistance). The resistor will see a large voltage across it when the output is shorted, and most individual resistors won't be rated to handle the multi kilovolt output of your transformer. So, construct the current limiting resistance out of several resistors in series. Unless they are rated for high voltages, most resistors aren't designed for more than a couple hundred volts. Here again, err on the safe side and give yourself some margin on the ratings by using more resistors in series to achieve the needed current limiting. When assembling your resistors in series, be careful to leave plenty of clearance between each, so that the current doesn't just arc between adjacent resistors.

do i connect i end of the secondary to the toroid ? and what about the other end ? i have a confusion as to what do i do with the ends of the secondary ?? thanx for replying BTW .

Which schematic are you using? I've seen it both ways.