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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: 5,337
the house on the left.
cogen80
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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
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Anonymous
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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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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: 3,372
St. Charles, MO
wingman
Uncreative Title
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Uncreative Title
Joined: Jun 2004
Posts: 3,372
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
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Too Many Posts
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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
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Posts: 15,478
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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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Re: what is the purpose of a ballast resistor?
[Re: copper74]
#443022
08/20/09 11:02 AM
08/20/09 11:02 AM
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Joined: Aug 2007
Posts: 6,095
Valencia, España
NachoRT74
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master
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Quote:
what is the purpose of the ballast resistor? can they be jumped?
Save the coil from max voltage on normal drive, graduating the voltage level as far the enviroment is getting hot at engine bay. With hotter enviroment, gas needs less spark power to ignition.
On Start up moment, resistor is bypassed from ign switch, feeding directly the coil at brown wire spliced at resistor, to max voltage, being engine/gas is theorically cold and harder to burn out.
ballast has NOTHING TO DO with distributors &/or modules, JUST with coils.
Double ballast have the secondary voltage to ECU, I guess to JUST graduate the dwell or something like that on spark control system, but I don't think to really FEED it. There is ppl who has been able to run 5 pins modules with single ballast, what does not mean was working good or perfect. 4 pins modules have the secondary resistor built in.
On multi spark systems, the multi sparks setup makes not to get full power constantly during teh spark moment, so every milisecond between sparks gets the time to get cold at least enough to not burn out the coil. At the ends works like a time dimmer, or a voltage relay regulator ( mechanical regulator ) but NOTE: not with the same object, That it was to give you an idea.
With a Charger born in Chrysler assembly plant in Valencia, Venezuela
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Re: what is the purpose of a ballast resistor?
[Re: Stanton]
#443023
08/20/09 11:16 AM
08/20/09 11:16 AM
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Joined: Jul 2003
Posts: 2,344
Cincinnati, OH
6T6Cuda
top fuel
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top fuel
Joined: Jul 2003
Posts: 2,344
Cincinnati, OH
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Quote:
Well just out of curiosity, what did GM and Ford use so as not to burn out coils ????
I know GM does, they have a "resistance" wire that was part of the wiring harness..
Think changing a ballast resistor is hard in a mopar, try it in a GM
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Re: what is the purpose of a ballast resistor?
[Re: aarcuda]
#443025
08/20/09 12:08 PM
08/20/09 12:08 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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Quote:
i dont agree with the post that says a ballast resistor is supposed to change resistance with temperature. .
You might not agree but you would be wrong. The fact that a BALLAST changes resistance is the entire reason it's called a ballast. Otherwise it would simply be a resistor. MOST resistors used in electronics are intended NOT to change resistance, even though they do somewhat, but they are NOT "BALLAST" resistors.
In the case of Chrysler, this is exactly what they are. Somewhere in the pile of old books around here, I've got documentation to back this up. I am NOT gonna spend time looking for it
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Re: what is the purpose of a ballast resistor?
#443027
08/20/09 12:34 PM
08/20/09 12:34 PM
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Joined: Mar 2003
Posts: 15,478
the boonies
aarcuda
I Live Here
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I Live Here
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the boonies
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Quote:
Quote:
i dont agree with the post that says a ballast resistor is supposed to change resistance with temperature. .
You might not agree but you would be wrong. The fact that a BALLAST changes resistance is the entire reason it's called a ballast. Otherwise it would simply be a resistor. MOST resistors used in electronics are intended NOT to change resistance, even though they do somewhat, but they are NOT "BALLAST" resistors.
In the case of Chrysler, this is exactly what they are. Somewhere in the pile of old books around here, I've got documentation to back this up. I am NOT gonna spend time looking for it
okay. youre right. i retract my previous comment. I have just never heard that about a ballast resistor before you said it and my thinking was that a ballast resistor was simply a resistor.
i googled it and yes. youre right. a ballast resistor changes resistance based on the current flowing through it.
thanks for teaching me something i never knew
Quote:
Home > Library > Science > Sci-Tech Encyclopedia
A resistor that has the property of increasing in resistance as current flowing through it increases, and decreasing in resistance as current decreases. Therefore the ballast resistor tends to maintain a constant current flowing through it, despite variations in applied voltage or changes in the rest of the circuit. See also Resistor.
The ballast action is obtained by using resistive material that increases in resistance as temperature increases. Any increase in current then causes an increase in temperature, which results in an increase in resistance and reduces the current. Ballast resistors may be wire-wound resistors. Other types, also called ballast tubes, are usually mounted in an evacuated envelope to reduce heat radiation.
