Originally posted by AfterPentax Mark II Kobayashi.K explains it rather well, better than I did. There so many devices that you can charge from a usb connection of 5v. Smartphones, tablets, Walkmans and so on that all require a higher voltage than the usb output. An USB-C charger has different output voltages to comply with the backwards compatibility and chooses the correct one on connecting. In ancient Roman times they were able to let water flow from lower ground to higher ground, do not how they did it, but they did
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Well, I will say this, fluid flow is something that I do understand pretty well. Water can flow from a lower elevation to a higher elevation, but it cannot flow from a lower pressure to a higher pressure, and thus cannot simply flow uphill (as in a stream flowing up a mountain) in defiance of gravity. I'm not sure what you are referring to regarding "Roman times" technology, but things like water wheels and siphons used in irrigation since ancient times only appear to defy gravity. In the water wheel you are exchanging flow for pressure (elevation head), thus the conservation of energy law holds - you are only exchanging kinetic energy for potential energy. Siphons work because you have a differential in potential energy at two points in a closed system - water will flow from the higher potential (head) to the lower potential (head), but only until the two potentials are balanced. In electricity, voltage is analogous to head. Battery chargers that I am aware of operate exactly like a water siphon - If you have a battery charger that delivers 8.4v, then it will deliver current (flow) to a battery, but only until the battery's voltage equals 8.4 volts, at which time the potential energy (voltages) are in balance and no additional flow (current, as measured in amperes) will occur.
There is a thing called a "current source", that I have only just now read a bit about thanks to you and Kobayashi.K, and find it completely baffling, so I am aware that I don't know everything.
Originally posted by angerdan Couple of things. I think I mis-stated earlier when I said something like "the USB-C specification supports multiple voltages". I believe the USB specifications followed by a letter (A, B, C) only refer to the physical configuration of the connector, while USB specifications followed by a number (USB 1.0, USB 3.1, etc.) deal with things like voltages
Also, it looks like the new charger on that table you referenced in the other thread specifies a voltage of 5.0 volts, while the older chargers specify 8.4 volts. I am confused how a 5.0 volt charger could charge a battery pack to 8.4 volts.
Thanks for indulging my tangent on this thread. I will move to the other thread you referenced to seek additional answers.
~ Jon