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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / September 2006Ignition Coil Overheat
I have an old jeep with an 302 ford engine in it & I keep burning up the 12 volt accel ignition coil that is mounted on the firewall. I have checked the wire connections & the vehicle ground & they appear to be good. Does anyone have any suggestions? This is my third coil I have put on.... I was told by Accel that I still needed the ballast wire in the Jeep ignition wiring when running my Accel Supercoil which cuts the running voltage down. The coil will run on either alternator voltage or the lowered ballast wire voltage. I wanted as 'hot' a spark as I could get so asked about it. They mentioned I would have ignition module issues with overheating though. Are you sure the ground is good? Jeeps are bad for losing the body ground and having ground theft through other paths happen. The 6's have a mesh ground strap from the engine head to the firewall as well as a mesh strap across one engine mount to ground the frame. The mesh one to the firewall gets rotten easy. I also have seen the main ignition ground via the distributor go bad. Basically the hold down foot for the distributor is one main ground path and it gets rusty. I have my coil right on the block by the dipstick but I have a 258 six. It is over 6 years old now and runs strong still. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) > I have an old jeep with an 302 ford engine in it & I keep burning up > the 12 volt accel ignition coil that is mounted on the firewall. I have > checked the wire connections & the vehicle ground & they appear to be > good. Does anyone have any suggestions? This is my third coil I have > put on.... > I was told by Accel that I still needed the ballast wire in the Jeep > ignition wiring when running my Accel Supercoil which cuts the running [quoted text clipped - 28 lines] > > good. Does anyone have any suggestions? This is my third coil I have > > put on.... Hmmm... you should probably read up on coils and ballast resistors a little. If your coil is designed use with an external resistor, you need to use one for sure. (BTW, coils for use without ballast resistors usually have one built within the coil itself) Running without a ballast is usually tough on points too. Also, on the block is a terrible place to mount the coil. All those heavy copper windings don't do well with the extra engine vibration. Try to avoid areas close to exhaust manifolds and other hostile areas as best you can too. Good Luck, Erik > > I was told by Accel that I still needed the ballast wire in the Jeep > > ignition wiring when running my Accel Supercoil which cuts the running [quoted text clipped - 43 lines] > > Erik I actually asked Accel about their SuperCoil. It can run with 'either' voltage. If the OP has one that is only set up for a ballast line voltage and he doesn't have it, it will burn out. Mike > I actually asked Accel about their SuperCoil. It can run with 'either' > voltage. Don't know what you mean by 'either' voltage. Having a ballast resister or resister wire doesn't change the voltage to the coil in any measurable way. It does reduce the current (and temperature). You would need 2 resisters one to the coil and one to ground to reduce the voltage input. -jim > If the OP has one that is only set up for a ballast line voltage and he > doesn't have it, it will burn out. > > Mike >> I actually asked Accel about their SuperCoil. It can run with 'either' >> voltage. [quoted text clipped - 4 lines] >need 2 resisters one to the coil and one to ground to reduce the voltage >input. Reducing the ignition primary voltage is exactly what a ballast resistor accomplishes. Battery/coil ignition systems didn't change appreciably when most manufacturers switched to 12 volts from the previous 6, back in the '50s. They just added a resistance, and continued using the same coils. Most systems used a bypass circuit to supply full battery voltage to the ignition during cranking. Provided a little more energy to fire plugs when the engine was cold and the mixture was more difficult to light. When the start motor was disengaged, the resistor came back into play, stepping the voltage down to about 8 volts. > >> I actually asked Accel about their SuperCoil. It can run with 'either' > >> voltage. [quoted text clipped - 15 lines] > difficult to light. When the start motor was disengaged, the resistor > came back into play, stepping the voltage down to about 8 volts. The starter also draws huge amounts of current, dropping system voltage while in use. The bypass circuit compensates. Without a ballast resistor bypass, starts would especially difficult with a partially discharged battery. Erik > > I actually asked Accel about their SuperCoil. It can run with 'either' > > voltage. [quoted text clipped - 6 lines] > > -jim Not on any I have seen. When I turn my Jeep ignition to 'start', I have a 12.6 (battery) volt feed from my starter solenoid directly to the coil. When I then turn my ignition to 'run', a second circuit cuts in with a ballast wire or resistor wire. In the CJ7's case, it is a 1.35 ohm resistance wire. This drops the battery voltage down to 9 or 10 volts from the 12.6 is should be. With the engine running, it drops the alternator voltage down the same percent. The Accel Supercoil can run on either the volts the alternator puts out or the lowered ballast voltage according to Accel. