Capacitor discharge through a coil, need to find current

**nrlightfoot** · Nov13-09, 10:34 AM

I'm designing a circuit to discharge a capacitor though a coil of wire to make a large magnetic field, which is basically an undriven RLC circuit which starts out with a charged capacitor in series with an inductor and a resistor (the coil having a certain resistance in addition to its inductance).

I'm trying to find an equation for the current through the coil (inductor) as a function of time after starting to discharge the capacitor. I need to find this so I can select proper components to give a sufficient magnetic field without burning out the coil.

I also know that the capacitor will have a small amount of inductance which needs to be factored in. Please let me know if there is anything else like that I would need include in the calculation.

**Bob S** · Nov13-09, 11:06 AM

Please read through all posts in this thread:
http://www.physicsforums.com/showthread.php?t=327153
Bob S

**nrlightfoot** · Nov13-09, 04:04 PM

Thanks Bob,

That thread was helpful, I think if I had that program you were using I could figure out what I need to know. What's the name of that program, and do you have that RLC circuit file you made that you could send me if I can get the program?

-Nick

**Bob S** · Nov13-09, 04:15 PM

Hi nrlightfoot-
I was using free LTSPICE IV available on the web. Please look at my posts #26 thru 32 in the referenced thread:
http://www.physicsforums.com/showthread.php?t=327153
Here is a 16,000 amp, 2 ms wide half-wave current pulse using series diode in thumnail.
Bob S