Distributor Condenser

Back a lot of years my chevy truck was changed from 6 to 12 v. I doubt the condenser was changed. A few years ago the truck started acting like a fuel problem. The condenser was the problem. Again don't know if a 12 v condenser was installed. Last week I had the same problem. I changed the condenser with a 12 v. this time. I guess my question is will a 6 volt condenser work in a 12 v system, and just quit sooner, or not work at all. From my past experiences condensers last a long time, and hardly ever go bad. Stan

They are all rated at 300-400 volts due to absorbing the voltage surge from the points . All it cares about is the application , it doesn't care about 6 or 12 volts .
Hey are you going to the Vista this year ? 3rd & 4th weekends in June , google AGSEM for more info ....

A condenser does not care if it is hooked to 6 or 12 or 24 or even a whole lot more volts.

The capacitor that condenses the spark occurring from the points opening is nothing more than two conductors (aluminum sheets) separated by a dielectric (non conductor) sheet. The type material and thickness of the insulator determines the voltage rating of the capacitor. Put it in a container with two leads, one per conductor, maybe a mounting strap, seal it up, stamp it and there you have it.

The value is in the order of .01 microfarads and that value seldom comes in very low voltages as that's just not a lot of C to have to package. These units are usually referred to as paper/plastic types as the insulation could be either. So to have the unit capable of several hundred volts is probably the norm. Don't remember seeing the rated voltage on the unit, just the paper box they came in if it were there at all and I don't remember that.....just a part number.

I don't know the exact voltage that occurs across the points when they open with the capacitor present, but the purpose of the capacitor is to slow the rate of rise of the voltage spike and limit the amplitude of it to keep these values below arcing values and prevent the points from arcing as arcing will burn them up in short order.

There is a mathematical equation expressing that voltage and shape and it requires knowing the value of primary inductance of the ignition coil, the actual current flowing when the points open and the value of the capacitor.

So, with all that hooplah, I doubt (too) that your previous capacitor failed due to voltage rating. Lots of griping on here about sub standard imported units.

HTH,
Mark

Stan, When I was young and foolish, all my cars were 12v points and condenser ignitions. Even lawn mowers had points and condenser. I can't recall ever having a condenser go bad. Points went bad all the time, burnt and pitted, so I changed out the points and condenser. Glad my cars and trucks today have electronic Ignition. Also glad distributor ingition is around too. My old Jubilee still has points and condenser and so does the mag in my Farmall C. Like Old said, all condensers are made the same, 6 and 12v are the same. I't been too long for me to remember, but if the condenser is too small, I think you won't get a hot spark. If condenser is too large, you may fry the points faster. Again, I'm not totally sure of any of this, been decades. Same may apply to ballast resistors. Too big of ballast, weak spark. Too small ballast you fry the points.


BTW, I'm no longer young.

The capacitance of an automotive condensor is roughly matched to the inductance of the coil. The coil and condensor form a resonant circuit, and in theory if they're matched properly the point life increases. In practice, the capacitance is not that critical. Since all automotive coils have the same inductance (whether the system is six or twelve volts), all automotive ignition condensors are pretty much the same.

Just for the heck of it, dig your old condensor out of the trash and re-install it in your truck. I'll bet even money your truck starts right up.

Heres the deal: The Voltage Withstand Rating of an automotive ignition condenser is wayyyyyyyyyyyyyyyyyyyyyy higher then 6 or 12 volts anyway, more like several hundred, so it will work in a 6 or 12 volt coil ignition not a problem. More important is its capacitance rating. If its too high the coil wont fire at all, if its too low it will still fire but a weaker spark PLUS the points will burn out prematurely. If its the correct size the points will wear evenly on each side without a hole/valley in one versus a build up on the other.

Ive seen many new out of the box condensors be bad or out of spec. If in the right rating they can last a long time. Ive also seen them fail only after a good warm up.

Hope this helps, post any questions

John T

(quoted from post at 17:11:57 06/05/15) ........................I can't recall ever having a condenser go bad.......................


BTW, I'm no longer young.

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I never had one go bad either until a couple of years ago but one did .................. last thing I thought of :roll: BTW, neither am I :shock:

Mark,
By design, doesn't a coil not only had inductance, it has mutual capacitance because the coils of wire act like the plates of a capacitor, that makes a parallel resonance circuit. But it been almost 50 years ago that I was in an E&M class in college. Good chance I may be wrong. The condenser provides path for the oscillating tank circuit to be grounded to the frame. If I recall, the spark is AC that makes about 10-15 oscillations before it dampens out. This is ancient history for me, might have forgotten a lot too.

