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Technical Ignition coil ground ?

Discussion in 'The Hokey Ass Message Board' started by Chopperman, Feb 28, 2021.

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  1. Chopperman
    Joined: Sep 26, 2006
    Posts: 1,272

    Chopperman
    Member

    I’m working a 429 Cad, with a Pertronix II and I’ve got a low rpm / idle miss issue. I’ve traced it back to ignition. Already ruled out the easy stuff like wires, plugs, etc

    I’m thinking I have a grounding issue and wondering if I would do damage to anything by physically grounding the negative side of the coil to an actual known ground on the engine block.

    I’m questioning how solid my ground is on the dizzy as there is a cork washer there, chrome external, chrome clamp, and painted block.

    seems like a lot of mixed opinions out there as to how to “ground” the coil.
     
  2. Boneyard51
    Joined: Dec 10, 2017
    Posts: 6,442

    Boneyard51
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    You could, but it won’t run!







    Bones
     
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  3. Sandgroper
    Joined: Jan 20, 2019
    Posts: 307

    Sandgroper
    Member

    Nope won't run, old school kill switch, security trick.
     
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  4. FityFive
    Joined: Aug 9, 2010
    Posts: 338

    FityFive
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    How clean is your carburetor?
     
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  5. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 2,212

    Elcohaulic

    I would put the stock points ignition back in. If you want a performance ignition use the points to trigger a CD box like the MSD6AL or the Vertex Z-6..
     
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  6. The coil is grounded two ways. Through the points or the "electronic" system and the block. You don't ground the coil to anything else.
     
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  7. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    There are two electrical sides to the coil...the primary side, which is not grounded (both the + and - sides are connected to other parts of the ignition system), and the secondary side, which is grounded to the coil housing, using the mounting bracket. So, you need to ground the coil housing. Chrome is ok, paint is not so good, cork is not so good.
     
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  8. Is there a grounding strap from your engine to the body or frame ?
     
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  9. blowby
    Joined: Dec 27, 2012
    Posts: 8,661

    blowby
    Member
    from Nicasio Ca

    I've wondered about the secondary, I noticed on an Accel super coil a long time ago there appears to be no metal path to ground. Also same thing on Harley coils. Are there two different designs?

    Capture.JPG cd.JPG
     
  10. Man, that's weird. :eek: I was just thinking the exact same thing. :rolleyes:
     
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  11. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    the neat thing about the ground path for the secondary side...it'll find a ground somewhere. Most likely, through the primary side wiring.

    Anyways, my guess is that the miss in the OP is not due to a lack of coil grounding, but it's something else.
     
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  12. 34Larry
    Joined: Apr 25, 2011
    Posts: 1,701

    34Larry
    Member

    I'm most certainly not the sharpest tool in the shed on electric stuff but. I chased a higher RPM miss most of last spring, summer, early fall only to find out where I had mounted the coil caused it to really get hot, real hot. I moved it to the fire wall and that solved the problem. It was mounted to the intake just in front of the front carb. I also changed to MSD through out, dizzy, cap, wires and oh yeah new plugs. That location was not getting the air flow it required either I do not believe as the radiator was kind of blocking a good cooling air flow. Here's a shot of where it was. Like I say, I'm pretty damned ignorant on stuff ignition but maybe this will help a little, maybe ? may 13-20 1.jpg
     
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  13. Chopperman
    Joined: Sep 26, 2006
    Posts: 1,272

    Chopperman
    Member

    brand new 1406.
     
  14. Chopperman
    Joined: Sep 26, 2006
    Posts: 1,272

    Chopperman
    Member

    yes
     
  15. Chopperman
    Joined: Sep 26, 2006
    Posts: 1,272

    Chopperman
    Member

    Someone needs to walk me through this - coils come from the factory painted, aftermarket coils are powder coated, and some are made of plastic with no external grounds.

    Does the coil body REALLY need to be grounded?

    I'm going to scuff the coil, bracket, and dizzy clamp just to make sure.
     
    Last edited: Mar 1, 2021
  16. Doublepumper
    Joined: Jun 26, 2016
    Posts: 1,535

    Doublepumper
    Member
    from WA-OR, USA

    No, the coil case does not need to be grounded. The only benefit to grounding the case would be for RFI suppression.
     
