How to specify, find a transformer, given circuit schematic?

[Charlweed]

I'm an electronics neophyte, looking for a transformer, to generate a spot of plasma at the end of two leads. In particular, I am trying to build the circuit here:


This circuit is published in a couple of magazines. The last component I need to finish the circuit is the transformer that converts 12vDC to “a few kv” at kilohertz frequencies. The author calls the transformer a Tesla Inductor, and suggests obtaining one by pulling one out of a furnace ignition system. I have had no luck finding a used furnace ignition system that has a transformer.

I would buy one new, but neither the schematic nor the articles detail the specifications of the transformer, and I do not know enough to infer them.
I have figured out that I need a low current, high voltage transformer. This may be known as an ignition, or spark, transformer. I think I need to know at least the impedance and operating frequency, as I have inferred the input voltage (12) and input current (10 ma) from the 555 timer. Some vendors seem to want me to specify windings, winding ratios, resistance etc.

Thanks for any help!

 

[jiripolivka]

To generate sparks ~ 20 kV, the car ignition coil can be used, with 12 vdc primary switched by a 2N3055 transistor controlled by a 555 timer. You can also find discarded CRT monitors and analog TVs, with HV flyback transformers. Those generated 20-25 kV from 12 VDC, too. You may even use the original driver circuit and reve the "load", the CRT.

With all above devices, please take care- the HV can be lethal!! Use extreme caution when you try to activate the device. 20 kV spark can be ~2 cm long or more, and the current is enough to kill you.

Less lethal are the HV pulsers used for cattle fences, but the HV pulse can burn you, too.

- - - Updated - - -

correction "remove the load", the CRT.

 

[Charlweed]

Thanks, 'Ill try that. I may have a 1959 Triumph coil in the garage. But can you give any guidance on what characteristics of a car ignition coil make it suitable? In terms of transformer parameters?
And what should I use as a power source? I was thinking D cells. Would a 12v car battery fry my circuit?

 

[Inti Innovations]

http://www.kronjaeger.com/hv/hv/msr/spk/index.html
This article can give you an idea of the length of sparks you should expect at given voltage.

 

[jiripolivka]

Thanks, 'Ill try that. I may have a 1959 Triumph coil in the garage. But can you give any guidance on what characteristics of a car ignition coil make it suitable? In terms of transformer parameters?
And what should I use as a power source? I was thinking D cells. Would a 12v car battery fry my circuit?

THe current depends on the 2N3055 switch current setting and switching pulse width. The ignition coil is adjusted for 2-3 A at 12 VDC, so a car battery is fine. D-cells would live only an hour.

On making Tesla transformers you can google an avalanche of designs. Beyond your safety with HV, please be aware that such devices generate RF interference around, and your neighbors may complain.