Got it backwards old man......grin (I'm gray too). Larger capacitor takes longer to charge so voltage is less and opportunity to arc the points is minimized. Got to keep the cap small enough to discharge fully at your highest rpm.

You are talking about interwinding shunt and primary to secondary coupling capacitance, plus some strays to other objects in the vicinity. On automotive circuit frequencies, these capacitances are so small they are down in the mud.

On the too big part, reason is the capacitor keeps the coil current flowing so there is no big interruption like from 5 amps to 0 and V = L di/dt so with a low value of di, the voltage developed across the coil secondary (aka transformer) will be too low....needed about 18kv for a good spark in the old days.

On too small, it doesn't limit the rate of rise and absolute value of the voltage across the points to a value below the arcing onset and arcing occurs, not quite as much as no cap. but arcs none the less.

And folks, "That's the rest of the story".....Paul Harvey.

George, any capacitance in the coil is insignificant and not by design.

You are correct that when the points open, there is an ac transient. If not for the condenser, the points would arc so badly that they would quickly fail.

The condenser can hold a lot more volts than what they are rated at. I used to work at a shop where the jokes were rampant. One of the gags that got played on the rookies was to take an ignition condenser and ground out the case to the frame of a lawn mower. The coil of the lawn mower was unhooked from the spark plug and then it was gapped about a half inch from the lead to the condenser. The staryer rope to the lawn mower was pulled so that the coil of the lawn mower arced to the electrical lead of the condenser and about 5-6 sparks were put into the condenser. The condenser was now charged with about 10K of volts.
The condenser was then innocently put on the break table where the rookies would sit. Curiosity would take over and they had to play with it....and would get hit with the 10K volts of charge. I saw one kid jump out of his chair.
Warning: I don't recommend playing this joke on anybody. Voltage and milliamps across the heart is never good.

"The value is in the order of .01 microfarads"

In reality, you need to move the decimal point one place to the right, and double or nearly double your number.

Tex,
When I was young, there were sun or son oscilloscopes used to look at the spark pattern coils produced. The LC circuit does produce a hi frequency dampened wave. I can't remember, but there are about 10-15 cycles it goes through, not just one spark, lasts microseconds. So the spark is alternating current. I can't find where I read about the LC tank circuits in coils, I'm thinking internal capacitance makes up a parallel tank and the condenser is part of the series LC tank. But the frequency of the AC is determined by the built in capacitance, just like radio electronics.

Really no big deal one way or the other. Nice chat. Geo

> but there are about 10-15 cycles it goes through, not just one spark

George, the spark occurs as the instant the points open. The subsequent oscillations are caused by the residual energy in the bouncing back and forth between the condensor and coil until that energy is dissipated in the resistance of the primary circuit.

What happens is that resistance through an inductor can't change instantaneously. But when you open the points, you're demanding the current through the coil primary to change, so the coil develops sufficient voltage to arc across the point gap. (That's why points always wear out over time.) The sudden change in current through the coil primary causes the coil's magnetic flux to also change, which induces a high voltage in the secondary winding. That voltage will rise to whatever it takes to jump the spark gap. Most of the energy in the coil is expended in this spark.

Meanwhile, the condensor gives the current through the coil primary an alternate path once the points open. This limits the voltage induced in the primary and reduces arcing across the points. As current passes through the condensor, its voltage rises and it accumulates energy. The subsequent "ringing" is the result of that energy flowing back into the coil, then back to the condensor, etc. It's the solution to a second order differential equation (i.e. a sine wave), and is really no different than, say your car bouncing when you hit a bump in the road.

To all, your engine is more likely to run with 10X too much capacitor than no capacitor at all. Why? Because with no capacitor far too much of the coil's stored energy is lost in the arc across the points instead of exiting via the coil secondary. Try it. I have.

That voltage surge is coming from the coil (field collapse) not from the battery.

(quoted from post at 15:28:09 06/06/15) That voltage surge is coming from the coil (field collapse) not from the battery.

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rom the master of the obvious!.......and it is "free energy", too, right Teddy? :roll: :lol: :lol: :lol: :lol:

My 2 cents is I have had condensers go bad and yes it is mostly this newer import stuff.

The good news is that my dad (and now I) have saved all of our known to be good condensers over the years anytime we did a tune-up which for him was rare but he did do them on occasion.

So I have a small assortment of known to be good condensers. Some are 6 volt but most are 12 volt. When I suspect a condenser problem, I simply replace it with any of my known to be good condensers from unknown applications that will fit where it has to mount.

When the tractor starts instantly I know my old one was bad and immediately cut the wire of the old one and scrap it.

