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Ballast Resistor Help

Toddshonor

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Hi everyone,
I am looking to get a spare ballast resistor for our 69 GTX. The only thing written of the current one is R55. The car has electronic ignition conversion with the blue box. I have no idea what brand. The person who restored the car for us said that he can't remember what brand they used as they do not keep documentation for the cars. He told me it had a 5.5 ohm drop and could order it online. I can't seem to find one with that. Thank you for any help you can give me!
 
Ohms don’t “drop”. Voltage drops across a resistance provided by the ballast resistor to provide the coil what it need. (In the electronics world, this is called a “voltage divider” circuit) A ballast resistor should provide 6 bolts to the coil when the key switch returns to the run position.
If you have a 12v coil, you need to bypass the ballast resistor. If you have a 6v coil (stock or stock replacement) you need the resistor
 
Find out what the voltage requirement of the coil you are using is, and proceed from there.
If you need the resistor, order one for your year car online or at a decent parts store.
 
Find out what the voltage requirement of the coil you are using is, and proceed from there.
If you need the resistor, order one for your year car online or at a decent parts store.
IMO...
IF the electronic control unit (ECU) is an origional and the coil is the recommended unit, the ballast resistor would be either 0.5 ohms OR 0.7 ohms. Just be wary of the resistor with the solid back (DALE by brand name) as they tend to run VERY hot and their failure rate is high. Consider a NOS unit available thru @HALIFAXHOPS, a well known supplier on this site. I would suggest you consult with him, as he has very reasonable prices.
BOB RENTON
 
Yep, it matters on whether or not the OP has points or electronic ignition - and on what coil he's running.
I have an original Mopar electronic ignition conversion kit on mine plus a MSD Blaster II coil.
Both of those say they require difference impedance ballasts.
I have no idea what to run on the damn thing as a result.
 
Yep, it matters on whether or not the OP has points or electronic ignition - and on what coil he's running.
I have an original Mopar electronic ignition conversion kit on mine plus a MSD Blaster II coil.
Both of those say they require difference impedance ballasts.
I have no idea what to run on the damn thing as a result.

Ballast resistors function to limit the current flowing thru the coil's primary winding AND to limit the current the transistor on the ECU must switch. Resistance is measured on OHMS. The coil's primary winding is measured in ohms (resistance) AND impedance (or inductive reactance), which is a measure of the rate at which coil's primary winding accepts the current. Just thought you might like to know......
BOB RENTON
 
Ballast resistors function to limit the current flowing thru the coil's primary winding AND to limit the current the transistor on the ECU must switch. Resistance is measured on OHMS. The coil's primary winding is measured in ohms (resistance) AND impedance (or inductive reactance), which is a measure of the rate at which coil's primary winding accepts the current. Just thought you might like to know......
BOB RENTON
I know most of that Bob, thanks - but the question for me remains "how do I rectify the different requirements of both
these things in one, single ballast?"
 
I know most of that Bob, thanks - but the question for me remains "how do I rectify the different requirements of both
these things in one, single ballast?"

Short answer.....you don't. Do you know the resistance of the primary winding of the coil you are using now? If not, can you measure it? Measure between the two screw terminals...polarity is not important. By Ohm's Law, using the coil's resistance, and a 5 volt drop across the ballast resistor, compute the ballast resistor value. IF using a different coil, the ballast resistor MAY have to be changed (+/-) to keep the ECU's current at a nominal value. BUT the unknown quantity is the ECU'S current switching transistor's capability....unless you know its specs. Its better to error on the conservative side by increasing the value of the ballast resistor value. Just my opinion of course.
BOB RENTON
 
Its better to error on the conservative side by increasing the value of the ballast resistor value. Just my opinion of course.
BOB RENTON
Pretty much where I wound up, by choosing the higher of the two required resistance numbers.
I don't know if that's right or wrong, but it's worked so far.
 
Is the one you have no good? No resistance?
If it isn't "open" just measure it.
 
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Find out what the voltage requirement of the coil you are using is, and proceed from there.
If you need the resistor, order one for your year car online or at a decent parts store.
All I know is the coil says use external resistor so I "assume" it is 6v. I am sorry, I am new to this stuff. From what I have read, there are different resistors for electronic vs coil. I am sorry, but I am lost. The car didnt originally have electronic ignition, so I dont think I can just go to the local parts store and get one for the car
 
All I know is the coil says use external resistor so I "assume" it is 6v. I am sorry, I am new to this stuff. From what I have read, there are different resistors for electronic vs coil. I am sorry, but I am lost. The car didnt originally have electronic ignition, so I dont think I can just go to the local parts store and get one for the car

You cannot just assume, because the coil says to use sn external resistor, that the coil is 6 volts. Measure its resistance....to compute the inductive reactance, you will need to know frequency (average) that the coil will operate at....or RPM (average of idle speed thru max) as reactance is fixed but a function of frequency at which the coil is turned off and on.
The formula for calculating the inductive reactance of a coil is: inductive reactance, or XL, is the product of 2 times p (pi), or 6.28, the frequency of the ac current (or the pulsing DC current in this case), in hertz, and the inductance of the coil, in henries. XL =2p x f x L.
This information plus the coil's resistance will determine the current required and switched, and ultimately the ballast resistor value......or guess conservatively.
BOB RENTON
.
 
Again, this is only for the MSD Blaster and High-Vibration Blaster coils - but from their
instructions:
"If installing on a stock, points style ignition system, a 0.8 ohm ballast resistor or resistor wiring
MUST be installed. MSD offers this Ballast Resistor as PN 8214."
NO mention of any resistor required if used on electronic ignitions....in their own instructions.
So - again, just in my case - I reverted back to the chart @HALIFAXHOPS has that shows what
ballast to use with which Mopar ECU unit. It's all I got to go on, really.
 
Not all ECU's talke the same value, this might help. Check your FSM in chapter 8 also. Theses are factory not NORS colors.
ecu III.png
ECUApplication.jpg
ecuII.jpg
 
That's the chart, @HALIFAXHOPS , thanks again. :)
Funny how it calls for different value ballasts for the same control boxes, eh?

On a side note, am I seeing correctly that the newer Accel Super Coils are still oil filled and made in USA?
Y'all got me thinking I want one...
 
Set up for different RPM's I bellieve. Have been playing with them when I have time and it definatelly makes a difference to have them matched. Seems like 1 ohm is what most people use for the single ballast most of the time, no idea why.
Prob what the parts store gives you.
Most NORS ECU's are good to 5500 rpm from testing no mater what brand.
 
That's the chart, @HALIFAXHOPS , thanks again. :)
Funny how it calls for different value ballasts for the same control boxes, eh?

On a side note, am I seeing correctly that the newer Accel Super Coils are still oil filled and made in USA?
Y'all got me thinking I want one...

A curiosity question....WHY ???? do you want or feel you need a new or different coil, like the revered Accel Super Coil??? I don't believe it "makes more" horsepower....but if it does, it would seem that everyone would want one..... just asking.....
BOB RENTON
 
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They are a ok coil just make sure it is mounted verticaly.
 
A curiosity question....WHY ???? do you want or feel you need a new or different coil, like the revered Accel Super Coil??? I don't believe it "makes more" horsepower....but if it does, it would seem that everyone would want one..... just asking.....
BOB RENTON
He never said he wanted a new coil. He's just looking for a spare ballast resistor with the correct rating to match what he has.
Like I said earlier all he needs to do is measure the resistor in the car. Remove the wire from one side and put a good meter on it.
 
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