Quote:
Originally Posted by philso
This will not work due to the high ESR inherent to Super Caps. They are only meant for applications where the current draw is much less than 1 mA. The datasheet gives values ranging from 14 to 600 Ohms. If the supercap is charged to 5 Volts, a 300 mA input current (into the Raspberry Pi) through the 14 Ohms would cause a 4.2 Volt drop giving an input voltage of about 0.8 Volts at the Rasperry Pi). We made this mistake at work when they first became available and we were able to verify this. Note that the ESR will limit the charging current just like it would limit the discharge current so there is no concern about large charging currents.
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I agree but I am not sure about the relativity of large currents.
The Nichicon super caps that arrived yesterday are rated for 200mOhms ESR.
I could have gotten them with 100mOhms at higher cost.
My intention was to charge them higher than the 5V and then accept the loss that will be present anyway because of the on-board Raspberry Pi linear regulators.
My previous example feeding from a 7805 was merely an example.
The rest is a great contribution to the topic. Thank you.