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To Power the Future, Carmakers Flip on 48-Volt Systems

nytimes.com

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Re: To Power the Future, Carmakers Flip on 48-Volt Systems

#21

Post by revelation »

maxerickson wrote: post #2

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).

A basic lack of fundamental understanding has caused the author to quickly fall into an expertly laid trap by marketers that seek to equate 48 volt systems with some sort of "green, hybrid, clean" spirit, leading to such bizarre statements like "The advantages of the new 48-volt systems are considerable. They offer fuel economy improvements of up to 15 percent"

Of course it's all about saving a few dollars on copper.

Re: To Power the Future, Carmakers Flip on 48-Volt Systems

#22

Post by phkahler »

maxerickson wrote: post #19
cameldrv wrote: post #14

Earlier quoted context omitted.

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…

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

At one particular RPM.

Re: To Power the Future, Carmakers Flip on 48-Volt Systems

#23

Post by phkahler »

mcguire wrote: post #13

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

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.

Re: To Power the Future, Carmakers Flip on 48-Volt Systems

#24

Post by madengr »

bigiain wrote: post #18
saltcured wrote: post #6

Earlier quoted context omitted.

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, an…

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…

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.

Re: To Power the Future, Carmakers Flip on 48-Volt Systems

#25

Post by 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.

Re: To Power the Future, Carmakers Flip on 48-Volt Systems

#26

Post by mindslight »

bsder wrote: post #17
PhantomGremlin wrote: post #10

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] T…

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 acr…

The V in V^2/R would be the voltage drop along the wire, not the total system voltage.

Re: To Power the Future, Carmakers Flip on 48-Volt Systems

#27

Post by bigiain »

madengr wrote: post #24
bigiain wrote: post #18

Earlier quoted context omitted.

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…

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.

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?

Re: To Power the Future, Carmakers Flip on 48-Volt Systems

#28

Post by pilom »

bigiain wrote: post #27
madengr wrote: post #24

Earlier quoted context omitted.

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.

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 “typi…

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.

Re: To Power the Future, Carmakers Flip on 48-Volt Systems

#29

Post by GeorgeTirebiter »

twic wrote: post #11
sowbug wrote: post #8

Earlier quoted context omitted.

Thanks. I had always understood PoE's relatively high voltage as helping deal with the attenuation from long runs of thin copper wire. I couldn't find a succinct explanation in the article why cars would benefit from this spot in between merely sending information (digital levels like 1.8, 2.2, 3.3, 5.0, etc.) and using electricity to do "real" work (120V, 240V, 480V, etc.). As I understand your answer, yes, they'd l…

The specific number of 48V is presumably inherited from telecommunications: https://electronics.stackexchange.com/questions/10851/why-do... There's lots of telecom equipment that works at 48V, so it's presumably cheap and easy for carmakers to find suppliers.

There is practically no overlap between automotive and telecom. When I was at Tesla, we couldn't find even one manufacturer for common use subsystems (e.g. window motors). It's a chicken and egg problem for now. That's why 'everything' is still at 12V.

Re: To Power the Future, Carmakers Flip on 48-Volt Systems

#30

Post by csours »

maxerickson wrote: post #2

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).

48 volt is what the industry calls mild hybrid. It allows for much better stop-start systems, which automakers get points for on EPA and European emissions testing.

It also allows for 48 volt super-charging and e-assist turbo, as well as a small amount of actual propulsion power (for instance to both start the engine and start the vehicle moving from a complete stop after the stop/start system has been engaged).

All of these systems fall under the term "mild hybrid".

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