
Upping the volts will make hybrid cars much cheaper - edward
http://www.economist.com/news/science-and-technology/21704778-upping-volts-will-make-hybrid-cars-much-cheaper-last-48-show
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manicdee
This article is seriously confused. Current BEVs use 400+ Volts for the motive
power, but still have 12V for accessories due to the established market.

Increasing to 24V or 48V means less current for the same load, which means
smaller cables for accessory power. Above 30V or so you get into "high
voltage" by electrical safety standards.

A 48V electrical system is not going to be driving hybrid vehicles, it is
purely to reduce the cost of wiring looms.

~~~
TorKlingberg
I have always heard that <50V is considered low voltage by electrical safety
standards, which is why 48V is a good choice.

~~~
dfox
For electrical safety, <50V DC is common definition for ELV. For some
(probably business oriented, ie. to do price differentiation for telco
equipment) reasons, some electronics manufacturers classify anything over 30V
as high voltage.

~~~
asmithmd1
The US National Electric code defines <50V as low voltage but UL defines
anything over 20V as high voltage.

UL generally deals with products so that is probably why they are more
conservative. Picture a baby sucking on something and you can imagine why they
want anything over 20V to be double insulated. If car manufactures want to
comply with UL standards that would mean they would no longer be able to use
the car's frame for the current return path.

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kevhito
Even the opening sentences are wrong:

> VOLTAGE is to electricity what pressure is to water: the more you have of it
> the more oomph you get. That is why electrical power lines work at high
> voltage.

No. Losses in transmission lines are proportional to current squared [1]. High
voltage is used because it results in lower current (for the same power), so
lower losses.

[1]
[http://www.bsharp.org/physics/transmission](http://www.bsharp.org/physics/transmission)

~~~
pietjepuk88
I think the analogy holds up quite well, even though they don't go into the
details that you mention. Losses in water transmission lines for example are
also proportional to velocity squared.

~~~
seanp2k2
Voltage is how hard the nozzle sprays, current is the diameter of the hose.
High pressure + small hose can be as much flow as a fire hose just gurgling
out. Correlates well to how much current a given wire gauge can handle as
well. If you hook the garden hose up to a fire hydrant and open it up, the
garden hose might explode since it can't handle all the water. A pressure
washer might use a thin hose, but the water sprays so hard that it can cut
your skin.

Idk, that's how I learned it growing up before I learned about stranded vs
solid core wire, skin effect, resistance, etc.

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iaw
I'm seriously waiting for auto-makers to pull their heads out of their asses
and start putting kinetic energy capture systems into _every_ car, economy to
performance.

The absurdly priced Porsche 918 is the only car to date that takes advantage
of this technique in an ideal fashion (small batteries, small electric motors
augment the engine and brakes).

After that, what about ICE's that run at optimal load/RPM for the highest
possible efficiency to charge a smallish electrical system?

Batteries are still a long way off from gasoline in their energy density.
Gasoline will never be "clean" but the way we burn it in our existing
automotive fleet is horribly inefficient.

There's this beautiful middle ground in the technology that no one is
exploring and it's such a shame.

~~~
thomas11
Isn't the Chevrolet Volt what you describe in your third paragraph?

~~~
iaw
Edit: corrected a mistaken assessment here. Yes, Volt is closest on the market
but it's a horrible car.

My point is that every single car produced from VW to Ferrari can get 50%
better fuel efficiency if the auto manufacturers changed their approach to the
problem.

~~~
bluGill
50%? That is only in the worst case of stop and go traffic.

The volt and pirus are a small aerodynamic cars. They would get in the upper
30mpg range with a traditional power train. On the highway they could get
better mpg with the right traditional power train (0-60 times would be in the
20 second range - there are obvious reason nobody does this). That hybrid
system is just extra weight once the battery is exhausted so you need a
slightly bigger engine to haul it around on pure highway driving.

