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Re: what is the purpose of a ballast resistor?
[Re: copper74]
#443004
08/19/09 03:42 PM
08/19/09 03:42 PM
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Joined: Dec 2007
Posts: 7,759
So Cal
HealthServices
Why would you even post that?
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Why would you even post that?
Joined: Dec 2007
Posts: 7,759
So Cal
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for coils not designed to take battery voltage.
Allen
Here's a novel idea, let's not throw a bunch of parts at the car hoping it will fix the problem and instead spend a little time diagnosing it first.
Life was a little easier when I was just a wrench.
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Re: what is the purpose of a ballast resistor?
[Re: 71sat440]
#443008
08/19/09 04:00 PM
08/19/09 04:00 PM
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Joined: Nov 2007
Posts: 5,336
the house on the left.
cogen80
master
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master
Joined: Nov 2007
Posts: 5,336
the house on the left.
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Quote:
To constantly fail thus requiring you to keep a spare in your glove box.......at least thats what I have always been told 
lol. isn't that the truth
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Re: what is the purpose of a ballast resistor?
[Re: cogen80]
#443010
08/19/09 04:15 PM
08/19/09 04:15 PM
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Joined: Nov 2006
Posts: 653
Pennsylvania
WingedSixBBL
mopar
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mopar
Joined: Nov 2006
Posts: 653
Pennsylvania
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Quote:
Quote:
To constantly fail thus requiring you to keep a spare in your glove box.......at least thats what I have always been told
lol. isn't that the truth
Only 1 spare? I keep 3 in each car. Ever put one on in a rainstorm, along the side of the road, only to find out the "new" one was a P.O.S.? 
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Re: what is the purpose of a ballast resistor?
[Re: cudaboy]
#443014
08/19/09 05:10 PM
08/19/09 05:10 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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And now, for the CORRECT answer. Ballasts change resistance with current as they heat and cool, and thus provide a sort of buffer for the coil. Coil current will be different at higher and lower RPM.
But the REAL nitty gritty reason is "easier starting."
A normal system runs close to 14V, and Mopar coils used to run anywhere from 8-10V AT THE COIL at the bottom end of the ballast.
When you crank the engine for start, the switch bypasses the resistor, so the coil STILL GETS about 10V--so a nice hot spark for starting.
This is something the ol' 6V cars never had.
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Re: what is the purpose of a ballast resistor?
#443015
08/20/09 01:46 AM
08/20/09 01:46 AM
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Joined: Jan 2003
Posts: 27,421
Balt. Md
383man
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,421
Balt. Md
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Quote:
And now, for the CORRECT answer. Ballasts change resistance with current as they heat and cool, and thus provide a sort of buffer for the coil. Coil current will be different at higher and lower RPM.
But the REAL nitty gritty reason is "easier starting."
A normal system runs close to 14V, and Mopar coils used to run anywhere from 8-10V AT THE COIL at the bottom end of the ballast.
When you crank the engine for start, the switch bypasses the resistor, so the coil STILL GETS about 10V--so a nice hot spark for starting.
This is something the ol' 6V cars never had.
Thats the best answer. The ballast reduces the current flow thru the coil at low speeds and keeps the coil from overheating. As was said the coil can handle more amperage but not for long periods of time. So at idle and low eng speeds the points have more time to be closed and thus the current heats the ballast up and causes it to have more resistance and drop current flow at lower eng speeds when full coil output is not needed. When you go faster and speed the eng up the points have less time to be closed so the ballast cools down some and the resistance drops causes more current to flow thru the coil and letting the coil output higher when it is needed at higher eng speeds. And when cranking the ign system needs full output to help start the eng so the ign switch bypases the ballast and gives full battery volts to the coil while cranking. Ron
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Re: what is the purpose of a ballast resistor?
[Re: 383man]
#443016
08/20/09 01:53 AM
08/20/09 01:53 AM
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Joined: Jun 2004
Posts: 3,370
St. Charles, MO
wingman
Uncreative Title
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Uncreative Title
Joined: Jun 2004
Posts: 3,370
St. Charles, MO
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I thought it was there to burn the  out of your finger the first time you touch one...
1969 Dodge Coronet Super Bee 383 A4
1970 Plymouth Road Runner 440 FC7 (sold)
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Re: what is the purpose of a ballast resistor?
[Re: Tesla_HV]
#443017
08/20/09 01:58 AM
08/20/09 01:58 AM
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Joined: Feb 2003
Posts: 21,318
Manitoba, Canada
DaytonaTurbo
Too Many Posts
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Too Many Posts
Joined: Feb 2003
Posts: 21,318
Manitoba, Canada
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Quote:
The ballast resistor also drops some of the voltage but voltage reduction is not its primary function.
 Aftermarket ignitions like the multi-spark boxes of the ready2run distributors have current-limiting circuitry in them so you don't need to run a ballast anymore.
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Re: what is the purpose of a ballast resistor?
[Re: Tesla_HV]
#443019
08/20/09 08:36 AM
08/20/09 08:36 AM
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Joined: Mar 2003
Posts: 15,478
the boonies
aarcuda
I Live Here
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I Live Here
Joined: Mar 2003
Posts: 15,478
the boonies
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Quote:
Automotive coils are current-driven devices. In the days of points, if the ignition system were left powered up with the points in the closed position (the key left on with the engine not running), the coil would effectively short out the battery and the coil would overheat. The ballast is a series resistor which limits the current in the coil. The ballast resistor also drops some of the voltage but voltage reduction is not its primary function.
I agree with this.
i dont agree with the post that says a ballast resistor is supposed to change resistance with temperature. yes, resistors DO change resistance as the temperature changes but I dont believe thats what makes a ballast resistor a ballast resistor. and i dont believe this is a something the system needs or is desirable- its a physical propert y of the resistor and I bet, if they could make a more stable resistor as a reasonable cost, they would but since slight changes in resistance due to temperature changes isnt critical, they dont worry about it
afaik, a ballast resistor is just a big resistor that can handle more power than your typical 1/4 or 1/8 watt resistor. Ballast resistors need to be big and bulky to dissipate heat because the current draw through the coil generates lots of heat. as the resistor will limit the current to keep the coil from melting, the ballast resistor heats up and needs to be big and stout so IT wont melt as well.
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