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  17. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,671

    jaw22w
    Member
    from Indiana

    Well, I don't know much about grounding a coil, but I do know that a couple of days ago I had my car running with the coil sitting on carpet. My coil is mounted under dash and I was changing coils. I wanted to test it before I crawled up under the dash to install it. So I had it laying on the floor. Seemed to run just fine. Maybe I was just lucky?
     
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  18. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    Look at the skee-matic. Ignition coils are not grounded.

    There is a polarity, although a coil will work connected either way. There is about a 25% reduction in spark output when connected backwards. Strangely enough this coil polarity has nothing to do with whether the car is negative or positive ground.
     
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  19. No. There's two circuit paths through the coil; one is the primary, the + and - terminals. The secondary path is between the - terminal and the high tension tower to the distributor, so the - terminal is 'common' to both circuits. In operation, when the points close power is applied to the primary side, causing a magnetic field to form. When the points open, this field collapses and generates the spark voltage in the secondary. The path to 'ground' is to the distributor and through the capacitor ('condenser'), which is why when a condenser fails the motor won't run. Crude diagram....

    coil operation.jpg
    It may be helpful to think of the secondary side of the coil as a 'battery' separate from the rest of the wiring system. One end of the secondary is grounded (the 'negative' terminal), the coil produces the voltage (the 'battery') and the output goes out the 'positive' terminal to the spark plug, where it jumps the spark gap and returns to ground, completing the circuit.
     
    Last edited: Mar 1, 2021
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  20. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    I stand corrected, thanks for the picture.

    But...not quite...it's actually "grounded" through the other side of the primary system.

    ignition.jpg
     
  21. Either way will work, but you can run into 'reversed polarity' depending on how the coil is constructed. You're still grounding at the distributor, you've just added a small resistance from the primary coil (typically 3 ohms or less) in-line is all. Seeing how the generated voltage is in the KV range, any voltage drop will be too small to measure. Bottom line, no 'extra' grounding is needed and if you're running points having a good condenser is a requirement. Connections are the same in either case as any differences will be internal to the coil, just pay attention to the terminal markings on the coil.
     
    Last edited: Mar 1, 2021
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  22. AChopped1950ford
    Joined: Sep 5, 2018
    Posts: 240

    AChopped1950ford
    Member

    Your low idle miss could just be a bad coil. I would change out the coil for a new one. I have seen new coils not to be 100% perfect, causing an intermittent miss.
     
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  23. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 12,603

    Johnny Gee
    Member
    from Downey, Ca

    [​IMG]
     
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  24. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    It can't be, capacitors block DC. That is why they are often called "Blocking caps" in audio circuits. There is no pathway for direct current to pass through a capacitor, the 2 plates are insulated.
     
  25. TRENDZ
    Joined: Oct 16, 2018
    Posts: 386

    TRENDZ

    Different coils are built differently... but in general terms, the coils used in the cars that this site caters to, only require a ground on the (-) terminal through the ignition control device (points/ box/ module)
    The coil case does not require a ground. Adding a ground to the coil case will not improve coil performance. If you ground the (-) terminal, the car will not run.
    Stepping into more modern coils.... throw all the previous comments out the window.
    The drawing is not correct on the negative connection. The secondary winding can not be connected to the (-) control circuit.
     
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  26. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    I agree, it cannot be. The "ground" is through the spark plug. If the other end of the circuit was also at ground potential it could not create a current.
     
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  27. jaracer
    Joined: Oct 4, 2008
    Posts: 2,419

    jaracer
    Member

    Old standard coil secondary circuits are grounded at the spark plug not the housing. The primary and secondary are connected typically at the negative terminal. circ_ic.gif
     
  28. You are correct about the DC, but forgetting that the spark voltage power produced by the coil isn't DC, it's technically AC. You can only transform AC, not DC, and the coil is a step-up transformer.
     
  29. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    No, that is not correct. The transformer does not know and does not care whether the current is direct or alternating, all it knows is that a magnetic field from a primary coil is collapsing which induces a current in a secondary coil. The current can be either DC or AC. Typically this is done with AC because each time the current reverses polarity the magnetic field collapses. That makes it very convenient to operate a step up transformer, but doesn't have to be. Vintage car radios used a vibrator on a lower voltage DC to induce a higher voltage DC. I see nothing to indicate an ignition coil generates an alternating current in the secondary coil, it is definitely DC. In order to generate an alternating current in the secondary, the primary would also have to be AC, and it is not.
     
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