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) >>> I actually asked Accel about their SuperCoil. It can run with 'either' >>> voltage. [quoted text clipped - 27 lines] > Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 > (More Off Road album links at bottom of the view page) On old GM's that had points, there were two terminals on the starter - one that fed the ballast, and one that bypassed it for starting the car with full battery voltage. > When I then turn my ignition to 'run', a second circuit cuts in with a > ballast wire or resistor wire. In the CJ7's case, it is a 1.35 ohm > resistance wire. This drops the battery voltage down to 9 or 10 volts > from the 12.6 is should be. Yes I guess when the points are closed you do see the voltage drop. But not when the points are open. Then the measured voltage should still be the same as battery voltage. When the engine is running the peak voltage can't really be accurately measured with a DC meter. Anyway, the resister is limiting the current which which is what causes the coil to heat, which I believe was the topic of discussion. -jim > With the engine running, it drops the > alternator voltage down the same percent. [quoted text clipped - 8 lines] > Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 > (More Off Road album links at bottom of the view page) > > When I then turn my ignition to 'run', a second circuit cuts in with a > > ballast wire or resistor wire. In the CJ7's case, it is a 1.35 ohm [quoted text clipped - 9 lines] > > -jim They say a picture is worth a thousand words; http://www.wrenchead.ca/HTML%20Presentation%20folder/sld018.htm Where would we see the ballast resistor drop voltage? Before transistor turn on/points close? Nope, voltage is clearly system voltage. After transistor turn on/points close? Nope, voltage is already being pulled to ground by the transistor/closed points. > Where would we see the ballast resistor drop voltage? > [quoted text clipped - 4 lines] > Nope, voltage is already being pulled to ground by the > transistor/closed points. With the points closed, the voltage measured at the coil positive will be lowered. It's measurable because the resistor's decreasing of the current though it will cause a voltage drop. The resistance of the coil prevents a full drop to ground potential. You will NOT find zero voltage at the coil positive with points closed; that would represent a short circuit through the coil and heating would be a huge problem, to say nothing of the fact that no work would be getting done. You'd burn out wiring instantly. Zero potential will be found only at the coil's negative terminal with points closed (unless they're burned and need replacement). I went through all this recently while restoring my '51 International. I had to install a 12-volt system but stayed with points and condenser ignition, and used a nichrome heater motor resistor to get the 5-volt drop. I don't like resistor wires (or fusible links, either) because they fail due to vibration and can be hard to find. And I teach it in college aircraft systems courses. You might want to review Ohm's law. Dan > > Where would we see the ballast resistor drop voltage? > > [quoted text clipped - 15 lines] > found only at the coil's negative terminal with points closed (unless > they're burned and need replacement). Correct. > I went through all this recently while restoring my '51 > International. I had to install a 12-volt system but stayed with points > and condenser ignition, and used a nichrome heater motor resistor to > get the 5-volt drop. But the purpose is not to get a voltage drop. If you discuss voltage drop you at least need to be clear about when in the ignition cycle that happens. The purpose is to reduce current. The voltage doesn't matter. In fact while the car is running the effect of having a resister in the circuit to the positive terminal of the coil actually increases the voltage to a higher level than the battery voltage *some of the time*, but it would be just as incorrect to claim the purpose of the resister is to increase voltage just because it happens during part of the ignition cycle. -jim > I don't like resistor wires (or fusible links, > either) because they fail due to vibration and can be hard to find. > And I teach it in college aircraft systems courses. You might > want to review Ohm's law. > > Dan In article <1158161749.021298.286760@p79g2000cwp.googlegroups.com>, > With the points closed, the voltage measured at the coil > positive will be lowered. It's measurable because the resistor's > decreasing of the current though it will cause a voltage drop. So, the resistor drops the current. Which do you suppose is the intent and which do you suppose is an observed reaction? Consider; One part number ignition coil fits two vehicles of the same make, one vehicle has a firewall mounted ballast resistor, the other doesn't. Why does one need the voltage reduced to the coil and the other one doesn't? (both vehicles have electronic ignition) > I went through all this recently while restoring my '51 > International. I had to install a 12-volt system but stayed with