Ignition coil saturation time

[Matthew Lee Franklin]

On Fri, 24 Mar 1995 08:30:05 -0500, Mr. Wales wrote in reply to Mr. Lewis:
>>>Should you run the coil until the current saturates?  Slightly less, or
..
>The answer for your coil can be found by trial and error. Build a variable
..
>   |_____|-----|
>A  B     C     D
>
>A is the before switch on time
..

Yup, a great way to look at it.  But another question is what voltage do 
you want to drive it at?  The reason for the 5.5 amp current limit current 
in the HEI was so you could ramp up to saturation *fast* with 12+ volts
directly from a battery and *low* primary resistance but not fry it.  
This let the *high* inductance coil still keep a short time constant for 
charging -- oops! make that saturating.  I have to keep remimding myself 
that capacitors charge, but coils saturate.  I'm only an ME not an EE.

Does anyone remember the amps vs. time equation for an L-R coil load?  This 
would help the thinking on the tradeoff between coil *energy* (as others 
previously posted) and rise time for the current till saturation.

Isn't it something like I = V / R *(1-e^-((L/(R*t))) ?

I think it is the Huntzinger SAE paper (750346).


Later,
Matt