Projects by members > Haithar

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haithar:
Took some measurements today.
Coils are both 1,2mH, the cap without water is 4,2mF (!).
That means it built a resonance circuit for 50Hz without water, unfortunately with water the capacitance is > 300mF and the resonant frequency shrinks to 5Hz.
Damnit i never have thought that the capacitance can be too big. I hope the LCR-meter used the wrong method and calculated a much larger value :/

does anyone have a good way of measuring capacitance? my plan to use 230V grid voltage wouldn't work out that well, if the cap is really 4,2mF then it would draw > 250Amps at 230V. Not a good idea.

Update: had the great idea to use my 230V:12V transformer and measure reactance in series with 12 ohm resistor on the 12V side. Didn't work out as my cable on the 230V side overheated and broke in a second. Anyway i then took apart the tubes and dried them. The white coating already started to build nicely, but on the inner side of the outer tube.
I put everything back together dry again and this time my RLC meter showed a more stable value (no water) of 270pF or 0,27nF which is much more likely.
If insulated and filled with water the capacitance should be around 21nF +- 2nF and the resonant frequency in the range of 22kHz.

Update 2: Found out that RLC meters use direct current and measure how long the cap needs to be charged fully. Not the best method and it only works if it's absolutely sure that there is no charge left on the cap. So i think the 270pF is probably the more accurate value.

Donaldwfc:
I've read a lot of posts where people can't get the right capacitance, one thing i remember reading is that some instruments will measure the impedance and not the capacitance, and then people start talking about how the cell is a resistor as well as a capacitor and so on...

Your project is coming along good, I hope you find some results soon :)

Steve:
Some say you have to calculated the surface of the tube...

Steve

haithar:
I don't think the mathematical approach works here, too many imperfections.

Anyway, i got ~130V out of the transformer and probably 50V to the cap. When i played around with duty cycle and frequencies i noticed a point where very few little bubbles seemed to come out of the tube, amp meter showed 0,1mA like always on the hv side, but i guess i must have been mistaken. couldn't find the point again later.
i wrapped the coil in saran wrap btw, 12V dc / <0,1A current.
next step is to find out how the bifilar behaves and then how it works together with the cap. i'll also change the frequency generator to 100Hz steps, i'll have a range from 0 - 100kHz then. the 1n4007 gets hot when there's a current >1A at the primary, will need to change it too.
the good thing is with the saran wrap the voltage on the secondary does not break down.

Bubz:
Is your transformer designed for 50-60Hz?