[QUOTE=Bill Mac;2773791]Just to add to Davids's post.
The primary winding actually discharges through and into the condenser across the points.
The condenser then discharges back into the primary winding.
This produces a sawtooth decaying magnetic field.
This is called a "series bell ring oscillator"
This induces the high secondary voltage decaying sawtooth spark.
This can be seen on an oscilloscope.
So, it is not one single spark but a series of decaying sparks all happening extremely quickly
The condenser is an essential part of the spark generating circuit and is not there to "protect the points"[/QUOTE]


The condenser in a points distributor serves two primary functions: AI answer from the internet

1. Prevents arcing between points: When the breaker points open, the condenser absorbs the energy released by the collapsing magnetic field, preventing arcing between the points and reducing wear on the points and surrounding components.
2. Allows for faster magnetic field collapse: The condenser enables the rapid dissipation of current oscillations in the primary circuit, which in turn facilitates a faster collapse of the magnetic field in the ignition coil. This faster collapse strengthens the induced current in the secondary circuit, ultimately leading to a stronger spark.

Rgds
David

 

With all what is being said here, it would be interesting to see if a varistor would work in place of the condenser; like on an SU fuel pump.

Bill, the condenser may act as you describe, but I believe it also protects the points, just as it does in an SU fuel pump.

I like what David said in his #2 explanation, because when the condenser starts to fail, the spark does become week causing misfires and a stumbling engine.
Or the condenser can short internally, and ground the whole circuit out; there would be no spark at all in this case.

 

I will stand on my "dig" and say that the primary reason for the condenser is that it is part of an oscillator circuit
The magnetic field collapse does not work in the concept of a DC (direct current) simple spark.
It is an AC (alternating current) system where the magnetic field goes through a number of + to - (plus to minus) oscillations before gradually collapsing.
The primary coil and condenser make up this series oscillator which transfers oscillating magnetic energy to the secondary high-tension winding.
As previously mentioned, this is best seen on a cathode ray oscilloscope.

Yes, a failing condenser will produce a weak spark, and I advocate that a new condenser should be fitted every time new points are fitted.
And yes, a failing condenser will allow points to become burnt.

 

I'd agree that the condenser serves more than one purpose. Receiving the charge of the initial current flow and protecting the contact breaker from arcing are essentially the same process, basically carrying the AC part of the spark current. In doing that, it will probably also reduce some RF interference as well.

It remains that the DC in the spark (the net flow of charge) requires a route back to the secondary and that is via the battery. Most of the texts (including Bosch) happily state that the high voltage finds ground via the spark plug. That's pretty meaningless (for AC and DC) without mentioning how the other end of the secondary is connected to ground. The system might work without any DC flow, but charge would build up in places causing problems when the points close again (or when someone touches the engine).

 

I think we have got to the stage that everybody is agreeing violently with one another.

 

Found a reference to Bill's point on the multiple reasons for condenser

Basic Points Type Inductive Discharge Ignition Systems
by Dan Masters, danmas @ aol.com , and Bob Sykes, s1500 @ worldnet.att.net

Capacitor (Condenser) - The capacitor performs several functions.

· It prevents the points from arcing and prevents coil insulation breakdown by limiting the rate of voltage rise at the points.

· Its primary function is to provide for a rapid decay of the primary coil current.

· The capacitor also "third-harmonic" tunes the coil, raising the peak output voltage and increasing the secondary voltage rise time. This increases the efficiency and the amount of energy transferred to the spark plugs. If the coil secondary voltage rises too quickly, excessive high frequency energy is produced. This energy is then lost into the air-waves by electro-magnetic radiation from the ignition wiring instead of going to the spark plugs where we would like it to go. Voltage rise time should be more than 10 microseconds; a 50-microsecond rise time is OK. Conventional systems have a typical rise time of about 100 microseconds.

We are all learning about Lucas's Mastery of "Induction Ignitions Systems" many years ago.
Rgds
David