ignition coil questions

Electrical and Ignition

  1. pjc360

    pjc360 Well-Known Member

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    Today i was looking at some ignition coils, and i noticed that different brands post what the primary and secondary resistances of there coils are.
    Is it better to have low primary and secondary resistance? what does it mean to have a low or high primary or secondary resistance? like for example the mallory canister coil the chrome one has a primary resistance of 1.4 ohms and a secondary resistance of 10.0 ohms, the taylor coil has a primary resistance of 0.7 ohms and its secondary resistance is 4.7 ohms.
    Out of curiousity i pulled the coil off my engine and tested it, its a borg warner select ignition coil that i got from oreilly auto parts and it came with a life time warranty, the primary resistance of my borg warner is 2.0 ohms and the secondary resistance is 9.83 ohms.
    What is a good number of ohms to have on a coil? and what are the differences between ohms in a coil? does a lower or higher resistance give more power to the ignition or give more spark? this is something i know nothing about so just curious to know.
     
  2. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    Coils are much more complicated than just resistance. First, the two secondary figures you mentioned, taylor at 4.7, and your BW at 9.83 ARE INCORRECT

    Look carefully at your meter. I have no idea what you have, it may have an "auto" (automatic range) function, or completely manual range. in the same way that the voltage goes up in steps of range, so does resistance measurements.

    The Taylor you mentioned, if 4.7 is the correct DIGITS, will be 4.7K, or in other words 4700. K means thousands, (not the fraction thousanths) and M means Mega or millions, so say, 4.x M ohms means 4.x MILLION ohms.

    So your meter may have resistance ranges of something like 1000 (zero to 1000 ohms, or 1 K) 10K or more (zero to 10,000, or 10K, with better accuracy above 1000 ohms), then 100K, and on up to 1M for 1 million, etc, etc.



    Same with your BW coil. It surely must be 9.83K, or 9830, or nearly 10K or 10,000, in round numbers.

    Generally, lower primary resistance means the coil draws more current, makes more magnetic field, and is capable of making higher voltage spark.

    Generally, the lower the primary, and the higher the secondary means higher voltage output. This is known as a "high ratio" coil, a term which you may run into.

    BUT THAT is not the real story. Coils have a magnetic core, and beginning with such systems as modern epoxy coils and the GM HEI, engineers began to experiment and develop better core materials, as well as stuff like the GM "E core" meaning the shape of the core.

    These things affect the way the magnetic field is formed, collapses, and generates the spark.

    It is important to make sure that whatever combination you have IS COMPATIBLE with each other. Research your ignition system, whether Mallory, MSD, HEI, or whatever, and make sure that the coil you have employs the proper ballast resistor IF NEEDED

    In my particular case, I'm running a stock Mopar factory coil driven by a GM HEI module, with no ballast. I started out with short runs, monitoring coil heat "by feel." After I got past an hour or two, and finally one hot summer day of nearly 3 hours of almost continuous running, with no excessive coil heat, I decided "all was good."

    Multimeters, used to be called "a VOM" for volt - ohm - milliameter, have all kinds of different ways of changing ranges. Here's a photo of an old standby, the "famous" Simpson 260

    If you look at the very top "ohms" scale, you can see that on the far left it goes to 2K, or 2000 ohms

    This scale is selected by "R x 1", and if you select "R x 100" you multiply the scale by 100, so the top reading in that case s 2000 x 100, or 200,000, or 200K. I've never understood why these were so well liked, because the scale selection was just plain crappy. On this meter, you would be forced to use the "R X 10,000" scale for the secondary, so on the top scale, 9.83K of your BW coil would be WAYYY down at the right between the 2 and the 0. (2 in this case would be 2 x 10,000, or 20K, so the little mark halfway between the 2 and the zero (far right) is 10K, or 10,000 ohms. Like I said, crappy.

    When I was in Navy electronics as a young man, THAT is what we had, along with a "PSM-4" which in my opinion was a much better meter.

