
To Power the Future, Carmakers Flip on 48-Volt Systems - dwynings
https://www.nytimes.com/2018/02/08/business/electric-cars-48-volts.html
======
PhantomGremlin
It's too bad that automakers didn't make this change a long time ago.

One thing the article didn't mention is that power losses in a wire are a
function of the _square_ of the current. So, let's say one needs to deliver 48
watts to a load. In a 48 V system, that's 1 A of current. Using 12 V, that's 4
A of current.

Power loss is 16x greater at 12 V for same diameter of wire, loss = (4 A * 4
A) * resistance of wire.[1] Therefore, wires are made thicker in 12 V systems
to avoid this. That's a lot of extra weight in a car.

Before the nitpickers chime in, I know the above is simplified. But it also
clearly explains why long distance power transmission lines run at such high
voltages, 230 KV or higher.

[1]
[https://en.wikipedia.org/wiki/Copper_loss](https://en.wikipedia.org/wiki/Copper_loss)

~~~
bsder
You're not wrong, but you should probably tell the whole story if you're going
to post on HN.

Primary Objection: Um, Ohms law gives V=IR. And P=IV. So, P=I^2R. Except that
P _ALSO_ can be calculated as P=V^2/R. So, we got squared losses anyway and R
should go the other direction. WTF?

The answer is that a copper wire is a distributed system, not a lumped system.
So, you derive the power loss from the generated heat across a differential
slice of the line and then integrate over the whole length of the line--which
gives you Power=RI^2 in the limit (and V->0 for any individual slice as the
differential ->0).

It is one of those (un?)fortunate happenstances (like the Bohr hydrogen atom
model) where the system in the limit sums to something we already know and
leads to a bit of misunderstanding when you confuse two things which appear to
be related but really aren't...

~~~
mindslight
The _V_ in V^2/R would be the _voltage drop along the wire_ , not the total
system voltage.

------
ju-st
> It is diesel's decline, executives and analysts say, that has finally set
> the stage for mass electrification. While diesel pollution problems became
> notorious with the Volkswagen test-cheating scandal, the subsequent shift to
> gasoline is bloating carbon dioxide (CO2) emissions, making the next round
> of European Union goals harder to meet.

> PSA Group, which had previously seen no need for 48V hybrids, now plans to
> introduce them "across the board" in response to diesel's faster-than-
> expected decline, the Peugeot maker's programs chief Patrice Lucas told
> Reuters.

> "What automakers are finding is they need more than just advanced combustion
> engines to reach the fleet average reductions," said Mary Gustanski,
> Delphi's engineering boss.

quoted from
[http://europe.autonews.com/article/20170923/ANE/170929892/vw...](http://europe.autonews.com/article/20170923/ANE/170929892/vw-
psa-volvo-others-adopt-48-volt-mild-hybrids-in-response-to-diesel)

------
ggm
This article conflates two things. One: adoption of a 48v standard for powered
systems because it's a sweet-spot for efficiency, current draw, systems
design. Two: PHEV and the adoption of electric transmission and drive train,
which permits a non throttled engine of any form to run at constant high
efficiency or not at all and use batteries.

Two things. One story. Cars are becoming like common rail deisel with a
unified power model for systems integration and cars are becoming like
locomotives which use electric traction for systems efficiency.

~~~
klodolph
The 48 V DC "sweet spot" is mostly safety / regulatory. As soon as you get to
50 V, the safety requirements (NEC) change. You can hold on to bare conductors
with a 48 V potential across them just fine, even though 120 V AC will kill
you and make it hurt the entire time you are dying.

48 V devices can require connections that are inconvenient and large,
depending on what you want to power with them. Try running an air conditioner
off 48 V and measuring the peak current draw.

[https://electronics.stackexchange.com/questions/267789/how-s...](https://electronics.stackexchange.com/questions/267789/how-
safe-is-48v-dc)

~~~
MrBuddyCasino
> You can hold on to bare conductors with a 48 V potential across them just
> fine

Even with wet hands? I was under the assumption the unconditionally safe upper
limit was around 24V.

------
csours
> _" But skeptics may wonder why engineers are devoting so much effort to
> developing the mild hybrid systems that could be seen as stopgap measures on
> the path to a fully electric vehicle fleet."_

Let's do some napkin math.

Assumptions:

1\. Gasoline will never exceed $10/gallon. (assumes eventual plant/algae
sourcing/some kind of magic). 1a. Vehicles achieve 50 mpg (2 gallons/ 100
miles) via tricks like 48-volt.

Thus future gasoline MHEV vehicles cost 20 cents/mile to power, so $20 per 100
miles

2\. Batteries get stuck at about $100/kWh. (maybe lithium etc never scales)
2a. Consumers are satisfied with 60 kWh batteries.

Thus BEVs cost $6000 more than comparable MHEVs (napkin math)

4\. Electricity costs $0.20/kWh (assume some surcharge for the charging
station). 4a. Your BEV gets 34 kWh / 100 miles (99 MPGe)

Thus to power your BEV costs $6.8 / 100 miles.

