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How many ohms resistance in a 3-position light switch ???

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Alberta Mike

02-22-2003 16:11:31




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In the old-style 3-position light switch that many tractors had (40's and early 50's), there is a small resistor (wound around a mica plate) wired into the "full-in position" that controls generator output for a 3rd brush generator system. I'm trying to measure how many ohms of resistance the original resistor had. So far (with the pieces of wire that are left here that I have) I measure about 3 ohms. Is that close to what the original switches had?

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Keith

02-27-2003 18:09:47




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 Re: How many ohms resistance in a 3-position light switch ??? in reply to Alberta Mike, 02-22-2003 16:11:31  
I was interested in the same thing and here's my thoughts on it. The resistor limits the amount of ground applied to the field terminal on the generator to reduce the output of the generator. If you ground the generator field terminal it will produce the maximum charge based on the position of the 3rd brush (which is what happens when the switch is in is lights on or high charge position). You can then move the 3rd brush to adjust generator output to the maximum spec. For the oliver 70 I'm working on the specs for max output are 14-16 amps. The low charge spec (meaning with the resistor in place) is 4-6 amps. I haven't done it yet, but I was planning to experiment with some resistors of various values or find a low resistance potentiometer and adjust it until I got the desired low spec output from the generator with the tractor running and the resistor on the field. Based on the resistance values I've gotten from the resistors in one of the voltage regulators I've got here I was going to start with about a 10 ohm resistor and then go either higher or lower depending on whether I needed to produce less or more output respectively.

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