Measuring Self-Capacitance & Self-Inductance of a Coil

In summary, the self-capacitance and self-inductance of a coil can be calculated by using formulas L = - (dI/dt)*(1/Us) and R = ro*(l/S), where ro is the specific resistance and l is the length of the coil. These equations can be used to determine the number of turns in the coil. The self-inductivity is given by: L = - (dI/dt)*(1/Us)
  • #1
Jonathan
365
0
the self-capacitance and self-inductance of a coil? Are there equations for these where I won't need to know the number of turns? Since I think #2 is no, are there meters I can buy to measure this, or can I use the measurements from a volt/resistence meter I already have?
 
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  • #2
the self-inductivity is given by :

L = - (dI/dt)*(1/Us)

where dI/dt is speed of current variation (dI is current variation, dt is time of variation), and Us is sefinductivity voltage.
 
  • #3
Thanks for repling! How do I know the self-inductivity voltage? Any ideas about self-capacitance? L seems like it should be proportional to the # of turns or the length of wire or something, why not?
 
  • #4
oi couldn't figure the easier way for determining selfinductivity if you already have em. coil, so here it is :

we need basic three values about coil, it's current, voltage, and resistance. i believe you already know voltage, so you can measure the resistance of coil with normal ohmmeter, and then get current with I = U / R.

we need to know number of turns too. use the formula R = ro * (l/S), where ro is specific resistance (you can find those values on the internet for every material, for copper is 0,0175), l is length of wire and s is surface (in mm2). then you can use simple geometry to determine number of turns. you need to know the surface value for that. N = lair / 2*sqrt(S/3.14). lair is length of coil, not of wire, and you can use normal meter to measure it.

in my previous post i gave that formula. Us is selfinductivity, and L is inductivity. Us is voltage that appears when magnetic flux changes inside the coil as direct effect of current change trough coil. so we need to know inductivity to determine selfinductivity.

Us = -L*(dI/dt)

inductivity : L = N^2 / Rm . we already calculated number of turns so onlything that's left is Rm, the electromagnetic resistance.

Rm = theta / fi

theta = I * N , the magnetomotoric force. we have both of values required, the current trough coil and number of turns

fi = B * S, the magnetic flux. note that S here isn't same as surface of the wire, it's the surface of electromagnetic pole. you can determine it by measuring the radius of the coil, and then using r^2*pi.

B = [mi-zero]*[mi-relative]*(I*N)/l , the field strenght. [mi-zero] is permeability of free space constant, and it equals 1,257e-6 (0,000001257). [mi-relative] is permeability of core. if your coil doesn't have iron or other core beneath it, then youre using air coil, and [mi-relative] is 1. for other materials refer to this URL : http://www.oz.net/~coilgun/theory/materials.htm.
 
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  • #5
That was a little over my head and more work than I was expecting. I'm thinking maybe I should just buy a digital inductance/capacitance meter...
 
  • #6
it's not that hard. if you post here all specifications you have on your system, i'd be happy to do the math for you.
 
  • #7
I don't yet have a particular system in mind. When I do, I will PM you, thanks.
 

1. What is self-capacitance and self-inductance?

Self-capacitance is the ability of a conductor to store an electric charge, while self-inductance is the ability of a conductor to store energy in the form of a magnetic field.

2. How do you measure the self-capacitance and self-inductance of a coil?

To measure self-capacitance, you can use a capacitance meter or an LCR meter. To measure self-inductance, you can use an inductance meter or an LCR meter. Alternatively, you can also use a bridge circuit and vary the frequency of the input signal to determine the self-capacitance or self-inductance of the coil.

3. What factors affect the self-capacitance and self-inductance of a coil?

The size and shape of the coil, the material it is made of, and the number of turns in the coil all affect its self-capacitance and self-inductance. Additionally, the frequency of the input signal and the presence of nearby conductors can also impact these values.

4. How can the self-capacitance and self-inductance of a coil be used in practical applications?

The self-capacitance and self-inductance of a coil are important parameters in the design and functioning of electronic circuits. They are used in applications such as radio frequency circuit design, impedance matching, and power transmission.

5. Can the self-capacitance and self-inductance of a coil be changed?

Yes, the self-capacitance and self-inductance of a coil can be altered by changing its physical dimensions, such as the number of turns or the diameter of the wire. It can also be affected by the surrounding environment, such as the presence of other conductors or the surrounding material. However, the intrinsic properties of the material used to make the coil will also play a significant role in determining these values.

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