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Resistance of Ballast Resistor on old Points ignition
On Thu, 28 Mar 2019 09:33:40 +0800, Rheilly Phoull
wrote: On 28/03/2019 8:23 am, Rheilly Phoull wrote: On 28/03/2019 6:20 am, wrote: Does anyone know the correct resistance of the ballast Resistor on old Points ignition? I have an old Farmall M tractor. That resistor (which is a large ceramic power resistor), only measures 3 or 4 ohms I was expecting it to be at least 100 ohms, if not 500 or 1k. I measured this with nothing connected to it, using an analog multimeter. This resistor is between ignition switch and the ignition coil and points. It drops the 12volts to about 6 volts. Some information I got about this tractor says the voltage should be about 8 volts after the resistor. I dont know how much tolerance is allowed, but I'd rather see a higher spark plug voltage than a lower one. The tractor now runs, after it failed due to what appears to have been a bad condensor (capacitor). But it runs rough after replacing the points, condensor, plugs, dist cap and rotor. The spark on a test sparkplug seems kind of weak to me..... Kind of makes me wonder if this resistor needs replacement? (The sparkplug wires were replaced about 2 years ago, so they should be fine, since I dont use the tractor all that much). Presumably you know ohms law, just calculate the value to give the 8 volts after starting. I also assume you know that the ballast resistor is used to apply a higher voltage to the coil by bridging it on start then opening the bridge when running. This one is NOT wired that way. The resistor is in line with the coil all the time. The tractor is a Farmall Super M. I just replaced all the low voltage wires because the old ones were cracking (dry insulation). Anyhow, it goes from battery to a simple two terminal ignition switch (push pull type). On to the resistor and to the coil/points. Thats it... I just replaced everything in the ignition system except the switch. New low voltage wiring, the resistor, coil, points/condensor, plugs and plug wires. The stock coil that I bought says "For 6 or 12 volt systems". "Resistor must be used on 12 volt systems". These tractors were originally 6 volt. Most are converted to 12 (including mine) these days. I assume these stock coils are 6v but work on 12v with the ballast resistor. Without it, I would think the coil would be damaged. But I like the idea of full voltage at starting. So I may try it. I'd just need to run another wire from the push type starter switch to the coil. I may give that a try. (the starter switch is a separate switch from the ign switch. It's a push buttom spring loaded contacter). I also have to add a light to the "dash" to remind me the ignition switch is on. I know that I am supposed to turn off the ignition when the tractor is off, but if I run out of gas, by the time I get more gas, the battery is drained because I never remember to shut off that darn switch. And I imagine that is hard on the coil and points. Possibly why the old coil was weak and the old resistor was not allowing enough voltage to the coil. After changing all these ign parts, it really runs better, but now I have to rebuild the carburetor. That thing tends to get flakey every so often. But the tractor is over 60 years old, so it was due for all new ignition parts, and a carb rebuild. Plus new fan belts are in order next. They look bad.... |
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