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EFV-8 Club Forum / General Ford Discussion / Ignition Resistor

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Posted By Discussion Topic: Ignition Resistor -- page: 1 2 3     supereal 02-23-2011 @ 10:21 AM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 Right on! Some Chrysler products retained the 6 volt coils long after the rest of the system went to 12 volts. The voltage drop caused by the starter can starve the ignition. As I have often mentioned, that is why we install a diode protected circuit to apply full battery voltage to the coil as long as the starter is running. As mentioned above, some starters or solenoids did the same thing to "goose" the coil. Early46 02-22-2011 @ 5:09 PM reply profile send p.m. Member Posts: 18 Joined: Feb 2010 Hey Super, I was about to post that the reason for the lower design voltage of about 3.5 volts for the Ignition Circuit was the fact that on starting, the battery voltage will be significantly lower than the nominal "6" volts. All batteries have an internal resistance, all though quite small, it is significant when the starter is engaged! A good exercise for someone, put a voltmeter across the battery and hit the starter button! Many of the 50's to 70's cars used either a ballast resistor ( looks like a ceramic block ) or resistance wire. An extra contact on the starter solenoid shorted out the resistor so that full battery voltage could be applied to the coil circuit during start. Most early 12 Volt coils were really 9 Volt coils with the ballast dropping 3 Volts. Of course now with confusers (opps I meant computers..) and electronic ignition all that goes away! Looks like there are enough EE's on this forum that we could start a E=IR school!! Keep the smoke in them parts! supereal 02-22-2011 @ 11:24 AM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 It probably would be more apt to call the "resistor" a "voltage regulator", not to be confused with the generator regulator. Most, if not all, electrical devices are designed for a specific input voltage. That is why transformers are so rated. The Ford coil uses 170 turns of primary wire, with the secondary being constructed of 16,500 turns. This "step up" transformer uses about 3 volts input to produce spark voltage of 12,000 to 17,000, depending on variations in input and rate of interruption by the points. As you know, a transformer does not operate on direct current, so the coil relies on the "on-off" power produced by the contact points. The system voltage of the car varies considerably, from a low in the order of 4 volts when the starter motor is engaged, to over 7 volts when the generator kicks in, but the current draw of the coil remains fairly constant. To keep the input voltage fairly even so the car will start when the battery is drawn down, yet not burn away primary winding and coil insulation as system voltage climbs, the regulator (resistor) permits about 3 volts, roughly half the battery voltage, when cold, and as the voltage rises, it offers further restriction because the nichrome resistance wire, similiar to that in a toaster heats, increasing resistance. In practice, the wire coil can approach red heat. The design was made even more complicated because the power flow through the coil is not constant, and must be measured as the "root mean square" of the wave. The voltage control certainly isn't as precise as today's regulators, but does serve to protect the ignition system. Many of us have had the experience of forgetting to turn off the ignition switch when the car is parked. If, by chance, the points are closed, the coil will be "cooked". I hope this will answer your question. The "resistor" is meant to both allow a somewhat stable power source and to prevent damage by preventing overloading. TomO 02-22-2011 @ 7:48 AM reply profile send p.m. Senior Posts: 7385 Joined: Oct 2009 Alan, I agree with you. Henry used the external resister, while the other manufacturers hid the resister in the coil or the primary wire. He probably would be amused at this discussion, also. Tom ford38v8 02-21-2011 @ 8:50 PM reply profile send p.m. Senior Posts: 2883 Joined: Oct 2009 I've been reading with some interest all the EE explanations of the reason why a resistor was included in the ignition system. The obvious answer, Gentlemen, is all too clear to me, a lowly IE: Old Henry had a keen sense of practical jokes, and of downright mean dirty tricks, although never did he share his chuckles with others, but rather, took his pleasure privately. The true history of the resistor in the Ford ignition dates to Henry Ford's memories of his father scolding him to keep his hands where they belonged, in the dirt from which they could do something productive on the farm where he grew up. Therefore, the resistor was placed high and nearly inaccessible behind the steering wheel in order to tempt young fingers, and to harshly scold those dirt diggers who gave in to that temptation. This then, was Henry Ford's respect of his father's words, that every man should toil within his capabilities lest he be burned. Alan Dustbowl 02-21-2011 @ 4:17 PM reply profile send p.m. Member Posts: 74 Joined: Feb 2011 Supereal, In spite of your great explanation, I am still more than a little puzzled. My fundamental question was why the old Fords needed a resistor, and the key sentence in your explanation was:"Too little power sapped the necessary spark, and too much would eventually destroy the coil and points." I understand the first part of this sentence but hung up on the second part: why would 6v damage the coil and points. Apologies for my persistence, and maybe stupidity. Dolman 02-21-2011 @ 2:05 PM reply profile send p.m. New Member Posts: 177 Joined: Dec 2010 Supereal, Maybe we should start a new thread "Reminiscing". When I was about 11 or 12 a neighbor saw me stringing a long wire from my bedroom window to a nearby tree. "Building a crystal set are you?" When I nodded yes, he said, "Be right back". He returned with Radio Engineering by Frederick Terman, handed it me and said, Here's your future, son". That book was my bible. I went on to build all sorts of bread board radios and was repairing other people's radios when I was 14. Electrocuted myself more than a few times. Is there a faster way to check for B+ voltage than a damp fingertip? I would mow someone's lawn and as soon as I got paid I would run to the post office for a money order to buy the parts that I wasn't able to scavenge from the junkyard. I love old radios. Some of them were junk the day they left the factory but others have had nearly an eternal life. Atwater Kent, Hallicrafters, RCA, Zenith to name a few. Back to the early Fords, It's amazing what those engineers were able to do with the limited devices and materials available at the time. It was simple because that's the only way it could be. Haven't fully swallowed the positive ground yet, but I'll get used to it. supereal 02-21-2011 @ 12:28 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 Dolman: It is interesting to see many of the old radios being brought back to life, particularly the big consoles that sat where the TV is today. Many of these old sets used the big speaker coil as a choke to reduce noise, and produced incredible, for their time, clarity. In the vogue of "everything old is new today", tube type amps are now treasured by audiophiles for their tone, as opposed to solid state reproduction. I only wish my hearing was that good! Dolman 02-21-2011 @ 11:19 AM reply profile send p.m. New Member Posts: 177 Joined: Dec 2010 Tom, I meant the post as a bit of humor. Two old EEs overlooking the obvious gave me a chuckle and I am never reluctant to laugh at myself. I certainly don't remember all I learned either. Sometimes I have to reach way back to solve a simple algebra problem. The problem for us old folks is that there isn't a managed file delete system for our brains to clear out the 75 years or more of useless clutter to make the good stuff easier to find. TomO 02-21-2011 @ 10:01 AM reply profile send p.m. Senior Posts: 7385 Joined: Oct 2009 Dolman, I did not want to send you back to school, that is why I did not go into all of the theory behind the resister. Besides that I don't remember all that I was taught about electronics, so if I did try to send you back to school, I would not be able to answer your questions. Tom

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