Register now to get rid of these ads!

Technical ballast resistor removal

Discussion in 'Traditional Hot Rods' started by evobuilder, Mar 31, 2018.

  1. evobuilder
    Joined: Aug 27, 2007
    Posts: 427

    evobuilder

    OK, so I have a 56 Chevy ex race car (gasser) that has the most basic of wiring, and I mean basic. I have a early Mallory Unilite electronic ignition so obviously no points anymore. Question is.... if I remove the ballast resistor from the firewall, which I know I don't need anymore now that I am running elec ignition, do I need to replace the ballast with anything else (breaker, fuse, etc.) or can I just remove it entirely from the wiring?
     
  2. Are you sure that Unilite doesn't need a ballast resistor? Not all electronic ignitions are the same, some need them and/or you have to be careful about the coil primary resistance.
     
  3. evobuilder
    Joined: Aug 27, 2007
    Posts: 427

    evobuilder

    I'm not, and I can always leave alone to be on the safe side.
     
  4. I ran a car without the ballast resistor because of a roadside repair that required shorting out the unit. I was running a Mark 10 (Heathkit) CD unit, and never got around to replacing the resistor until after approximately 20 years, the CD packed up one rainy night.
    The vehicle ran just fine, but I am sure that the higher voltage, and current would have been harder on the points and the stock coil.
    Bob
     

  5. What sort of ignition problems are you having that have lead you to wanting to remove the ballast resistor? Do you just not like the looks of it or are you expecting future problems?
     
  6. Mr48chev
    Joined: Dec 28, 2007
    Posts: 27,526

    Mr48chev
    ALLIANCE MEMBER

    Have you done a search for that model of distributor by the model number to see if there is an instruction sheet online?
    As far as the ballast resistor goes all it does is reduce the operating voltage from the switch to the coil. It serves no other purpose and has no other task.
     
  7. evobuilder
    Joined: Aug 27, 2007
    Posts: 427

    evobuilder

    Just cleaning up the old wiring and trying to decide if the ballast resistor is still needed now that I am running an electronic ignition. One less thing on the firewall.


    Sent from my iPhone using H.A.M.B.
     
  8. midroad
    Joined: Mar 8, 2013
    Posts: 284

    midroad
    ALLIANCE MEMBER

    Mallory Unilite MUST have a resistor. If you want to run without one you should change to a different brand of distributor. MSD or similar.
     
  9. The ballast resistor must be used to reduce the voltage, if not you will fry the electronic eye unit. It happened to me on my drag car many years ago. I had to learn the hard way!!
     
  10. G-son
    Joined: Dec 19, 2012
    Posts: 664

    G-son
    Member
    from Sweden

    CDI ignitions has a diffrent working principle than points type and other electronic ignitions that feed low voltage (6/12V) to the coil. In the low voltage type systems the current is on to let the coil "slowly" build up a magnetic field (well, quick in human eyes, slow compared to how electricity works in many other situations), and when the current is interrupted by the points opening or equivalent the magnetic field collapses and induces a high voltage in the other coil winding.

    In a CDI type ignition, a capacitor is charged to a couple of hundred volts, and when it's time to get the spark it's quickly discharged through the coil. This quick jolt makes the ignition coil work more like a transformer than a "classic" ignition coil.

    In a points/basic electronic low voltage type ignition you want the current to flow through the coil long enough to peak, that means the magnetic field has reached maximum strength - inductance in the coil makes this take some time, while the current increases. If the current is left on longer, all you gett is waste heat in the coil, and since points ignitions has no automatic dwell change with rpm, the current is left on way too long on low rpm. On high rpm you get the opposite problem, not enough time to charge the coil, so you get a weaker spark - sometimes too weak, especially on a high rpm V8.

    Basically, the coils resistance (impedance really, but let' stay with more common words today) of the coil starts high, and lowers until max current has been reached. Let's say the actual, measured, resistance of the coil is 1 ohm, at 6V it would eventually have a current of 6A, but in the first moment it might be equal to more like 10 ohms - making the initial current merely 0,6A. (Okay, I'm pulling numbers out of my ass here, but the principle is important, not the actual number.)

    Let's put a 1 ohm ballast resistor on that same coil, and feed it all with 12V. They both have the same resistance, so eventually they'll get half of the 12V each - 6V on the ballast, 6V on the coil, and 6A current. But the interesting bit is what happens initially, when the coil starts out with 10 ohm - the total resistance of the coil and ballast is 11 ohm, making only 1/11 of the total voltage going to the ballast (about 1,1V), while the coil gets 10/11 of the voltage, 10,9V, making the coil get a big kick in the nuts to get current flowing initially, 1,1A instead of 0,6A. This speeds up charging the coil, making it work better at high rpm, without cooking it at low rpm. That's the REAL benefit of the combination of a lower voltage coil and a ballast resistor to limit current through it.

    A CDI system has none of this problem, the short capacitor discharge doesn't really change intensity with rpm, therefor ballast resistors shouldn't be needed there - unless the manufacturer of the CDI system says otherwise ofcourse. Other electronic ignitions may or may not have automatic dwell timing adjusting how long the coil gets current, follow the instructions about using or not using ballast resistors.
     
    Last edited: Apr 1, 2018
    alanp561, pitman and Hnstray like this.
  11. evobuilder
    Joined: Aug 27, 2007
    Posts: 427

    evobuilder

    Thanks all, I’ll keep it as is.


    Sent from my iPhone using H.A.M.B.
     
    72yenkonova likes this.
  12. You could fasten it on the opposite side of the firewall & it would be hidden and not seen in the engine bay.
     
  13. Blues4U
    Joined: Oct 1, 2015
    Posts: 4,879

    Blues4U
    Member
    from So Cal

    Sorry man, but I don't think you understand this as well as you think you do, or you're not describing it very well. Whichever, all this really makes very little sense.
     
