Condenser/ Capacitor

[TheBartman47]

As the coil magnetic saturation collapses, the magnetic force passes through both the primary windings, and the secondary (where the high voltage is produced). At the instant the points break open, the ~4 am circuit is shut off, but in reality the voltage still tries to cross the increasing gap. The condenser (at that moment is not charged at all, and the voltage pushes into that "reservoir" limiting the arcing at the points. the coil magnetism is still collapsing and produces much higher voltage in the form of high frequency ac of 350 volts Peak to peak. This is also absorbed and reflected by the condenser as the coil magnetism is spent across the spark plug and the resistance in the wires/components. This is called "ringing".
In an AC electric motor the purpose of the capacitors is to modify the AC input phase in the starting windings this causes far greater starting torque from stopped and is a short term issue designed to be taken out of that circuit with a governed switch. The phase change issue is something to look up rather than spend a page of writing. The running capacitors on some motors also modify phase relationships increasing the efficiency of the design. Those are intended to stay in the circuit without heating. Jim

Yep, the run capacitor is to compensate for phase lag that would be there without it... maybe it would help reduce switch contact arcing as an inconsequential side benefit, but still wouldn't be enough difference to bother implementing. A motor that doesn't come with a matching capacitor for phase balance is probably because it's not big enough to cause all that much phase lag, but if you really wanted to maximize efficiency, you could still add a capacitor to it.

 

[Janicholson]

Generally (not perfect or exact) if an automotive condenser is weak, open, or too small in rating, you might still get a spark albeit weaker snd points burn sooner,,,, However if way too big you may not get a spark at all and if dead shorted no spark at all

An analog ohm meter can help indicate if a condenser is totally bad like open or shorted (old kick back test) however it can’t show if it’s good or it’s rating like a true capacitor tester

A friend that runs a mag shop told me over half new condensors he buys are bad ir out of spec

Some condensors were used to reduce radio interference had nothing to do with ignition.

John T

Failed (punctured) dielectric can allow condenser action up to the failing voltage whereupon it arcs and stops the wringing Low voltage testing cannot identify that. you are correct as usual. Jim

 

[da.bees]

It's actually true" they don't makeum like they used to" when it comes to condensers. Maybe in part because they no long cause warranty claims for cars. Interesting to see them selling at yt parts for less than Ebay and Amazon.
Now that the pump is primed I have a question. Auto part stores often don't have catalogs for tractors,much less older tractors. If old Ford owners know how to navigate catalogs for Ford cars they can buy correct condenser,points and coil for Ford tractor.
Can someone explain why mid 50s and mid 60s car part #s are same but differ from late 50s early 60s?

 

[John T]

Just wondering what is the MDF of mag or auto condenser?
Isn't the job of the condenser to provide an AC current path from one side of the coil to ground? The spark will be a few AC waves. It's not a DC spark
I can't get my head around how a condenser saves the points. There will always be a spark when the points open and turn off the 4-5 amp primary current off.
If a condenser saves the points, a switch, Would a condenser save the contacts on a water pump switch or air compressor switch?
Please keep your answer simple so a first grader like me can understand.

You asked for a simple answer so here’s one albeit not perfect exact or accurate. The condensor saves points premature burn up because it reduces the spark energy, heat and current that would arc jump across the points surface otherwise.

It would take lots more theory and science to explain it correctly but I tried my best to give you the short sweep simple answer you requested so no complaints please lol

John T

 

[Geo-TH,In]

John, I had a brain fart, The capacitor is in parallel with the points so it bridges across the open points.
So why don't they use a capacitor to protect pressure switches when they open?
I guess I am as smart as a first grader.
How many MFD is the condenser?
Happy camping.

 

[Jim.ME]

The noise suppressor you were thinking of in your earlier post (#7) hooks to the ignition switch side of the coil (+ for neg. ground system) and its shell grounds to the coil bracket, generally. Those types could also be found on the output terminals of some alternators. Those are not the condensers for the ignition.

The condenser for the points is inside the distributor and is connected parallel to the points, its lead connects to the wire from the coil (- side of the coil for negative ground system), inside the distributor on the terminal the points' power strap hooks to. The condenser shell is grounded to the distributor breaker plate the same as the base of the point set. When the points open the field collapses in the coil secondary windings making the spark for the plugs. There is also some high voltage discharged into the primary side windings and wiring as well. The condenser acts like a shock absorber catching that spike to reduce what the points see, which reduces pitting and burning. It is discharged when the points close and primary voltage is lower. The condenser shell is grounded, the internals are not. Right or wrong, that's my simple explanation, for what it is worth.