Ballast resistors have been used to compensate for variations in line voltage, as in some automotive ignition systems, or to compensate for negative volt-ampere characteristics of other devices, such as fluorescent lamps and other vapor lamps. See also Fluorescent lamp; Vapor lamp; Voltage regulator.
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Re: what is the purpose of a ballast resistor?
[Re: Evil Spirit]
#443028
08/20/09 12:41 PM
08/20/09 12:41 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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Quote:
Quote:
Quote:
i dont agree with the post that says a ballast resistor is supposed to change resistance with temperature. .
You might not agree but you would be wrong. The fact that a BALLAST changes resistance is the entire reason it's called a ballast. Otherwise it would simply be a resistor. MOST resistors used in electronics are intended NOT to change resistance, even though they do somewhat, but they are NOT "BALLAST" resistors.
In the case of Chrysler, this is exactly what they are. Somewhere in the pile of old books around here, I've got documentation to back this up. I am NOT gonna spend time looking for it
According to Wikipedia, a ballast resistor can be fixed or variable . The Mopar variety are probably variable to adjust for the different secondary current needed to fire the plugs under different loads.
http://en.wikipedia.org/wiki/Electrical_ballast
You misunderstood what they meant, there. A fixed resistor is a resistor that cannot be physically changed BY YOU. A variable resistor is like a volume control on your radio--has a knob on it or other manner to adjust the device.
A quote from the site:
"Ballasts are used where an electrical load cannot effectively regulate its current use. These are most often used when an electrical circuit or device presents a negative (differential) resistance to the supply. If such a device were connected to a constant-voltage power supply, it would draw an increasing amount of current until it was destroyed or caused the power supply to fail. To prevent this, a ballast provides a positive resistance or reactance that limits the ultimate current to an appropriate level. In this way, the ballast provides for the proper operation of the negative-resistance device by appearing to be a legitimate, stable resistance in the circuit."
What they mean by "positive resistance" is referring to temperature---As the coil / points circuit effective resistance goes down, because of changes in RPM, the coil tries to draw more, but as more current goes through the ballast it tends to heat up, and because it is a ballast instead of a "regular resistor" it has a POSITIVE temperature coefficient. That means that as it heats up it INCREASES in resistance, which now causes current through the circuit to try and drop.
All resistors have a temp coefficient, but ballasts specifically are designed to have a VERY LARGE one so that they DO change on purpous
"Ballast" sorta means "something to make something else stable" whether it's weight in the bottom of a sailboat or electrical.
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Re: what is the purpose of a ballast resistor?
#443030
08/20/09 01:02 PM
08/20/09 01:02 PM
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Joined: Jan 2005
Posts: 3,699
Newport, Mi
Evil Spirit
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Newport, Mi
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From the same Wiki article. Self Variable Resistors Some ballast resistors have the property of increasing in resistance as current through them increases, and decreasing in resistance as current decreases. Physically, some such devices are often built quite like incandescent lamps. Like the tungsten filament of an ordinary incandescent lamp, if current increases, the ballast resistor gets hotter, its resistance goes up, and its voltage drop increases. If current decreases, the ballast resistor gets colder, its resistance drops, and the voltage drop decreases. Therefore the ballast resistor reduces variations in current, despite variations in applied voltage or changes in the rest of an electric circuit. These devices are sometimes termed barretters. I only stated that there were fixed and variable ballast resistors, and I speculated which were used in autos. Even if the ones in cars are fixed, there are still (self) variable ballast resistors, which regulate current themselves without turning a knob. 
Free advice and worth every penny...
Factory trained Slinky rewinder.........
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Re: what is the purpose of a ballast resistor?
[Re: Evil Spirit]
#443033
08/20/09 01:16 PM
08/20/09 01:16 PM
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Joined: Dec 2003
Posts: 531
USA
540DUSTER
mopar
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mopar
Joined: Dec 2003
Posts: 531
USA
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evilspirit,I hear ya,that was always good for a laugh!
Last edited by 540DUSTER; 08/20/09 01:17 PM.
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Re: what is the purpose of a ballast resistor?
[Re: NachoRT74]
#443034
08/20/09 01:23 PM
08/20/09 01:23 PM
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Joined: Aug 2007
Posts: 6,095
Valencia, España
NachoRT74
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Quote:
Quote:
what is the purpose of the ballast resistor? can they be jumped?
