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Technical SBC ballast resitor ????

Discussion in 'Traditional Customs' started by Jawsmon, Mar 30, 2021.

  1. Jawsmon
    Joined: Dec 29, 2010
    Posts: 28

    Jawsmon
    Member

    I don't have room for an HEI distributor so I'm running an old-style points distributor. Why does GM call for a ballast resistor in the run circuit?
    It is bypassed in the start circuit so the coil sees full battery voltage. What purpose does the ballast resistor serve? Please enlighten me.
     
  2. Hotter spark during cranking.
     
  3. AngleDrive
    Joined: Mar 9, 2006
    Posts: 913

    AngleDrive
    ALLIANCE MEMBER
    from Florida

    Ballast resistor drops voltage so points do not burn. As RichB said, while cranking, resistor is bypassed.
     
    Nicholas Coe likes this.
  4. Full voltage would burn up the points pretty quickly.
     
    Nicholas Coe likes this.

  5. arkiehotrods
    Joined: Mar 9, 2006
    Posts: 6,288

    arkiehotrods
    ALLIANCE MEMBER

    Without ballast resistor in run circuit, points burn up in no time.
     
  6. jimmy six
    Joined: Mar 21, 2006
    Posts: 8,516

    jimmy six
    Member

    Sometime in the 60’s GM went to resistor wire from the ignition switch to the coil. You can alway go to a Pertronix ll and catch a lot of flack here but not from me. I bought their unit and coil..
     
  7. Mimilan
    Joined: Jun 13, 2019
    Posts: 810

    Mimilan
    Member

    When the engine is cranking there is a battery voltage drop to about 9 volts . So bypassing the ballast gives 9 volts direct to a 9v coil. [making it easier to start]
    When the engine is running the battery is at full 12v which will eventually fry a 9 volt coil, so a ballast resister is used to drop the voltage back to 9v.

    Voltage generally does not affect the points [which is a simple switching device] In fact 6 volt to 12 volt conversions can use the same points.
    It is the resistance in the coil windings from too much voltage that will fry the coil.
     
  8. saltflats
    Joined: Aug 14, 2007
    Posts: 10,611

    saltflats
    Member
    from Missouri

    I put a switch under the throttle pedal to bypass the resistor at WOT. ;)
     
    pckasmin, ffr1222k and Nicholas Coe like this.
  9. Truck64
    Joined: Oct 18, 2015
    Posts: 4,415

    Truck64
    Member
    from Ioway

    I think the ballast resistor is there in RUN to limit the current through the points (heat) as about 3 amps is the limit. Could be wrong, but I doubt it.
     
    Blues4U, nosford and Driver50x like this.
  10. putz
    Joined: Jan 22, 2007
    Posts: 551

    putz
    Member
    from wisc.

    why not use a smaller style hei , don,t need points ........ coil and ballast only .
     
    ffr1222k likes this.
  11. Jawsmon
    Joined: Dec 29, 2010
    Posts: 28

    Jawsmon
    Member

    I might go to the smaller size HEI ready to run distributor from summit racing. I really appreciate all the input. This forum is full of guys that are willing to share their knowledge without making me feel like a dummy for asking. Thanks to all of you. Keep it up!!!
     
  12. Hot rods run perfectly fine with points ignition, and in many cases longer than with new fangled electronic gizmos or with imported distributors.
     
  13. 61SuperMonza
    Joined: Nov 16, 2020
    Posts: 490

    61SuperMonza
    Member

    Running points works just fine and I carry a points plate with me in case I have a problem with my XR-700.
    With that said, if you are running points the condition of the dizzy becomes more critical. You want to make sure the drive and bushings are all within tolerance. Any play in the shaft and your timing will be all over the place.
     
    Truck64 likes this.
  14. 61SuperMonza
    Joined: Nov 16, 2020
    Posts: 490

    61SuperMonza
    Member

    And the ballist resistor is to protect the coil not the pionts.
     
    kevinrevin and 26 T Ford RPU like this.
  15. jaracer
    Joined: Oct 4, 2008
    Posts: 816

    jaracer
    Member

    Use your points and a Chrysler ignition module.
     
    Elcohaulic likes this.
  16. The condenser is what protects the points. JW
     
    kevinrevin likes this.
  17. 61SuperMonza
    Joined: Nov 16, 2020
    Posts: 490

    61SuperMonza
    Member

  18. Truck64
    Joined: Oct 18, 2015
    Posts: 4,415

    Truck64
    Member
    from Ioway

    Embrace the power of "And" ... the ballast resistor in a contact point ignition extends the life of the points by limiting the voltage/current through the primary ignition circuit. Heat.