points [quoted text clipped - 3 lines] > And I teach it in college aircraft systems courses. You might > want to review Ohm's law. Will Ohms law teach what is an intended action and what is a an observed inconsequential action? > In article > <1158161749.021298.286760@p79g2000cwp.googlegroups.com>, [quoted text clipped - 13 lines] > doesn't. Why does one need the voltage reduced to the coil and > the other one doesn't? (both vehicles have electronic ignition) The electronic module may have an internal means of reducing the amperage to the coil during run, while permitting full flow at start. > > I went through all this recently while restoring my '51 > > International. I had to install a 12-volt system but stayed with points [quoted text clipped - 6 lines] > Will Ohms law teach what is an intended action and what is a an > observed inconsequential action? Ohm's Law says E=I*R (Voltage = current times resistance), or E/R=I (voltage divided by resistance = current), or E/I=R (voltage divided by current = resistance), or I*R = E (current times resistance = voltage). If we have a nominally 12 volt system and a coil with a 3-ohm primary, the current flow through it will be 4 amps. We will be able to read 12 volts across the coil when the points are closed. If we install a 2 ohm ballast resistor in this circuit, the circuit's total resistance will be 5 ohms, and the amperage will drop to 2.4 amps (12/5 = 2.4). That 3 ohm coil with the 2.4 amps running through it will have a 7.2 voltage indication across it (3 x 2.4 = 7.2), which is what we wanted. None of this is inconsequential. We wanted a reduced current flow through the coil, and do do that we had to reduce voltage as well. Leaving 12 volts at the coil would give us the initial 4 amps. It's easier to measure voltage than amps (don't have to break the line to put an ammeter in series), so we can calculate the current flow like we did above using the coil's resistance, the resistor's resistance, and the supply voltage. When the engine is running, the points (or EI module) are constantly breaking the flow. The meter won't read accurately because of the lag and the constantly changing flow, not to mention the inductive, negative spike emitted by the coil's primary at every break. The condenser will absorb most of that spike, but it would still mess up readings. We need to use Ohm's law, or a good oscilloscope, to find out what's really going on. Of the two, Ohm's Law is cheaper. http://www.the12volt.com/ohm/ohmslaw.asp http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmlaw.html http://www.grc.nasa.gov/WWW/K-12/Sample_Projects/Ohms_Law/ohmslaw.html Dan > > In article > > <1158161749.021298.286760@p79g2000cwp.googlegroups.com>, [quoted text clipped - 62 lines] > > Dan So the long and short of that is the OP can just put the key in run with the engine off and measure the voltage between the positive pole on the coil and the negative of the battery and tell from the drop if it has a resistor in the circuit or not. No resistor would mean he would have battery voltage. With the jeep 1.35 ohm resistor in the line, he would have somewhere around 10 volts. It is a simple way to use a multimeter to tell if he is smoking out the coil from too much power or if the Jeep resistor wire is still in there to match the Ford application coil. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) > So the long and short of that is the OP can just put the key in run with > the engine off and measure the voltage between the positive pole on the > coil and the negative of the battery and tell from the drop if it has a > resistor in the circuit or not. Yup. But he would have to make sure that the points are closed. If it's an electronic system, there *might* not be any flow at all until he starts cranking. > No resistor would mean he would have battery voltage. With the jeep > 1.35 ohm resistor in the line, he would have somewhere around 10 volts. Depending on the coil primary's resistance. A lower resistance would increase current flow, and in that case (according to Mr. Ohm) the ballast resistor would drop the voltage more than if the coil resistance were higher. A good manual will give the coil's resistance range. Or the Accel people should have it. > It is a simple way to use a multimeter to tell if he is smoking out the > coil from too much power or if the Jeep resistor wire is still in there > to match the Ford application coil. Exactly. Dan > > So the long and short of that is the OP can just put the key in run with > > the engine off and measure the voltage between the positive pole on the [quoted text clipped - 4 lines] > If it's an electronic system, there *might* not be any flow at all > until he starts cranking. No matter at all, the method just measures the voltage drop across the coil power wire from the battery. The coil negative can be disconnected for this static test. > > No resistor would mean he would have battery voltage. With the jeep > > 1.35 ohm resistor in the line, he would have somewhere around 10 volts. [quoted text clipped - 4 lines] > resistance were higher. A good manual will give the coil's resistance > range. Or the Accel people should have it. Real life says the meter reads around 10 volts depending on the condition of the battery. Jeep uses the Ford ignition