Re: 12V Conversion coil question for John T or oth

Posted by Bus Driver on April 01, 2007 at 05:59:34 from (66.226.63.228):

In Reply to: 12V Conversion coil question for John T or others posted by Ron in Nebr on March 31, 2007 at 19:45:41:

Just in case anyone is not absolutely clear about the resistors/diodes/lamps used in alternator conversions, one resistor in the supply conductor to the coil is used if the coil is for 6 volt or if the coil requires an external resistor. A diode or lamp will not substitute in this instance. The resistor limits the current primarily to prolong the life of the ignition points. The other device, I personally prefer and use only resistors, is used between the power source and the exciter terminal on the alternator. The most logical power source is the ignition switch since the alternator needs to be excited only when the engine is running. Once charging, the alternator sends/can send power back through that exciter conductor. That would keep the ignition "on"- power to the coil- until the engine stopped for lack of fuel. The resistor/lamp/diode either stops this power feedback or limits it to an amperage value less than that required to power the ignition. Thus moving the ignition switch to "off" really does stop the engine. IH used a 25 ohm resistor for this purpose on the early alternator equipped tractors. I use a 5 watt, 44 ohm wirewound resistor with a shop-made mount and also use epoxy to prevent the resistor from wiggling in the mount. It is mounted to the back of the alternator. Never a failure. The lamp used on many vehicles will have about 55 ohms resistance. Diodes limit current flow to one direction only. Only one of these devices is needed in any particular exciter circuit.

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