Also, there's no reason you couldn't play internal series/parallel (or transformer, or DC-DC converter) games to charge the thing up at a higher voltage (and thus lower amperage) while discharging it at normal phone operating voltage.
Capacitors aren't charged by voltage, they're charged by current. One does not apply a voltage to a capacitor, one applies a current. If you doubt this, try connecting a capacitor to a high-powered constant-voltage power supply. But first, step back.
A capacitor's charging rate is determined by its value in farads and the applied current. Nothing else matters. One farad, one ampere, one second produces one volt and one joule of stored energy. Nothing could be simpler.
If you raise the voltage expecting to see a faster charging rate, you will see the opposite, because a higher voltage for a given power rating means a lower current, and a lower current will require more time to charge the capacitor.
Heck, why not charge it at full line voltage?
Why not indeed? But don't be in the same room when this idea collides with reality.
What other laws of physics have changed since I was in school?
Sorry for the late reply -- I'm traveling. What I said in my original post is quite uncontroversial. When charging a capacitor one must not think in terms of voltage (which is an effect, not a cause of charging) but of current.
The important factor for charging time is how many joules/second you can stuff in, not how much current (coulombs/second) is flowing.
You're confusing cause and effect. Capacitor charging is accomplished with current -- voltage is an effect, not a cause.
The voltage on a capacitor is the time integral of past applied currents. Want to change the charge level on a capacitor? Apply a current and let the voltage change in response.
You can pull a helluva lot more joules/second out of a wall outlet than you can a micro-USB connector.
Non sequitur, the issue is how much current the capacitor can tolerate. And attaching a capacitor to a wall outlet will not work for multiple reasons.
The ideal charging source for a capacitor is a constant-current supply set to provide a high, but not damaging, level of current, then when the capacitor's voltage limit is approached, shut down the current supply.
The worst possible source for a capacitor is a constant voltage with substantial power available, which will destroy the device.
As I originally said, "Capacitors aren't charged by voltage, they're charged by current." Concise, and quite accurate.
Comments
Capacitors aren't charged by voltage, they're charged by current. One does not apply a voltage to a capacitor, one applies a current. If you doubt this, try connecting a capacitor to a high-powered constant-voltage power supply. But first, step back.
A capacitor's charging rate is determined by its value in farads and the applied current. Nothing else matters. One farad, one ampere, one second produces one volt and one joule of stored energy. Nothing could be simpler.
If you raise the voltage expecting to see a faster charging rate, you will see the opposite, because a higher voltage for a given power rating means a lower current, and a lower current will require more time to charge the capacitor.
Why not indeed? But don't be in the same room when this idea collides with reality.
Really? So C=Q/V isn't a thing any more?
What other laws of physics have changed since I was in school?
The important factor for charging time is how many joules/second you can stuff in, not how much current (coulombs/second) is flowing.
You can pull a helluva lot more joules/second out of a wall outlet than you can a micro-USB connector.
Sorry for the late reply -- I'm traveling. What I said in my original post is quite uncontroversial. When charging a capacitor one must not think in terms of voltage (which is an effect, not a cause of charging) but of current.
You're confusing cause and effect. Capacitor charging is accomplished with current -- voltage is an effect, not a cause.
The voltage on a capacitor is the time integral of past applied currents. Want to change the charge level on a capacitor? Apply a current and let the voltage change in response.
Non sequitur, the issue is how much current the capacitor can tolerate. And attaching a capacitor to a wall outlet will not work for multiple reasons.
The ideal charging source for a capacitor is a constant-current supply set to provide a high, but not damaging, level of current, then when the capacitor's voltage limit is approached, shut down the current supply.
The worst possible source for a capacitor is a constant voltage with substantial power available, which will destroy the device.
As I originally said, "Capacitors aren't charged by voltage, they're charged by current." Concise, and quite accurate.
The voltage of the interconnect doesn't need to match the voltage at the capacitor. Buck converters for the win!
Yes -- translation: "Capacitors are charged by current, not voltage."