Ballast Resistor

[zsn0w]

I’m pretty savvy with electronic ignitions and the wiring for the systems in our cars, but I cannot wrap my head around something and I feel like I must just be missing something obvious. If the ballast resistor was originally implemented to limit the voltage at the points of a mechanical ignition to 7 volts or so, how is this done with a RESISTOR? V=IR and we’re working with a constant voltage source of 14 volts at idle, so adding a resistor should just set the current at a specific value, not modify the voltage. Is there something more to a ballast resistor than just a resistor in a ceramic block?

 

[wvmarv]

I’m pretty savvy with electronic ignitions and the wiring for the systems in our cars, but I cannot wrap my head around something and I feel like I must just be missing something obvious. If the ballast resistor was originally implemented to limit the voltage at the points of a mechanical ignition to 7 volts or so, how is this done with a RESISTOR? V=IR and we’re working with a constant voltage source of 14 volts at idle, so adding a resistor should just set the current at a specific value, not modify the voltage. Is there something more to a ballast resistor than just a resistor in a ceramic block?

https://www.motortrend.com/how-to/mopp-1110-ballast-resistor-guide-ballast-blast-off/#:~:text=In simple terms, the ballast,breaker points of the distributor.
"In simple terms, the ballast resistor in a Mopar limits the amperage, or current flow, through the coil while the engine is running, thereby extending the life of the coil and breaker points of the distributor. When the ignition key is in the start position, full current is applied to the coil and increases voltage to the spark plugs".

 

[pnora]

Just google does a resistor decrease voltage and you will see answers. Its all in OHM'S law.

 

[Don Frelier]

A ballast resistor is not a fixed resistance as you might think.
It's actually a current limiting device which has higher resistance at lower engine speeds (it gets hot and adds resistance).
As the engine speeds up the resistor cools and allows more energy through the coil.
Yes it is still subject to I=V/R and since the coil has resistance as well and they are in series it becomes a voltage divider circuit where the excess energy in the resistor turns into heat.
Wasteful but it works.

 

[zsn0w]

https://www.motortrend.com/how-to/mopp-1110-ballast-resistor-guide-ballast-blast-off/#:~:text=In simple terms, the ballast,breaker points of the distributor.
"In simple terms, the ballast resistor in a Mopar limits the amperage, or current flow, through the coil while the engine is running, thereby extending the life of the coil and breaker points of the distributor. When the ignition key is in the start position, full current is applied to the coil and increases voltage to the spark plugs".

This is what I had always thought and what the wiring would make me think is happening. I've been reading about points ignitions, though (which I don't have any experience with), and found that the authors of the articles I was reading claimed that the ballast resistor also reduced the voltage.

A ballast resistor is not a fixed resistance as you might think.
It's actually a current limiting device which has higher resistance at lower engine speeds (it gets hot and adds resistance).
As the engine speeds up the resistor cools and allows more energy through the coil.
Yes it is still subject to I=V/R and since the coil has resistance as well and they are in series it becomes a voltage divider circuit where the excess energy in the resistor turns into heat.
Wasteful but it works.

I was thinking it couldn't be a voltage divider on account of the single resistor, but I hadn't thought of the coil acting as a separate resistor in the circuit. That makes sense, thank you.

 

[Mopars & Missiles]

Basic Ohm's law here at play. Yes, a resistor limits current in a circuit. Yes, a resistor will drop voltage across a device when looking at the entire circuit. It is very difficult to teach electronics on an internet forum bit by bit, especially with many individuals short attention span and desire only for a quick all encompassing answer.

 

[RemCharger]

The other guys used a Not easily replaced "resistance wire" instead of a replaceable stand alone resistor.
Till the end of time , this has made the mopar a seemingly strange vehicle to the brand x masses.

 

[dadsbee]

I always just look at a resistor as a restriction in a pipe, it reduces "flow".

 

[Geoff 2]

It is easy to understand using some simple proportion numbers. The Mopar coil ballast res is 0.5 ohm. Assume system voltage of 12v & coil pri res of 1.5 ohm; voltage drop across the res is 3 v & remaining 9v is across the coil. If ballast res resistance increases with heat, coil voltage will drop.

 

[RJRENTON]

Basic Ohm's law here at play. Yes, a resistor limits current in a circuit. Yes, a resistor will drop voltage across a device when looking at the entire circuit. It is very difficult to teach electronics on an internet forum bit by bit, especially with many individuals short attention span and desire only for a quick all encompassing answer.

ABSOLUTELY CORRECT....OHM'S LAW definitely applies.....but so does Kirchoffs Law of circuit analysis applies....but....to NOT cloud the subject......Ohm's Law is simpler and easier to understand....
BOB RENTON

 

[RemCharger]

ABSOLUTELY CORRECT....OHM'S LAW definitely applies.....but so does Kirchoffs Law of circuit analysis applies....but....to NOT cloud the subject......Ohm's Law is simpler and easier to understand....
BOB RENTON

Exactly.

 

[383man]

The other guys used a Not easily replaced "resistance wire" instead of a replaceable stand alone resistor.
Till the end of time , this has made the mopar a seemingly strange vehicle to the brand x masses.

Thats right as GM and Ford used a resistor wire in the wire harness in the primary coil wire. Also as far as I know the resistor wire they used on their points cars and Ford used it on some electronic ign also is not temp sensitive as the Mopar ballast is. In other words the resistor wire stays at the same ohms even at low or high eng speeds. Ron