system. > > It is a simple way to use a multimeter to tell if he is smoking out the > > coil from too much power or if the Jeep resistor wire is still in there [quoted text clipped - 3 lines] > > Dan >> > So the long and short of that is the OP can just put the key in run >> > with [quoted text clipped - 9 lines] > coil power wire from the battery. The coil negative can be disconnected > for this static test. Not so fast! If the points are open any measurements you take at the coil or ballast resistor will show battery voltage. The points do need to be closed...... Bob > >> > So the long and short of that is the OP can just put the key in run > >> > with [quoted text clipped - 14 lines] > closed...... > Bob You are right, that should just be a resistance reading from the battery with the key to run and the engine off to see if the line has continuity and/or a resistor in it. Mike > > > So the long and short of that is the OP can just put the key in run with > > > the engine off and measure the voltage between the positive pole on the [quoted text clipped - 8 lines] > coil power wire from the battery. The coil negative can be disconnected > for this static test. Without current flow, there's no voltage drop. A better way to check for a resistance in the circuit to the coil + would be to measure voltage from battery + to coil +.. hook a ground wire up on coil - and see what happens to your voltage reading. This would give you actual voltage drop and eliminate variables like changes in battery voltage. Jim > > > > So the long and short of that is the OP can just put the key in run with > > > > the engine off and measure the voltage between the positive pole on the [quoted text clipped - 16 lines] > > Jim I was thinking a plain resistance reading, I spit that out wrong. A resistance reading from the battery to the coil with the key in run will tell if he has a ballast resistor in the line or not. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) > > In article > > <1158161749.021298.286760@p79g2000cwp.googlegroups.com>, [quoted text clipped - 35 lines] > If we have a nominally 12 volt system and a coil with a 3-ohm > primary, the current flow through it will be 4 amps. The problem is Ohm's law only applies to a purely resistive load. A coil is not just pure resistance. -jim > We will be able to > read 12 volts across the coil when the points are closed. If we install [quoted text clipped - 24 lines] > > Dan > The problem is Ohm's law only applies to a purely resistive load. A coil > is not just pure resistance. > > -jim I know that, and the presence of any condenser adds a reactive factor to it. But we were talking here of key on, engine not running, where the coil, once flow is established, is nothing more than a resistive load, and we can use Ohm's Law. We use that characteristic to see what the ballast resistor, if any, is doing. Some manuals with good troubleshooting sections will call for such measurements. Inductive calculations are useful only in make/break or AC activity, not in established and steady DC flow. When the engine is running, the readings make much less sense because of the coil's inductive qualities, as I said here before in this thread, and I quote myself: "When the engine is running, the points (or EI module) are constantly breaking the flow. The meter won't read accurately because of the lag and the constantly changing flow, not to mention the inductive, negative spike emitted by the coil's primary at every break. The condenser will absorb most of that spike, but it would still mess up readings." Dan > > The problem is Ohm's law only applies to a purely resistive load. A coil > > is not just pure resistance. [quoted text clipped - 5 lines] > where the coil, once flow is established, is nothing more than a > resistive load, and we can use Ohm's Law. Well yes, if you never plan on starting the engine that's great. But if you do ever run the engine you will find that due to the inductance of the coil that the voltage at that point where you are measuring voltage is higher than battery voltage much of the time (you will need an oscilloscope to make this observation accurately). From that fact should we conclude that the purpose of the resister in front of the coil is to increase the voltage to the coil while the engine is running? -jim >We use that characteristic to > see what the ballast resistor, if any, is doing. Some manuals with good [quoted text clipped - 13 lines] > > Dan > Well yes, if you never plan on starting the engine that's great. But if > you do ever run the engine you will find that due to the inductance of [quoted text clipped - 5 lines] > > -jim Where did ANYONE suggest that the resistor was there to increase the voltage while running? And maybe you could explain why the voltage is higher some of the time. The inductive spike is negative, not positive, and will tend to reduce the positive voltage at the coil's positive as the points open, not increase it, though a proper measurement across the coil would indeed find a higher voltage, just backwards to normal polarity. The presence of the resistor has nothing to do with that; that spike is there in non-resistor systems, too. Dan > > Well yes, if you never plan on starting the engine that's great. But if > > you do ever run the