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.
Actually this article is talking about mild hybrid technology: Which is about upping the voltage for traditional non hybrid vehicles from 12V to 48V, giving them some hybrid like features on the cheap.
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.
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.
> 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.
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.
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.
Only if you take the wire gauge as fixed. If instead you use the cheapest (smallest) you can get away with, you'll find yourself using smaller wires at higher voltages, with higher resistance and so less then quadratic loss reduction.
So you can have (1 volt @ 100 amps), or (100 V @ 1 amp) and still get (100 watts). If both are the same, wouldn't the low voltage solution be safer, and more desirable?
Massaging the same equation a little bit, we can model our losses along the power lines. Substituting V = IR you get...
P = (I^2)R
It's difficult to make conductors less resistive without using expensive metals or unconventional techniques (like cryogenically cooled wires). So to cut our losses, we'll go with high voltage, low current.
Since we're getting pedantic, as HN is wont to do, I'm not sure if the parent complaint is about the first sentence...
> VOLTAGE is to electricity what pressure is to water: the more you have of it the more oomph you get.
... or about the claim that follows:
> That is why electrical power lines work at high voltage.
The former sentence (aka the hydraulic analogy, [1]) is a very well-established thing. It's not a perfect analogy, but it's quite reasonable. The latter (high voltage power lines) is demonstrably not correct, as the two of you have pointed out.
Extending your power formula to the hydraulic world and simplifying the calculus to steady-state algebra:
Power = (Volumetric flow rate) * (pressure)
Though, to be fair, the analogy breaks down a little there; the Poiseuille equation [2] (the fluid equivalent of V = IR) involves 6 variables instead of 3. But the point is, you still end up with a final equation of similar form to P = (I^2)R.
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.
I've just bought a new-to-me Prius and I think the way it works is the way forward until the issues with electric-only cars are resolved (i.e. how to refill it in 2 minutes as opposed to 2+ hours):
The ICE is connected to the drive shaft via the 'hybrid synergy drive' which is a gear box and electric drive in one. It can drive the vehicle either under electric mode with the ICE off, with both electric and ICE, or in electric mode while the ICE charges the battery.
When you brake it cuts power to the ICE (either just cutting the fuel, or stopping it completely) and charges the battery. There are also normal brake disks if you push the peddle extra hard.
I like it because it's relatively mechanically simple, which means less things can break. The ECU does a lot of work, but try and find a car that doesn't nowadays. Also it only needs electric motors in one place - the rest of the axle and drive system is exactly the same as a normal car.
The only thing really letting it down is the low capacity battery pack, but I guess that's for cost savings. There is also a plug-in version which can do 26 miles on electricity alone. Toyota offer this as an option in most of their cars, even the Rav4 SUV, so I expect in the next 10 years it will become standard across their range.
Good points - I should also note that one of the motor generators actually doubles in functionality as the starter motor for the internal combustion engine. The Prius transmission system is truly a work of wonder and deserves more recognition by the wider community.
Oh I forgot about that one. It basically replaces the automatic transmission, starter motor/alternator, clutch and braking system with one simple unit. It has a total of six fixed gears in a planetary arrangement. Unlike a normal automatic transmission (which quite often fails in older vehicles) it doesn't change gears, so should last a lot longer.
Here are some good articles explaining how it works with diagrams:
They are exploring it, it's just slow. Lots of cars now come with "mild hybrid" systems which capture kinetic energy and store it in a supercapacitor, using it to charge the battery and power electrical loads (which are significant these days, with things like electric power steering). Mazda's i-eLoop is one such system (available only on high-end vehicles at additional cost), and Volvo has a similar system, and I imagine some other automakers do too.
The reason you don't see this kind of system everywhere is most likely cost; these systems cost extra. I have the Mazda system on my car; there's a pricey supercapacitor for storing power, plus a pricey DC-to-DC converter under the driver's seat, plus a special high-voltage alternator, plus a special battery. It improves fuel economy by 1-2mpg, which is the other reason you probably don't see them that much: an extra $500 or more in the new price of a car is a lot for an extra 1-2mpg when gas is $2/gallon and everyone's buying SUVs.
Such systems could be done better, but that's likely going to cost even more; to get a more significant improvement you really need to go full-hybrid with a large traction motor, which of course is going to make the vehicle cost even more. Take a look at the Chevy Volt for a good example of what you can achieve here: it's a serial hybrid with a small gas engine with generator plus a traction motor that actually moves the car. It can go 50+ miles without using any gas, which is pretty cool, but when the gas engine comes on (like for long trips) it can only get fuel economy in the low 40s because of the lossiness in the system. On top of that, having all that hardware in the car (engine, generator, motor, battery pack) limits the useful space, and the cost of the vehicle is rather high. Or you can get a Toyota Prius which is a parallel hybrid (engine drives wheels) and gets much better highway economy, but it can't go very far without burning gas and it's pretty expensive for an economy car with very anemic performance.
> After that, what about ICE's that run at optimal load/RPM for the highest possible efficiency to charge a smallish electrical system?
I've long wondered about that given so many trains and ships run that way using electrical transmission from the prime mover ("that's what "diesel-electric" is), I know little about the concerns so I must be missing some significant drawback on the scheme given so few hybrids are "series" and most manufacturers go for either parallel or split topologies.
Of note, an other potential advantage of a series hybrid is you can run alternative ICE topologies e.g. with high but very short efficiency bands.
A mechanical gear transmission is more efficient than a generator and motor. Can you make up that difference? For trains nobody has the ability to make the required parts of that size (this might be in part that you can't fit them in the space required - I think you could build the machine to make them if you wanted it)
It is only with the most recent emissions standards that the losses from non-optimal RPM is a significant factor and the generator/motor is better.
