Page 1 of 1

Alternator: which is the field terminal?

PostPosted: Tue Apr 27, 2010 7:18 pm
by rwsrws12
I am trying to use my spare AmplePower 4023-S alternator fed by a SAR12-V2 smart regulator and supported by an EMONII.
Question: Which of the two adjacent alternator spade lugs takes the field wire from the regulator? Neither are marked F or R as indicated on the print.

Looking at the print shows that it's the one closest to the alternator's negative post, but the resistance to ground on that terminal is only three ohms. Since the Field wire from regulator TB2-10 is at 12+ volts even with the engine not running (no ignition switch, everything is hard wired), that means I'll be drawing about 4 amps just sitting there at the dock.

The other, heavier gauge spade terminal (tachometer output?) aparently has a diode behind it, as it's resistance to ground is "open" to positive voltages, and about 14 ohms to negative voltage (relative to chassis ground). This would seem to mean that connecting a positive-voltage field power wire to it will not work.

I'm loathe to just plug it in and try either of them. Anybody know the answer? thanks.
(When I unplugged the old one, I didn't know there were two choices and hence didn't looks to see which is which. ...can't tell by looking at the old spade for wear marks).

Re: Alternator: which is the field terminal?

PostPosted: Wed Apr 28, 2010 12:13 pm
by Coulomb
The one that shows 3 ohms is the field terminal.

It doesn't draw current until the regulator is activated by an ignition switch or oil pressure switch.