 

[wore out]

John, I had a brain fart, The capacitor is in parallel with the points so it bridges across the open points.
So why don't they use a capacitor to protect pressure switches when they open?
I guess I am as smart as a first grader.
How many MFD is the condenser?
Happy camping.

Since a well pump is commonly run on AC, with a capacitor ACROSS the pressure switch terminals AC current would continue to flow through the motor after the contacts opened.

Unlike an ignition circuit that is DC except for the short period after the points open when the coil is "ringing".

 

[John T]

John, I had a brain fart, The capacitor is in parallel with the points so it bridges across the open points.
So why don't they use a capacitor to protect pressure switches when they open?
I guess I am as smart as a first grader.
How many MFD is the condenser?
Happy camping.

I always forget typical condensor mfd ratings they aren’t all the same and some mags are different than battery powered coil ignitions. I’m not at home but bet the other fine gents can tell you ignition condensor mfd ratings. It’s rating may also be subject to the coils inductance.

A capacitor passes ac with its impedance subject to frequency. ,,for dc at time t. =
0+ it conducts current but then opens to more dc current flow once charged up. A capacitor opposes voltage change while an inductor opposes curent change

Can’t cover ee 101 here lol

John T

 

[47fivewindow]

John, I had a brain fart, The capacitor is in parallel with the points so it bridges across the open points.
So why don't they use a capacitor to protect pressure switches when they open?
I guess I am as smart as a first grader.
How many MFD is the condenser?
Happy camping.

Most of the ones I have tested are in the .25 to .29 MFD range. I have never seen a recommendation for any dist. I was taught that points that grow little mountains that need to be filed need new condensers.

 

[wore out]

Most of the ones I have tested are in the .25 to .29 MFD range. I have never seen a recommendation for any dist. I was taught that points that grow little mountains that need to be filed need new condensers.

"Illustrated parts Guides" put out by various parts manufacturers such as Standard, Echlin, etc. list the values of SOME (but not all) condensers by part number.

Note that this diagram is for a (+) ground system, reverse the legends for a (-) ground system.

(From John Deere FOS-20.)

 

[47fivewindow]

"Illustrated parts Guides" put out by various parts manufacturers such as Standard, Echlin, etc. list the values of SOME (but not all) condensers by part number.

Note that this diagram is for a (+) ground system, reverse the legends for a (-) ground system.

(From John Deere FOS-20.)

Thanks for the info.

 

[GChief]

Remember J.C.Whitney in Chicago? They fed the aftermarket market pretty well for the day. I don't know what happened to them.

The internet.

JC Whitney - Auto Parts and Car Culture

Explore JC Whitney for premium auto parts & accessories, dive into car culture, & stay updated with the latest automotive events & tech trends

www.jcwhitney.com

 

[MarkB_MI]

Mark,
It's been a lifetime ago we had cars with points and condensers. Some time in the Early 70's cars went with electronic ignition and electronics voltage regulators. I recall converting my old mechanical regulator, one with relays, to an electronic voltage regulator.
I may be wrong, but I recall some places sold large condensers that were too big to fit next to the points. You mounted them next to the coil.
Some claimed the larger than normal condenser shortened the life of the points. I replaced condensers annually when I replaced points. I don't recall having a bad condenser back in the day. I had a Cub cadet lawn mower and never replaced the condenser.
Again that was a lifetime ago. Of course my long term memory is better than my short term memory. I open the Refrigerator door and have to ask myself, "Why did I opened the refrigerator door?"
I bet no one has that problem!

I may be wrong, but I recall some places sold large condensers that were too big to fit next to the points. You mounted them next to the coil.
Some claimed the larger than normal condenser shortened the life of the points.

They did make radio noise suppression capacitors that went on the battery side of the coil, or on the alternator output. Also, there were early electronic ignition systems called 'capacitive discharge', but I think those units had capacitors inside them.

 

[MarkB_MI]

Just wondering what is the MDF of mag or auto condenser?
Isn't the job of the condenser to provide an AC current path from one side of the coil to ground? The spark will be a few AC waves. It's not a DC spark
I can't get my head around how a condenser saves the points. There will always be a spark when the points open and turn off the 4-5 amp primary current off.
If a condenser saves the points, a switch, Would a condenser save the contacts on a water pump switch or air compressor switch?
Please keep your answer simple so a first grader like me can understand.

I can't get my head around how a condenser saves the points.

Two of the first things we learned in DC Circuits 101 is that current through an inductor can't change instantly, nor can voltage across a capacitor change instantly. When the points open, the current through the coil primary wants to keep flowing through the open points, so it the coil will generate enough voltage to jump across the point gap, UNLESS the current has another path to take. The condensor provides that alternate path, reducing arcing and preventing the points from burning out. And, as you say, since the coil and condensor form an RLC circuit, you get an alternating current pulse, such that the spark at the plug is actually AC.

