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Current vehicle electrical systems almost entirely use a 12 V nominal DC power distribution. An alternator generates three phase AC, which is then rectified to DC, which is then used to power accessories like brushed DC windshield wiper motors, fuel pumps, washer fluid pumps, window motors...wait, why
are all these motors using DC? As demonstrated by none other than Nikola Tesla, AC motors are far more efficient and reliable.
Simply tap the alternator before rectification, and power all these motors with three phase AC. Do away with sparking commutators and rectifier voltage drops. Switching these loads is easier than DC as well. Mechanical switches can take advantage of the periodic zero volt crossing to quench arcs, and cheap TRIACs can be used for solid state switching.
Lights (as long as manufacturers keep using incandescents) can operate equally well on AC or DC, and the three phases can be balanced between bulbs. Computers and other electronics still require DC, but AC input allows efficient transformers to lower the voltage before rectification. Without all the inductive feedback from motor brushes, this low voltage rail will have less noise to filter out.
Unfortunately, one of the biggest electrical hogs, the starter motor, still requires DC. At least until someone develops an AC battery...
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Because most of the motors and such either need to
be able to function without the engine running, or
are used so infrequently that any net efficiency
gain would be negligible. Designing a system that
could switch them between AC and DC would
probably be overall less efficient, and certainly less
reliable. Also, hybrids and electric cars would be
totally unable to use AC powered anything, since
they operate powered entirely by batteries. |
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So it basically boils down to increased cost, added
complexity (and possibly weight), decreased
reliability, and virtually no benefit. |
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Cost; most existing systems use the vehicle chassis as the return
path. With 3 phase, that's a minimum 200% increase in cabling. |
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You can't just connect all the phases at a lamp and put the other
terminal to earth; it has to be star or delta, or you need rectifiers ... |
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3-phase systems are more efficient mostly when the topic is
"induction motors". Such motors "induce" the armature to rotate,
and 3-phase induction motors are certainly a lot more efficient than
single-phase induction motors. When DC motors aren't using
permanent magnets, they send current to the armature to create
magnetic fields that interact with the magnetic fields of the stator.
This is directly a more-powerful interaction than the induction of
AC motors, and therefore is also somewhat more energy-efficient
than even 3-phase types. |
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On another topic altogether, it IS possible for a kind of "AC battery"
to exist. An energy-storage flywheel, with an AC motor/generator
can do that.... |
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// wiper motors, fuel pumps, washer fluid pumps, window motors ..... power all these motors with three phase AC // Very funny: all these motors running synced with the combustion engine. Because you know three phase motors runs at proportional speed of the line frequency, don't you ? |
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Ha! there's good money in this for Schneider and the like to start mass producing miniature VVVF drives for all of these little 3-phase motors everywhere. |
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Maybe a 3 phase lamp could be manufactured, with 3
filaments inside it... |
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Indeed it could, but 3 LEDs would be rather more efficient. |
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Star, or delta ? If star, neutral return ? |
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British Leyland had a three-phase electrical system.
Phase One was everything worked, even the cassette
player; this lasted about 4-8 weeks. Phase Two was
all the essential things still worked. Phase Three
was only some of the essential things worked, but by
then the body had rusted anyway. |
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Sp. "eight-track cartridge" |
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// all the essential things still worked. // |
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Unfortunately, in that era CERN had not yet developed sub-attosecond
counters to the point where they were field-deployable, so definitive
data could not be collected. |
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// Phase Three was only some of the essential things worked, but by
then the body had rusted anyway. // |
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... and then it was rolled off the production line for shipment to the
distributor, who would store it outside in the wind and the rain for
months before shipping it to the main dealer, who would sell it to the
final "customer" (Sp. "victim") |
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The Austin Princess ... the road vehicle that made the
Ford Edsel look like a sound investment. And as for the Allegro ... well,
let's not go there. It didn't. Go anywhere. Ever. (at least, under its own
power). |
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Did you know that if you translate "Triumph Acclaim" into German, it
comes out as "Sieg Heil" ... ? |
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mutter, mutter ... 6R4 ... mutter ... Group B ... mutter ... WHAT WHERE
THEY THINKING ... mutter, grumble ... Quattro ... Lancia Delta ... Group
B ... <nostalgic sigh> |
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//Sp. "eight-track cartridge" // No, this was
Britain. |
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Ahh, the shellac 78 ... we shall not see its like again ... thankfully. |
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Many aircraft had 3 phase electrical systems, until
they figured out that it sucked around 1940. |
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//Many aircraft had 3 phase electrical systems |
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How many times was it really necessary to run a milling machine in an aircraft? |
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3 phase is efficient only if running continuously and at
a steady and usually mandatory speed. |
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For a directly-wired squirrel-cage, yes, but if
you're prepared to pay for an inverter drive
then you can have anyy speed you like. |
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Cars have enough problems packaging the wiring
in them as it is. |
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