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Electronic Ignition Units & Ballast Resistors

Discussion in 'The Hokey Ass Message Board' started by blackjack, Jul 14, 2013.

  1. A friend is getting ready to fire up his engine for the first time since rebuild.

    He's got a Mallory electronic breakerless ignition module on stroked 383 SBC with MSD Blaster coil (we're fairly sure it is a 12v). The MSD instructions recommended using a ballast resistor if using anything other than a MSD unit to avoid damaging points. However, the Mallory unit has no points. Anyone set up a similar system. Are there any wiring diagrams around? We're in the UK and help and advice is a bit thin on the ground.
     
  2. 36tbird
    Joined: Feb 1, 2005
    Posts: 1,080

    36tbird
    Member

    Should be able to find something on the web, just do a "Mallory wiring" search. I just did this trying to figure out how to wire a Mallory magnetic pickup module for a flathead Ford.
     
  3. GassersGarage
    Joined: Jul 1, 2007
    Posts: 4,868

    GassersGarage
    Member

    I had a fiberglas '32 3 window. The car came with an HEI. I had the car rebuilt to look more traditional. The shop thought the HEI looked terrible (and it did) so the went with a stock distributor and converted it to electronic. They burned up the module when they started it. They tried another one and burned it up too. I asked them if they installed a ballast resistor. They said no, the instructions said you didn't need one. I told the it was a fiberglas car, it doesn't have a factory ballast resistor so they installed one. It worked perfect after that.

    By '65 Chevy had a ballast resistor wire which went bad and they don't make that wire anymore. I went with regular wire and added a ballast resistor.
     
  4. Chucky
    Joined: Mar 15, 2009
    Posts: 1,636

    Chucky
    Member

    Pertronix says run a coil with 1.5 ohms or more resistance, or run a ballast resistor. You need the instructions for your distributor and then most likely measure the ohms of your coil to determine if they will work "as is" together.
     
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  5. plaintoast
    Joined: Oct 23, 2012
    Posts: 13

    plaintoast
    Member
    from mora

    the mallory unit says no ballast resistor if using theirs or other high performance coil.
    i used an msd blaster 2 with mine and no ballast. got about 400 miles out of it and with no warning it stopped making spark, never to work again. wired improperly? not according to their own instructions.
    put a pertronix on now wired exactly the same way with the same coil and its working like a charm.
    hope you have better luck than me. I've got another mallory distrib sitting at my shop that makes no spark, i am officially done using their products.
     
  6. Ballast resistors were originally installed to extend point life; running the full 12v to the coil increased current enough that if you did this beyond just when starting car they'd burn quickly. This is one reason electronic ignitions came in; if the 'electronic switch' in the unit was stout enough, you could run more current through it and get a hotter spark. Match the coil primary resistance to the unit you have; as long as the primary resistance in ohms is equal to or more than the recommended minimum, you'll be good to go. Go below that minimum, and a dead module will be the result.
     
  7. 1971BB427
    Joined: Mar 6, 2010
    Posts: 5,481

    1971BB427
    Member
    from Oregon

    I don't care what Mallory says about no ballast resistor. If you don't want to replace the $70 module in that Unilite, you'll use one. Mallory dist. are very sensitive to over voltage, and anything over about 13.5 v. will wipe it out.
    Just went through this on my gasser project. Using a Mallory Unilite magnetic pickup dist. with a ballast resistor ahead of it. My MSD 6AL was out for repair, so I bought a ballast resistor to protect the Mallory while it was out. I simply wired the 12v. from the ignition switch to the ballast resistor, and then to 12v.+ on the coil. The rest wires just like any points distributor. Mine worked great for the 3 weeks I ran it until I got my MSD back from repair a few days ago.
     
  8. 1971BB427
    Joined: Mar 6, 2010
    Posts: 5,481

    1971BB427
    Member
    from Oregon

    And don't believe MSD on their info either! I printed out their instructions for wiring the MSD to a Mallory Unilite magnetic distributor, and it wouldn't fire a spark. Called MSD and told them what was happening, and that their instructions were bogus. The tech told me to wire it like a points distributor, and not as a magnetic. When I asked why their instructions showed differently, he just repeated to wire it like points.
    Wired it like a points distributor, and it worked great. Never did get an answer as to why their printed instructions show different wiring diagram.
     
  9. I have a ballast resistor with my pertronix unit in the Willys. Ignition has never been a problem.
     
  10. 1971BB427
    Joined: Mar 6, 2010
    Posts: 5,481

    1971BB427
    Member
    from Oregon

    I don't use a ballast resistor ahead of either Pertronix units I have. But they don't seem to be susceptible to higher voltages that alternators put out.
     
  11. hoop98
    Joined: Jan 23, 2013
    Posts: 1,362

    hoop98
    Member
    from Texas

    You need the ballast resistor. The module does not have a current control like a Pertronix II or III.

    [​IMG]

    Hoop
     
  12. GMC BUBBA
    Joined: Jun 15, 2006
    Posts: 3,189

    GMC BUBBA
    Member

    Looks like we need to write up a ignition only post one of these days.:eek:

    The system needs a total resitance of approx 3-4 ohms total. Usually the coil should be 1.5 ohms across the positive and negative terminals then use a 1.5 ohm ballast resitor. This does a number of things , one drops the primary current going thru the module and divids the wattage (heat) between the coil and ballast.
     
