Role of the condenser

[John Hofstetter <hofs@domain.elided>]

>
>Tom,
>
>I was playing with my points when my MSD failed.  First I tried to wire 
>it without the condenser.  Nothing! Put in the condenser, Perfect! Then I 
>began to think about why I needed the condenser.  
>
>When the points break the current flow to the coil in order to cause a
>field collapse and generate the spark, the condenser serves as the ground
>portion of the circut for the secondary side.  The coil isn't grounded
>throught the case like I thought it was.  As the field is collapsing, the
>current behaves as alternating current, not the DC we are all thinking 
>about.. Thus the condenser serves as a path to ground. 
>
>Look at the circut sometime.  Check where thepossible ground paths are.
>
>Steve

When Steve lost his MSD and was trying to move back to points alone, he 
was testing his circuit by making and breaking the current manually and 
was getting no spark. My son told Steve and me that he didn't know quite 
why, but this would not work without the condenser in the circuit. He was 
right as Steve found out when he put the condenser back in the circuit, 
but apparently it started Steve thinking or researching the subject.

After the posts on the subject of the condenser, including the rather 
scholarly explanation of modern ignition systems and the function of the 
condenser by John L., I thought about telling folks that Steve had drawn 
me a diagram of how the condenser causes the current to act as 
alternating current, and that the diagram made very good sense, but then 
I was afraid someone would ask me to explain how it worked, so I didn't 
make the post. Now that Steve has said it, he can answer any questions. 
At any rate, Steve has convinced me that this kind-of-alternating current 
production is part of what makes the points, condenser coil system work. 
It's interesting to me to speculate about when distributors first 
replaced magnetos, and whether or not those who put the condenser into 
the circuits had any idea that it was doing anything more than reducing 
arcing. I suspect not.

John L., were you agreeing with me that the voltage of the spark across 
the gap of the spark plugs is determined by the conditions from the coil 
on, rather than by the primary circuit? Up to the voltage maximum of the 
coil, of course. I think you were, and if you weren't, we need to talk.

John H.