Re:mAh Is an Industry Mistake
by magicalhippo on Thursday October 12, 2023 @10:43AM
(#37857876)
> which is more difficult to scale up effectively than voltage
For those who don't know, this is because losses scale as current squared, instead of just proportionally like it does with voltage.
For example, charging a power bank with 20W of power at 5V you need to supply 4A of current. If you have a good USB cable with 0.1 Ohm resistance, that results in P = V*I = (I*R)*I = (4*0.1) * 4 = 1.6W of loss in the cable[1].
If instead you could use 20V to charge, then the current would only need to be 1A and hence the loss just (1*0.1) * 1 = 0.1W.
For those who don't know, this is because losses scale as current squared, instead of just proportionally like it does with voltage.
For example, charging a power bank with 20W of power at 5V you need to supply 4A of current. If you have a good USB cable with 0.1 Ohm resistance, that results in P = V*I = (I*R)*I = (4*0.1) * 4 = 1.6W of loss in the cable[1].
If instead you could use 20V to charge, then the current would only need to be 1A and hence the loss just (1*0.1) * 1 = 0.1W.
[1]: https://en.wikipedia.org/wiki/Ohm%27s_law