engine you will find that due to the inductance of [quoted text clipped - 8 lines] > Where did ANYONE suggest that the resistor was there to > increase the voltage while running? I asked a question - why aren't they saying that since increased voltage is what happens (at least part of the time). >And maybe you could explain why the > voltage is higher some of the time. EMF, oscillating magnetic fields the usual suspects >The inductive spike is negative, > not positive, and will tend to reduce the positive voltage at the > coil's positive as the points open, not increase it, though a proper > measurement across the coil would indeed find a higher voltage, just > backwards to normal polarity. The presence of the resistor has nothing > to do with that; that spike is there in non-resistor systems, too. You are measuring voltage from the battery to ground over time. You really need an oscilloscope to observe this. If you connect the coil directly to the battery with no resistance between then all you will ever see at the coil is battery voltage (around 12 volts). If you put resistance in there, when the engine is running, you will not see battery voltage but instead see a dynamic wave form where the voltage is higher than battery for part of each cycle. If you don't believe me lick your finger and put it on the positive terminal of the coil while the engine is running. If the voltage was lower than the battery you would feel nothing. -jim > Dan > You are measuring voltage from the battery to ground over time. You > really need an oscilloscope to observe this. If you connect the coil [quoted text clipped - 8 lines] > > -jim The spike is negative, not positive as the battery's feed is. You sure will feel a jolt, but it's a negative jolt, not a positive, and it works against the battery's voltage and will reduce it at that point right through zero and into a negative value, not increase its positive value. If there's any increase in voltage at that point it will be negative, and the resistor has nothing to do with it. The resistor did not generate or increase that voltage spike; the coil did. The resistor's only function is to reduce overall current flow though the coil during the dwell, which it will do in any AC or DC circuit. The coil is an inductor and by definition will resist any attempt to increase or decrease current flow through it. When the points open and the flow is arrested, the field in the coil collapses and tries to keep the flow going in the same direction. Since the coil no longer has the battery pulling electrons through it (electron flow is from negative to positive), and the coil is now pushing electrons out of its positive terminal, it's a negative spike and will read as such on any scope. It would read negative on any meter that could resond fast enough; instead of the positive pulling electons OUT of the meter's positive lead, the negative jolt would push electrons INTO the lead and show a negative. I have scoped 600 volts from the master solenoid coils in our aircraft when they're shut off. That's the reason your ignition switch shuts the radio off during start: so that the starter solenoid (and the starter's windings themselves) doesn't fry the radio when you release the starter. Dan > > You are measuring voltage from the battery to ground over time. You > > really need an oscilloscope to observe this. If you connect the coil [quoted text clipped - 26 lines] > positive terminal, it's a negative spike and will read as such on any > scope. Not on mine, not on yours either if you had actually tried it. A ignition coil is not a solenoid. You're boring me with your lack of knowledge. bye, -jim > It would read negative on any meter that could resond fast > enough; instead of the positive pulling electons OUT of the meter's [quoted text clipped - 5 lines] > starter's windings themselves) doesn't fry the radio when you release > the starter. > Not on mine, not on yours either if you had actually tried it. A > ignition coil is not a solenoid. > You're boring me with your lack of knowledge. bye, > -jim A coil is a coil and will behave as a coil whether it's in a solenoid, an ignition coil, an RF choke, or a transformer. Faraday's and Lenz's Law applies to them all. See http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/indcur.html#c1 and http://www.hnsa.org/doc/radio/chap9.htm and study up on it. Dan >> Not on mine, not on yours either if you had actually tried it. A >> ignition coil is not a solenoid. [quoted text clipped - 13 lines] > > Dan It looks like he'd rather remain ignorant. > It looks like he'd rather remain ignorant. Ah, we've got another guy who has never hooked an osciloscope between the ballast resistor and positive terminal of the coil on a breaker point ignition system. But he's gonna read a book and tell us all about it. -jim >> It looks like he'd rather remain ignorant. > [quoted text clipped - 4 lines] > > -jim Yea, don't bother reading any books or checking the links Dan gave you. It's all just a bunch of bullshit written by people who aren't nearly as smart as you. And since I'm always willing to learn, what in the hell would you possibly expect to see when you hook an oscilloscope between the ballast resistor and positive terminal of the coil on a breaker point ignition system? I wouldn't expect to see much of anything if the circuit is good. > >> It looks like he'd rather remain ignorant. > > [quoted text clipped - 13 lines] > and positive terminal of the coil on a breaker point ignition system? I > wouldn't expect to see much of anything if the circuit is good. Actually, if you hooked the positive lead of the labscope to the positive side of the ballast resistor and hooked the negative lead to the other side of the ballast resistor, you'd get a very nice rendition of the current waveform thru the ignition primary. Sort of a poor mans low-amps probe. Naturally, the voltage (amperage) values measured wouldn't necessarily be spot on accurate, the time values would be accurate though, and the waveform would be rendered accurately. Ammeters were (maybe still are) just measuring a voltage drop across a calibrated resistance (shunt). >> >> It looks like he'd rather remain ignorant. >> > [quoted text clipped - 28 lines] > Ammeters were (maybe still are) just measuring a voltage drop > across a calibrated resistance (shunt). Hey Neil Like usual what you are saying is true. But what jim is doing is hooking up to both ends of the wire which connects the ballast resistor to the coil. That's why I said I wouldn't expect to see much if the circuit was good. Add a little resistance to the circuit and it would be much like hooking up on both ends of the resistor. Bob > Like usual what you are saying is true. But what jim is doing is hooking up > to both ends of the wire which connects the ballast resistor to the coil. No, that is not what I'm doing. If you had been following the discussion, it was about the voltage seen at the positive terminal of the coil when a resistor is in the circuit between the coil and the battery. I guess I assumed the readers would have enough knowledge of how to go about measuring voltage without a detailed explanation of where to attach the leads. But apparently I assumed too much. To observe the voltage on a scope you need to connect the positive probe to the positive side of the coil and the negative lead to the negative post of the battery (or any good chassis ground). When you do measure the voltage with the engine not running you will see steady battery voltage (about 12 volts) if the points are open and less than battery voltage (maybe 9 volts) if the points are closed. When the engine is running you will see a dynamic waveform where some of the time the voltage is below battery level and some of the time it is above battery level. -jim > That's why I said I wouldn't expect to see much if the circuit was good. Add > a little resistance to the circuit and it would be much like hooking up on > both ends of the resistor. > Bob > When the engine is running you will see a dynamic waveform where some > of the time the voltage is below battery level and some of the time it > is above battery level. I should add that the the shape of the dynamic waveform that is observed on a oscilloscope is influenced by a multitude of things. The condition of the coil, points, condenser, spark plug wires, spark plugs, cylinder compression, fuel mixture and timing all have some effect on the shape of the observed waveform (i.e. they all affect the voltage at various points in the ignition cycle). And of course the actual amount of resistance between the battery and coil will affect the scale of the observed waveform. Given all that, I can't imagine how anyone could read a book or a web page and thereby predict exactly what is going to be observed. -jim > No, that is not what I'm doing. If you had been following the > discussion, it was about the voltage seen at the positive terminal of [quoted text clipped - 16 lines] > > -jim You won't see much waveform with the resistor out of the circuit because the battery has an extremely low internal resistance (on the order of about 0.2 ohms) and acts an excellent shunt to ground for any spike. That doesn't mean that the spike isn't being generated; it just means that the resistor holds back enough of it to measure. Again, the resistor does not cause the spike to form. The coil does that whether there's a resistor in the circuit or not. Dan > Actually, if you hooked the positive lead of the labscope to the > positive side of the ballast resistor and hooked the negative > lead to the other side of the ballast resistor, you'd get a very > nice rendition of the current waveform thru the ignition primary. > Sort of a poor mans low-amps probe. Yes you could do that. I'm not sure what your reasoning is in suggesting that. The discussion was what happens to voltage at the positive terminal of the coil. To observe that you would hook the positive probe to the positive side of the coil and the negative to ground. But if you hook it up as you suggest you will see the same wave form - only now it will be inverted and shifted down by 12 volts (battery voltage). -jim > Naturally, the voltage (amperage) values measured wouldn't > necessarily be spot on accurate, the time values would be > accurate though, and the waveform would be rendered accurately. > > Ammeters were (maybe still are) just measuring a voltage drop > across a calibrated resistance (shunt). > Yea, don't bother reading any books or checking the links Dan gave you. It's > all just a bunch of bullshit written