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Posted by David Sherman [24.32.202.83] on Tuesday, September 15, 2009 at 17:19:05 :
In Reply to: Re: Ballest Resister posted by Robert N [208.57.182.24] on Tuesday, September 15, 2009 at 16:56:30 :
Right. The ballast resistor is just there so you can bypass it while cranking, and the coil is designed to work on somewhat less voltage. The thing is, the coil primary has a resistance of around one ohm, and the ballast resistor is usually right in that range too, but the ignition circuit wiring can easily have almost that much resistance by itself (an ohm or so for a bunch of 16 gauge wire running from the fuse block to the ignition switch, to the coil, and through various connectors. In fact, I some cars just used a carefully-prescribed length of wire in the ignition circuit as the "ballast resistor", leading to much confusion when guys started monkeying with it.
The bottom line is that the ballast resistor isn't hugely more than the resistance in typical wiring, so the setup will generally work okay without it. But for optimum performance and coil life, it's best to use heavy enough wire and good enough connections that the ballast resistor can be "in control" of the resistance in the circuit, and wire it up so the resistor gets bypassed during cranking. Also, ballast resistors get hot, so don't mount it on anything plastic or let any wires or hoses lay across it. I've seen them tie-wrapped to the side of the spark coil, but that's asking for trouble. Not only does that heat up the coil, which is exactly what the ballast resistor is supposed to prevent, but if it gets hot enough to melt the tie-wraps, who knows where it's going to fall down to and short out against.
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