Re: Alternator again

Posted by Bus Driver on March 11, 2006 at 16:38:18 from (66.44.255.183):

In Reply to: Alternator again posted by Andrew Z on March 11, 2006 at 08:45:10:

The purpose of the terminal to which the light/diode/resistor is connected is primarily to supply a current to the alternator to get it to start charging- an exciter current. Once charging starts, additional exciting is not required as long as the engine runs at a reasonable speed. Exciting the alternator with the engine not running will discharge the battery. While charging, that exciter terminal on the alternator feeds current back through the wire connected to it. If that wire originates at the ignition switch, the back feed will continue to feed the distributor, if the tractor has one, and the engine will not stop normally when the switch is turned off. The light or resistor, if used, limits the back current to an amount less than that required by the ignition, thus the engine stops when the switch is turned off. The diode permits current flow in only one direction-to the alternator. My thought is that the light is the most fragile of these devices and the resistor is the most durable. IH used the resistor when they first put alternators on their tractors in the 1970's. It was a 25 ohm wirewound. I use a 5 watt wirewound 44 ohm unit on my conversions. The typical lamp used is about 54 ohms, so the ohm value is not critical. I selected the 44 ohm resistor as a popular size between 25 and 54. Works fine.

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