    [​IMG]

    [​IMG]


    Here is just a random digi multimeter I Googled up. It is strictly manual range switching, no automatic ranging

    [​IMG]

    Notice that down at the bottom of the switch it says 200, then going CW around the switch, you have 2K, 200K, and 2M

    So you would start at 200, and if that is out of range, go up until you get a usable reading. In the case of your coil primary, you would be on 200 (up to 200 ohms) and for the secondary, you would end up on 20K--(up to 20,000), and your BW coil secondary would SAY 9.83, but because you are on the "up to 20K" scale, that would mean "9.83K" or 9THOUSAND ohms, or in other words, 9,830 ohms

    In the case of the Fluke 70-series like this 73, the range switch is the button in the center of the switch. You put the switch in the ohms position (upside down U for Omega) and to change ranges, you keep pushing the button until the range is where you want This meter can "auto range" so if you just turn it on, and to the correct function without touching the center button, it will "seek" the correct range. Fluke, by the way, are excellent meters.

    [​IMG]
     
  3. KitCarlson

    KitCarlson Well-Known Member

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    As 67Dart273 suggests coils are more complicated than resistance. They are a transformer, and have about 150 more turns on the secondary than the primary. While most think of a transformer with four wires, a coil has three, since two are internally connected. Since transformers are made with a magnetic core and windings they are also inductors. Inductors store energy, this is what happens in the dwell period. The total energy stored, E = 1/2 L * I * I. In this equation, E is energy in watts, L in inductance in Henry, and I is the current in Ampere. I * I is current squared. Not all the energy goes to the plug, some is lost due to the resistance losses in the coil, and plug wires. Some energy is lost in the distributor gap, and some energy is not delivered when the spark is unable to maintain the spark due to gap distances.

    So energy is increased by L and I squared. L increases with turns of magnet wire on the core, however more turns increases resistance. More resistance decreases the maximum current, following Ohms law, I = V/R or the battery voltage divided by the coil primary resistance. With a mopar box the ballast resistor is in series with the coil, so is added to the coil resistance. Without the ballast, current builds to excessive levels, and may damage the coil and mopar box.

    One property of inductance is to oppose change in current. When coil is first energized by points or mopar box, current increases in time, to the maximum amount limited by resistance. The time to reach maximum maximum current is typically between a few milliseconds to several milliseconds. This time is about right at 6,000 RPM and firing 8 cylinders. At 600 RPM with points, or mopar box the dwell time is much too great, the ballast limits the current to a safe value. A HEI module avoids the excessive current by limiting the dwell time to a few milliseconds, prior to spark. There is more to the story, too much current can saturate the coil, when that happens, inductance drops as if there is no magnetic core and spark will be non-existant.

    Modern ignitions are a step beyond the HEI, they better control the dwell with a micro-controller and are direct fire.
     
  4. KitCarlson

    KitCarlson Well-Known Member

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    And inquiring minds wonder how 10 to 20KV is possible to fire a plug. This happens because V = L di/dt. L is the coil inductance. di/dt is the change in current with time. When the points, or transistor in the mopar box opens the current goes from a high value to zero quickly, resulting is a high voltage. The mopar box creates a higher voltage than points, because points bounce and have leakage when opening. A transistor is better switch to interrupt the current.
     
  5. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    I don't have the math skills to do an in-depth analysis of all that is involved with ignition, and of course there are at least 4 different major systems

    Magnetos, which generate their own primary power

    The old (Kettering) points systems, which work the same as the Mopar ECU/ breakerless system, IE an electronic switch

    The HEI style systems which operate somewhat differently

    The various capacitive or inductive discharge systems, which work more like an electronic strobe/ flash on a camera --they charge up a large capacitor and then discharge that energy into the coil

    But the OTHER aspect of high performance coils that I'm aware of involves the secondary SYSTEM, IE, coil wire, cap/ rotor, plugs, wires. Coils do not produce voltage "in the way" that say, your 12V battery or 120V wall outlet does, IE a fairly stable voltage over a fairly wide range of current.

