How do you calculate an inductor's impedance to pulse dc?

[sebosfato]

hi sephirot

You are probably achieving saturation of your core. so inductance drops and you have more current than expected, Try to remove you core measure the inductance and make the test again. with no core you can't saturate. than you will know why you are getting this behavior.

It could also be the capacitance of your signal generator in series with your inductor creating a series resonance...

Check that,

More info about LC circuits on my thread here i explain some effects of inductance in respect to frequency check it,

http://www.energeticforum.com/renewable-energy/4617-stanley-meyer-true.html

[Sephiroth]

hi sephirot

You are probably achieving saturation of your core. so inductance drops and you have more current than expected, Try to remove you core measure the inductance and make the test again. with no core you can't saturate. than you will know why you are getting this behavior.

It could also be the capacitance of your signal generator in series with your inductor creating a series resonance...

Check that,

More info about LC circuits on my thread here i explain some effects of inductance in respect to frequency check it,
http://www.energeticforum.com/renewa...eyer-true.html

You've completely lost me What behavior are you talking about?

Edit : and I don't think it is possible for the core to saturate in a solid state oscillator sicne there will be pracitcally no trigger current by the time to core saturates. The core material doesn't make a difference there, though air core is more desirable for other reasons.

[sebosfato]

You ask a question without giving much informations about your circuit, propose, components... Is hard to guess what are you doing wrong.


What is the dc resistance of your coil?
What is the voltage you are using ?
Are you sure about the frequency?
Are you sure about the inductance value? How did you measured it? Does it has a core? What kind, how big? What wire size and how many meters?


I pulse coils with dc and mosfets here and never got this huge difference as you described.

[Sephiroth]

I think there has been a misunderstanding...

All I asked was how to calculate the impedance of an inductor to pulse dc.

The circuit is working perfectly.

[Armagdn03]

The impedance formula posted immediately after you asked will work fine. Impedance in this case only refers to a resistance to change. This resistance can take the place of a change in current over a given time, be this DC or AC, the only thing taken into account is how quickly the change happens. Even DC ripple will have an impedance to the AC component.

[Sephiroth]

The impedance formula posted immediately after you asked will work fine. Impedance in this case only refers to a resistance to change. This resistance can take the place of a change in current over a given time, be this DC or AC, the only thing taken into account is how quickly the change happens. Even DC ripple will have an impedance to the AC component.

though duty cycle isn't taken into account... If ac is applied to an inductor then each polarity of the sine wave is being impeded by the flux generated by the previous polarity.

With pulse dc the impedance will also vary depending on the duty cycle and I reasonably sure that a 50/50 duty cycle of pulse dc won't have the same impedance as 50/50 ac.

[derKonigsten]

I believe that impedance is a term that applies only to reactive components (capacitors and inductors) as far as sine waves are concerned. This term refers to it's equivalent resistance. That is, how much current will flow through when a voltage is applied at a given frequency. We know that the general formulas for reactance apply only to sine waves because of the inclusion of 2pi
Now, when dealing with pulse waves:

--For inductors: (think about being concerned with current)
--the current through an inductor (which is simply a coil) will be limited only by the actual resistance of the wire of that coil. However, the nature of inductors is to produce expanding and collapsing electrical fields which happens to produce a 'ringing' effect after a falling or rising edge of a pulse. We can also control the voltage developed across a coil by controlling the amount of current allowed to flow through it with something called a constant current source.
For this we can use this formula:
Vl=-L(di/dt) where L is the inductance in henrys, and di/dt is
the amount of current in a given time.

--For capacitors: (think about being concerned with voltage)
--The voltage across a capacitor (two plates of metal seperated by an insulator) the charge developed is a function of the amount of current (or amount of electrons) which are allowed to pass through it in a given time.
This formula can then be described as :
Ic=1/c(dv/dt) where Ic is the current, c is thecapacitance in fahrads, and dv/dt isvoltage/time

[Farmhand]

The calculator at this link might help.

If you input the voltage across the inductor.
the inductance of the inductor in micro Henries
and the saturation current of the inductor, ( I just use an arbitrary figure I think is reasonable )
ie. about the current I desire through the inductor.
Then the calculator outputs the recommended time "on" the recommended
frequency the max power and the energy in the coil at saturation.

To get an idea start with 10 volts, 100 uH and 1 amp, to see a recommendation
of 10 micro seconds "on" time at 50 kHz with 4 Watts Max power and 50 micro
joules of energy stored. Changing the inductance changes the frequency and
energy at saturation but the power remains the same, change the voltage or
the current and the power changes as well.

It's a handy tool, but real life things are mostly slightly different, very very
helpful though, I used this tool to determine the frequency and "on" time to
use for my boost converter coils, I just use it as a guide mainly but I find it
very useful.

Inductor Current and Maximum Power Calculator


Cheers

[quantumuppercut]

What I see is when an inductor is switch on till 5 time constant, it travels through a range of frequency from infinite (initially on) to 0 (~5 time constant). Therefore, the effective impedance is related only to the pulse width in this case. Frequency can be seen as inverse proportional to pulse width.

effective impedance ~ L/(pulse width *R)

This is not exact but it seems to be able to describe the behavior when various parameter is change. If you keep everything the same and increase inductance L, impedance increase. If you lower your pulse width, the impedance also increase. This makes sense because when you pulse your coil with close to zero time pulse, there will be no current flowing through the coil.

[boguslaw]

I need help. Most important is to find out the max flowing current in RCL resonant circuit at resonance. Do you have idea how to compute it ?

[wings]

I need help. Most important is to find out the max flowing current in RCL resonant circuit at resonance. Do you have idea how to compute it ?

Help me calculate the resonant frequency and current and resonance? - Yahoo! Answers

Series Resonance in a Series RLC Circuit