Rheostat power rating

[Kerrowman]

It's interesting that you, in effect, got + and - 3.7kV across the output of the coil. That is certainly the sort of level I would expect, in which case I would expect more than the 3V I get when I attach my secondary to my load (water cell). Which brings me full circle to my earlier question, why am I getting only 3V across my water cell terminals when your simulation and your ignition coil experiments show much more?

Perhaps I should build a Tesla coil and zap my water cell with that?

As a square wave can be thought of a complex mix of different frequencies of sine waves (Fourier analysis) I think using a square wave in a transformer will result in higher losses at the higher frequency end so producing a rounded square wave output with some enhanced ripple. When that encounters the water cell that will undoubtedly modify the waveform but I haven't observed that yet.

 

[HarryA]

Your getting  just 3 volts suggest an impedance mismatch between the transformer and the cell.  In looking at using automobile ignition coils for high voltage I see a number of videos and articles where they get huge sparks from the coils that I can not get. I feel like you; where is the spark! I am thinking my coil is a dud!

See for example: https://www.youtube.com/watch?v=PTt5sM3moqQ  There are a number of similar videos there  using ignition coils for  high voltages.

[Kerrowman]

Thanks Harry,

I will certainly look into using ignition coils or perhaps a Tesla coil.

If it's a question of impedance matching then surely I only have the option to up the secondary coil's impedance. Given that at the moment its resistance is about 1 Ohm, then does it make sense to add a 1 MOhm resistor in series with it to bring it more in line with the 1.6 MOhm resistance of the water cell? Or will that not work or introduce other problems?

Julian

[HarryA]

There is something about pulse transformers dealing with the pulse width. If the input pulse width is two short
the current never has time to build up completely do to the lagging current in an inductor/coil. That would look like an impedance mismatch also.

If the pulse is to wide current is wasted when the coil is fully energized.

For example see  https://www.youtube.com/watch?v=vvXbTIqBY4o

[Kerrowman]

Hi Harry,

That makes sense but in the case of the ignition coil HV systems, like in the link you gave, they can operate at a similar frequency of say 200-500Hz and still give very powerful sparks so is the construction of an ignition coil, and also a flyback transformer, different to such a degree that they avoid this pulse width issue?

I'm inspired to build one or other of the attached, although the 555 based one has some useful duty and frequency adjustment. Maybe one of these will deliver 10+kV to my cell without significant losses?

Julian

[uziao]

Hello friends. Very interesting topic you have here. You can model the electrodes underwater as an capacitor in parallel with a resistor (a leaky capacitor). Maybe this is why he used a bifilar coil... Bifilar coils are self resonant coils because of their capacitance. You can see this article here:

https://sci-hub.st/https://doi.org/10.1002/cta.2830

The autor proposed a resonant tank circuit without the capacitor, using only the capacitance of the bifilar coil.

If the electrodes underwater behave like a true capacitor, he wouldnt need 2 coils... Only one coil would do the job... Maybe the trick lies in the coils only...