Vehicles vary in alternator wiring

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Changing the alternator on different vehicles I've noticed how some vehicles have different alternator wiring setups (beside the B+ terminal.) The most common alternator will use the [Pulse - Lamp - Field Monitor - Sense] wiring to get the alternator to work and adjust to load demand, but some of these vehicles will either use 1 or three of these connectors for the alternator to work. P is almost unused. Toyota's I've worked on use a 3 wire terminal (L-F-S). On most GM's it's either 1 wire (L) or 2 wire (L-F) but some guys add a 3rd wire (S) as a remote sense to the battery for combat dimming lights under load. One BMW e46 I replaced the alternator only has one wire to the connector. So how does the alternator adjust to load demand, especially those 1 or 2 wire alts without sense wiring.
 
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Its mainly regular and self exciting. Self exciting use one wire for everything and you may need to rev it a bit once to kick-in the charging. My Bobcat has one but I do not believe it was original. Hot rods and boats may also have them. The normal alternator has output, excite and sense. The sense can be connected all the time but the excite needs to be switched by the key. Obviously the output will be the largest wire.
 
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sense wiring is done by monitoring the voltage on the output terminal, it is wired internally back into the voltage regulator. look up motor magazine for articles on alternator and vehicle charging. the PLFS is old school before microprocessor voltage regulators. Today the voltage regulators are purpose built to interface with the engine computer (PCM/ECM). the way an alternator works is the rotating iron armature induces a voltage/current into the stator windings and it's AC, with the frequency based on how fast armature spins. the stator AC output goes to a rectifier which turns it into DC, and the voltage regulator then maintains voltage between 13 to 15 volts or however commanded by the PCM. the way you make an alternator output more or less is by varying the field current- which is the power going to the windings around the spinning armature which is an electromagnet. the stronger you make that spinning electromagnet, the more power generated into the stator windings that then makes it's way to the alternator output terminal. I know GM uses pulse width modulation (PWM) on the field current to manage alternator output, it's voltage regulator is 1 wire and when the pcm puts 5 volts to it that's the turn on signal and the alternator will output... it's not an exciter wire. the voltage regulator which is a microprocessor or ASIC then handles everything, and if there's a fault then that one wire from the pcm gets connected to ground through the voltage regulator and is how the PCM knows there is an alternator problem. this is on GM 1998-2002 f-body cars. since then things have gotten more complicated, pcm programming can now control alternator voltage output directly... lower voltage = less parasitic load on engine. and some of those motor magazine articles i remember went into detail on newer bmw's... where it's to the point you can't change your own battery because charging algorithm is based on battery age which can only be reset by a bmw dealer. most alternators retained the traditional 4-pin plug physical connection, and they may be marked PLFS or whatever. Electrically it can be used however the automaker decided to use those 4 electrical connections so you need to be careful.
 
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^^^nice post^^^ the 1-2 wire alts have the regulator circuitry built in. they don't have the "intelligence" that comes with ECU-controlled alternators such as temperature compensation or delayed engagement or temporary cut-out (like under WOT) but they spin and make juice and charge batteries all day long. The regulation is generally just to keep voltage in a certain range, and produces whatever current is needed to keep it there. Older regulators also may have considered dropping output as amps increases max, but I haven't seen one of those in forever. Early regulators were in fact mechanical--- a relay would keep the field coil energized until max V was hit then release... it would immediately re-engage--- the terminals would buzz in real operation and the rate of buzzing would vary with rpm and demand... magnetic-mechanical regulator. Don't know if they ended when alternators came out or if the alternators saw them too-- the hookup/wiring connections were the same.
 
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Originally Posted By: meep
Early regulators were in fact mechanical--- a relay would keep the field coil energized until max V was hit then release... it would immediately re-engage--- the terminals would buzz in real operation and the rate of buzzing would vary with rpm and demand... magnetic-mechanical regulator. Don't know if they ended when alternators came out or if the alternators saw them too-- the hookup/wiring connections were the same.
Did those sudden changes limit the life of the electrical components? My father had a 1972 Honda motorcycle, and he said the charging system often gave him a problem.
 
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