Save the coil from max voltage on normal drive, graduating the voltage level as far the enviroment is getting hot at engine bay. With hotter enviroment, gas needs less spark power to ignition.
On Start up moment, resistor is bypassed from ign switch, feeding directly the coil at brown wire spliced at resistor, to max voltage, being engine/gas is theorically cold and harder to burn out.
ballast has NOTHING TO DO with distributors &/or modules, JUST with coils.
Double ballast have the secondary voltage to ECU, I guess to JUST graduate the dwell or something like that on spark control system, but I don't think to really FEED it. There is ppl who has been able to run 5 pins modules with single ballast, what does not mean was working good or perfect. 4 pins modules have the secondary resistor built in.
On multi spark systems, the multi sparks setup makes not to get full power constantly during teh spark moment, so every milisecond between sparks gets the time to get cold at least enough to not burn out the coil. At the ends works like a time dimmer, or a voltage relay regulator ( mechanical regulator ) but NOTE: not with the same object, That it was to give you an idea.
quoting myself to keep clear that.....
----> once again, ballast resistor doesn't have to make anything with dist NOT EVEN ON POINTS ( at least directly )... points is just a mechanical impulse on regular voltage, AMPLIFIED by the coil, exactly like reluctor and pick up coil makes but being magnetic impulse. Points doesn't drive the high spark voltage.
Of course the deal on the reluctor and pickup coil change is to save the physical contact that even with low voltages/amperages can burnt the points at some point ( also saves the distributor lobe friction and worn ), but BALLAST HAS NOTHING TO DO WITH.
With a Charger born in Chrysler assembly plant in Valencia, Venezuela
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Re: what is the purpose of a ballast resistor?
[Re: Evil Spirit]
#443036
08/20/09 03:00 PM
08/20/09 03:00 PM
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Joined: Jan 2003
Posts: 1,756
London, England
Gavin
top fuel
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top fuel
Joined: Jan 2003
Posts: 1,756
London, England
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OK, interesting info. If you had asked me I would have said that its purpose is to ensure the engine gets a good spark during crank.
When cranking you are relying on battery power alone and the starter is using a lot of current (taxing your battery). The engine is cold and turning at low rpm. You need a good spark, so a full 12V is applied to the coil. It's designed so that in normal usage (running, hot) it does not require that voltage, in fact it would wear it prematurely, but it does need some extra zip for starting. The solution - provide 12V during crank and a reduced voltage once running - this is the purpose of the ballast resistor.
I didn't know the other stuff about varying the resistance with heat (yes I know that can be a function of a resistor but didn't think about the automotive ballast). Makes sense, but I think the primary benefit is the 12V start/reduced V running, and suspect that any variation in the (reduced) running voltage is really just further refinement to save more wear and tear
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Re: what is the purpose of a ballast resistor?
[Re: Evil Spirit]
#443037
08/20/09 05:52 PM
08/20/09 05:52 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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Quote:
From the same Wiki article.
Self Variable Resistors
You will never find, in any electronics technical reference, theory textbook, nor will you ever hear an electrical engineer refer to something as a "self variable resistor."
What I'm trying to tell you is, there are fixed resistors, and there are ballast resistors.
Ballasts BY DESIGN are designed to change resistance on a far greater scale. That is WHY they are referred to as "ballasts."
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Re: what is the purpose of a ballast resistor?
[Re: Evil Spirit]
#443038
08/20/09 05:56 PM
08/20/09 05:56 PM
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Joined: Aug 2007
Posts: 6,095
Valencia, España
NachoRT74
master
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Joined: Aug 2007
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Quote:
On a points dist, all the power that goes to the coil passes through the points. Running constant 12v through the points usually burns the points up faster.
somehow true but also false... there is not anykind of points able to drive 15K volts from a coil, even less 45K volts. Neither 1K volts. Barelly can drive 12 Volts, and coil produces between 15K to 45K volts depending on performance.
Points makes a "small" volt level impulse AMPLIFIED by the coil and then routed back to distributor center cap center contact, rotor etc...
The voltage impulse is a SHORT ( by a ground contact ) made with the energy saved at condenser...
the - terminal at coil EFFECTIVELLY gets ground by the small short to create the amplified magnetic field variation going through and routed by the spark plug wires to the plug.
BUT EVEN IN THAT WAY still with electronic ( not points ), ballast is regulating the output at coil output to plugs at same ratio.
With a Charger born in Chrysler assembly plant in Valencia, Venezuela
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Re: what is the purpose of a ballast resistor?
