Ignition only

[Bruce Plecan]

> >From: "James Ballenger" <vtjballeng at yifan.net>
> >> As an fictional example:
> >> Combustion side.  40,000V = 10000ohms*4amps
> >> Waste side 5,000V = 1,250ohms*4amps
> >> Same current passing through both of them... it is just like a
> >> series circuit with the voltage source in the center as I see it.  If
this
> >> is wrong, please tell me why.
> >Ya, well meaning and good but.
> >Your trying to expalin things as a DCv,  and it's just not that way.
> >This has to "balance" on both sides, doesn't apply.
> No, he's right. The *current* in a simple series circuit, which is
> a fancy word for "loop", is the same at all points. (If there is
> leakage, that constitutes a 2nd, parallel circuit, and it's not
> a simple series circuit anymore.) This has nothing to do with AC
> or DC, it's true either way. Imagine oil pumped in a closed loop,
> with oil filters, oil coolers, etc. The same *amount* of oil
> (current) passes through each, the pressure drop (voltage) may
> not be the same in each.
> A spark plug can be modeled, pretty closely, as a resistance.

a resistance of what value?.

>It's
> inductance and capacitance are low by comparison. The trick is it's
> a variable resistance, also it has what's called a "negative
> resistance" characteristic.

Negative resistance?.
So it generates a Current?

>It's like a little neon lamp. It's an
> open circuit (roughly) when not lit, but put enough V across it
> and current through it, and it becomes a low resistance device.
> If you could put an ohmmeter to it when firing (somehow), you'd
> see that the R has become pretty low.

Can we stick to the subject at hand?.

> >Does any one know of a on-line picture or scan of a scope pattern
> >of a plug firing?.
> No pics, but I had a couple ignition systems on the bench scope for a
> few weeks a while back, and I'm afraid I have to totally disagree
> with you about the AC/DC thing. The main part of the spark on the
> systems I looked at was a single consistent polarity, in the single
> digit milliseconds range. If the spark actually fired, there was
> very little ringdown, and no spark during ringdown, since the first
> spark heavily damped the RL oscillation on the secondary side. If
> there was no spark during the cycle then ringdown was impressive
> indeed... but as I said there was no spark in this condition, and
> certainly not multiple alternating polarity sparks.

Geesh the spark voltage itself is AC, very high freguency.

> Further, I put inductive pickups (attached to a scope) on the
> plug wires of a couple different systems. These pickups are
> sensitive to the direction of current flow in the plug wire as
> well as rate of change. They showed the same thing, one single
> spark in the expected direction.

Then too heavily dampened.
The A/C is on the firing line, not that is passes thru *ground*

> Maybe there is some confusion between the use of "A/C" to include
> a varying signal with the same polarity (or the A/C components of
> a signal) vs. a varying signal that regularly switches polarity
> (i.e. 60Hz power line signal).
> If you're looking at the coil primary (I had the scope on that too),
> things may get a bit confusing to say the least. The ringing there
> may look severe because (if the ignition driver is fully off) that
> half of the circuit is now open. The voltage will go higher because
> of this, but there is virtually no power being lost out that side,
> and it does not really correlate directly to how the actual spark
> looks.
> >If it was a DC spark then one electrode would really wear.
> >If DIS truely fired both plugs equally all the time they would wear out
2x
> >as fast, hmm, and with the EPA tuneup reguirements that would be a
definite
> Well, it doesn't fire them equally, not as far as arc voltage anyway,
> which someone just pointed out. plug erosion is very dependent on the
> breakover voltage (spark current being equal), and not necessarily
> linear, so the easy spark on the wasted side is much less erosive than
> on the live side.
> Also see below about platinum plugs in 1/2 of some engines.
> >It's an EE thing.
> >The spark is A/C so nothing is backwards
> Disagree strongly. I even heard lately of some OEM DIS system that
> required platinum plugs on 1 of 2 cylinders fired by each coil. Wish
> I could remember now which it was... late model Ford v-6 IIRC.

They burn just fine on my GN, a poorly designed system that needs a crutch
is hardly an example of the norm...

> >There is a 50-50 chance on which way the spark lights, and for the first
> Disagree strongly. In my circuit the direction is 100.0% predictable,
> and had to be because part of the setup was a spark monitoring
> circuit, for which the polarity had to be correct. Also the Toyota
> systems (which are part of what I was replacing) have a similar
> circuit with the same requirement.
> >It's the repeated colapsing on the magnetic fields that generate the
current
> >to maintain the firing line on a scope.
> Disagree strongly. The inductance on most coils secondaries is so
> high the field *cannot* ring quickly. Big inductors charge and discharge
> slowly. The coil *does* ring, but if things are right it fires on the
> first segment of ringdown. If the spark does jump at that time it
> draws off most of the coil energy, and subsequent phases of the
> ringdown do not generate a spark. This is a millisecond thing, not
> a microsecond thing.

How do you fire a plug on 1,400 volts then?.
Why do CDs with a primary of 400v have a faster rise time.
How come on a waste fire coil you can short one side together and it still
fires the other plug?.
Bruce


> Don wrote:
>
> > I'm having trouble understanding the concept of firing the second plug
> > backwards. After the spark jumps the gap on the first plug, isn't the
> > "path of least resistance" going to be head-block-chassis instead of
> > trying to jump the airgap of the second plug??
>
> No, because the spark needs to get back to the *other terminal of
> the coil*, *not* to ground or Vbatt. In a typical dizzy ignition
> the coil secondary is wired to Vbatt or ground, so the spark path
> *is* back through the block, chassis, battery. A waste fire system
> has to use floating coils (not grounded or connected to Vbatt on the
> secondary side). One coil HV terminal (when firing) might be at -30kV,
> relative to the ground/head/block potential voltage, the other HV
> terminal might be at +15kV. This lets the engine block/chassis stay
> grounded, but the spark plugs still all fire.
>
>
> Anyway... I'm not trying to be negative or confuse people; I am
> trying to report what I've seen and help sort things out. Obviously
> I have not had every ignition system on the bench, but the few I
> did have were very consistent in the details that I've reported.
>
>    Chris C.
>
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