    I run a 1.5 ohm coil now for 20 years without issue, no ballast, direct battery voltage through a Pertronix Ignitor. The difference here is the solid state module is capable of flowing about 8 amperes, contact points will roast somewhere north of 3 amperes. See the difference?
     
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  19. Torana68
    Joined: Jan 28, 2008
    Posts: 1,242

    Torana68
    ALLIANCE MEMBER
    from Australia

    so what happens in the many systems that don't have a ballast resistor, poor buggers are running around changing their points all the time? no were not so how does that fit ? as others have said its to reduce voltage to a lower voltage coil and is bypassed for starting.
     
  20. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 1,778

    Elcohaulic
    Member

    Use the points to trigger a CD ignition.. One of the best and simplest ignitions going..
     
  21. hepme
    Joined: Feb 1, 2021
    Posts: 32

    hepme
    Member

    MSD makes a billet distb. that's small and ready to run. I have one with the 3x2 i run (no room in back).
    Its not cheap but does the job. I've also used a pertronix conversion prior to that and it worked well for me also-keep it as a backup for trips.
     
  22. Genek
    Joined: Mar 26, 2021
    Posts: 21

    Genek

    Yes you need the ballast resistor. But check which coil you use. Some coils have internal resistor and the coils should have print on them saying not to use with external resistor.
     
    Bob Lowry likes this.
  23. Truck64
    Joined: Oct 18, 2015
    Posts: 4,415

    Truck64
    Member
    from Ioway

    I can explain it to you, but, I can't understand it for you.

    Since you asked: The primary winding of the ignition coil, and the rest of the wiring, connections, ignition switch, the points themselves, etc, all of it together has a primary circuit resistance. An external ballast isn't required, you're right. That isn't the, ah, point. What is required though, is that the primary current flow doesn't exceed about 3 amps.

    Ignition coils are sold with different internal primary resistance from around 0.5 ohm to 3 ohms, maybe more. Contact point ignition systems are limited to about 3 amperes total current flow, or stuff starts burning up in use. It's the Law. Ohm's Law.

    All of this stuff is outlined in the manuals and Tune-Up specs.

    Another way to see this in action is to leave the key in the RUN position without the engine running. If the points happen to be closed the now continuous current will run about 5 amps, likely burning up the coil and the points. Hope this helps.
     
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  24. Jawsmon
    Joined: Dec 29, 2010
    Posts: 28

    Jawsmon
    Member

    I'm running a tunnel ram intake. Just barely enough room for a small diameter distributor. I'm installing a RTR Summit distributor today. MSD is very proud of their distributors so I will pass on them for now.
     
  25. 1971BB427
    Joined: Mar 6, 2010
    Posts: 6,539

    1971BB427
    Member
    from Oregon

    I too have no room for an HEI, but didn't want to screw with points anymore. After hearing all the horror stories about Pertronix conversion kits i decided to avoid them. Instead I went with an Accel electronic points conversion kit. Extremely easy to install, inexpensive, and it still uses the ballast resistor in the circuit. I've been extremely pleased so far with it, and at under $75 it's a bargain. #2010ACC for a Chevy points distributor.
     
    olscrounger likes this.
  26. G-son
    Joined: Dec 19, 2012
    Posts: 722

    G-son
    Member
    from Sweden

    A ballast resistor does a lot of things. One of the important ones that most don't understand is that a (suitable) coil-ballast combo can produce full strength sparks more often than just a coil meant to work alone. In other words, a good thing in motors running (relatively) high rpm and/or with many cylinders.
     
  27. pgj
    Joined: Dec 24, 2010
    Posts: 136

    pgj
    Member
    from aurora co.

    I've had a pertronix kit in my olds for 10+ years and have installed several of them in customer cars and have never had a problem with a single one.
     
    Bigdavid likes this.
  28. 1971BB427
    Joined: Mar 6, 2010
    Posts: 6,539

    1971BB427
    Member
    from Oregon

    Yes, I put one in my OT Camaro when they first came out, and it was still in it almost 40 years later when I finally sold it. Not saying that some don't work forever, but sure hear plenty of failures in recent years.
     
    Truck64 likes this.
  29. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 1,778

    Elcohaulic
    Member

    So your saying the resister kind of acts like a battery or a capacitor. I often wondered about that. I know when you raise voltage you lower current (amps).
     
  30. Budget36
    Joined: Nov 29, 2014
    Posts: 5,834

    Budget36
    Member

    That’s assuming resistance is increasing as well ie 12 volts 1 ohm resistance is 12 amps, 24v and 1 ohm resistance is 24 amps.
     
    Truck64 likes this.

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