Points...what do they do exactly

I"m working through some ignition problems on an M with a 6v coil system and just wanted to know more about the whole ignition system than just put the parts all in and adj. to the manual.

Do the open points cause the coil to charge and fire in that moment? (I can see the coil is grounded through the points when closed) And what of the gap? Why the critical nature of the point gap?

And if I may one more?

What is the purpose of the condenser?

The link below is a better explanation than I could compose.

Basically, point gap ensures that they stay closed for the proper amount of time for the coil to build up the necessary zap for the spark. You're right, the spark occurs when the points open, which interrupts the currwent through the coil, causing the electromagnetic field that was building up to collapse and discharge.

Points set too closely allow the current to build for too long and are hard on coils. Points set too wide don't allow enough time for the coil to build enough energy for a good spark. Set them too wide and they won't even close to do their job. Mis-gauged points can also affect timing. If they open too early (points set too close), it can advance your timing and the opposite for opening too late.

The condensor is a capacitor and is there to protect the points from any backflow current from the coil.

I've gone on too long, the link is better.

HTH
Ignition

Scotty is right on. The whole point of the ig system is to set the time of the firing of the compressed air/gas mixture in the cylinder to force the piston down creating energy to be used as power.

My point in writing is to say that if you have a 6v ig system with a magneto my advice is to not convert to 12v. If anything have the mag rebuilt to factory specs and in my humble opinion is more reliable than the 12v coil/distributor on that tractor.

Dave,

QUESTION:

Do the open points cause the coil to charge and fire in that moment? (I can see the coil is grounded through the points when closed)

ANSWER: NOT EXACTLY BUT SOMETHING LIKE THAT: For the coil to develop high voltage across its secondary winding, its must FIRST draw current (when points are closed, they act as a current On/Off switch) and an electromagnetic field is developed. THEN when they open (CURRENT IS INTERRUPTED), that magnetic field collapses and induces a higher voltage into the secondary windings. i.e. the coil fires when the points break open AFTER they were first closed so the coil drew current and an electromagnetic field was developed which collapsed when current was interrupted.

QUESTION

And what of the gap? Why the critical nature of the point gap?

ANSWER: The gap determines in part how long the points were closed (to draw current to build up the sufficient magnetic field), its (dwell time) not any problem in older and say 2 or 4 or 6 cylinder engines at low RPM but if you had an 8 cylinder at fast RPM there could be issues with insufficient point closure times (dwell). Also, when they open a voltage develops across them and the gap has also to do with the arcing n sparking and arc extinguishing (that a word lol). They also have to be the right width to correspond to the rise from the cam lobes so they open to interrupt current but not so wide they dont close back fully when the cam height drops. The cam height and points gap plus the necessary dwell time plus the arcing are alllllll factors in proper points gap.

QUESTION

And if I may one more?

YES YOU MAY

What is the purpose of the condenser?

ANSWER; A primary function is to extend the life of the points by absorbing some of the current (that lil arc across points right when they break open) to reduce premature burning and deterioration of the nice silvery points coating. The coil will still fire if theres no condensor buttttttttttttt the points will burn up sooner PLUS the spark isnt as it would be if a proper sized condensor were present. Think of it as sort of a shock absorber analogy, it absorbs some of the shock (electrical current flow). Its size rating in microfards is also important as that sort of controls the rate of energy discharge when that magnetic field collapses. If the condensor is too big, theres no spark becasue theres not any rapid enough magnetic field collapse BUTTTTTT the points will sure last a long time as theres little current arcing across them. However if the condensor is too small the points will burn up rapidly although she will still spark, just weaker.

DISCLAIMER its impossible in a few sentences here to explain this vey well so this may be over simplified and NOT perfect or all 100% technically exact, but it ought to give you a basic idea. Read the stuff Scotty linked to and theres whole libraries on this subject and its impossible to cover here.

If you need, I have a canned troubleshooting procedure for non sparking I can post it if you wish, let me know

John T Longgggggg retired Electrical Engineer

Dave
Glad that you asked this question, when I first read it I said, OH BROTHER EVERYONE KNOWS THAT.
I knew the answer, and I knew that I knew it, but if I would try to explain it to someone I probably wouldnt be able to, good to have people around with a variety of skills, like communication etc.
P.S. I wish I knew how to work that Microfard word into a conversation. (humor)
Bob S.

John,
Thanks for the great info. Little by little light is being shed on the dark areas. Actually I found your trouble shooter last night and it went over to the repair site today (thank you!). Unfortunately, I still have no spark from a new coil with confirmed voltage to it and points that seem to be operating correctly (as per your trouble shooter).

That's alright though, Ive since pulled the distributor assembly and discovered a very sloppy drive gear and tired springs on the spark advance mechanism. So this all will get repaired as I continue my quest to better understand technology from the 40's.

Sorry for any misunderstanding. The ignition system is not a mag system. Its battery powered coil. (I'm not even really sure how to correctly name it)

Very well explained. Good link, thanks

Just to add to the excellent responses...the primary and secondary side are inductively "coupled" so the secondary side wants to "follow" the lead from the primary side.