  14. Yep, G-son apparently pulled the whole thing out of his a$$....

    I'd really like to hear the theory behind the statement 'Let's say the actual, measured, resistance of the coil is 1 ohm, at 6V it would eventually have a current of 6A, but in the first moment it might be equal to more like 10 ohms'....'
     
    Blues4U likes this.
  15. Blues4U
    Joined: Oct 1, 2015
    Posts: 4,879

    Blues4U
    Member
    from So Cal

    Yeah, that one right there piqued my interest. Say what????
     
  16. G-son
    Joined: Dec 19, 2012
    Posts: 664

    G-son
    Member
    from Sweden

    Inductance. Any coil that makes a magnetic field will resist changes in current going through it. That means it will take some time for the current to rise after you turn it on, and when you turn it off (as when the breakers open) it will create a high voltage pulse trying to force it to continue - that's what becomes a spark on the points if the condenser is bad, or makes a good spark at the spark plugs if the condenser is able to prevent the current to continue past the breakers so the voltage spike gets high enough.

    Sorry, english isn't my first language, and everything doesn't translate very well. Might take someone speaking better english to make it all make sense.
     
  17. Blues4U
    Joined: Oct 1, 2015
    Posts: 4,879

    Blues4U
    Member
    from So Cal

    Then there's this one. Uhmmmm, an ignition "coil" IS a transformer, that is exactly what it is.
     
  18. Blues4U
    Joined: Oct 1, 2015
    Posts: 4,879

    Blues4U
    Member
    from So Cal

    Technically, it reduces CURRENT through the coil, which may also result in reduced voltage (potential), but that is a side effect; the purpose of the resistor is to reduce current.
     
  19. G-son
    Joined: Dec 19, 2012
    Posts: 664

    G-son
    Member
    from Sweden

    A transformer transforms input voltage to output voltage at the same rate as the number of turns in the primary winding compared to the secondary winding.

    If you have 100 turns in the primary winding and 10000 turns in the secondary winding, output will be 100 times input. With a CDI, if you give it a 200V jolt, you will get 20 000V out. There's the "just like a transformer" bit.
    In a 6V or 12V ignition coil you also have something relatively close to the same 1:100 ratio, but 12*100 only makes 1200V, not enough for a good spark. In this case, you get the current going through the coil, then the breaker interrupts it, and induction causes a several hundred volt pulse in the primary winding. THIS is what gets transformed to the secondary coil, where you get tens of thousand volts and a good spark. The low voltage has to induce a voltage spike, CDI gets a high voltage from the electronic box and just transforms that. Both coils are made in the same basic way, but do quite diffrent things to achieve the same result.
     
  20. alanp561
    Joined: Oct 1, 2017
    Posts: 1,183

    alanp561
    ALLIANCE MEMBER

    Heck, even I understood that, and I don't speak Swedish.
     
    G-son likes this.
  21. OK, there's inductance, but that doesn't materially enter into the equation until you have a complete circuit on the other side of the coil. The coil resistance will start at whatever it's static measurement is and will rise slightly as the current rushes in. Once the coil reaches saturation, it's back to a straight resistance and continuing to apply power simply produces heat (which will raise the resistance). The inductance comes in when you remove power from the primary side of the coil; the collapsing magnetic field induces voltage in the secondary side and you get a spark. You do get a counter EMF, but rather than materially reducing voltage or changing the resistance, this throws the voltage/current out of phase. That's one purpose of the capacitor, to help bring them back into phase. It also provides the 'jolt' to raise the spark energy (not the inductance) when it discharges into the primary side of the coil. This is why you won't get a good or any spark if the capacitor is defective.

    I'm not totally discounting the effect of inductance/impedance, but in most circuits its effect is so small it's ignored. A 10% change over straight resistance would be large. The only times it's addressed outside of electronic applications is in commercial power usage at industrial plants with lots of motor loads, where the cumulative out-of-phase effects can add up to the point where the current usage can exceed the watts enough that the transformers/wire feeding the plant can prove to be inadequate.
     
  22. evobuilder
    Joined: Aug 27, 2007
    Posts: 427

    evobuilder

    I like the idea of moving it inside the firewall, but it really doesn't both me that much, it was more of a question of.... do still need. Seems like I do, so I am leaving it alone. I will be moving my fuse block inside of the firewall though.
     
  23. I'd leave it on the firewall; it'll get decent air circulation there for cooling and won't collect dust (a possible fire hazard).
     
  24. image.jpg image.jpg image.jpg From the Unilite bible....They all use either a ballast resistor or the "loom resistance wire'' (G.M. Stuff I think). If you need more I can scan the whole lot for you. I have it connected as per diagram 1, with the ballast resistor mounted on a stand next to the distributor.
     
  25. Mudgy
    Joined: Dec 4, 2010
    Posts: 231

    Mudgy
    Member

    Swedish fella is correct. All points/ecu ignition is kettering.

    A collapsing field thru reflection. - primary/secondary windings on an iron core. Whatever the input voltage.
    or the switching /sensor mechanism. All these things do is "look" for a spot to charge up the primary side..... then "see' the spot where they have to switch off, and on again.
    Magnetos are a reversing field, hence fat spark even at hi RPM. Great , but unless you have a radio and/or electronics.....
     
    G-son and alanp561 like this.
  26. 1971BB427
    Joined: Mar 6, 2010
    Posts: 5,874

    1971BB427
    Member
    from Oregon

    I've run my Unilite for years without a ballast resistor, and no issues. But I run an MSD 6AL box feeding my Unilite to ensure I don't blow out the module in my Unilite and get a hotter spark.
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2020 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.