Comment by bigiain | Hacker News Reader

Comment by bigiain | Hacker News Reader

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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.

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?

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.

When I was studying electrical engineering, we were taught that at 30V, current may be able to pass through the skin (depending on a number of conditions presumably). Once it's under the skin, you only need a tiny current through the heart to kill you.

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