So..when the points open, the primary voltage goes to zero/discharge, the secondary will attempt to follow this lead, and (hopefully) the least-resistant path of discharge is thru the center plug wire, thru the distributor rotor lined up with the appropriate cylinder plug wire and jump the gap across the spark plug electrode to ground, thereby starting internal combustion of the air/fuel mixture.

Fun stuff!

Some useless but maybe interesting comments:
Michael Faraday discovered that current in one coil would induce current in another coil nearby.
I don"t have the dates exactly, but I think it was around 1830. A few years earlier, another researcher, a Dane named Oersted, accidentally discovered that a current in a wire creates a field around the wire (he noticed that bringing a compass near to the wire caused the needle to move)(Uri Geller tried to show that he could do the same thing using his magical powers; turns out he used tiny magnets). Faraday took up where Oersted had left off. The farad is named for Faraday.
Other useless information: the original condensers were big glass jars (Leyden jars)lined inside and out with foil. Static-electricity generators fed current to each side of the glass. When the current was released, there could be quite a jolt. Seems it was a parlor trick in the late 1700s to shock your guests with current in a Leyden jar.

Other terms named for individuals: Ohm and ampere. Poor Mr. Oersted apparently didn"t get anything named for him.
Some of the writers answering say that the ignition system will work without a condenser.
I have seen engines--way back when--that wouldn"t run when the condenser failed. Has anyone seen an engine run without a condenser?
Perhaps with a very wide gap, to make it hard for the current to jump the gap?

The condenser certainly has the function of keeping the points from burning (because the electrical current "wants" to keep going across the gap and will make a considerable spark without a condenser to absorb the current briefly), but it is also true that if the current continues across the points, there will not be much of a breakdown in the magnetic field across the secondary winding of the coil, hence a very weak or maybe even no spark.
Hope I"m not repeating what others have said.

(quoted from post at 17:51:00 11/20/08) Some useless but maybe interesting comments:
Michael Faraday discovered that current in one coil would induce current in another coil nearby.
I don"t have the dates exactly, but I think it was around 1830. A few years earlier, another researcher, a Dane named Oersted, accidentally discovered that a current in a wire creates a field around the wire (he noticed that bringing a compass near to the wire caused the needle to move)(Uri Geller tried to show that he could do the same thing using his magical powers; turns out he used tiny magnets). Faraday took up where Oersted had left off. The farad is named for Faraday.
Other useless information: the original condensers were big glass jars (Leyden jars)lined inside and out with foil. Static-electricity generators fed current to each side of the glass. When the current was released, there could be quite a jolt. Seems it was a parlor trick in the late 1700s to shock your guests with current in a Leyden jar.

Other terms named for individuals: Ohm and ampere. Poor Mr. Oersted apparently didn"t get anything named for him.
Some of the writers answering say that the ignition system will work without a condenser.
I have seen engines--way back when--that wouldn"t run when the condenser failed. Has anyone seen an engine run without a condenser?
Perhaps with a very wide gap, to make it hard for the current to jump the gap?

The condenser certainly has the function of keeping the points from burning (because the electrical current "wants" to keep going across the gap and will make a considerable spark without a condenser to absorb the current briefly), but it is also true that if the current continues across the points, there will not be much of a breakdown in the magnetic field across the secondary winding of the coil, hence a very weak or maybe even no spark.
Hope I"m not repeating what others have said.

Click to expand...

Well, Len, don't feel too sorry for poor old Hans Christian Oersted, as he did make it into history........
Oersted, a unit of magnetic field intensity, symbol=H, the units being amperes/meter. He and many others just didn't make it into the vocabulary of the masses, along with names such as Joule (energy) and Weber (vector magnetic potential).
With NO condenser at all, soooo much of the energy is lost in the arc across the opening points, that little remains to be delivered at the secondary for the plug. Yes, there is a little, but unless you were to gap the plugs very, very small, the running of an engine like this is truly a hit & miss situation, i.e., rare & poor. I have never made it happen, even though I have observed the very small spark.

Very interesting forum.
I'm glad my "poor Mr. Oersted" DID get something named for him!
I have been looking for the past few days through various auto-repair books, trying to find a good engineering-type explanation for the phenomenon we are all writing about. Have found very little that goes beyond the "current wants to continue across the arc" explanation, and that the arcing current is large enough to burn the points. I did think of a kind of poor-man's analogy: Remember those water pipes that thumped when you turned off the water, until you either put some kind of tight hangers on them OR installed a tee and a piece of pipe to absorb the shock? The tee was full of air, and acted as a shock absorber by letting some of the water that was suddenly shut off escape briefly into the "shock absorber." I don't suppose this is a good engineering explanation, but it helps me, at least, the function of the condenser, a sort of electrical shock absorber.
Electrical engineers, please, please forgive the
amateur analysis. You're probably wringing your hands by now!