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| A typical alternator wiring diagram. An alternator
is a three phase A/C generator. It produces 3 phase power just like power
found in factories. This A/C power is then run through diodes to convert
it into Direct Current for the truck's system. The regulator keeps the
voltage and current under control. It does this by varying the amount of
current fed to the field coils. The highter the current, the stonger the
magnetic field and output power. A single phase system would work, but
would not be as efficient, and the output power would pulse badly. Contrary
to popular belief, an alternator doesn't put out full power at engine idle.
It's efficient enough to charge the battery, but it needs at least 2000
rpm to put out full power. It will produce much more current at idle than
a generator will due to the powered field coil and 3 phase output to the
diode set.
A/C=Alternating Current DC=Direct
Current
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Testing the alternator. The scope shows the
pulse train from the regulator, and the meter shows the average D/C being
read on the field terminal. The digital meter is a Fluke 87, and the scope
is a Velleman handheld 5Mhz oscilloscope.
Fluke 87 DMM:
http://www.jensentools.com/
'scope:
http://www.velleman.be/kits/hhs5.htm
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| This is the waveform on the field terminal. This
is what the regulator actually puts into the field coil. It switches current
at high speed to make an average power in\put to the field coil. A DC volt
meter will show about 7 -10 volts DC, but this is what the power really
looks like as it powers the field coil. |
This is the waveform on the auxillary or relay
terminal. (called either depending on who makes the alternator) It's the
feedback circuit to the regulator so it knows when to switch power to the
field coil.
An alternator with the regulator and battery disconnected
and field coil powered up, will put out enough power to run 120 volt drills,
saws and whatnot. The catch is, the diodes usually won't take the high
voltage and will croak. Also, the power is 120 volts DC and runs
only certain power tool motors. Plug in a TV or refrigerator and watch
the fireworks!! |
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Measuring the 'cleanlyness' of the charging
system's output. A perfect system would be a completely flat line of direct
current, but the ignition system's pulsing current draws, and the alternator's
"drops" between it's phases and output diodes produce this waveform at
the battery. This is the reason you need to connect directly to the battery
for a good sound system. The farther you get from the battery, the worse
this pulsing gets. Hooking up to the fuse box, and grounding to the nearest
screw, causes more alternator whine problems in stereo systems than anything
else. At the fuse box, you have to factor in current drop in the power
wire to the box, and other accessories that draw power from the same fuse
panel.
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This is the voltage being fed to the battery
and measured right on the battery terminals. This is actually very clean
power because the variations are only about 0.11 volts. If one or more
diodes fail in the alternator, this waveform will get extreme. This is
where the "alternator whine" in your stereo system comes from. The complexity
is from the ignition system drawing pulsing current from the system and
any other accessory that may be running.
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