    Ignition coils are "load sensitive," meaning that the LOAD which the rest of the secondary system presents to the coil affects it's power and voltage output. You can SEE this in a scope pattern. What is called the "firing line" is the point and the time in which the plug fires, and it "drags down" the secondary voltage, depending on plug gap, cylinder conditions including pressure and A/F mixture, etc. A fouled plug will pull the voltage down even more

    In the pattern below, the first high spike is a very short moment in time when the points open or the ECU triggers, and the spark starts to form. If there was no plug / wire connected, this spike would be HUGE, much bigger. The little "squiggle" immediately to the right is the plug firing, the "firing line." This shows grapically how the spark voltage is "loaded down" by the plug and wire impedance. When the plug stops fireing, which is due to the coil voltage finally "running out", you see the little "ramp" sliding down as the relatively small amount of coil energy falls off, and the step at the right of that is the points closing, or in the case of a Mopar ECU, the ECU turns the coil back on to recharge. This "recharge" known as "dwell time" is the time that the points are CLOSED or that the ECU is turned on. The next spike happens all over again as the points OPEN, or the ECU triggers and turns the coil OFF

    [​IMG]

    Years ago, Champion spark plugs came out with a plug (forget what the hype was) which had a GAP inside the insulator, which was supposed to allow a better spark to build. A Champion rep explained to me that "these actually worked, UNTIL....." Many of you who are old enough remember that the old GM distributors used to have a LONG and a SHORT rotor. It turns out that the short rotor NEGATED the advantages of the Champion plug. Additionally, for years you could buy "spark boosters" that went either on your plugs or one in the distributor cap coil wire. These were the very same thing --a "spark gap in a can." They were supposed to "intensify" the spark, and were advertised to help old engines which burn oil.

    I realize this is not an ANSWER, but I was trying to show that even the old breaker points ignition is more complicated than it appears.
     
  6. bohica2xo

    bohica2xo Well-Known Member

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    Don't overlook the role of the condensor in the Kettering ignition.

    If you really want to learn about transistor switches for the coil circuit, buy a Velleman ignition & build it yourself. For about 20 bucks you can say you made your own electronic ignition:

    http://www.vellemanusa.com/downloads/0/illustrated/illustrated_assembly_manual_k2543.pdf

    And if you blow it up you can fix it too. Not clearly mentioned in the instructions is how it limits current. That TIP162 is a fast darlington, and it handles the current limit in the low side of the coil.

    I have one of those units on a 6v tractor, that has been running for decades. Can't do that with a GM module.

    B.
     
  7. KitCarlson

    KitCarlson Well-Known Member

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    OEM ignition coils are well designed. It is possible to use math to optimize wire sizes, number of turns, and magnetic core material to fit in the package, most likely that was done and verified. Mopar kept with the design specification for decades.

    It takes several thousand volts to initiate a spark, once that happens, the spark voltage is about 50V, with a plug gap near 0.030". Designing a coil for extra high initial voltage may result in less spark current due to impedance mismatch.

    Like most things, too much someplace, may result in less of something else, in another area.

    The Velleman circuit uses resistors to limit the coil current, they are on the circuit board. It is a Kettering style ignition with transistor coil drive. Similar to Mopar box, except designed to interface with standard points.
     
  8. pjc360

    pjc360 Well-Known Member

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    so what would be a good coil to go with for performance? is the borg warner coil i have good enough? or should i step up to the taylor or mallory coil? if i step up to a taylor or mallory or a msd blaster or an accell coil do i need to upgrade my ballast resistor? i have been told the the lower the ohm on the ballast the better? is this correct? and who makes some good ballast resistors? are the echlin ballast resistors good?
    I guess i could go to all the different part stores and do an ohm test on there ballast resistors untill i find the one with the lowest ohms.
     
  9. pjc360

    pjc360 Well-Known Member

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    Oh and to give some information about my multimeter its a craftsman and i believe it is an auto range switching? i put brand new batterys in it, so i believe it is working properly, and i have been told craftsman is good stuff.
     
  10. pishta

    pishta I know I'm right....

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    The "load sensing" ability of a coil is the heart of that one ignition system, the name escapes me....A guys name....

