Follow-Ups to Answer from Expert John Campbell

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Graham wrote at 2009-11-13 15:10:08
I know its about 3 years too late to help the original poster but anyway...



The tractor alternator is a single phase permanent magnet alternator. There is no field winding.



The two yellow wires are the ends of the single AC winding.



The rectifier/regulator gets its earth reference from its own mounting. There is no field winding to control, and the rectifier/regulator does indeed work by diverting excess current flow.



This arrangement (but with a star wound 3 phase alternator) is very common on Japanese motorcycles. In the case of a bike there would be 3 wires from the alternator into the rectifier/regulator, a wire out to the battery, earth via the mounting, and usually, but not always, a wire to positive via the ignition switch.



Many 1980s Suzuki models had a rectifier/regulator with no wire to the ignition switch; they were notorious for failing. Hondas and Yamahas of the same era did have a wire to the ignition switch, and they could be used to replace the fragile Suzuki rectifier/regulator provided you connected the extra wire.



You can replace a single phase rectifier/regulator as described in this tractor with a motorcycle 3 phase rectifier/regulator. Simply connect the two wires from the alternator to any 2 of the 3 inputs to the unit.



I have used a mid 1980s Honda CB250 unit to convert a 6 Volt bike with a single phase (2 wire) alternator to 12 Volts. The tractor installation would be electrically identical.



Obviously avoid old Suzuki rectifier/regulators!

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