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dav

automotive ignition

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dav
i have just reread the article by Ken Williams on changing to an automotive coil. he stresses changing the condenser. why? years back i changed my Big Ten to auto ignition but dont remember anything specific about the condenser. i am about to do it to my Landlord so i looked up the article to refresh my mind. should there be a fuse between the battery and the on/off switch or is it protected by the size of the wire? the coil i have avauilable has no writing on it. how do i tell if it is an internal resistor coil? thanks for any input

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HubbardRA
Most automotive coils are externally ballasted, so they do not have the internal resistance. A Kohler coils is internally ballasted. I will attempt to explain the difference in an understandable way. An internally ballasted coil is a coil that is designed to run with a points triggered system directly on 12 volts. A coil that does not have the internal resistance is basically a 6 volt coil. Automobiles used this system so that when the ignition switch was in start mode it would have 12 volts running through a 6 volt coil to produce a very high energy spark, then once the engine starts and the ignition switch is released back to the on position the current is run through the external ballast to effectively produce a 12 volt system. If this coil were run continuously without an external ballast, the points would have a very short life span. In other words the ballast resistor, whether internal or external, is there to lower the current going across the points and provide long point life. You asked about the condenser. I have a B/S 243431 10Hp engine that I converted to battery-coil ignition over 20 years ago. I used the original B/S points and coil. So far I have not replaced either. Guess I may have to replace they sometime. Actually the value of the condenser (capacitor) is related to the whole electrical circuit. The reason for the condenser is to stabilize the arc across the points. Without a condenser an engine will run, but the current flow across the points will cause metal particles to move from one contact to the other and very quickly build up a deposit on the points. The condenser attempts to neutralize this effect. If the value of the condenser is nearly perfect for the circuit, then the points will last a very long time.

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Al
Hi. The capacity (ie micro-farads)varies to go with the coil you have. Capacitors have capacitive reactance in which the phase shift causes the voltage peak to lead and the current peak to lag. The coil in reality an inductor the inductive reactance phase shift, the current peaks lead the voltage peaks. When the two are connected in a parallel circuit, the combination of opposite reactance determines the resonant frequency of the circuit. When the points open the collapsing field actually becomes an oscillation. If the capacitor size is increased, the frequency will be lower. If the inductor is increased,(could be added turns in the primary or more iron in the core, the resonant frequency will go down. When the system is designed the capacitor size is picked to match the coil. Using the wrong value capacitor will not cause it not to work, but the right match makes the system work more efficiently and provide the hottest spark. I definitely would put a fuse in the circuit between the switch and t he battery if you don't connect to a circuit that is already fused. I can't tell you about the coil. If it is off a car, it almost always needs a resistor. If it is a Kohler coil etc, most likely no resistor. If it is from a car, I would use the condenser that the car used and if possible I would use the resistor the car used. Al Eden

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dav
okay Al, ya lost me on most of that but the reccomendations are clear. most likely the coil is from one of my Fiats. Fiat electrics are even worse than Lucas electrics. i did a lot of cussing at the 11 British cars i owned over the years, mostly at the electric or brake systems. come to think about it, i've done a lot of cussing at the Fiat electrics and brakes. anyway, i'll toss the coil and get a known item. there are several kohler 'wrecks' behind the shop at work able to donate a coil. and i have a fuse holder ready to install. thank you much for the help

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Dark
The mechanical points and condenser type of ignition has been used in the automobile since 1910, first used in Cadillac. The electronic ignition system for automobiles was introduced in 1960 by General Motors. Point and Condenser Ignition The original ignition system in the Model A consists of a coil, points and condenser. The points are opened and closed with lobes on the distributor cam. The four lobes on the distributor cam control the ignition firing to each of the four cylinders. When the points open, the ignition primary circuit is interrupted, But the flow of current can not be stopped instantaneously. The current continues to flow and arc across the points. To stop this flow, a condenser is connected across the points so that when the points start to open, the current surges into the condenser. By the time the condenser is fully charged, the points are open wide enough to prevent an arc and the current flow stops and the magnetic field in the coil collapses quickly. The speed of collapse is aided by the discharge of the condenser back through the coil primary windings in reverse direction. Therefore, the purpose of the condenser is to reduce arching at the points, thereby increasing point life, and to speed up the collapse of the magnetic field of the coil. The period of time that the points remain closed is called "dwell time". The Model A dwell should be about 31 degrees on the cam. A point gap of .018" will result in about 31 degrees dwell on a standard distributor cam. At that setting, maximum saturation of the secondary windings is completed, allowing the coil to produce its maximum high voltage to the spark plugs. The above explanation of point and condenser operation points out how critical "point gap" is for efficient running of the engine. Point gap is changed by 1.) wear on distributor cam, 2.) wear on point block, 3.) wear on distributor shaft and bushings, 4.) wear on point contacts, 5.) and engine rpm (causing point bounce. [url]http://www.hotforhotfours.com/evsd.htm[/url]

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timflury
wow Al, That's pretty cool. I haven't heard words like that since I was an apprentice. DC Theory is something we all need to learn and remember. I do remember that GM ignition coils had an internal resistor in them. In this case, they did operate on 12 vdc. Chrysler coils needed the ballast resistor to knock down the voltage to about 7vdc. I remember my dad having a spare resistor in the glove box with a nut driver to change the resistor when it got damp. Visually, the coils looked the same. You could check the coils with an ohmmeter to see which one required a ballast resistor. In addition to Mark's comments, GM in the mid 60's or so, did away with setting the point gap with a feeler gauge and instead used a tach dwell meter and an adjustment screw through a little window on the side of the distributor would adjust the point gap. We were taught this in High School auto shop and we went a step further by setting the dwell, then removing the cap and checking the gap with a feeler gauge. When I was a young Airman in the service, my supervisor asked us what this little tiny spring scale was used for. Turns out it was used for checking the spring tension on the points. If the tension was too low, then you replace the points and condenser.

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dav
okay, i have a coil. turns out i had one in the shed from a motor i scrapped. no writting due to a paint job but i know it's from a single cylinder kohler. there is a condenser on it to suppress static in nearby radios. should i use this? i dont know if radio technology has advanced to the point that condensers are obsolete but i havent seen one in a car for many years.

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HubbardRA
Dav, If it is a Kohler coil, that condenser that is on the coil is not for radio suppression, that is the condenser that works with the points. Kohler did not put the condensers under the covers with the points, they mounted them on the coils.

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1Litre
Briggs mounted the condenser under the cover . You do not see condensers any more with the absence of points in the electronic ignitions. Distributors have gone the way of points as well as many spark plug wires too.

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timflury
quote:
Originally posted by dav
there is a condenser on it to suppress static in nearby radios. should i use this? i dont know if radio technology has advanced to the point that condensers are obsolete but i havent seen one in a car for many years.
Don't be concerned about radio interference, unless you have a radio mounted on your tractor. I'm not sure that condenser will work. I did learn that condensers do have a shelf life. I would spend the extra $$ and buy a known new one.

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HubbardRA
Dav, I have done them both ways with no problems whatever. According to what many of the others have said, you should use the one on the coil. Whichever way you choose to go, I would recommend that you replace the condenser with a new one. I can attest to the fact that a condenser will go bad with time, but that is another story.

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