Don't get me wrong, hybrid makes sense for most people. However it isn't that
the system is more efficient for everything, it is that for the way most
people [want to] drive it pulls in enough advantages to be worth the
negatives.

~~~
dragonwriter
> The volt and pirus are a small aerodynamic cars.

Priuses (except the first generation Prius and the current Prius C) aren't
particulary small; they are midsize sedans.

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sandworm101
This is not the first 48v debate. Several years ago is came and went over the
desire for electric brakes, solenoids rather than hydraulic calipers. They
would theoretically be cheaper and simpler to manage electronically. 48v or
higher would be needed for such things (also for running AC pumps). But brakes
are very established and mature tech. They are also the primary safety system.
Antilocks work well enough as is. Manufacturers balked at the idea of starting
from scratch with purely electric brakes. With the need for higher voltages
mooted, the debate came and went.

Anyone worried about hacking cars, imagine the nightmare should brakes be
completely electric, with no hydraulic or mechanical option should either the
power or control system fail.

As for saving weight on cables, smaller metal doesn't mean smaller cables.
Higher voltage would require greater shielding, thicker cables. The increased
risk of sparks/shorts would also be a thing, as would the risk of
electrocuting those working on their cars. With 12v you can get away with
stuff that at 48v might put you in hospital.

~~~
ollie87
Surely any electric brake would fail closed? Just like air-brakes on large
trucks. That would make them safer right?

~~~
peterwwillis
Only truck brakes are designed to fail closed. Passenger vehicles aren't, even
though they could be. In fact, there's a lot of safety systems that passenger
cars don't have, for no discernible reason.

There's no warning light for the brake fluid reservoir or pressure, even
though it would be trivial to add. The oil warning light for passenger
vehicles is so useless, when it comes on you have to stop your vehicle
immediately. Gasoline gauges are designed to trick people into thinking
they're on empty and then provide an extra gallon or two, even though they
could actually design the gauge to display average miles based on the rated
mileage of the car and size of the tank. Transmission, diff, brake, and engine
oil fluids could be measured or at least timed for when they need to be
replaced and a warning given to the user that it's time to maintain it. Only
in modern [usually expensive] cars do you find tire air pressure sensors.

Why don't we have these basic maintenance and safety systems built into cars?
Too expensive? Too technically challenging? Nope - they want you to bring your
car into the dealer regularly to regularly charge you for maintenance you may
not need.

~~~
MertsA
>There's no warning light for the brake fluid reservoir or pressure, even
though it would be trivial to add.

What deathtrap are you driving? This is a common thing. Even my old 96 Camry
has it.

~~~
peterwwillis
Hmm. Well it seems like it's possible the cars i've had have shared the same
indicator for multiple brake notifications. But i've not noticed a dedicated
light for brake fluid. There's one for the e-brake engagement, and one for
ABS, for no particular reason, because it's a non-critical brake feature....
but i've not seen a dedicated brake pressure light.

~~~
sandworm101
Sometimes they are linked to other systems. My 92 bmw shared the brake fluid
reservoir with the clutch. A leak in the clutch triggered the brake warning
light.

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bsder
Question: Why not go to 96V?

Everything wants to go higher for all manner of reasons, and the semiconductor
switches probably don't care all that much. If the jump has to be made, make
the jump as far as possible so that the jump doesn't have to be made again.

Is there a safety reason or something?

~~~
msandford
Inertia and fear of the unknown. Also below 50V is generally considered
"safer" and anything around 100 and up is "dangerous" due to the impedance of
the human body.

~~~
mixedCase
Dangerous as in a bad kick, but it can't fry you like current AKA amps can
(which is usually the worst part, which you want to avoid).

~~~
mindslight
That's like saying that falling off a building can't kill you (because it's
actually the stop that does).

You lower the current by lowering the voltage.

~~~
IanCal
> You lower the current by lowering the voltage.

I assume you meant increasing there.

~~~
tempestn
If you're talking about a controlled situation where you need to provide a
given amount of power - ie driving the accessories of a car, then yes, a lower
voltage would require higher current. P = IV

When you're talking about safety though, the issue is what happens if the
voltage gets applied to your body. In that case the relevant formula is I =
V/R. R is the resistance of whatever circuit you've mistakenly formed through
your body. The higher the voltage applied across that circuit, the higher the
current that will flow. (This is also why it's more dangerous if you're wet,
or in bare feet, for instance, because those things lower your resistance,
resulting in greater current for a given voltage.)

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snarfy
A shock from 50V DC can be fatal.

This is more a cost cutting measure than a feature. Instead you lose a
feature: safety.

~~~
cnvogel
It would be very hard to get several mA of current through your body from only
50V. That's why up to 50V is generally consisted safe low voltage which is not
harmful to touch.

