2 ms·

> (Hoping USB-PD, with it's bump from 20 up to 48V, once again proves another huge win!) Can someone explain to me why 48V? Is there something special with 48V

> (Hoping USB-PD, with it's bump from 20 up to 48V, once again proves another huge win!) Can someone explain to me why 48V? Is there something special with 48V or beyond? The reason I ask is because some cars now have electric turbos and the manufacturer had to switch to a 48V system. Just curious what the benefits of higher voltage is and if 48 is somehow special. Thanks in advance.

aparks517 4y ago
Power is the product of current and voltage. To transfer much power at a low voltage requires a large current. Supporting a large current without getting hot and melting requires large-diameter wire. Other components may also be bulky or expensive if they have high current-handling requirements. I seem to recall that somewhere around 50 volts is a magic number from a safety/regulatory perspective. It might also have something to do with semiconductor breakdown voltage, but maybe I'm out of date on that.
Dave_Rosenthal 4y ago
My understanding is that 50V is the established threshold above which safety to humans starts to be a factor. So, applications that want high powers, without the penalty of large wires nor the penalty of the safety requirements of an HV system, converge to 48.
- avhon1 4y ago
  > the established threshold above which safety to humans starts to be a factor Specifically, 50 volts is approximately the threshold above which electricity can pass through the skin and shock you. Lower voltages will only shock humans if they have a way to bypass some of the skin, like wounds or tight-fitting metal jewelry. Otherwise, the resistance of skin is high enough to prevent the flow of electricity. That's why you can touch both terminals of a 12V car battery at the same time and almost certainly not be shocked.
spookthesunset 4y ago
At 48v you can use much smaller gauge wire than at 12v. Which means lower cost, less weight and a smaller footprint for your wire harnesses. One of the things that can “get you” with these higher voltage systems is you can’t use them to jumpstart the present majority of cars. While I’ve yet to actually see a higher voltage car, I would hope they’d put warnings by the battery to remind the user that “hey, don’t try to jumpstart your friends car with this battery!”

aparks517 4y ago

Power is the product of current and voltage. To transfer much power at a low voltage requires a large current. Supporting a large current without getting hot and melting requires large-diameter wire. Other components may also be bulky or expensive if they have high current-handling requirements. I seem to recall that somewhere around 50 volts is a magic number from a safety/regulatory perspective. It might also have something to do with semiconductor breakdown voltage, but maybe I'm out of date on that.

Dave_Rosenthal 4y ago

My understanding is that 50V is the established threshold above which safety to humans starts to be a factor. So, applications that want high powers, without the penalty of large wires nor the penalty of the safety requirements of an HV system, converge to 48.

avhon1 4y ago
> the established threshold above which safety to humans starts to be a factor Specifically, 50 volts is approximately the threshold above which electricity can pass through the skin and shock you. Lower voltages will only shock humans if they have a way to bypass some of the skin, like wounds or tight-fitting metal jewelry. Otherwise, the resistance of skin is high enough to prevent the flow of electricity. That's why you can touch both terminals of a 12V car battery at the same time and almost certainly not be shocked.

spookthesunset 4y ago

At 48v you can use much smaller gauge wire than at 12v. Which means lower cost, less weight and a smaller footprint for your wire harnesses. One of the things that can “get you” with these higher voltage systems is you can’t use them to jumpstart the present majority of cars. While I’ve yet to actually see a higher voltage car, I would hope they’d put warnings by the battery to remind the user that “hey, don’t try to jumpstart your friends car with this battery!”