Re: Pertronix Ignitor Inside Info.

[Darrel Kline <darrelk@domain.elided>]

I wrote:
>>If you ever talk to him again it would be interesting to know how the
>>Ignitor compares to the GM HEI, and what the peak output current is. 

John Landry responded:
>Forgive my ignorance, but I'm not sure I understand what you mean by "peak
>output current."  Do you mean the maximum current (amps) that the Ignitor
>can switch on and off?  

I'm taking about the maximum amperage that can flow in the primary
circuit...what the Ignitor can/will supply without cooking. When you say
"the maximum current (amps) that the Ignitor can switch on and off?" it
sounds like the Ignitor is nothing more then a switch. That it's only
function is to open and close the circuit. I haven't researched the
Ignitor, but it is a switch *and* an amplifier, correct?

>Or are you talking about the coil?  As far as I
>understand things, the peak output of the coil is more a function of *its*
>design, the resistance in the secondary circuit (the plug gap for example)
>and whether or not the primary field is fully saturated.

These are real factors for sure, but they do not determine the output
current...they just subtract from the potential output current. The output
of a transformer is determined by it's primary to secondary windings ratio.
With a step-up transformer the output current is always going to be
something less, much less, then the input current. But still, the more
current in, the more current you will get out. And IMHO the more powerful
your ignition module the better off you'll be.

Here's the x-former formula:

Np       Is
---  =  ---
Ns       Ip

n=number of windings
p=primary
s=secondary
I=current

>>Does Pertronix recommend any particular coil?  There's some really hot
>>coils on the market now that will only work with certain ignition modules,
>>other modules will burn out.

>According to the instructions that came with the Ignitor, any coil which is
>compatible with a breaker-point ignition system is acceptable for use with
>the Ignitor.  The coil should have a minimum resistance of 1.5 Ohms across
>the primary coil terminals.  Pertronix specifically states *not* to use a
>GM HEI coil.  Apparently the HEI coil has too little resistance and allows
>an excessively high current load through the Ignitor.  This undoubtedly
>results in possibly immediate or more likely premature failure.  Like a set
>of breaker-points, the Ignitor module can only handle so much current
>before it fries.  

That's somewhat disappointing...Still seems like a great unit for only $60,
I mean we only run these truck motors to 4,000 RPM. I measured the coil
(Crane - PS91) for my Crane HI6 ignition at .5 ohms. Interestingly, the
instructions state that the MSD6 will fail if used with the PS91. I think
that the low resistance of the PS91 coil, and the ability of the HI6 to
work with it, is the reason it delivers twice the spark-gap current of the
MSD6.

>Taking Pertronix's requirement for at least 1.5 Ohms of
>resistance in the coil primary circuit, and further assuming about 14 volts
>input to the coil, then the Ignitor is apparently capable of safely
>handling (switching) up to about 10 amps of current.

>Regards,
>
>John

I'm still thinking that the Ignitor would put out something more then the
battery voltage of a breaker-point system. Again, it does do more then
simply open and close the circuit? I would guess that the Ignitor is
basically a power transistor, in which case we can't use the Ohm's
Law/series circuit formula to solve for the output current.

Kindest Regards,

Darrel Kline
Colorado Springs