coil question and introduction

[gary noblit]

"Well I'll be a monkey's uncle!" (another phrase I have heard all my life)
Learn something new all the time.

Speaking of learning something new, anyone know how to check a condenser? I thought I had that info somewhere, but since I am a senior (somewhat), I can't find it.
Can a condenser go bad gradually? or is it like a light bulb, when it goes, it goes.
Can you help us out on this David?

I can pass on what I learned to do. With multi-meter in continuity mode touch pos. to wire on condenser while holding neg. to body(not in your hand or on metal surface) The meter should show climbing numbers quickly then stop.To discharge condenser simply reverse pos/neg...I've had this work many times and fail many times. Because I collect "old stuff" I spend $8. for a new condenser to put on to begin with..Old Chevy cond. work on almost anything.Not a scientific answer but it works for me ,quite well...To me it's the cheapest way to know ....

 

[gloughery]

Here is a resistor on our 70. I'm debating if I need this on all my CCs. What is the general consensus for when you need to add a resistor?

 

[digger]

Here is a resistor on our 70. I'm debating if I need this on all my CCs. What is the general consensus for when you need to add a resistor?View attachment 144181

Put the correct coil on it and throw what ever the heck that thing is away!

 

[Greg Riutzel]

Shade tree work arounds just complicate things. They make for trouble in trouble shooting.

 

[jerry.a.johnson]

Thanks for this thread. Very informative.

 

[bcarl]

Found out something else I already knew. LOL! You can google this stuff on the internet. Imagine that! Darn migraines are messing with my head.
One thing though, you can't believe everything you read/see on the web though. Helps to check several sources, unless you were to ask Charlie!
The condenser is a version of a capacitor.
I have read it can go bad gradually, or all at once. Would like some input on that statement.

I have only had one condenser ever go bad. It was all at once. I initially checked points, coil, spark plug, etc. as there was no spark. Finally swapped a condenser from another engine which solved the problem.

 

[Greg Riutzel]

If your multimeter has a capacitance setting/selection; you can check it with that. The specification IIRC is .025 Mfd or micro farads
In 30 years I've only seen 2 go bad, the most recent being a melted one on my 94 Corolla. Usually they're so cheap it's insurance to change them when doing points or other ignition work.

 

[Greg Riutzel]

Edit: my last post was off a decimal. The microfarad reading of an ignition condensor should be around .25 Mfd. A failing condensor may show as under capacitance with build-up occurring on the moving contact of the points.

 

[jlord]

The purpose of a condenser in the ignition system is to minimize arcing at the points when they open by absorbing the back EMF ( electromotive force ) pulse that's generated in the primary windings of the coil when the magnetic field collapses.

The collapsing magnetic field in the coil simultaneously induces a back EMF into the secondary windings creating our needed/wanted high voltage.

As condensers age their values can diminish and if less than specified for the application, can and will cause arcing at the points resulting in "burnt" point contact faces.

Depending on circuit design, an ignition circuit usually incorporates either primary resistance wire or a ballast resistor to control the amperage in the ignition coil.

In my '82 Dodge D150 pick-up w/ a 225cid slant six, a two circuit ballast resistor is used. Half the resistance is shunted out of circuit when the starter is engaged in order to boost the current through the coil during cranking resulting in a hotter spark to make starting easier.

 

[mfrade]

Sorry Jlord but that is incorrect. The purpose of the condenser is to allow voltage to flow to ground, it completes the circuit and in a controlled fashion allowing the primary winding in the coil to "saturate", and when the points open the circuit collapses causing a voltage spike and discharge through the secondary winding. The spike of voltage through the circuit will happen ir-regardless and if high enough voltage it will arc at the points.

 

[bwstevens]

If one wishes to understand how a condenser works , a good description is available at the magneto guys website.

 

[mgonitzke]

Sorry Jlord but that is incorrect. The purpose of the condenser is to allow voltage to flow to ground, it completes the circuit and in a controlled fashion allowing the primary winding in the coil to "saturate", and when the points open the circuit collapses causing a voltage spike and discharge through the secondary winding. The spike of voltage through the circuit will happen ir-regardless and if high enough voltage it will arc at the points.

You are saying more or less the exact same thing as Jlord but with different words. When the points break, the condenser is not charged and provides a direct path to ground, so most of the current flow as the primary discharges goes through the condenser instead of jumping the point gap. Even with the condenser there will still be a slight arc across the points as they break, but it is far less than if there were no condenser at all. That slight arc is what eventually wears out the points.

