[udba]

A high power workload on a phone might require ~5-10W over 100ms, i.e. ~0.5 joules. At 4V capacitor voltage, you would need ~30mF capacitor. Not likely to fit in a phone.

This assumes you’re powering the phone solely off the cap. Even with a battery you’d still need something in the mF range to make up for the battery’s degradation.

[Dylan16807]

The first data sheet I pulled up has an option for 47mF at 4.5V in 20x15x2.3mm of supercap. So it would fit if you really wanted.

[Dylan16807]

Okay the reply got deleted but I already did all this math so I'm going to post anyway.

> [only able to use the cap from 4V to 3V]

> (C * 1V * 1V)/2

> [you'll need 1000mF]

Wrong equation. That's the energy from 0V to 1V. Each incremental volt stores more power than the last. 0V-3V is 9x that amount, and 0V-4V is 16x that amount, so 3V-4V is 7x that amount, and you'll need 140mF.

But also it shouldn't be connected directly in parallel to the battery; so I'd think of it more as 4.2V to 2V of supply. That would mean you need 74mF.

So put in two and you'll more than hit the target.

Even better, if you expect the battery to contribute some, you only need the one.