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Chad..... .re: 6 volt and 12 volt coils. No electrical transformer designer (ignition coils are transformers) would willingly put additional internal resistance into a transformer for any reason. It causes the transformer to be "inefficient" and to overheat. Bottom line, there is NO INTERNAL RESISTOR in any 12 volt ignition coil PERIOD!!! Basic transformer design is several college level courses long, I can not teach you how to design ignition coils over the net, but I will try to explane a little. The now available 12 volt frontmount coil really needs about 10 volts at the coil terminal. The instructions that come with the coil say something to the effect "max 13 volts". 12 volt alternators generally output 14.7 volts to charge the 12 volt battery to about 12.6 volts full charged. Therefore, since the alternator output is also running the 12 volt ignition coil, the 14.7 volts really causes the coil to draw too much power (amps) and thereby overheats and melts the tar insulation inside the coil. Its an "OHMS LAW" kind of thing. It is so much eazier to tell someone to just measure the voltage at the coil terminal than to tell them to measure the coil current (max 3 amps) because you have to put the ampmeter in series with the coil input wire. We're dealing with the "electrically challenged" here. You would need college electrical engineering studies to fully understand. Basically, its the ignition points that govern the coil current, by that I mean the area of the points govern the amount of power they can handle before points overheating. Therefore, the ignition coil designer knows that the internal coil resistance must be such that only 3 amps of current will flow thru it which determines the total length of the primary wire which inturn controls the number of turns of the primary coil winding. Since according to "ohms law" I=E/R, that is current (in amps) is directly porportional to the voltage applied and inversely porportional to the resistance. That means if the coil resistance stays constant and the voltage increases because the alternator is charging, the current MUST increase. Thus overheating the ignition coil. If the current increases, then the power must also increase. More power, more heat, more heat, insulation tar melts. Melted tar, shorted turns, shorted turns, less resistance, less resistance, more current, more current, more power, more power, more heat, more shorted turns, fewer turns less sparkies and pretty soon nuttin runs. Remember, the frontmount OEM 6 volt ignition coil current is actually controled by the "infamous ballast resistor" mounted on the back side of the N-Tractor dash panel. This is a tempature sensitive device that actually changes resistance depending how hot it is. When it is cold, less resistance, more current, more current, more sparkies, more sparkies, eazier to start the cold engine. As the current flow heat up the ballast resistor, it increases in resistance, more resistance, less current..... etc....and this is all auto-magical. It also prevents the coil from overheating because this all happens in under 1 minute. This is why we tell those with front mount ignition coil problems to measure the coil voltage and tell them that the coil terminal voltage for a 6 volt OEM frontmount coil should be about 3.5 volts (3 min, 4.5 max) with the points closed and battery voltage with the ignition points open. And anyother voltage value is going to give you sparkie problems. Bottom line.....control the current flowing in your coil by using the appropriate external resistors..... ...Dell
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