Gentlemen:
It sounds a lot like we are getting to the point of trying to "one up" each
other, and on the verge of getting nasty. There are numerous rather large
books and fields of study that could be applied to this thread. Why can't
we each simply try to help each other , and respect the others that are
doing the same thing for whoever asked the original question. If someone
else has a different answer than your own, so be it, it just might work.
There are very few absolutes, a circuit that was designed for a given input
voltage may in fact work exceedingly well at +-10% or more, and infact need
to due to numerous variables, not the least of which is environmental, I
have not seen anyone mention variances induced by temperature or humidity
yet.
Just my $.02 worth, I have seen some of the other lists that I follow get
totally flooded with some topics that started not unlike this one, which
doesn't help anyone.
Dereck R. Bauer
Impact Solutions
----- Original Message -----
From: "Randall" <randallyoung@earthlink.net>
Cc: "triumph list" <triumphs@autox.team.net>
Sent: Tuesday, July 10, 2001 8:50 AM
Subject: Re: ballast resister voltage drop - electrical guru needed
> George Richardson wrote:
> >
> > Sorry Randal, but power is used to drive the ICs in the unit as well as
> > supply voltage to the base of the transistor that turns on the coil.
>
> Well, assuming it has ICs, that's exactly what I meant by "the amplifier
> for the signal".
>
> > The
> > ICs, if they're anything like those in the Piranha ignition system,
> > require a minimum of 5 volts to operate.
>
> Right, unless of course they are CMOS equivalents, good to about 3
> volts. And they would also require a modest amount of regulation.
> Lessee, two diodes, a resistor, and a capacitor or two : Presto ! A
> moderately regulated 5v from the _AC_ waveform across the coil,
> regardless of whether there is a ballast or not. We're not talking
> rocket science here.
>
> > And although it may not make
> > any difference in the majority of cases where the connection is made, in
> > the case of a coil and resistor that are not matched, there could be a
> > problem supplying adequate voltage.
>
> Which is one of the reasons why the instructions specify the ballast
> resistor value range. The other reason of course being that there is a
> definite limit on how much current the unit can switch. And since the
> instructions specifically mention lower resistance aftermarket coils,
> IMO it's safe to assume that the designer considered and designed for
> this case.
>
> > ( 12 volts/2.8 ohms)*1.1 ohms = 4.714 volts across the coil when the
> > ignition is on, not accounting for the voltage drop of the switching
> > transistor.
>
> Only when the transistor is on. And if you know how to design something
> like this, you know that the voltage is _not_ "4.714", but rather
> "approximately 4.7", because the "12 volts" is actually "something
> somewhere between 9 volts and 15 volts, maybe". Not accounting for
> various transients, etc. which can be hundreds of volts in either
> direction ...
>
> > By the way, I designed my first electronic ignition more than 25 years
> > ago.
>
> That would be about the time I designed, built, and tested my first
> multiple-spark capacitive-discharge ignition in my spare time. One of
> the few things I built that worked perfectly, the first time. However,
> a missed shift on my Audi cut short the testing, and I never went back
> to it, even after I finished the rebuild ...
>
> Tell me, when you pick up a spec sheet that says a particular IC
> requires 2.8v to operate correctly, do you immediately say "Oh, I
> designed an IC once and it required 5.0v, so I'm going to use that
> instead" ???
>
> Randall
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