Good example and shows the same power loss, but I think carrying it a bit
further, you also need the wire to be able to deal with the power loss.
In other words resistors are not just rated on ohms, but also watts.
So it's not just about "efficiency" in terms of power loss, but it's also about
heat.
In your example, it may be true that both wires waste the same energy, but they
also must absorb that energy.
Bigger wires can dissipate 100 watts/foot no problem....But for tiny wires,
dissipating 100 watts/foot may prove a problem.
Also for distribution lines, increasing the voltage and decreasing the wire
size means that the actual Electric field that must surround the wire is going
to get super intense not justbecause of the voltage, but also because the wire
is smaller. And this also causes all sorts of problems with ionization.
That's why instead of having 3 wire for 3 phases, they
often little groups of 3 wires for each phase, because this simulates a larger
wire for the phase.
Then also we have mechanical issues. A wire 1/4 the diameter is only 1/16 as
strong. 40 AWG wires might be adequate electrically, but the are very fragile.
Then we have corrosion issues. Higher voltages accelerate corrosion so
smaller wires at higher voltages will corrode faster. For the same
lifetime, you might even need thicker wires..
Not trying to be negative, but maybe just pointing out that things might be a
little more complicated.
On Saturday, October 5, 2024 at 08:48:24 PM PDT, Cor van de Water via EV
<ev@lists.evdl.org> wrote:
Note that if you want to save on copper and are only interested in
delivering the same power with the same percentage of wire losses, then
going 4 times up in voltages allows you 16 (!) times smaller wire surface
area, because current is 1/4 but also 4 Volt loss in a 48V system is the
same percentage as 1V in a 12V car. So if you needed a 1/4" diameter wire
(2 AWG) in a 12V car then you only need 1/16" diameter wire (14 AWG) for
48V to transport the same power with the same losses.
In different words: going up 4 times in voltage means you only need 6% of
the copper for the same performance.
Now you may get why distribution lines are so high voltage.
Cor.
On Sat, Oct 5, 2024, 6:50 PM Lee Hart via EV <ev@lists.evdl.org> wrote:
> >> On aircraft, 28 volts (24 volts) has been the standard low voltage
> forever.
> >> It is the standard on specialized military vehicles and equipment as
> well.
>
> Also in large trucks and buses.
>
> > "42 volts" is the threshold for "low voltage" in the US National
> Electrical
> > Code, but as I recall, that is for AC rather than DC.
>
> Yes, also UL and ETL. They specify 30vac or 42vdc peak as the maximum safe
> limit for voltages you can touch.
>
> > I suppose if you are going to make a departure from the industry
> > standard of 12 volts, then why not go all the way to 48 volts.
>
> 48v actually exceeds the "low voltage" classification for NEC, UL, and ETl
> etc. There is also a problem with arcing. Switch, relay contacts, fuses,
> circuit breakers, motor brushes, etc. are all typically limited to 30vdc
> max before arcing will not extinguish itself.
>
> To me, it makes more sense to increase vehicles from 12v to 24v, in line
> with a huge number of other vehicles. There are already lots of 24v
> accessories. Going to 48v means essentially no standard components or
> accessories can be used.
>
> That said... The auto companies routinely ignore electrical safety
> standards. They use undersized wire gauges, combustible wire insulation
> that melts at lower temperatures, inadequate fuses, switches and relays,
> etc.
>
> Lee
> --
> Excellence does not require perfection. -- Henry James
> But it *does* require attention to detail! -- Lee Hart
> --
> Lee A. Hart https://www.sunrise-ev.com
>
>
> _______________________________________________
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>
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