 

[mfrade]

You are saying more or less the exact same thing as Jlord but with different words. When the points break, the condenser is not charged and provides a direct path to ground, so most of the current flow as the primary discharges goes through the condenser instead of jumping the point gap. Even with the condenser there will still be a slight arc across the points as they break, but it is far less than if there were no condenser at all. That slight arc is what eventually wears out the points.

That is not what I am saying at all. The purpose of the condenser is to complete the ignition circuit to ground. It is essentially controlled "leakage" so the coil can be refilled. If there was no flow in the circuit - the coil couldn't refill / saturate. That is all I am saying. Any side benefit is also a product of the winding counts ( primary & secondary ) and the mfd of the whole circuit.

 

[mgonitzke]

That is not what I am saying at all. The purpose of the condenser is to complete the ignition circuit to ground. It is essentially controlled "leakage" so the coil can be refilled. If there was no flow in the circuit - the coil couldn't refill / saturate. That is all I am saying. Any side benefit is also a product of the winding counts ( primary & secondary ) and the mfd of the whole circuit.

Well, in that case you are wrong. The points complete the circuit to ground to allow the coil to "refill" when they are closed. After the points break, the condenser is initially a dead short, but charges up and turns into an open circuit as the magnetic field collapses and produces voltage in the secondary circuit.

 

[Greg Riutzel]

If I may, here's a refresher in Engine/Ignition 101. The condenser is a small capacitor, there is no path to ground through it or it wouldn't be a condenser ( or capacitor). It's primary mission is arc suppression. If an arc on points opening was allowed to propagate, beside point erosion you would have a tremendous waste of high voltage energy with little left for the plug to fire. Try getting a plug to fire without one and you'll see 1st hand what I mean. When the points open and the coil's field collapses; beside initial high energy going to the plug, a back EMF (back voltage) is also induced in the primary circuit and this what causes the arcing as well as stoppage of current. The condenser absorbs this higher primary voltage as capacitors do and after the 1st decay of high voltage at the plug the condenser releases the stored energy multiple times until dissipated. This is called a "ringing" effect from an inductive/capacitive circuit which is what the ignition system is. You can see this on an O scope, such as the old engine analyzers have, as "Spark Lead", the initial high voltage spike followed by ever decreasing smaller spikes and the plug actually fires more than once when the plug's gap is bridged by the 1st spark. The plug firing is only X thousandths of a second, but it's more than one spark in a well tuned system.

This may be controversial, but the Kohler book has it wrong in their description of the condenser and its purpose in a points ignition system.

 

[John Wyrick]

Greg is correct. In the late 70’s and 80’s I taught Auto Mechanics and we use a Sun oscilloscope with a large screen as a diagnostic and teaching device. The dissipation of voltage was evident in the pattern. You could choose display patterns for individual cylinders or use the superimposed mode to see all at once. We loved to see high spikes in the display pattern because those meant high resistance on one or multiple cylinders and was an easy fix. Usually bad spark plug leads or worn plugs. Low spikes were a reason to perform a compression test. Low compression meant it took less voltage needed to jump the air gap on the plug. Finally, my old electronics professor said a condenser doesn’t condense anything. It is a capacitor because it has the capacity to store electrons. Calling it a condenser was a way to sell more parts. We always replaced points and plugs as a tuneup but not functioning condensers. That is until GM created the “uniset” one piece points and condenser to force you to change both!

 

[mfrade]

Well, in that case you are wrong. The points complete the circuit to ground to allow the coil to "refill" when they are closed. After the points break, the condenser is initially a dead short, but charges up and turns into an open circuit as the magnetic field collapses and produces voltage in the secondary circuit.

Well, we will have to agree to disagree. The "condensor" is a true capacitor named wrong. To recharge the coil there has to be a flow of electrons. Guess how that happens!?!?

 

[hdeloach]

Interesting discussion. What is main cause of the capacitor to fail? I have had ones that never fail--years and years--then some that will last for hours and croak.

 

[dkirk]

The back EMF voltage can be as high as 400 V...obviously high enough to cause arching at the points.

 

[mgonitzke]

Well, we will have to agree to disagree. The "condensor" is a true capacitor named wrong. To recharge the coil there has to be a flow of electrons. Guess how that happens!?!?

We can do that, but you'll still be wrong...

As to how that happens, the coil recharges when the points are closed, completing the circuit through the primary from the battery to ground, as has been stated previously several times in this thread.