Re: [ihc] ignition coil condenser

["Allan Ericson" <lowvolt@xxxxxxxxxxxx>]

Tom-

You will find it said in many tech manuals that the condenser is there to
protect the points. It's just not true.

If you put a square wave signal into a transformer (voltage straight up and
straight down, nothing gradual) there is almost no transfer of signal from
primary to secondary.

If you put a "sloped" signal into the primary of a transformer, it shows up
on the other side, with some changes that vary with the shape of the signal.
A pure sine wave goes through looking the same, and anything more
complicated goes through some changes.

What the points would do without the condenser is simply change the
voltage/current through the primary of the coil to "present" and "not
present" in pretty much an instant. No signal on the high voltage side.

Adding the condenser "slows down" the rate of change, but since the points
have to be open for it to affect the circuit, it only happens when they
open. In a capacitive circuit, you can calculate the rate of charge/change
by multiplying capacitance (in farads) times resistance (in ohms) to get the
amount of time (in seconds) to reach 63% of total voltage applied. The
condenser (capacitor) needs to be barely large enough to take enough time to
"shape" the discharging signal in a manner that allows it to transfer
through the coil.

There are other factors, but they are minor, and (even more) academic for
this particular circuit. I've posted the waveform of a points ignition
system on my photo gallery section on binderbulletin under Allan E if you
want to take a look at it.

When the switch is made to electronic ignition, the wave shaping is done in
the circuitry, so the condenser has no function. The signal is applied
through a transistor of some type, and the rise/fall time of the voltage is
simply accomplished in a different manner. I leave the condenser in my
points distributor that drives my MSD, but it would work fine without it,
and the points would last just as long. I just leave it there in case I need
to  bypass the MSD. Cheap insurance.

-Allan
----- Original Message ----- 
From: "Tom Harais" <THarais@domain.elided>
To: <ihc@domain.elided>
Sent: Thursday, September 09, 2004 3:47 PM
Subject: RE: [ihc] ignition coil condenser


> Uh guys:
>
> I'm no electronics expert, but I've always understood the capacitor inside
> of the distributor's function to be that of a "choke" or "shock absorber"
> which prevents the points from arcing when they first get close together
as
> the distributor cam allows and then again when they break contact as the
cam
> continues to rotate.  That was why you no longer saw them on electronic
> ignitions.
>
> I do remember, back when dinosaurs still roamed the earth, that a
sometimes
> cause of backfiring on an engine with a points distributor was failure of
> the condenser.  And, IIRC when you purchased a "tune up kit" for such
> vehicles, a new condenser was included along with the points.
>
> Of course, I can't remember the last time I played with a points
distributor
> even on my archaic IH vehicle. :-)
>
> Tom H., '76 Traveler