    That E-SUN does capacitance and transistors too, pretty cool. Nice for troubleshooting flat screen power supply caps! Autoranging is nice. I got an old Tripplet 7 analog, nabbed it from my old telephone van before it got auctioned off and an newer LG digital.
     
  11. pjc360

    pjc360 Well-Known Member

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    ok so what coil should i go with? if i go with like say a mallory coil or a taylor coil or msd blaster do i need to run a special ballast resistor? like the lowest ohm ballast i can find?
     
  12. KitCarlson

    KitCarlson Well-Known Member

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    I have no idea if you are using points or mopar box with electronic distributor, or HEI conversion. If HEI then no ballast is needed, the internal dwell control limits the current by time not dwell angle.

    If you are using points or mopar box, then you might get away with a lower ballast resistor however there may be early failure. A failure is burned points, broken box or damaged coil. A failure will most likely occur with key on and engine stalled, or low RPM driving for long time. Your coil will also heat more at low RPM. Avoid parades :).

    The newer Pertronix 2 has micro-controller dwell control, that might be an option. No ballast required. Or use MSD CDI system.

    Better coils or lower value ballast do not help other ignition defects such as failed plug wires, plugs, rotor and cap. They make things worse.
     
  13. berlins

    berlins BerlinS

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    bump
     
  14. pjc360

    pjc360 Well-Known Member

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    I'm running the mopar electronic ignition, i'm using a standard ignition module a borg warner select coil with an echlin cap and rotor and borg warner supermag plug wires. I'm just wanting to know what the best set up would be to get more juice to the plugs? i need to learn this ballast resistor and coil thing too, because i was thinking about getting the mallory canister coil with mallory pro side winder spark plug wires, mallory also sells a ballast resistor that i guess i coul get, but its 15 bucks and i can get a borg warner or echlin ballast for around 5 bucks.
    But i do want to have my coil and ballast set up correct so i am not frying 1 or the other.
     
  15. berlins

    berlins BerlinS

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  16. wjajr

    wjajr Well-Known Member

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    Berlins:
    .

    Yup they run hot, so do light bulbs, and stove burners; they are all resistors.

    Circuit analyses here showing why two resistors in parallel won’t work:

    http://physics.bu.edu/py106/notes/Circuits.html
     
  17. berlins

    berlins BerlinS

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  18. KitCarlson

    KitCarlson Well-Known Member

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    pjc360,

    If it were me I would stick with what you have, it sounds good. It should be reliable, and provide proper ignition. I would think more HP could be found in ignition timing advance curve modifications, along with fuel mixture, not a hotter coil. To do that requires much work, measuring changes, and working towards positive results. It takes equipment and time.

    To go farther consider crank fire with electronic advance based on RPM, manifold pressure and temperature. The system could also be coil-on-plug or direct fire with coil packs. Such system have correct dwell control, not requiring ballast resistors. While you are at it, might as well go fuel injection, it makes for better tuning. At that point might as well buy a new Challenger.
     
  19. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    The "lowest ohms" is not necessarily what you need, and I already tried to tell you that much in a roundabout way.

    As I said earlier, with a GM HEI module, I'm quite simply using a stock Mopar coil.

    I ran all stock Mopar ECU for years on a slightly warm 340 and 440

    Most of us don't have the capacity to operationally test the many many ignition, coil, and ballast combinations out there

    WHAT IS WRONG WITH THE ONE YOU HAVE NOW?

    In other words, you just might be fixing something that "ain't broke."

    What is the engine power level? Is the ignition system giving you any trouble now?
     
