Reactive Generator Research for everyone to share

[tim123]

Close up pics of the cap switchbox, FYI...

[Farmhand]

Hi Tim, Maybe I can help.  I use Two MOT's in parallel in the power supply of my Tesla coil, They measure about 236 mH each, but when in series they are of course double that. I'm on 240 volt grid as well. During the day with the solar array feeding the grid the voltage rises to over 260 volts.

A 240 volt MOT as compared to a 115 volt MOT would have a fair bit more inductance and so requires less capacitance to get resonance i think. But the lower frequency of 50 Hz means we need a bit more C than those on 60 Hz kind of thing.

For mine I require almost 38 to 40 uF across the MOT's in parallel but I forget how much when in series. 

The reason I put the capacitors across the MOT's and tune them to near resonance is that it makes the voltage drop less and the output more, it also improves the power factor (PFC).
I get up to 0.97 power factor on the supply to my spark gap Tesla coil, it varies with the energy used.

I'm not sure what exactly Luc tunes for, but my guess is the MOT's the caps and the motor make the circuit L/C way past resonance.

L/C resonance calculator.
http://www3.telus.net/chemelec/Calculators/LC-Calculator.htm

We must not forget that with 240 volts and so much capacitance these setups are extremely dangerous and definitely can be lethal. I employ line filters on the supply to the MOT's, they have a parallel resistor in them that bleeds the charge off the caps. 240 volts should pump twice the current through a body as would 120 volts. Risk is increased.

Cheers

[tim123]

Hi Farmhand,
  your Tesla coil sounds like a beast. I'd like to see it running.

I'm finding this all very interesting and informative. I've learned a lot already, and I'm grateful to Luc for bringing this up. I never really 'got' power factor, and now I can see it on the scope - and on my wattmeter...

I think this LC resonance calculator is better:
http://www.1728.org/resfreq.htm

My MOT primary is 292mH, so a capacitance of about 35uF should give a resonant frequency of 50Hz. However, I had the secondary shorted - which made it exactly 50mH, (so a capacitance of about 202uF should give a resonant frequency of 50Hz.). Luc, can you measure yours?

I will have a play again later/tomorrow and see if I can observe the resonance... I think I need to try capacitance / load on the 2ndary too - and see what that does.

Regards
Tim

[tim123]

Update: I put a 1uF cap across the MOT secondary, and the bulb lit at 12.3w - i.e. better than without the reactive circuit. I tried a range of caps up to 100uF, but it didn't seem to make any difference after the initial 1uF.

I tried another 100w bulb on the secondary as a load. It didn't light, but the main bulb lit again at 12.3w - so it does help.

Both together in series or parallel - still 12.3w.

It looks like the circuit is doing a fairly good job of correcting the power factor from the variac...

[hartiberlin]

Hi Tim,
well done.
Maybe oyu can also try to measure voltage and current BEFORE the Variac with your scope.

Be sure to not short out the grid´s hot pole, so put the current shunt into the ground pole
and not in the hot pole side !

Please post scopeshots or a Youtube video where you show this if you can.

Many thanks in advance.

Can you already verify that the power factor does not change at the input when you load the output ?

What pahse angles do you get between current and voltage ?
Are you on a 230 Volts 50 Hz system or 60 Hz 120 Volts system ?


Regards, Stefan.