Hello, I would like to know if there is any formulea for calculating the peak current through an inductor, i am under the impression that when a voltage is passed across an inductor, the properties of the inductor limit the current. I know ohms law will work for resistors etc.

I am using the inductor as a coilgun, its resistance is 1.2Ω and inductance is 1.315mH, it was wound with half a pound of 18SWG wire(not sure how many turns?)

I am discharging 200V from a capcitor bank of 2000uF.

Thank You.

 

The "Ohm's law" for inductance is v = L di/dt where v is the voltage across the inductor, L is the inductance, i is the current and t is time.

For capacitance it is i = C dv/dt.

So if you understand calculus, you can write a differential equation that, when solved, will allow you to calculate the current.

If your maths is not up to the task, then use a circuit simulation programme such as Switcher CAD III.

__________________
Len

 

Thanks ljcox, my maths is pretty good (I think, lol) i'll write those down and see what values i can come up with, i am assuming it is:

V in Volts
I in Amperes
L in Henrys
D in Metres
T in Seconds

When I rearrange it i get I= ( (V*D*T) /L ) /D
Is this right??

Thanks

 

No, that's not correct.

"D" is not a length. The expression "di/dt", is intended to mean the time derivative of the current. Written another way looks like V = L* d/dt[i(t)]

Where i(t) is the current as a function of time. The d/dt part means "the derivative of." If you are proficient in calculus, you will understand this.

 

So I'm led inexorably to the conclusion that a lack of calculus training leads to an interest in coil guns!

Sacre Bleu! and lol

 

When you lack the background to realize the full potential of electronics, you are drawn to weapons first because they have the appearance of being easy to grasp intuitively and tend to have a coolness factor that is easy to comprehend and test, and gets instant results once you get it working!

The reason the timer-derivative is there on the inductor formula is that an inductor does not limit current the same way a resistor does. A resistor permanently limits current, while an inductor kind of slows down the change in current.

That is why you parallel a bunch of capacitors. Doing so will increase the capacitance and reduce the total parasitic inductance.

 

Or disasterous and regrettable results when you get it wrong, which you will, according to the principals enunciated by one Edwin P. Murphy. I hold such people in the highest contempt.

 

Yeh, it's the kind of thing that looks deceptively simple because at first glance, you can intuitively grasp some of the concepts and feel like you got a handle on things, but if you have the background to think it through...it really isn't. THat's what makes it so dangerous.

Wolf in sheeps clothing.

 

Sorry about the misconception, i haven't really done calculus, i am fresh out of secondary school, thanks for all the replies

 

What's secondary school? Is that High school equivelant (Grades 10-12)? Kind of strange they didn't offer calculus if it is.

 

Ages 11-16, i'm still 15 (have a birthday later in this year) we did do some calculus, i'm of to college soon to do A-levels, i am taking maths, so i am expecting to do some of calculus. (Oh Joy)

 

GOod luck. Be prepared to be amazed at the convoluted ideas some people come up with (whether they be true or not) lol. Anyways, yeah, no one ever uses d as a variable in electronics (at least at the point I am currently at) because it appears so often in the calculus equations. (Plus dy/dx would be written as y/x if the d was a variable since it would just cancel).

 

I am as prepared as i'll ever be (i think lol)

convoluted, thats a nifty word for complex or intricate, i think i might use that sometime recent...


Now thats an idea... a convoluted one??!

LOL

 

Intricate and complex implies some form of elegance. Convolution implies complicated with ridiculousness, non-sensicalness.

There's actually an mathematical operation called convolution (like addition or multiplication). The first time you come by it that's exactly what it will be lol. It's still kind of a pain in the ass to do by hand. You're basically super impose two graphs on top of one another and slide them through each other in little steps, each time doing a little addition and multipying between each point where the graphs overlap (imagine doing with two equations instead of graphs). Sadistic sense of humour those mathematicians have.

 

They DO have a sadistical sense of humour, must be all of those numbers and formulea sucking out their true humour... saphire,irony and other comical means of comunication lol

i think we've strayed from the original question somehow...

thanks for the replies.