The big issue with trains is starting to move: that requires a slipping clutch, which is inefficient and maintenance-intensive. Also you tend to loose power while switching gears. Lower-power trains (e.g. around 300 kW per motor) are still available with mechanical coupling.
In ships, gears are used up into the multi-Megawatt range, but there you don't need a clutch and have a lot of space and mass available.
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.
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.
One word: customers. People wouldn't buy them. The cost to add a motor/generator and storage battery to a car is substantial, and for most buyers, they'll never recover the cost in fuel savings over their ownership.
Close, except for they lobbed a motorcycle engine into an electric car and called it a "range-extender" but the engine can't generate power to meet maximum demand of the car's electrical system.
So, instead of putting the motorcycle engine in as an afterthought take a 1.5l turbo as the primary source of electricity generation.
> So, instead of putting the motorcycle engine in as an afterthought take a 1.5l turbo as the primary source of electricity generation.
This is kinda what they did on my new 225xe.
7(?)kWh battery, decent electrical drive, and said 1.5l turbo for if the car needs more power or range.
Under real-world conditions, the battery seems to be good for about 40km of electrical driving in my current temperate climate (where I don't really need cooling or heating).
The 225xe looks like a completely different system, it's not a series hybrid where the ICE feeds into the electric engine, it's a parallel hybrid with completely separate drivetrains, the electric engine in propulsion and the ICE in traction (which can be used at the same time for 4WD).
Why put a bigger motor in? You really don't need to meet the max power consumption of the electric motors, that's what the battery is there for.
However, I will point out that the i3 REX gets relatively poor fuel economy when running on gas -- only about 40 mpg, nowhere near what a parallel-hybrid Prius can get.
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.
I can't imagine how electric brakes could be cheaper than hydraulic calipers. Existing brake calipers are dirt cheap.
Now, when you add the cost of the ABS/TC/DSC system module, maybe it works out better, I dunno, but the amount of copper you'd need in 4 separate electric brake motors would be pretty high, so I don't see how they'd be cheap.
The real advantages for a 48V system are weight and size of existing electric systems. Modern cars have a lot of motors, including now the power steering system (run by a motor attached to the steering shaft). These can all be downsized with higher voltage, saving copper ($$$) and weight. There's also smaller motors in the car, like those in the seats, and in luxury cars there's all kinds of motors (for opening and closing doors and liftgates, adjusting the steering, etc.). Finally, the wiring weight can be reduced all over the car, as well as the wiring cost (since again, copper is very expensive). Your statement about shielding is BS: yes, higher-voltage wire needs thicker insulation, but not that much going from 12V to only 48V, and insulation jackets weigh very little compared to the copper inside them. Furthermore, with a reduced diameter of the copper conductor, the diameter of the insulation will also decrease, so the insulation weight will probably be the same, if not a bit less. Besides, I'm pretty sure most wiring used on cars these days can handle hundreds of volts, and is sized not for electrical insulation properties, but instead mechanical properties (they make it thicker and tougher to handle being handled during assembly and repair, and also so it doesn't get worn through from vibration over the car's lifetime). If they actually sized wire insulation for only 12V, the wires in cars would barely have any insulation on them at all.
In the Prius, most of the accessories including the air-conditioning compressor are electrically driven from the traction battery so your proposal can easily be made to work.
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.
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.
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.
Not on passenger cars. The fail-closed thing is only done on larger vehicles. There is a reason. Fail-on systems have a max applicable force. Basically, they are some sort of spring pushing the brakes on 24/7 and the control system fights against this spring. So when the system fails, the brakes default on. But that means that stamping on the brake pedal harder and harder doesn't translate into greater braking force. The spring sets the max force. That is OK on a truck or train where human muscle is irrelevant, but in a passenger car or motorcycle human muscle is more than enough to lock up the tires (ie go beyond maximum braking potential).
Large vehicles also do not have the same performance envelope and so can generally survive a braking system that suddenly fails "on". A truck+trailer can lock its trailer brakes without, normally, going out of control. So too with a train or even an aircraft on landing. If that happened on a motorcycle, the rider would die. No questions, just death. Cars are somewhere in the middle. Some cars could survive but many would become instantly uncontrollable.
(Remember there are limitations on antilocks in no-power situations. They cannot antilock forever and so will eventually lock up.)
With 48v and several hundred amps behind it, that's not a hard thing to do. You won't shock yourself with 48v, but when working with DC batteries that can source those kind of currents, you need to be very careful. If you cause a short upstream of a fuse that is a very dangerous thing. Even with just 12v automotive batteries people get hurt from time to time by accidentally shorting them.
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.
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.
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.)
Semiconductors care a lot. There is a sweet spot in the <= 48V range, and even more in the <= 24V range. High voltage devices are much harder to miniaturize, and the conversion ratios for the inevitable logic supplies can be done a lot cheaper at lower voltages.
Safety is of course a huge component. 48V is about the limit before special isolation and insulation is required.
There actually is an existing sweet spot for 60V FETs, optimized for traditional 48v power systems. I've got to wonder if they're going to use -48v to allow simple driving of N FETs, or if the ubiquity of modern high-side drivers has made that a moot point.
>Question: Why not go to 96V?
>and the semiconductor switches probably don't care all that much
Yes, actually they do. Power MOSFETs are usually in the 30-60V range. When you go higher than that, costs go way up and you generally need to switch to IGBTs. MOSFETs capable of switching 30V loads at extremely high loads (like 100A) are dirt cheap. Power devices capable of switching 100V are not.
48V is the threshold before you're regulated as a high voltage device. That means all sorts of safety standards, larger or less efficient electronic components, risk of injury, etc which translates directly to cost, risk, weight, etc.
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.
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.