Re: ignition coil

From: 	William Noble[SMTP:William_B_Noble-at-msn-dot-com]
Sent: 	Tuesday, July 22, 1997 2:40 PM
To: 	Tesla List
Subject: 	RE: ignition coil

a comment - if you charge a capacitor to about 450 to 500 V and then discharge 
it into the ignition coil through an SCR you will get an excellent result.  
This is basically a capcitor discharge ignition.  Get an SCR rated at  1 or 2 
amps continuous (that will give you 40 to 100 amps pulse) and you are all set. 
 use a 555 oscilator to drive the gate at the desired freq, and use a short 
pulse (e.g. no square wave drive here).

[bill]  snip
 > I built a pulse generator (circuit found at
> http://www.geocities-dot-com/CapeCanaveral/Lab/5322/coildrv.htm)
> but the results with it were non-existant.
> What can I do?

OK, how does it work? It works by storing energy in the core via the 
primary and releasing it in both primary and secondary when the power 
supply is cut off from the primary. 

(1) How to maximise core energy? Since E = 0.5LI^2 and L is fixed, 
you must get I as high as the primary winding can stand. Since I is 
limited by Vapplied/Rwinding, the more V applied, the more I.  BUT,
applying V to an inductance means it takes time for I to build up to 
the resistance limited value. So dwell time must be set long enough.
The longer the dwell, the slower the breaks have to be if core energy 
is to be maximised.

(2) How to get _all_ energy from the core to the secondary? Not easy.
You have to break the supply from the primary without a spark across 
the break contacts. Fast parting contacts are the order of the day.
You can slow the rate of rise of core energy release by putting a 
small capacitor across the contacts, the ideal being that the 
contacts part company faster than the voltage across them rises.