  20. pjc360

    pjc360 Well-Known Member

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    My ignition is wired up wrong from the idiot who owned the truck before i got it, the engine is a crate 360 magnum it was purchased by my old man bvrand new from the local dodge dealership in 2002 it only has 20 to 25 thousand miles on it, it's rated at 300hp and 375 ft lbs of torque but its probly pushing 320 hp and darn near 400 ft lbs of torque with the headers and dual exhaust with an h pipe and and a dual plane edelbrock rpm air gap intake and a manual choke edelbrock 600cfm carb.
    I ordered a new electronic ignition wiring harness because the harnes thats on it is very old and hacked up, thats why i was asking questions on how to wire the ignition up, wich you helped me out with alot 67dart273, thank you by the way, i printed off what you told me and the pictures you showed me. I bought a new borg warner select ignition coil, a new borg warner select voltage regulator a new standard x-series ignition module and yesterday i purchased a brand new 2 prong ballast resistor from car quest. I wdecided to run the 2 pin ballast because it looked easier to wire up then the 4 prong ballast i have now, the standard ignition module i bought is a 4 pin module, i had that double checked by the way... so i figured since im going to be running a 4 pin module i might as well run the 2 prong resistor, make it as simple as i can because i am not the best there is at wiring, but i have been asking alot of questions and reading a bunch of stuff on the mopar electronic ignition. I'm going to pop the cap and rotor off and make sure they didnt get hurt, i think they should be ok, the cap and rotor i bought brand new in november and i got the echlin cap from napa and the echlin rotor from napa.
    Just like you had said 67dart273 the ignition on my truck is wired up wrong, i followed the wire from the positive terminal of the coil to the ballast resistor and the guy that owned it before has the coil running on the wrong side of the ballast, thats why when i turn they key on and test the coil im getting 12.5 volts to the positive terminal of the coil, instead of messing with this hacked up harness and digging thru this guys mess i decided to order a new harness and get a new coil and voltage regulator and ignition module and 2 prong ballast, i tested the new ballast with my meter and it shows 1.2 ohms wich i have been told is correct? Anyways i was just mearly trying to learn a little bit more about the mopar electronic ignition by asking about the coil and ballast, im sure once my ignition is wired up correctly it will sound much better and run much better and hopefully i will get better fuel mileage then i am getting with it right now, i think that ignition being wired all wrong has something to do with my 10 miles to the gallon regardless of how hard or soft i am on it. thank you for all your guys help with this, if any of you have some more information or pictures to share with me regarding the mopar electronic ignition and how it works and how to wire it up please feel free to share with me, i knew a little about the mopar electronic ignition from a 76 half ton dodge truck i owned a few years back, but it was wired up correctly and i never had any problems from it.
     
  21. pjc360

    pjc360 Well-Known Member

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    So i just tested my new 2 prong ballast resistor from car quest, it tested at 1.2 ohms, the primary resistance of my new borg warner coil is 1.8 ohms and the secondary resistance is 9.53 ohms, so with that set up i'm thinking i should get a pretty good spark wich should result in the engine firing up pretty good. correct? is the secondary resistance of 9.53 a good number? i heard a higher secondary resistance gives a hotter spark ton the plugs.
     
  22. KitCarlson

    KitCarlson Well-Known Member

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    I would worry more about correct wiring, than your coil and ballast resistor values. Check ignition supply voltage to ballast and see if it is close to battery voltage.

    A resistance test is only a small part of the picture, and not a good test of a coil. Things like turn-turn shorts will not show up since the resistance change is too small to measure. A turn-turn shorts caused by overheating damage on insulation makes for a sick coil. A coil failure may result in a weak orange or red color spark, or intermittent spark.
     
  23. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    YOU OBVIOUSLY did not read a thing anyone posted.

    YOUR SECONDARY resistance IS NOT 9 --some odd--ohms

    PLEASE don't get fixated by resistance values. You need to research what sort of coils you have --go right to who made or sold them--and find out what resistor(s) or range of resistance is OK.
     
  24. pjc360

    pjc360 Well-Known Member

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    I just checked the resistance of the coil with my meter the way my haynes dodge truck repair manual said to? same with the ballast..... i know its not 100 percent accuarate, but the repair manual said you want your ballast to read 1.2 ohms on your meter, thats what my new ballast reads? not trying to tick anyone off here... sorry if i did. i will make sure my wiring is correct, i should be getting my 5 pin ignition harness tommarrow, i'm excited to get it done right and see how it runs once its wired right, i could have made do with what i have, but the harness is so hacked up and old, everytime i have to cut into one of the wires on that 5 pin harness the wire is corroded looking. so i figured a new harness would probly be a good idea.
     
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