On the aircraft weapons systems I used to work on, every relay (and there were hundreds) had a diode wired across its coil to supress the coil's inductive kickback. The diode would be reverse-biased when the relay was energized, but would briefly become forward-biased when power to the coil was interrupted, protecting whatever device powered the relay.

 

[Geo-TH,In]

Two of the first things we learned in DC Circuits 101 is that current through an inductor can't change instantly, nor can voltage across a capacitor change instantly. When the points open, the current through the coil primary wants to keep flowing through the open points, so it the coil will generate enough voltage to jump across the point gap, UNLESS the current has another path to take. The condensor provides that alternate path, reducing arcing and preventing the points from burning out. And, as you say, since the coil and condensor form an RLC circuit, you get an alternating current pulse, such that the spark at the plug is actually AC.

On the aircraft weapons systems I used to work on, every relay (and there were hundreds) had a diode wired across its coil to supress the coil's inductive kickback. The diode would be reverse-biased when the relay was energized, but would briefly become forward-biased when power to the coil was interrupted, protecting whatever device powered the relay.

Mark,
Think about this.
Isn't a noise suppressor capacitor wired in parallel with the condenser ?
My 1960 Cub cadet the condenser was wired to the +inside of the coil.

It had a 10 HP Kohler engine. No room for condenser under the point cover located on the side of the engine.

 

[will-max dairy]

Mark,
Think about this.
Isn't a noise suppressor capacitor wired in parallel with the condenser ?
My 1960 Cub cadet the condenser was wired to the +inside of the coil.

It had a 10 HP Kohler engine. No room for condenser under the point cover located on the side of the engine.

Geo

To my thinking, the noise suppression capacitor would be wired across both coil primary and the condenser.... essentially top of the coil primary to ground.

The points and condenser are in parallel from "bottom" of the primary coil to ground.

The noise suppression capacitor essentially acts as a local storage of charge that can quickly cycle through the coil primary and points, without needing to travel the length of the coil's DC feed wire every cycle.

This reduction in loop area, charge travel distance and charge acceleration reduces conducted and radiated noise from the ignition circuit.

 

[will-max dairy]

Failed (punctured) dielectric can allow condenser action up to the failing voltage whereupon it arcs and stops the wringing Low voltage testing cannot identify that. you are correct as usual. Jim

Exactly... capacitors need to be tested at voltages up to their rating to prove if they are good or not.

For most people, the solution to crappy condensers is to just buy a bunch of them and change them until the vehicle works.

Completely testing a condenser either takes specialized equipment or PhD-level redneck ingenuity... like rigging up a scrap ignition circuit specifically for testing condensers.

 

[Jim.ME]

Mark,
Think about this.
Isn't a noise suppressor capacitor wired in parallel with the condenser ?
My 1960 Cub cadet the condenser was wired to the +inside of the coil.

It had a 10 HP Kohler engine. No room for condenser under the point cover located on the side of the engine.

Agreed, the condensers were not under the covers with the points. Any Kohlers I remember with that arrangement (many units having those engines were set up that way); the condenser was wired to the same side of the coil as the points, like this Cub Cadet wiring diagram for a negative ground system. If you had a positive ground system, the points and condenser would be wired to the + side of the coil.

 

[Geo-TH,In]

Agreed, the condensers were not under the covers with the points. Any Kohlers I remember with that arrangement (many units having those engines were set up that way); the condenser was wired to the same side of the coil as the points, like this Cub Cadet wiring diagram for a negative ground system. If you had a positive ground system, the points and condenser would be wired to the + side of the coil.

View attachment 101870

Jim.
I enlarged your diagram. My eyesight is a little fuzzy. I think you just proved the condenser is in parallel with the noise suppressor. They are connected with the black wire

 

[will-max dairy]

Mark,
Think about this.
Isn't a noise suppressor capacitor wired in parallel with the condenser ?
My 1960 Cub cadet the condenser was wired to the +inside of the coil.

It had a 10 HP Kohler engine. No room for condenser under the point cover located on the side of the engine.

Simplified circuit. Now... given what you're saying about a condenser wired to "+" inside of the coil... I don't know... the position of the points and condenser could be switched relative to the coil primary. But either way, the noise suppressor (C_Noise) would go across the whole shebang.

There are some true aficionados of old school ignition that may be able to point out some details I'm missing here... but it's the general gist of things.

The "Coil" would be L_Primary and L_Secondary... in the diagram...

For "positive ground" systems, you could just switch power and ground in the diagram on the primary side.

Based on comments, there is another diagram in the thread done as an autotransformer, which is a more accurate model for many ignition systems.