My last failure was in the middle of a hay field when my farmall h which was still 6 volt at that time quit on me. I dug through my condenser bucket and found a common run of the mill GM condenser that was brand new and still in the box. My 6 volt farmall tractor ran fine with a small block chevy condenser from the late 60's and early 70's which was for 12 volt application.

It got me going fast. I eventually replaced it with the proper spec condenser at a more convenient time when the hay was done. The small block chevy condenser went back in my bucket of spares for next time I need to troubleshoot.

Well, I am glad you agree!

Please explain to the nubees just where these hundreds of volts are coming from.

(quoted from post at 18:51:19 06/06/15) Well, I am glad you agree!

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ed, old boy, you are even more obtuse/dense than any of us imagined if you think that constitutes agreement!

Jessie, without a condenser, there is no way to connect one side of the coil to ground
either. The condenser passes ACV and blocks DCV. I wish I could find the book I read
about the internal capacitance in the coils and the roll they play.

BTW, The flyback transformer in old TV's worked the same way. When the sweep voltage was
shut off, The collapsing magnetic fields made a very high voltage spike, which went to
a diode and then to a capacitor, which the pic tube doubled over as the capacitor. Never
heard of that capacitor going bad, did you? Some of these pic tubes had 25kv and about.
That would reach out and touch you if you weren't careful.

Jessie,
The self-resonance and self-capacitance of solenoid coils.
If a solenoid coil has self-resonance and self-capacitance, why would an ignition
coil?

Yes, a condenser is essential, but so is what is going on inside a coil. You need
both to make a spark.

Read page 5. I know I'm getting old and forgetful, but electronics has always been my
hobby. I've even had formal training to repair radio and TV's. Took all the
electronics classes I could in college.
Geo.
self resonance and self capacitance

Yepper, the number I used was 12 undamped, but that is where you the user decide the significant oscillations have ceased as they decay exponentially and go on till all the energy stored is dissipated. As you probably recall you do this test by applying a triangular wave (sawtooth shape) to one winding of the device under test and when you get ready, current is at some predetermined value, you remove the power source and let her ring out.

In ignition systems, the voltage on the plug rises on the first ring (assuming everything is normal) to the plug breakover voltage. When that happens that 18kv or whatever it is clamped to something like 60 volts across the plug gap arc, as the energy stored in the coil (1/2 LI exp2) is dissipated in the Voltage-current across and through the plug gap.

The 60 volts is reflected back in the primary by the turns ratio and stays at that level (think of the voltage across the arc when arc welding) until most of the energy stored in the coil is dissipated...... that is until the coils depleting energy can no longer sustain the voltage drop/current through the plug.....this all happens in a few milliseconds (.001 ish type seconds).

At that time the the plug shuts off, the load on the coil (transformer secondary is removed), the voltage rises as a function of the current flowing at the time (L di/dt again at a new I), and the coil and the shunt cap (almighty condenser) across the points then finish the ringing out, unless the dwell is such that the points have closed and it shunts the cap and the remaining energy is dissipated in the primary circuit dc resistance as heat at the frequency determined by the coils inductance and internal capacitance.

This is surely helping me revive my rusty memory,

Thanks,
Mark

The old "Flyback" was just that, just like you originally mentioned about the 10-15 cycle ringout only you don't get a ringout exactly like that because on the + oscillations, the HV rectifier diode conducted and put the electron (picture) tube in the circuit (loaded the transformer) and having high voltage and beam current (V x I x Time = watt seconds/second) you were dissipating the energy stored in the flyback when you ramped up the primary current.....at a 15,750 Hz rate.......watt seconds x your rep rate of 15,750 Hz is volt-current-time x repetition rate is Watts because the time and frequency are inverse to each other and cancel out.

The Capacitor across the tube (filter capacitor to feed the tube when the flyback was swinging through the negative half cycle) was made by coating the outside of the picture tube with a conductive material like the "Aquadag" high voltage coating on the inside of the rear of the bulb.....definition of a capacitor, 2 conductors (graphite on the inside and outside) separated by a dielectric (the glass envelope of the picture tube). The flat face area where the phospor is illuminated by electrons accelerated by this high voltage (26kv on the larger sets of the day) was not coated. If it were you'd see nothing. The outer coating of graphite had a spring loaded "conducting" wire across it, touching it, which connected to the TV chassis to complete the circuit aka ground the high voltage output. Boy it's been a long time.

Mark

Correction on the TV HV circuit; like I said it's been a long time.

The rectifier was a negative half wave (6BK5 as I recall, tall tube with a high voltage cap on it, was in a tin shielded area because it produced X rays due to the high voltage and the rays burned the glass envelope to a brown tint). Reason was that the 26kv was fed to the cathode end of the picture tube. Had to be negative as electrons are what made up the beam and being negatively charged, they traveled to the unlike charge, +.

