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Re: Pulse Width for Ignition Coil



Original poster: "Finn Hammer by way of Terry Fritz <twftesla-at-uswest-dot-net>" <f-hammer-at-post5.tele.dk>



Tesla list wrote:
> 
> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<jimlux-at-earthlink-dot-net>

Snip..
> 
> Basically, you want to limit the current to around 5A. Knowing the nominal
> inductance (around 8mH), you can figure out how long it will take to get
> there (Ldi/dt = V... 12V = 8E-3 * di/dt.. 1500Amp/second, 5A is 1/300 second
> (3.33 msec))

snip

Oh Boy, would that be the formula that I`ve been looking after for so
long, the one that describes the charging inductor`s behaviour in a DC
system, during gap conduction? So that it is possible to determine how
high a current that will flow in the gap, by the time the ringdown is
completed, and it is time to quench?

Let`s see if I`ve got it right:

Voltage across inductor = 20000V
Inductor size           = 5H

20000/5=di/dt ........  =4000 Amp/Second
 after a ringdown time of 350ÁS, the current will rize to 
(4000*350)/1000000 = 1.4 amp. So if the gap can quench at 1.4A, then the
charging inductor has a good size.

Is this right?

Cheers, Finn Hammer