Hagen Brothers farms,Goodrich ND | Ed,I have rebuilt dozens of those old 10SI/12SI alternators in both 1 wire and 3 wire version,and yes,in many cases the standard 3 wire regulator will self excite like a true 1 wire regulator. Several times I have rebuilt a standard 3 wire alternator and hooked it to my home built test stand and found the alternator indicated normal voltage,but no amp output. It's about that time I realize that I have forgotten to connect the 12 V battery to the test stand,so the alternator has lit off with no exciter voltage from the battery,and indicates no amp output because there is no battery connected to load it.
The true 1 wire regulators are wired to sense system voltage internally through the diode trio, and do not use/need a "sense" wire connected from battery voltage to the #2 regulator terminal. With a true 1 wire regulator,nothing is connected to either the #1 exciter or #2 sense regulator terminal. The true 1 wire regulator has no electrical connection to the battery, as all battery voltage to the diode trio and then to the regulator is blocked by the 6 diode rectifier assy, and no excite or sense wire is installed,so it can not cause a slow battery discharge.
I buy the regulators,both 1 wire and 3 wire by the box of 20 for a cost of under $10 each,so I use which ever fits the alternator application. There is some difference between 1 wire regulator brands as to the sensitivity which determines the rpm needed to excite the thing. The amp rating of the stator winding,which is the part that makes an alternator a 37 amp,in steps on up to a 72 amp unit,has everything to do with the rpm needed to excite the 1 wire regulator from residual magnetism in the rotor core. The unit with a 37 amp stator will excite at usually half or less the rpm needed to excite the exact same everything else with a 72 amp stator installed. This can be important in an application where the rpm available to turn the alternator is limited and the electrical needs are not much more than ignition and lights on an older cabless tractor with a slow turning engine.
I know you have commented about the regulator voltage setting of many charging systems being too high and overcharging the battery,You might be interested in an option that was available on the Delco 27SI alternator that fits in a 10SI/12SI with slight modification.
The 27SI had a factory 1 wire option with an external device that allowed you to set the charging voltage in 4 steps from a low of 13.5 up to I believe 14.5 volts by simply inserting a little plug on the alternator in one of 4 positions. The setup consists of the internal regulator that has an extra threaded stud that must be connected by a jumper wire to battery voltage (internal end of the BAT stud).The adjustable part is a black plastic adapter that fits in place of the regulator plug with internal resistors that can be connected in different combinations to the regulator by installing the red square cap in 1 of 4 positions to set the voltage. Neat eh? the downside is that the regulator/adapter/plug costs $50-$70,so they are a spendy little devil. ( pic below shows regulator,note extra screw stud/black plug adapter/red adjustment cap.
Edited by Jon Hagen 8/20/2006 13:06
 (Adjustible 1 wire Delco.JPG)
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 Adjustible 1 wire Delco.JPG (24KB - 233 downloads)
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706IH no charging
