12v ballast resistor

mccsix

mccsix

Senior Member
Car I bought has a ballast resistor wire cut off and hanging loose in the engine compartment.
Can someone describe how this resistor should be wired into the 12v system, with points.
 
Makes me wonder why wire is cut off. If the coil was replaced with one that has an internal resister, then that may be the reason. Look on your coil....it should say if it has a resistor.
 
Yep, take a look at the coil. If it has an internal resistor it should say so.

Or, take a primary lead ohm reading. Or, measure the voltage at the points. If it needs the resistor just mount it in series.
 
Thanks for the tips. So the coil should be marked and if not, then assume it doesn't have built in resistor and I assume there is no visual difference between the two types of coil.
 
If the coil is not marked, remove one of the small wires from the coil, measure the resistance between the 2 small terminals. If it reads aprox 1.5 Ω it's a 6V coil, if it reads aprox 3 Ω then it's a 12 volt coil.
 
Perhaps this should answer the initial question in post 1.
 

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Perhaps this should answer the initial question in post 1, wiring the resistor in series and adapt for your system polarity.
 
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The coil should be wired as the battery. If - grd battery the - coil primary lead goes to the points. Hold points open and measure voltage, shouldn't be over 8-9v. If it is 12v then the resistor is needed. The resistor, again, is mounted in series and there is only one wire going to the distributor.
 
Are you sure it's a resistor and not a capacitor? If it's a capacitor someone might have installed it to suppress radio signal noise. A resistor is labeled in ohms Ω and a capacitor is labeled in mfd microfarads.
 
There is only one capacitor in a breaker type ignition system. It is referred to as the condenser. Coils only have wire windings inside that have a resistance to them but there is no resistor in there. A 1.5 Ohm primary winding type coil such as a can type coil, can work on 6-volts with no ballast. The Ford/Mallory plastic case coils used on the V8 cars of the later 30s & 40s did use an 0.8 Ohm resistor on 6-volts to control heat build up in the coil and make it last longer. The 1.5 Ohm primary type coil will also need a 1.3 to 1.5 Ohm ballast to function on 12-volts reliably. The 3 Ohm primary type coil will function on 12-volts with no ballast since it has modern materials that can take the heat.
 
CT Jack said:
Are you sure it's a resistor and not a capacitor? If it's a capacitor someone might have installed it to suppress radio signal noise. A resistor is labeled in ohms Ω and a capacitor is labeled in mfd microfarads.
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Ya know, thats a good point. Didn't give that a thought.

It very well could be a condenser/capacitor hanging there. Its somewhat common to hang a condenser off the coil or a capacitor for noise.
 
The condenser for the system can be mounted at the coil but it's not for RF noise. RF noise comes from ignition wires, voltage regulators, generators, electric motors, and King Seeley type sending units.
 
None of the coils I have are marked and without any inclination to measure them, I just ordered a replacement, ID'ed as being a resistor, and marked on the outside... no more problem.
Don't know why all manuf wouldn't mark them
 
rotorwrench said:
The condenser for the system can be mounted at the coil but it's not for RF noise. RF noise comes from ignition wires, voltage regulators, generators, electric motors, and King Seeley type sending units.
Click to expand...




Thats the difference between a condenser [ which as far as I'm concerned is also a capacitor] and a capacitor. They are there there [ if they are there] for different reasons.
 
mccsix said:
None of the coils I have are marked and without any inclination to measure them, I just ordered a replacement, ID'ed as being a resistor, and marked on the outside... no more problem.
Don't know why all manuf wouldn't mark them
Click to expand...



Did you get an oil filled or epoxy coil ?
 
Hold it horizontal, up by one of your ears, shake it back and forth, listen for the oil sloshing around or not.
 
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There was a time when tar was used as an insulator in inductor coils for automotive use. Most use epoxy in the modern era. Coils don't have resistors internally as many think. They are just coils of wire wound to give a core gap between the two coils. The primary has many windings of fine wire and the secondary has a much smaller amount of windings of heavier wire. The primary and secondary have an internal connection to each other but only at one terminal. This is where polarity plays a part in the function of an inductor coil. If the terminals aren't marked for + or - or they aren't properly marked then the polarity has to be checked another way in operation to see which way the high tension spark generated is directed. If polarity is off then the coil will give a weak spark.

A pulsating direct current breaker type system is the only way that DC current can be stepped up to high tension since an inductor will only work when there is either AC current or half wave pulsating DC current. The condenser in the breaker circuit is there for two reasons. It has to absorb the back flow of higher voltage that occurs when the magnetic field in the coil core collapses at opening of the breaker and it prolongs the induction process for a bit longer to insure a good spark. The points can't take a back flow of current like that with out a capacitor in the circuit plus the uncontrolled flow ruins the induction process. The capacitance level of the condenser is matched to the coil design. Not all condensers are the same in capacity rating.

The two wire coils inside have resistance since they are coils of wire but they are not resistors in this process. Ballast resistors are used to control current in the process if the current is higher than what is necessary to provide an efficient high tension spark. The excess heat will reduce the life of the coil. The resistance level of the primary coil will tell a person what voltage it will work best with. For 6-volts, a 1.5 Ohm primary will be efficient in most cases depending on coil design. For 12-volts, a 3 Ohm coil works best or a 1.5 Ohm coil with a ballast resistor of at least 1.3 Ohms to drop the current amount that it will normally draw.

If an automotive ignition coil has oil in it that is not solid as tar when cold, it should be avoided. Oil is a dielectric but it may be a dangerous type of oil. Dioxin used to be used for large transformer coils and that stuff is deadly.

With all the foreign made stuff on the market these days, there is no way to know the quality of the products available. I have a Nurex polarity check tool to insure polarity. I advise folks to be carefull about turning off the ignition on there older cars. If accidentally left on, the coil is an electromagnet if the points should happen to be closed and it will get hot. This has likely killed a lot of coils over the years and possibly a few batteries as well.
 
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