Powering microcontroller with a capacitor

Question

I have a ESP32-SOLO-1 microcontroller mounted on a moving part of a machine which moves in a circle. The idea is to power it with a capacitor and then charge the capacitor in a fixed location when the MCU/capacitor part comes around (for example via some sort of sliding contacts connected to a power brick.)

The main problem is the charging of the capacitor, as it has in the current configuration around 0.14 s to charge and it has to last about 8 s with a load of 0.04 A at 3.3V until it charges again (except the first time it goes around the MCU has to boot and it requires 0.1 A for about 1 s.)

I used so far a 0.47 F supercap with a rating of 5.5 V (here the datasheet.) I already had with a MCP1700-3302E-TO voltage regulator to have a fixed 3.3 V output. The cap has an ESR of about 16 ohm which in my understanding is far too much for charghing it in such a short time.

My idea was to use this capacitor --> 0.033F 25V and a very low ESR (0.027 ohm in the datasheet) charged with a 24V power brick and power the MCU with a DC-DC converter (this) that outputs 3.3 V.

What are your thoughts on this? Am I completly wrong or could it work? Do you have any suggestions on how to make it work?

EDIT: The MCU evaluates and sends data from a Hall sensor, which is used to mesure the distance of a magnet. So I would rather not have electromagnetic interference and therefore use "touching" parts. Also the goal is to avoid if possibly using a battery.

Answer 1

Sounds plausible.

Maybe you could use a Qi transmitter/receiver to produce 5V and use a simple LDO regulator down to 3.3V. I'm not sure they would switch on fast enough and give enough current for long enough to work. You would need (say) 1A for less than 500msec to keep an average 40mA going, which sounds to me like it might be worth investigation.

Regardless of how you get 5V to the target, a super-capacitor such as the AVXSCMT32F755SRBA0 7.5F 5.5V with 90m\$\Omega\$ ESR might do the trick (charged to 5V and with an LDO regulator) with room to spare. If you use brushes, maybe you can inhibit communication during the noisy bits and add a current limiter to the 5V supply to keep the peak current tame.