5\. The difference between 20 and 6.8 is 13.2 - so you are paying off your
battery at $13.2 / 100 miles. 6000/13.2 is about 450

\---

Conclusion: It will take 45,000 miles to pay off your battery, assuming the
competition is a 50 mpg vehicle and gasoline is $10/gallon.

Additionally, the initial cost for a BEV is $6000 higher, which is quite
significant for entry-level buyers.

\---

With 33 mpg and $5/g you have $15/100 mile, thus a 80-90,000 mile payoff.

With 33 mpg and $3/g you have $9/100 mile, thus 270,000 mile payoff

With 33 mpg and $2/g you have $6/100 mile, and you will never pay off the
battery investment.

With 20 mpg and $3/g you also have $15/100 mile = 90,000

\---

Home Solar: add $10,000 to your battery = $16,000

50 mpg and $10/g you have $20/100 mile = 80,000 mile payoff

33 mpg and $ 5/g you have $15/100 mile = 107,000 mile payoff

33 mpg and $ 3/g you have $ 9/100 mile = 179,000 mile payoff

33 mpg and $ 2/g you have $ 6/100 mile = 267,000 mile payoff

20 mpg and $ 3/g you have $15/100 mile = 80,000 mile payoff again

~~~
nimbius
>Gasoline will never exceed $10/gallon.

The consequences and repercussions of global warming and climate change plus
Nixon era doctrine of interventionalist policy in the interest of maintaining
global US oil hegemony have easily put real barrel cost easily above this.
Iraq didnt pay for itself twice, after all.

~~~
lafar6502
Why everyone talks about switching to electric cars while nobody ever mentions
electric heating of buildings as environmentally friendly alternative? Because
it isn’t? Why bother with electricity-saving lightbulbs while EV owners burn
the current like there’s no tomorrow...

------
maxerickson
This article is kind of weird. The push for 48 volt is mostly about secondary
systems that need a lot of power and doesn't have much to do with "mild
electric" or whatever it is implying.

The 21 HP direct boost mentioned in the article is going to be for performance
rather than running on electric, the vehicle comes with a 1 Kw-h battery (~5
minutes at full output).

~~~
cameldrv
Whether it's for performance or economy depends on how it's tuned and how the
engine is sized relative to the equivalent pure gas car. The attractive things
about these mild hybrid systems is that they're cheap, they don't weigh much
(so you're not hurting efficiency by hauling around a bunch of batteries and
electric motors), and they give you a lot of what a full hybrid (non-plug in)
offers.

If you're not plugging in, you don't need a big battery, because the hybrid
only needs to store the energy from braking, and then deliver it when the car
speeds up again. Even though the motor is only 21hp, it provides a lot of low-
end torque, which lets you have good acceleration from a stop. This is
something modern efficient gas engines are generally bad at, and the immediate
acceleration in a lot of modern cars is even worse because of aggressive
upshifting to save fuel. The electric motor papers over this deficiency, so
you can be more aggressive about using a smaller engine with less low-end
torque. The electric motor is also much more powerful than a normal starter
motor, so it allows the car to more aggressively shut off the engine at stop
lights and even when coasting, and turn it back on very quickly.

~~~
maxerickson
I buy what you are saying but that particular gas engine is 330 HP.

~~~
phkahler
At one particular RPM.

------
chiph
Some RV makers (both commercial [0] and DIY [1]) are already on 48V systems
for their house batteries. Advantages: lighter wiring, can use a higher-
voltage alternator that needs less heat dissipation. Note that the system in
the Sprinter van is able to run the air conditioner at 100% duty for 8 hours,
then allow the alternator to recharge the battery while continuing to run the
A/C unit. Which is really impressive (and should be, for the $200k their RVs
cost)

[0]
[https://www.youtube.com/watch?v=ofCcnxJxzeE](https://www.youtube.com/watch?v=ofCcnxJxzeE)

[1]
[https://www.youtube.com/watch?v=LV8fyzOTjsk](https://www.youtube.com/watch?v=LV8fyzOTjsk)

------
madengr
48 VDC will be good for amateur radio and car audio. Specifically the power
amplifiers for both.

~~~
uncle_bob
Noise from high power motors will be the bane of all operators, even when the
car just drives by. However the junk yard will soon be a good place to source
48v generators.

~~~
madengr
I have a Nissan Leaf, but don’t operate mobile with it. The AM reception on
its radio is fine, which I’ve heard is a problem in other EVs. Proper EMI
mitigation can be done, but these companies may not spend the expense to do
it.

------
_ph_
Certainly a nice technology, but I think it is 10 years late. This kind of
modernized eletrical design of combustion engined cars which enables mild-
hybrids should have been standard 5 years ago. Going forward I cannot see a
large future for combustion-engined cars at all - for a few few years, plugin
hybrids migth be popular for those, who need a lot of range. But pure electric
cars are now coming to the market in numbers. I don't think as stated in the
article, that in 2025 only 5% of the vehicles sold will be electric, I would
assume that number rather for 2020.

