Serious question from a beginner in electronics. For reasons I do not fully understand, I have become fixated on the idea of collecting small amounts of electricity from “interesting” sources. I don’t mean “free energy”, instead, I mean things like extracting a few mV from being so close to a AM radio tower using two tuned loop antennas in phase with each other, or getting a few mV from the rain’s kinetic energy with PTFE and using two electrodes which are shorted when a drop of rain hits it. In short, I’ve done small experiments to confirm that I can get a few mV and enough to get me excited but not much more. I know I’m not going to get much power out of this, but I’ve been able to charge a NiMH battery a few mV by being a quarter mile from an AM radio station with my antenna setup. It would be fascinating to me if I could store these small charges in something like a 5V USB power brick eventually.
The smarter idea would be for me to harvest energy with the sun or from the wind or a stream. I’m tinkering with this as well, but larger amounts of electricity scare me for right now. I guess I’ve seen enough experimental sources of harvesting electricity and I’ve gotten the itch to invent, which is a dangerous itch for a newbie like me to have.
The best advice I’ve seen online (ok, it was ChatGPT) is that it’s just not worth it to work with such small amounts of electricity, because the equipment required is too expensive and sophisticated (e.g, devices to read the charge of a capacitor without discharging it) to make anything that’s efficient enough to be worthwhile. Would you agree? Do you know of some other fascinating source of gathering electricity that I should also waste lots of time on?
I just have all these electronic components and magnets and when I move them together the numbers on multimeter get bigger. it’s neat.
It's a fun engineering challenge. Weird energy harvesting tech mostly has applications for sensor networks. Some of the new generation of bluetooth chips have ridiculously low power consumption -- so being able to deploy them without a battery somewhere without maintenance is occasionally useful.
Some currently used technology are piezo energy harvesting from mechanical vibration, low-light solar, and thermocouples.
My approach is usually to think around the TPL5110 and a pseudocapacitor. The TPL5110 is a timer that has a current consumption of 35 nA and can operate down to 1.8V. Every 2 hours, it would activate an ATtiny10 that can operate in the microampere range. That chip (very quickly) measures the voltage on the capacitor relative to a reference and decides whether it has enough power to "do the thing". If it does not, it signals to the TPL5110 to turn itself off for another 2 hours to let more charge build up.
If it does have enough power, the ATTiny10 either "does the thing" itself or switches a MOSFET to activate another system or whatever. The "thing" can be to use the power stored in the pseudocapacitor to charge a battery for a short time (e.g. around a second), if you want. Afterward, the system goes back to sleep until it has a relevant amount of power again. However it's often a battle to outpace the self-discharge of a lithium cell, so having the system "do a thing" without a battery present is often better.
This does result in practical stuff sometimes, especially when using low-light solar. Besides sensor networks, you can for example manufacture replacements for tritium indicator lights this way that only activate on at night. In my experience, an SMT indicator LED is quite visible at night with under 10 uA of current. I have a series of ridiculously overengineered indicator lights that stick to the top of doorframes so I don't hit my head on them at night (I am quite tall, and live in a traditional home in Asia).
Incidentally, I tried building a resonant circuit at 60Hz and was able to pick up a few mV from nearby fluorescent lights -- not enough to use. I used a ridiculously large coil of wire that I happen to have lying around. A more fun trick is to use LEDs as their own power source -- during the day they work as tiny solar cells, and that lets them flash occasionally at night :D