Posted by Janicholson on March 30, 2008 at 15:20:27 from (66.173.50.101):
In Reply to: Re: 10 ohm resister posted by james rumph on March 30, 2008 at 10:22:46:
Just educational Stuff. There are three terminals on the Alternator he is using. The large terminal goes (with 10 ga wire) to the load side of the Amp gauge. This wire is supplied with Overlapping DC pulses from the stator windings. There are 6 diodes in the housing of the alternator making 3phase AC into pulse DC. The output voltage is controlled by a internal transistor regulator. This regulator is fed DC reference voltage from the Big post through a 14ga wire going to the #2 labeled spade terminal on the edge of the alt housing. The regulator is initialized from a wire going to the ignition switch (also about 12.5v or so) This wire normally goes first to the idiot light on the dash of a car(or tractor if desired), then to the #1 terminal. The number one terminal appears to be a ground when the key is first turned on. This "Exciting" voltage (engine not started yet) is what causes the idiot light to illuminate. As the engine starts, the exciting voltage allows the regulator to start feeding real current to the rotor windings making the stator produce more voltage than the battery. It charges. The regulator senses the charge voltage and switches the #1 terminal to system voltage. Now the idiot light sees system voltage on both wires, and goes out. This indicates to the driver, that the alternator is charging. This system voltage on the #1 wire through the light bulb is not sufficient to keep the engine running (when the ign sw is shut off, The resistance of the light bulb is too high to allow enough current to make the ignition work. Though it is connected to the same terminal on the ignition as the coil. The engine stops, and the voltage regulator resets to have #1 terminal act like a ground, ready for the next time someone starts the tractor/car. A diode in the wire (in place of the idiot light bulb) will do the same thing. Preventing back flow from the #1 terminal to the ignition sw, and thus back to the coil. The band end of this (much smaller ~3 amp diode goes toward the alternator so the flow is blocked from that direction.
On the generator topic, The regulator and all circuits associated with generating charging voltage are separate from, and not connected to ignition circuits. Thus there is no way for a regulator to either prevent stopping the engine, or keeping it from starting when operating with the wires in the correct location in every setup I know of (Prestolite, Delco, Bosch, Lucas, and others not mentioned). Again, I have no grudge here, just 50 years of being trained (Factory, and Auto school in the late sixties))and teaching this topic every year since. JimN
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