~~~
paganel
2020 is only 2 years from now, we’re nowhere close to that 5% number.

~~~
_ph_
We are already at over 1% EVs in several important markets in 2017, and the EV
sales numbers almost double every year, so 2020 probably won't see 5%, but
should be pretty close to that - at least closer than 2025.

------
mcguire
About a decade ago, wasn't there some interest in moving to 24 volt systems;
nothing came of it due to switch failures, IIRC?

~~~
phkahler
It's always been 48V. The problem has been a chicken and egg sort of thing.
Its expensive to have both 12 and 48, but you can't go full 48 unless you can
source all components for that voltage. Suppliers didn't really commit because
there were no real customers.

~~~
solarkraft
How hard is it to put a DC-DC converter between the systems?

~~~
phkahler
That's technically and conceptually easy but it costs a lot of money. One
approach would be to put a large DC-DC converter on the car and run a 48V bus
next to the 12V one. That's a very expensive device, needing to be perhaps a
few kilowatts depending which devices are on 48V. It's also a lot of extra
wiring, and the need to manage the extra variations in vehicle systems.

A second approach would be to put a DC-DC converter only in the devices that
need 12V. But that's asking every supplier to change their design to
accommodate 48V and the vehicle manufacturers will bitch about the cost
increases. It'll be a moderate increase across a LOT of devices.

I'm working on a product that uses a highly integrated SoC that has all the
regulators needed to connect it directly to the 12V line (it'll run on 6-20V
or so). It even has an on-board 5V regulator for additional off-chip devices.
The best thing for us would be if the same chip existed but could be connected
directly to 48V (not sure what the range is on that) but from a silicon
standpoint there is a big difference as well. Adding an external regulator
would add cost, and invalidate some of the wake-up features and low current
standby capabilities of the chip.

There are always "reasons". The only way to make the transition is for someone
to make it happen, but again the suppliers who participate may be seeking
premium pricing in the beginning because there aren't options.

------
neonate
[http://archive.is/PYZ6G](http://archive.is/PYZ6G)

------
sowbug
There is a TLDR for this article, but as far as I can tell it cannot be
derived from the article itself.

Will someone please explain why 48-volt systems are newly desirable in cars?

~~~
saltcured
You want a higher voltage to allow more power without huge cables due to high
current. You want low voltage to avoid high-voltage safety issues which
increase engineering, assembly, maintenance, and emergency costs.

The 48V system sits right at the boundary where you can deliver enough power
for more auxilliary systems and some mild-hybrid techniques including frequent
start/stop systems, brief acceleration boost, and regenerative braking. Yet,
it's not high enough to require switching to a different electrical wiring
safety paradigm.

This is similar to the reason power-over-ethernet runs at the voltage it does,
or "low voltage" lighting exists for home applications where consumers are
moving fixtures around and interacting with the wiring.

~~~
bigiain
From my reading of the article, 48V has been chosen to comfortably fit in
under some regulation that defines 60V as “high voltage” which required
special (read “more expensive”) components.

Keep in mind there’s no such thing as a “48V battery” or a “60V battery” if
you have hard requirements on those voltages. If they’re using lithium polymer
batteries, they’re rated at 3.7V per cell nominally, but will be at 4.2 or
4.3V when freshly charged - so a 48V lipo battery will probably be 13 cells
and 48.1V nominal, but possibly as high as 55.9V fully charged (and one more
cell in a 14 cell pack would hit 60.2V fully charged). Even lead acid
batteries do the same thing, your 12V battery today is six 2V nominal cells in
series, but you’ll commonly see 14V when it’s fully charged, so four current
tech car batteries with a nominal 48V rating will have 56V fully charged.

I don’t think there’s anything “optimal” about 48V apart from it being as high
as you can risk going using available battery technologies without bumping
into the 60V “high voltage” regulations when your battery is fully charged.

~~~
madengr
I think it’s 50 VDC that is considered HV. Any equipment we buy at work 50 VDC
and over requires NRTL (i.e. UL) certification. Also interlocks and safety
boxes when working on circuit.

~~~
bigiain
I have no actual knowledge here beyond the article itself:

“Why 48 volts? Settling on this level holds the electrical system under the
60-volt safety threshold of what is considered high voltage, where power
cables must be orange and special connectors, costing 10 times as much, are
required, said Mary Gustanski, chief technical officer of Delphi
Technologies.”

I wonder if your 50VDC limit is driven by the same “typical peak voltages for
common battery chemistry” margin of safety I’m speculating exists?

~~~
pilom
My understanding is that 50-60VDC is approximately the voltage at which
electricity will arc through a person's chest (i.e. pass through their heart)
if they hold a wire in each hand. That makes it unsafe to handle without
special insulating equipment. That doesn't mean that 48V is safe necessarily
though. If your hand is wet or even just a little sweaty, you can arc from
pinky to thumb at ~48V.

