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Re: Ignition coils


From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: 	Monday, November 24, 1997 9:02 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: Ignition coils

Hi Matthew,

> From:   MATTHEW A PRICE[SMTP:ch038map-at-mode.lanl.k12.nm.us]
> Sent:   Sunday, November 23, 1997 1:58 PM
> To:     Tesla List
> Subject:    new- KV's and multimeters
> 
> 
> ALL-
>     Thanks for your input. I added to diodes (the biggest I have ever
> found, from a TV set), one at ground, and the other between the 555 output
> and the 3055. Then I threw in a fuse for good measure. So far it has
> worked good, but I think you are right about the 3055. After a minute of
> use in was very hot, but the TV transistor used to get pretty hot to. I'll
> put a better transistor on my things to get list. I was messing around
> with the 2 potentiometers that change the frequence, and notice how much a
> little difference a little change will make, If their set low (frenquency
> high) it won't evem spark. I was wondering if anyone knew what the best
> frequency to set them at is. The lowest I can go is about 440hz? any
> suggestions?

Power throughput for ignition coils is solely a function of applied 
primary voltage. ???? you say.  It is basically two chokes wound on a 
common core, one to put energy into the core, the other to remove it.
For a given applied primary voltage, energy stored is a function of 
time the voltage is applied to the primary winding (until the current
peaks at Vapplied/Winding resistance). If you apply the voltage to 
the primary for a time shorter than it takes for current to hit this 
peak value, you can do it more often but there is no average power 
throughput increase. It is pointless running above the break rate of 
whatever engine it was designed to generate sparks for. All you will 
do is increase core losses. 
     The big "if" in the above picture is "what if I suck power out as
the primary current is changing while the voltage is applied to the 
primary?" This is known as forward mode operation. You can do it, but 
how much additional power you get is inversely dependent on the 
leakage inductance and loading applied to the secondary, and leakage 
inductance in these things is high due to the huge airgap in the core
(it is a rod, not a ring, right?). The car uses it in flyback mode 
where energy is stored in the core during points dwell, and the 
sparkplugs remove it when the points break.
     The upshot is: if you want to push more power through it, you 
must apply a higher voltage to the primary. Energy storage is a 
function of I^2 and I is a time-related function of Vapplied/Lp. 

I can elaborate off-list if you like.
Malcolm