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Small Japanese Alternator Auxiliary Pin Functions

Small Japanese Alternator Auxiliary Pin Functions

Small Japanese Alternator Auxiliary Pin Functions

I work on a lot of small equipment that has similar belt drive alternators from Mitsubishi, Denso, and Hitachi.

From time to time they fail and I need to retrofit one for another or deal with start disconnect circuitry and other things that require me to understand the circuit more than just hooking the wires back where they say they go.

Generally speaking there is always a lamp terminal, which I understand, as they have been there more or less since 1960.

The others not so much. There is often an I wire which I presume is switched ignition, but what would its purpose be besides what the lamp wire already provides, especially since this terminal is often not connected?

Sometimes there is an S wire but all units I work on pretty much never use it, I presume because they are sensing on the output wire.

There is sometimes another letter designation which escapes me right now but I have not seen one with more than 3 auxiliary terminals.

And are there any OE manuals or discussion that describe the function of these terminals in more detail? Internet searches have turned up very little.

RE: Small Japanese Alternator Auxiliary Pin Functions

Been digging some more and found these schematics:


Both of them have some inconsistencies but I think I am understanding the general idea.

L stands for lamp and is power fed in to wake up the excitation via a ~50Ω external resistance (lamp).

IG is ignition and is direct switched 12V power from the ignition switch. Also called R for some reason I don't understand, maybe a different language. It goes through an internal 50Ω resistance provided inside the alternator instead of a lamp.

(IG/R will continue to power the fuel solenoid if hooked up in parallel w/o a diode and cause unintended run-on, ask me how I know this)

I guess no external reference is really possible with this style alternator because external voltage feed from IG/R is isolated from the voltage regulator section by either the lamp or the 50Ω resistor. Therefore the auxiliary "diode trio" as we used to call it, marked "sub diode" on one drawing, is always the highest reference point for this style alternator.

And the last terminal, P is simply an unrectified AC stator tap. For a tachometer or whatever.

RE: Small Japanese Alternator Auxiliary Pin Functions

"R" Internal Resistor??

"Why not the best?"
Jimmy Carter

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