Author Topic: Ok lets find the capacitance of our wfc?  (Read 11379 times)

0 Members and 1 Guest are viewing this topic.

Offline Login to see usernames

  • Global Moderator
  • Hero member
  • ****
  • Posts: 3607
What is resonance
« Reply #32 on: June 29, 2012, 22:20:23 pm »
Resonance arises from the fact that when you have an inductor and a capacitor in series, while the capacitor is being charged the current flowing induces a contrary voltage at the inductor, so in series the voltages sums to zero, this let the source to charge the capacitor to higher voltages as it appear like a short circuit for the source. When the current decay the voltage across the inductor becomes smaller while capacitors voltage raises. This is why an inductor has a voltage peak that appear 90° before the capacitor peak voltage.

There are 360° for a complete cycle, so lets examine it:
Consider the capacitor is not charged initially
1° 90° The current is maximum so as voltage across the inductor. The voltage of the inductor is a cosine function, while the capacitors voltage follow a sine function up to its max voltage
2° 90° current stops, and the capacitor completely discharge into the inductor.
3° 90° the inductor charge the capacitor with reversed polarity
4° 90° the capacitor discharge into the inductor.

Summing to that, at the end of the cycle, when current is zero, the capacitor has the full voltage across it, and the polarity is inverted, so you can aways add more energy to it. Because as you apply a contrary voltage to a capacitor charged the, energy at the end will be the sum of the energy you inputed + the energy originally at the capacitor. 

Its known that the time constant for a capacitor depends on its capacitance and the resistance in series.

As a Capacitor accumulates a charge Q the peak current will depend on the time constant. 

If you discharge the capacitor applying a contrary voltage to it, would the RC time constant be the same?

I think would become smaller, because you are forcing it so the peak current will be greater...

Of course resonance voltage is only limited by the real resistance of the circuit and to the voltage applied...

The resistance will affect the phase limit between voltage peaks therefore it will limit the resonance not only by dissipating power but impeding the voltages in series to completely cancel out.
« Last Edit: June 30, 2012, 16:07:49 pm by sebosfato »

Online Login to see usernames

  • Administrator
  • Hero member
  • ****
  • Posts: 4463
    • water structure and science
Re: Ok lets find the capacitance of our wfc?
« Reply #33 on: June 30, 2012, 10:34:59 am »
Thats correct and proven.  :)


Offline Login to see usernames

  • Sr. member
  • ***
  • Posts: 421
Re: Ok lets find the capacitance of our wfc?
« Reply #34 on: June 30, 2012, 14:38:32 pm »
Meyers indicated that each inductor in the VIC should have a resistance of of 11.6K.  How is it you say the resistance of mine is too much?

TS

Offline Login to see usernames

  • Global Moderator
  • Hero member
  • ****
  • Posts: 3607
Re: Ok lets find the capacitance of our wfc?
« Reply #35 on: June 30, 2012, 15:33:46 pm »
well, the Q factor of the coil say that it would not resonate. Meyer said this value but probably he was talking about impedance not ohmic resistance. Because than it makes sense if is a resonant choke. Choke.

Take the impedance matrix circuit as reference.

Offline Login to see usernames

  • Sr. member
  • ***
  • Posts: 421
Re: Ok lets find the capacitance of our wfc?
« Reply #36 on: June 30, 2012, 16:03:28 pm »
To achieve this resistance I did not use standard copper wire.  I used resistor wire.  I achieved 8.78k with about 400 turns.

TS

Offline Login to see usernames

  • Global Moderator
  • Hero member
  • ****
  • Posts: 3607
Re: Ok lets find the capacitance of our wfc?
« Reply #37 on: June 30, 2012, 16:15:56 pm »
I understood, I tried it also. You wire is very thin isn't.

Try to put this coil and a capacitor in series and find the resonant frequency. You will see that if any peak is observed the band width will be really wide.


Offline Login to see usernames

  • Global Moderator
  • Hero member
  • ****
  • Posts: 3607
Re: Ok lets find the capacitance of our wfc?
« Reply #38 on: June 30, 2012, 23:47:36 pm »
I found a thread discussing, dielectrics water...
http://www.overunity.com/9856/relative-permittivity-of-water/

Anyway the closer to reality value was found by Steve... 200nf

And they state water is not a dielectric because it conduct dc... many laughs
« Last Edit: July 01, 2012, 01:45:08 am by sebosfato »

Offline Login to see usernames

  • Sr. member
  • ***
  • Posts: 421
Re: Ok lets find the capacitance of our wfc?
« Reply #39 on: July 01, 2012, 17:31:45 pm »
Here is a link to various methods to test capacitance for unknown capacitors.  I will be trying out method 4 soon.

http://www.pupman.com/listarchives/1998/April/msg00625.html

TS