Conventional VR internal workings consist of at least two, if not three components that do the controlling. The first is a cutout relay. It is a normally open magnetically closed switch. It has two windings around the metal core of the unit. A pull in winding, and a hold in winding. This Cutout relay disconnects the generator from the battery by opening a heavy set of contacts. It is always open when the generator is not spinning. It will close when the newly spinning generator makes enough voltage on its own from residual magnetism in the field pole steel, to generate enough voltage to pull in the contacts. (Pull in winding). The hold in winding is heavy wire made to handle full gen output and more. It is of few turns, and holds the contacts closed firmly when the gen is putting out charging voltage. The cutout will disconnect the generator if the generator output (at idle for instance) drops below the charging voltage of the battery (less than bat volts). It does this so that battery current is not sent into the gen armature and then to ground. The battery would discharge rapidly in this case through the gen windings because it would be higher voltage than the gen. Electrons running the wrong way. The Cutout is also set to open when the tractor is shut off (again so the generator is disconnected and not sucking battery voltage to ground. This is super important, because the battery will drain in just an hour or so, and the generator will overheat and smoke will come out of the openings. Because it is not rotating and being cooled by the rotation and position in the airstream of the tractor fan. If you idle it down the amp gauge will show less and less charge. until it is discharging. at about 3 to 4 amps discharge, the Cutout relay will open and the discharge will be limited to the ignition draw, (adding any lights if they are on). The cutout is not connected to anything but the Gen terminal, and the Bat terminal, except that the pull in winding is grounded to the VR frame so it has a place to sent pull in voltage.
The Voltage regulating relay system is either one or two additional coils and contact systems. It is a voltage chopper. It is a vibrating set of contacts that have charging voltage (from the Armature terminal) running through its fine wire coil. This voltage goes to ground at the far side of the coil, to the VR frame. The voltage tries to open a set of contacts. These contacts are in the field circuit. There may be double contacts in this relay with two or more resistors connected to ground (usually under the floor of the VR). These resistors go to the contacts, and adjust how much the field windings in the gen are grounded. The more they are grounded, the higher the output voltage of the gen, and the more charge goes to the bat. This set of contacts is held closed by a spring that adjusts the exact amount of voltage allowed to go to the battery. As the voltage rises, the relay contacts stay poen longer (they vibrate remember) and this chopping of the ground circuit regulates the output voltage. It is very crude and electrically noisy making and breaking current that makes magnetism. it actually makes high quality static, and radio interference. It is also why many digital meters cannot be used with an older vehicle while it is running. It is such a noisy environment, that the meter reads AC voltages instead of DC, jumping all over and giving false readings. There may be that third coil in some regulators. It is a current limiting relay (also in series with the voltage control just mentioned. It is set to have all of the Gen out put pass through its thick wire coil. (it winds around both the Cutout relay, and the Current limiting relay on its way to the Bat terminal) Its contacts also are normally closed until the gen begins charging beyond its rated amps. (generators are not self limiting in current, and will smoke if charging into a load that is too heavy, alternators are self limiting) The heavy current opens the contacts again chopping the field ground path so that the gen output is regulated as to Amps. I have simplified this believe it or not.
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