Ignition question

[John Dammeyer]

At 07:09 PM 07/12/1997 -0800, you wrote:
>ref John and his .02 worth
>
>Then as I see things, a 120vpri, 12vsec (center tapped) transformer might
>be a good beginning for a high freguencey, high voltage source for doing 
>the above. power to the center tap, and two power transistors for 
>oscillating what would then be the primary.

Nope!  Standard mains transformers are best for 60Hz and don't do well at
higher frequencies.

>  Now, in the application I'm working on the max engine speed is 6,000
>rpm, and is a v-6, so there are three ignition coils.  (actually I would
>use three of the above high freg/HV generators).  Then pulse a SCR for
>1 millisecond when the point open signal was received.  The HV coils
>would be continually running.  While there might be some loss in timing
>accuracy, relighting the plug, would be more effective in making sure 
>there is a complete "burn" (IMHO). 

EDN magazine December 19, 1996 under 'Design Ideas' has an excellent example
of a high tech. Switching power supply.  The design was written by Kurk
Mathews and Jesus Rosales of Linear Technology Corp.  They use an LT1243 and
LT1431 and the rest are off-the-shelf Digikey type parts.  The custom
transformer is 0.6 cubic inches.

the cool thing about their circuit is their claim that they can repetitively
charge more than 1.5 ufd to 360V in less than 3ms with 3.2A input;  an
efficiency of 85%.

So what you need to do build is one high voltage supply,  use three IRF740
Fets and a PIC micro-processor to sense the flywheel position and fire your
coils.  Or with discrete logic you could turn the coils on at the advance
point using mechanical or inductive pickup points and use a TDC sensor for
each cyl.  to turn the FET off.  I'll be building, in the spring,  this
exact type of circuit for Chevy V8 engines modified with a gearbox for
aircraft use.

Cheers,

John

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