Jacob Pratt

Perhaps a silly question, but why don't portable power banks (when wired) use the 3.7V that both the battery and device it's charging already have? Why the need to convert to 5V (or higher), necessarily adding nontrivial losses?

Surely it's not only because that's what the USB standard says?

#electronics #technology

Mar 6 at 3:33amWeb
Show threadJason von Nieda 🐀Mar 6
@jhpratt Two things: yes, the USB standard says if you wanna be a USB port you gotta output 5v, and secondly, most batteries charge at about 4.2v. The 3.7 is nominal but charging to 80+% requires above nominal.
Show threadJacob PrattMar 6
@vonnieda Sure, there would still need to be some level of voltage regulation, not the least because it fluctuates with charge level. It just seems wasteful to always use 5V. There's all sorts of proprietary charging standards out there (still); I'm surprised no one has done this.
Show threadhackguyMar 6
@jhpratt wellll, the newer ones *kinda* do, it's called programmable power supply (PPS) mode, and one of the use cases for it is direct battery charging: The device can request a specific voltage between 3.3 and 21V, which can then be piped directly into the battery without further conversion
Show threadJajcuśMar 6

@jhpratt you would need much thicker cables and contacts than a normal USB cable provides or little of thar 3.7V would actually reach the device with any significant current. A lot of the power would be lost heating the cable and contacts. 5V is still a quite low voltage for power delivery.

And, of course, you need more than 3.7V to charge a 3.7V cell.