The control grids (first grid out from the cathode) had the video (BW picture) and were in the -150v give or take and the next grids in line called "screen grids" were the color gun grids were up in the hundreds. Then there was the accelerating anode, part of the gun at the far end (toward the face of the tube) which was at ground potential. So inside the gun (3 guns for a color TV) you launched the electrons via cathode heating (filament power) of the phosphorus coating of the cathode which emitted the electron beam at a - 26kv, pulled forward (accelerated) by the low voltage grids and finally the grounded accelerating anode and by that time they had so much kinetic energy that they kept on going and hit the phosporous coating of the picture tube face and produced luminance.

Color sets had a "shadow mask" that helped the electrons from each colored gun, strike their respective phosphor dot on the rear of the face of the tube. By sending the color information to each grid, you could produce different colors (aka color wheel theory) by varying the voltage on each grid which varied the intensity of each color to obtain the desired hue.
Skin tones (hues) were the toughest to get right and hardest for networks to repeat, network to network, program to program in the early days. Forever jumping up and changing the color controls every time a different program came on. Today it's totally academic.

I tell you what's neat. Today's digital TV, No bulky vacuum tube with a long neck protruding out the rear, no high voltage, no weight, no filament heat, NO CONVERGENCE MAGNETS, great cheap price, work forever, everything has a nifty remote control (even air conditioners), integrated entertainment centers are a dream.......wow we live in the right era in history.....the glass is more than half FULL!!!!!!!!

This is a nebulous subject in today's high tech world, but none-the-less it's a sloppy revisit to history and I want it right. I have had time to rethink what I said (what I do when I am supposed to be sleeping) and the HVPS is in fact positive 26kv.

The cathode of the gun is at ground (chassis) potential. The heaters were around 6 to 12v AC, fed off a filament transformer (the same one that powered all the other tubes in the set, producing an electron cloud at the cathode. The first (control) grid was around + 150v feeding identical video information to all 3 color guns and modulating electron velocity/density accordingly.

"Side note": The more electrons in a bunch the more times per unit time the phospor on the screen is hit producing more luminance. So black and white was just a matter of when you want a black dot you just turn off the grid voltage making the electron flow stop for that dot. When you want a white one, turn it on as hard as it will go (highest voltage applied), and when you want a shade of gray, just turn it on hard enough to produce the desired result. Color info did the same thing on each of the color (screen) grids and for a given program, you could turn the color intensity control all the way off and see a black and white show or turn it all the way up (color grids getting maximum voltage‚ and blossom the screen with an abundance and undesirable amount of color.

The whole time the electron gun is hitting the phosphor, the beam of electrons is swept across the screen by the vertical and horizontal sweep circuits producing 525 lines of video (top to bottom of the tube), interlaced at a 60 Hz rate (power line frequency chosen to help to reduce jitter).

The interlacing was a double lacing of the beam alternating from left to right and top to bottom 525 times to cover the whole screen: First scan of a scene is line 1,3,5,7, till the sweep was at the bottom of the tube immediately followed by 2,4,6,8.......525, happening so fast you didn't know it happened. The eye can catch 60 Hz buzz as a flicker, but by interlacing 2ea 60 Hz buzzes they were able to beat the eye and it didn't appear to flicker. Oh the 15,750 Hz was how fast the horizontal sweep circuits swept the beam across the screen in making the lines of video mentioned above. Fascinating.

Color info came in via a 3.5 MHz bandwidth spectrum with the colors on a sub carrier, each of a different frequency. They were picked off by tuned circuits, tuned for their Red, Blue, or Green color. Output of these circuits fed the color (Chrominance signal I think I remember it was named) "Screen Grids" which were in the gun, at a higher voltage, up in the hundreds as I recall.

Final acceleration in the gun was the Acceleration anode which was up around +3.000 V and was fed to the tube socket on the rear of the pic. tube along with all the above on a higher voltage wire. The electrons are not accelerated to a launch velocity and ready to leave the the guns, all of which are in the neck of the pic. tube.

Waiting for them is the + 26kv Aquadag coating on the inside of the tube encircling the exit point for the electrons and this (electrical suction) is what gives them the the final acceleration to continue forward in the vacuum of the tube and strike the phosphor on the screen producing visible light.

So what did all this hooplah have to do with tractors and condensers in the gassers of those tractors? Well looking at this "Boob Tube" is what a lot of farmers did while dressing and getting their morning coffee before having breakfast and going out, getting on their tractor with the condenser in the ignition system, and going out to the field. There. I'm legal. Grin

Now I can go back to bed and get some sleep.....yawn!

Mark