  13. hoop98
    Joined: Jan 23, 2013
    Posts: 1,362

    hoop98
    Member
    from Texas

    The other thing a ballast resistor does is vary the voltage at the coil. That's why it's called a "ballast". As the current drops with RPM it cools ans supplies more voltage to the coil, vice versa at idle it limits the current as it heats up by increasing resistance and lowering applied voltage.
     
  14. Thanks guys - I think we will find the resistance of the coil and use a ballast resistor if necessary.
     
  15. BillM
    Joined: May 26, 2007
    Posts: 247

    BillM
    Member

    Quote:
    <table border="0" cellpadding="6" cellspacing="0" width="100%"> <tbody><tr> <td class="alt2" style="border:1px inset"> Originally Posted by hoop98 [​IMG]
    The other thing a ballast resistor does is vary the voltage at the coil. That's why it's called a "ballast". As the current drops with RPM it cools ans supplies more voltage to the coil, vice versa at idle it limits the current as it heats up by increasing resistance and lowering applied voltage.
    </td> </tr> </tbody></table>
    I'm not aware of the law Current = ((Volts / Resistance) * RPM)

    According to Ohms law Current = (Volts / Resistance)

    What hoop98 should have said is that the ballast resistor is temperature sensitive and it's resistance changes with temperature and thus indirectly changes the voltage drop across the coil and thus the current through it. Ohm's law still applies.
     
  16. 1971BB427
    Joined: Mar 6, 2010
    Posts: 5,481

    1971BB427
    Member
    from Oregon

    Resistance changes with temperature? I wonder how much the ballast resistor resistance could really change in ambient temps? Amperage changes with temperature, as what we refer to as "free air" directly relates to the load carrying capacity of a device or conductor.

    In the case of my car I have a internal resistance coil that's marked on it "for use with or without ballast resistor". But knowing how susceptible Mallory modules are to alternator higher voltages, I used the ballast resistor in series ahead of the coil to hold voltages down, and protect the Mallory from high voltage issues. In a points situation the ballast resistor is there to keep the points from frying.
     
  17. hoop98
    Joined: Jan 23, 2013
    Posts: 1,362

    hoop98
    Member
    from Texas

    Naw, I had it right as far as ignition systems go, no laws were broken.

    Here is a look at a simulation of a 1.5 ohm V8 coil with no ballast resistor.

    [​IMG]

    Now you can see that the "reactance" of the coil, it's tendency to fight a change in current such as when we turn it on, reduces current flow as we increase the frequency of switching it.

    It has more "Resistance to the current".

    This decreases the current across the Ballast resistor which cools it and lowers it's resistance.

    The combination of the coils increasing resistance to the switching current lowers the current and Voltage Drop across the Ballast Resistor.

    If you measure the applied voltage to the coil it goes up with RPM thereby acting as a ballast to limit the high idle current, while it's resistance lowers as an effect of the raising RPM and it's outut voltage raises.

    True it is a passive device but it's effect when inserted into a primary circuit is to alter the applied voltage to the coil.

    You can tell you are looking at a ballast resistor charging curve, strangely enough by it's ballistic shape.

    [​IMG]

    Vs the predominantly straight charging line of a current limited primary.

    [​IMG]

    So when inserted into the circuit, a ballast resistor will react tp RPM by lowering it's resistance.
     
  18. hoop98
    Joined: Jan 23, 2013
    Posts: 1,362

    hoop98
    Member
    from Texas

    To add, the resistors on voltage regulators sense ambient temperature and are sensitive to it. Ballast resistors are current sensitive through the mechanism of self heating.
     
  19. 1971BB427
    Joined: Mar 6, 2010
    Posts: 5,481

    1971BB427
    Member
    from Oregon

    Bingo!
     
  20. hoop98
    Joined: Jan 23, 2013
    Posts: 1,362

    hoop98
    Member
    from Texas

    1:False

    In a system with a ballast resistor the applied voltage to the Coil positive climbs with RPM, starting at about 6-8 volts at idle in the typical 12 V system and going up the faster the coil is switched (RPM).

    2. SoSo

    Current through a resistance causes a Voltage, Voltage times Current generates wattage which may generate heat, movement, light or some combination thereof.

    yes on point amperage

    3 .Sometimes. depends on the Ignitor Module and Coil primary resistance, follow instructions.
     
    Last edited: Jul 14, 2013
  21. BillM
    Joined: May 26, 2007
    Posts: 247

    BillM
    Member

    Normally, but in the case of a ballast resistor which has a large temperature coefficient, the self heating caused by the current through it changes it's resistance.

    From http://what-when-how.com/automobile/conventional-ignition-systems-automobile/

    These graphs indicate that with increase in speed, an engine with 6 or more cylinders suffers a gradual fall-off in coil output. An output control ballast resistor, if installed in series with the primary circuit, compensates for this variation in output.
    Due to a high temperature coefficient of the iron-wire resistor, the hot resistance is about three times of the cold resistance. Since the temperature of the resistor depends on the current passing through it, the long dwell time causes the resistor to run hot when the engine is running at a low speed. As a result, the average current in the primary decreases so that the coil runs cooler and also the spark erosion due to high voltage is reduced. Also, the normal drop in primary current as the engine speed is increased permits the ballast resistor to run cooler. This causes reduction in its resistance value and as a result increases the primary current to offset the fall-off due to speed. This type ballast resistor has a cold value of about 0.25 Q.. The resistor can be installed either internally in the coil or externally in the circuit.
     

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