[Re: NachoRT74]
#443039
08/20/09 06:33 PM
08/20/09 06:33 PM
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Joined: Mar 2003
Posts: 15,478
the boonies
aarcuda
I Live Here
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I Live Here
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the boonies
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Quote:
Quote:
On a points dist, all the power that goes to the coil passes through the points. Running constant 12v through the points usually burns the points up faster.
somehow true but also false... there is not anykind of points able to drive 15K volts from a coil, even less 45K volts. Neither 1K volts. Barelly can drive 12 Volts, and coil produces between 15K to 45K volts depending on performance.
Points makes a "small" volt level impulse AMPLIFIED by the coil and then routed back to distributor center cap center contact, rotor etc...
The voltage impulse is a SHORT ( by a ground contact ) made with the energy saved at condenser...
the - terminal at coil EFFECTIVELLY gets ground by the small short to create the amplified magnetic field variation going through and routed by the spark plug wires to the plug.
BUT EVEN IN THAT WAY still with electronic ( not points ), ballast is regulating the output at coil output to plugs at same ratio.
the points are on the 12v PRIMARY side of the coil. not the high output SECONDARY side. so technically, he's right. all the primary power passes thru the points
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Re: what is the purpose of a ballast resistor?
[Re: Stanton]
#443040
08/20/09 06:41 PM
08/20/09 06:41 PM
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Joined: Jan 2003
Posts: 27,421
Balt. Md
383man
Too Many Posts
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Too Many Posts
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Quote:
Well just out of curiosity, what did GM and Ford use so as not to burn out coils ????
Both GM and Ford used a resister wire in the primary circuit in the wire harness. Both also had resister wire bypasses during cranking as GM did it with the small R terminal in the starter mounted starter solenoid and Ford did it with the I terminal on their fenderwell mounted starter solenoid. Ron
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Re: what is the purpose of a ballast resistor?
[Re: aarcuda]
#443041
08/20/09 06:59 PM
08/20/09 06:59 PM
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Joined: Oct 2005
Posts: 4,941
WI
Dcuda69
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Quote:
Quote:
Quote:
On a points dist, all the power that goes to the coil passes through the points. Running constant 12v through the points usually burns the points up faster.
somehow true but also false... there is not anykind of points able to drive 15K volts from a coil, even less 45K volts. Neither 1K volts. Barelly can drive 12 Volts, and coil produces between 15K to 45K volts depending on performance.
Points makes a "small" volt level impulse AMPLIFIED by the coil and then routed back to distributor center cap center contact, rotor etc...
The voltage impulse is a SHORT ( by a ground contact ) made with the energy saved at condenser...
the - terminal at coil EFFECTIVELLY gets ground by the small short to create the amplified magnetic field variation going through and routed by the spark plug wires to the plug.
BUT EVEN IN THAT WAY still with electronic ( not points ), ballast is regulating the output at coil output to plugs at same ratio.
the points are on the 12v PRIMARY side of the coil. not the high output SECONDARY side. so technically, he's right. all the primary power passes thru the points
Ding, ding, ding!!!We have a winner!ALL current flow thru the PRIMARY side of the coil is also carried by the points(or transistor in an electronic ign) 12v thru a 1ohm coil=12 amps when the points are closed(pri. on)knock that down to 9v(after the ballast)=9 amps. By-pass the ballast in crank and you still have 9-10v/9-10 amps(starter is using the bulk of readily available power)  15k-45k volts is only created when the primary is turned OFF!!!
Last edited by Dcuda69; 08/20/09 07:01 PM.
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Re: what is the purpose of a ballast resistor?
[Re: Evil Spirit]
#2103997
07/04/16 11:44 PM
07/04/16 11:44 PM
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Joined: Jan 2003
Posts: 15,304
Omaha Ne
TJP
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On a points dist, all the power that goes to the coil passes through the points. Running constant 12v through the points usually burns the points up faster. <img src="/ubbthreads/images/graemlins/Twocents.gif" alt="" /> CORRECT!! the purpose of the ballast resistor, or resistance wire used by GM and Ford was to limit the current going to the coil thereby prolonging the life of the points in the "RUN" position / condition. By limiting the current it not only prolonged the points but limited the heat the coil would generate and prolonging it's life as well. There are different coils that are designed to be used with the "resistance" IE: dropped voltage/ Current, and those that are designed to run at full voltage. the full voltage coils typically are not used on a points system Running full Current / voltage through a set of points will shorten their life substantially. 
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As to the resistors function, like I posted before, I thought it was to protect both the points and coil. 
