Scope pics...

[Eric Bryant]

> From: Bruce Plecan [mailto:nacelp at bright.net]
> Subject: Re: Scope pics...
> 
> The output side of transfomer is A/C.
> It's just that simple.
> You can argrue and dance around things all you want.
> Biased high or low, it's A/C  might be riding on an dc bias,
> A DC spark is lightning.

Damn, do I feel like I'm really wading into some sharky waters by replying
to this thread.

My definition of DC is a non-time-varying waveform, and a spark certainly
doesn't meet that definition.  So, I think we can say that this isn't a
strict DC event, certainly not anything like hooking a scope to an ideal DC
power supply.

You seem to be saying that the bias is variable, though, and I'm not sure I
agree with that.  I'm certainly no e-mag expert (I sleepwalked through both
courses in college, did great grade-wise, but I don't remember a damn
thing), but I do believe that the collapsing field on the primary side
creates a event on the secondary side that is indeed predictable, at least
with respect to current flow direction.  

Now, if you look at the waveform, there's certainly a lot of A/C riding
around on there.  After all, that's what creates all the spark noise that
wire-wound plug wires, condenser caps, etc. try to extinguish.  

But, having said that, I think you can establish a "negative" and "positive"
electrode on the plug.  I don't want to act like I'm sticking my head in the
sand, but I'm not going to believe that the spark current direction is a
50/50 proposition unless someone shows me.  If you look at the primary and
secondary of any transformer, the secondary has a phase or polarity that's
directly correlated with the primary.  Since we can always predict the
polarity of the event occuring on the coil primary, we can also predict the
polarity of the event occuring in the secondary.  

> If the plug was firing a DC voltage just one side would erode.

That would be true if electron flow was the only mechanism in plug electrode
erosion.  Since the electrodes see a very severe environment even without
considering the spark event, I'm inclined to believe that the spark is not
100% responsible for plug wear.


Eric Bryant
mailto:bryante at ghsp.com
http://www.novagate.com/~bryante 
 
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