by people who aren't nearly as smart as > you. I checked the links. I didn't spot anything that was incorrect. I didn't see anything that contradicted anything I have said either. Note: that if there is no resistance between the coil and battery all that a oscilloscope will show is a flat line at battery voltage. > And since I'm always willing to learn, what in the hell would you possibly > expect to see when you hook an oscilloscope between the ballast resistor > and positive terminal of the coil on a breaker point ignition system? I > wouldn't expect to see much of anything if the circuit is good. Well you won't see much with a scope if the engine isn't running. This whole thread has been a discussion about what happens to the voltage at that point in the ignition circuit. Now you jump in to reveal you have no clue - very helpful. -jim >> Yea, don't bother reading any books or checking the links Dan gave you. >> It's [quoted text clipped - 20 lines] > > -jim A good part of the thread has been directed at correcting your misunderstandings. "jim" <"sjedgingN0sp"@m@mwt.net> wrote in message news:1158018174_1703@sp6iad.superfeed.net... > Mike Romain wrote: > [quoted text clipped - 8 lines] > > -jim You came up with that all by your self and you say I have no clue? Lol... Ever heard of ohms law? In article <1158175291.536671.218210@e63g2000cwd.googlegroups.com>, > The electronic module may have an internal means of reducing the > amperage to the coil during run, while permitting full flow at start. Thank you. <snip> > We wanted a reduced current > flow through the coil, and do do that we had to reduce voltage as well. Thank you. > Leaving 12 volts at the coil would give us the initial 4 amps. It's > easier to measure voltage than amps (don't have to break the line to > put an ammeter in series), With low amp probes being relatively inexpensive now days, we don't need to break the line anymore. The part about easier to measure voltage reinforces the fact that teaching that the ballast resistor is there to reduce voltage and 'oh look a voltage drop' was merely a path of less resistance in making the circuit understood. > so we can calculate the current flow like we > did above using the coil's resistance, the resistor's resistance, and > the supply voltage. Yes we can, but this isn't about calculating resistances and voltages, it's about what purpose a component serves. > > When I then turn my ignition to 'run', a second circuit cuts in with a > > ballast wire or resistor wire. In the CJ7's case, it is a 1.35 ohm [quoted text clipped - 9 lines] > > -jim You have absolutely no idea what a resistor does or how a coil works do you? The coil gets a stable positive voltage that can be measured with any multimeter or even a VOM when referenced to the battery ground. We even hook the coil up 'directly' to the battery positive with a jumper cable to test for a bad solenoid or resistor wire. The points or in my case ignition module only affects the coil's negative feed. They pulse the negative in time to the engine to give you spark. You would need a fast meter to measure this pulsing of the 'negative', but any meter or even a light bulb will tell you if the coil has power... Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) > Hmmm... you should probably read up on coils and ballast resistors a > little. If your coil is designed use with an external resistor, you need > to use one for sure. (BTW, coils for use without ballast resistors > usually have one built within the coil itself) Not necessarily, it depends on the rest of the ignition systems. CD ignitions don't use ballast resistors, either inside the coil or outside. Neither does GM HEI. Maybe your dwell time is set too high, oversaturating the coil..  Signaturecorning_d3 http://www.automotiveforums.com > Maybe your dwell time is set too high, oversaturating the coil.. Normally if the dwell is really far off, you see other indications. > I have an old jeep with an 302 ford engine in it & I keep burning up > the 12 volt accel ignition coil that is mounted on the firewall. I have > checked the wire connections & the vehicle ground & they appear to be > good. Does anyone have any suggestions? This is my third coil I have > put on.... Got a radio? | I keep burning up the 12 volt accel ignition coil Is this an induction coil or transformer ? > I have an old jeep with an 302 ford engine in it & I keep burning up > the 12 volt accel ignition coil that is mounted on the firewall. I have > checked the wire connections & the vehicle ground & they appear to be > good. Does anyone have any suggestions? This is my third coil I have > put on.... First check the ground connection thoroughly. If the jeep is used offroad there's a good chance you have a poor or even intermittent ground. Next, try replacing the Accel Super-Duper coil with the standard Ford ignition coil and I'll bet the burned coil problem goes away. I just went and tested the old racecar. I got a 6 volt drop at the ballast resistor, and another 6 volt drop at the coil, all with the points closed..I thought the resistor dropped the voltage, because we were burning up coils with the 12v feed, now it's down to 6..... Signaturecorning_d3 http://www.automotiveforums.com |
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