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Ballast resister
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Author:  crickhollow [ Fri Mar 26, 2010 5:14 am ]
Post subject:  Ballast resister
A few Q's.

What is the purpose of the ballast resister (on my 61 Plymouth Valiant)?

I recently fitted a Pertronix electronic ignition unit and connected the red wire to the + coil contact and the black wire to the - coil contact. The car runs very well, but I was told I should have connected the red wire to the ignition side of the ballast resister so as to get 12 volts, not about 8 volts at the + coil contact.

If I move the red wire to the ignition side of the ballast resister will I get a better performing electronic ignition unit?

What will happen if I leave the red wire connected to the + coil contact?

Thanks
Author:  KBB_of_TMC [ Fri Mar 26, 2010 9:34 am ]
Post subject: 
The ballast resistor is intended to limit the current running through the coil primary; the 60's models were designed to get hot and increase resistance - roughly R[ohms]=0.5+0.0633*i[A], where the current is time averaged. This let you get extra spark energy when cranking by bypassing the resistor, limited the current at low RPM to prevent burning the points and overheating the coil, and then cooled off at high RPM to increase the spark energy over what it would have been with a fixed resistor. A slick idea, but a red-hot filament is somewhat fragile.

The time to get energy into the coil goes as R*L, where R is the total resistance of coil+ballast and L the inductance of the coil. The total energy stored in the coil E=0.5*L*I^2. Bigger L, the more energy in the coil, but the longer it takes to get it in there.
The NACA-TR-374 report of 1932 (http://ntrs.nasa.gov/archive/nasa/casi. ... 091446.pdf) gives lots of detail.

I would follow Pertronix instructions. I think the newer Pertronix (maybe all?) have an automatic dwell control to limit current & heat in the coil, so you may not need it, but if it was designed to work with a ballast and there isn't one there, it could eventually overheat and fail.
Author:  emsvitil [ Fri Mar 26, 2010 12:57 pm ]
Post subject: 
Pertronix I, doesn't have the dwell control; but can be used with a 3 ohm coil. With the 3 ohm coil you just bypass or get rid of the ballast resister.

I haven't had any starting problems with this setup.

Otherwise you use the 1.5 ohm coil with a ballast.


The Pertronix II has the dwell control, and can adapt to coils resistance. (like an HEI does)
Author:  crickhollow [ Fri Mar 26, 2010 2:44 pm ]
Post subject:  Ballast resister
To clarify your response - are you saying if I use a 3 ohm coil I can connect the red wire of my Pertronix 1 to the + coil contact, and therefore bypassing the balllast resister. If so, do I leave the ballast resister in place?

Are there other benefits / disadvantages in using a 3 ohm coil on my slant 6?

Thanks.
Author:  emsvitil [ Fri Mar 26, 2010 7:46 pm ]
Post subject:  Re: Ballast resister
Quote:
To clarify your response - are you saying if I use a 3 ohm coil I can connect the red wire of my Pertronix 1 to the + coil contact, and therefore bypassing the balllast resister.
yes

Quote:
If so, do I leave the ballast resister in place?
You can do whatever you want with it. Mines in place, but it's no longer a ballast resistor..... I connected the 2 terminals together with a normal wire.
Quote:
Are there other benefits / disadvantages in using a 3 ohm coil on my slant 6?

Thanks.
No ballast resistor to worry about going bad.
Author:  Aggressive Ted [ Wed Mar 31, 2010 3:38 pm ]
Post subject: 
and more voltage to the coil resulting in a hotter spark.
Author:  valiant1966 [ Wed Apr 07, 2010 2:35 pm ]
Post subject: 
Quote:
What will happen if I leave the red wire connected to the + coil contact?
No one ever answered this question and inquiring minds need to know.

I have the same situation but I bought the unit used and have no instructions at all. I have the 1.5 stock coil at present.

If I hook up to the ballast resistor, do you hook it up in tandem with the wires that are already there.

Thanks
Author:  Aggressive Ted [ Wed Apr 07, 2010 3:18 pm ]
Post subject: 
Go out to the Pertronix website and down load the instructions.
No ballast resistor required with any of the Pertronix ignition systems.
Or with MOPAR ECU's running 3 ohm coils.........
Author:  crickhollow [ Wed Apr 07, 2010 4:35 pm ]
Post subject: 
I understand if you still use the standard spec coil that originally came with the Valiant you should connect the red cable from Pertonix 1 to the ignition side of the ballast resister or another 12 volt ignition source. The black cable from Pertonix 1 is connected to the negative terminal of the coil.

Peter.
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