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.
Oh yeah, I hear you on LLMs. Technically, ChatGPT has not “heard” of anything. It’s generally something I use as a jumping-off point when I’m desperate and don’t know what search query to use.
Does passive RFID harvest its power? I don’t know much about RFID (I’ll probably head over to wikipedia after this comment) but I figured that it was a circuit that, when given a bit of energy from a reader, sends back an RF signal with an encoded ID and that in the absence of that powered reader, the RFID device wouldn’t be transmitting anything.
Yes, the circuit in an rfid device gets its power by harvesting energy from the RF source it’s being illuminated with. A smaller version of wireless power transmission first invented by Tesla (the person, not the car company). Similar principles were used in the Cold War for surreptitious listening devices. Neat tech.
The most basic RFID tags will just send back an ID. The complexity can shoot way up and have all sorts of integrated circuits, mostly around encryption.
I guess it's more of a semantic argument at this point, but would you not consider a tiny computer (RFID tag) that powers itself solely off of radio waves not a form of energy harvesting?
I would say “energy harvesting” is when the receiver and transmitter are not designed to be used together and they are not physically close together. Otherwise your electric toothbrush and Qi charger might count.
That's a good point. What about long range RFID skimmers? You could argue the tag wasn't designed to work with a skimmer. I guess that's more like energy injecting?
I guess the difference for me would be how long it stores that energy for, but the difference is probably semantic and easily changed with a few capacitors.
They do use capacitors to keep power. Here's a simplified diagram: