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.
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If you’re doing it to learn about electronics and physics it’s a great thing to do.
Tinkering is fulfilling in and of itself.
You may be interested in the Kelvin Water Dropper.
Oh yeah, i’ve seen that before! I’ll need to try to make one of these as well. Looks like a fun experiment!
There’s actually a decent amount of research into exactly this sort of thing, called, appropriately, “energy harvesting”. Depending on the application, it can be fairly effective. I know that vibration energy harvesting has been successfully in machinery monitoring applications, for example. I haven’t looked much into stray EM harvesting, but I’m sure it is possible…most likely to supplement a primary energy source rather than as the main source itself. But, yeah, for sure it’s an interesting topic with a fairly good amount of study into it…I think the University of Michigan had a few good research programs related to harvesting for ultra low power applications. You night check out some of what they’ve done
Fantastic, thanks! I’ll take a look
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.
I guess ChatGPT has never heard of passive RFID tags? LLMs have some good uses, but they’re not great at a lot of things. You can’t really advance science and engineering by strictly regurgitating scraped text.
There are reasons to grab small amount of electricity from the environment. Why have a battery in a pacemaker if you can generate power via mechanical forces? It really just depends on the use case on how practical and feasible it is.
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:
Depends on the use case. It is a very good idea to harvest small amounts of energy for example to use it in a calculator or a clock or a remote control or button or light switch. This way you never need to replace batteries or have them leak and destroy the thing.
Apart from that. There aren’t many use cases for those very small amounts of energy. You have to ask yourself what you’re going to use that small amount of energy for. Because batteries and wires are way cheaper. And they store amounts of energy you’d need 20 years of harvesting with equipment that costs a lot more. It just depends on the use case. And for little amounts of energy, the use-cases are severely limited.
You’re allowed to do this as a hobby, however ;-)
Inspiration for building something hit me when the following things happened:
- I learned that small amounts of electricity can be harvested from a single drop of rainwater, both from the kinetic energy and shorting two electrodes. I don’t know the how, but I’ve seen something like 200mV from a small trickle of water from a faucet.
- I moved to a place that where it rains a lot and bought a house with which I could do some experiments. This house is also on a slope.
- I got a 3d printer.
I figured that I could create a small, maybe 1cm x 1cm device that could harvest 200mV when a drop of water hits it. 200mV isn’t much, but if I had 100 of them hooked together in a 10cm x 10cm square, that could be somewhere between 1-100x that voltage (though, more likely lower than that unless it’s a downpour).
Then I got thinking, well it’s water, so after the kinetic energy and whatnot has been harvested it could go into a large bucket at the top of the slope. That large bucket could then be connected to a tube that’s connected to this mini 12v dc hydro generator I bought off amazon. Of course then I could use the energy generated/harvested during the day to pump water back up to the bucket at night… (ok, would have to be a large bucket and I realize this is still small amounts of electricity)…
I guess the reason we don’t see commercial systems like this has to do with energy density. After printing and prototyping and hours of trial and error, I may arrive at a device that can harvest/generate 0-15v depending on the weather. I imagine if I were to buy some TI energy harvesting devices and put them all together, I would be able to get enough energy to charge my phone in a day, but it may set me back the price of a house and may take up the size of a room to do so.
I guess my realisitic-use case would be to take something like what I just described and use it to power some outside LEDs. Then, everytime it rains, the LEDs would twinkle, and that would kind of be neat to see. Especially if these devices were installed in something like a raingutter system with individual LEDs, sort of lighting up roughly wherever rain drops were hit. No energy stored, just used as it’s harvested. It sounds like if it did work, it would be a big undertaking and would require quite a lot of time and money to build.
But still. twinkles!
I’ve seen that one before. Robert Murray-Smith shows a different approach which I’ve also experimented with. https://youtu.be/WYUwBGQS5_E?si=P_H8JJpeeSMnJKg-
Wow. Thanks for the link. Unfortunately this video isn’t very scientific. You don’t measure electrical energy in millivolts but in Jules (or watt-hours). Or in an experiment like this you would measure electrical charge (Coulomb) generated by a certain amount of water.
And I would expect the charge to come from the clouds or air or something. That would mean the water wheel shouldn’t generate any electricity in his experiment.
Measuring Voltage is kind of wrong. You also get a reading of a few hundred millivolts if you randomly stick your multimeter somewhere. Or take the probes in your hands and squeeze them. That also generates a few hundred millivolts. But it isn’t energy.
I’d love to see his experiments repeated in a bit more scientific way. And someone to figure out how to do that at scale. How to connect a square meter of those electrodes. And how to arrange them.
If you actually build something, make sure to document that in a blog with pictures or video for us. I kind of want to know if it’s really 50W per square meter of free energy in the rain drops.
I have aluminum foil and a spray can at home :-)
Here’s the best resource I can find on the tech he’s using. https://onlinelibrary.wiley.com/doi/full/10.1002/eom2.12116
Hopefully I picked the right video here, he has hundreds. In one of the videos robert measures mA with some of these in series and powering some LEDs, I believe, or I’ve confused that with another video.
From the paper, I just skimmed but it seems that most of the energy is kinetic, then possibly converted into static? I’ll obviously need to do some actual reading.
Thx. I think it’s a variant of the Kelvin water dropper
(Derek from Veritasium explains it here. At the end he explains how much energy is generated.)
ChatGPT is not a relevant or a reliable source.
https://www.ti.com/video/3878027903001
https://www.ti.com/product/BQ25570
https://www.ti.com/tool/TIDA-00242
https://www.ti.com/lit/ug/tiduc93/tiduc93.pdf?ts=1692465536615
https://www.ti.com/lit/ug/tiduew2/tiduew2.pdf?ts=1692465539544
https://www.ti.com/lit/ug/tidub22b/tidub22b.pdf?ts=1692465541647
https://www.ti.com/lit/wp/sszy004/sszy004.pdf?ts=1692465544492Absolutely. It’s just a well-read word-suggester. Thanks for the links!
Maybe take a look at BEAM robotics. Specially Pummer circuits.
The idea of Pummer circuits is to store energy from a small solar panel during the day and flash an LED at night. Energy is normally stored in super capacitors or NiCd batteries.
Might not be exactly what you are looking for, but it can give you some ideas to experiment with.
I can’t find it now, but i’m pretty sure there exists smart home light switches that are powered by you pressing it.
IIRC they run Zigbee to communicate with the smart home and had a bit more resistance when pressing (= more energy).
That would be super interesting for my ZigBee network
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
Kelvin Water Dropper
Very cool! I completely forgot that LEDs work as solar cells. Now I’ve got a few more experiments to try, just for fun. Never seen the TPL5110 or ATTiny10 before, they look very interesting. I’m new to pseudocapacitors, but at least now I know they are a thing!
Some cool stuff I saw when I worked in a lab in college working on wearables. Movement, heat, etc.
You likely aren’t going to get enough energy to make up for the losses incurred when boosting voltage to 4.2 volts or whatever your battery requires. There’s tons and tons of scam devices out there in the world that attempt to convince people these devices make sense, but they really aren’t usable for anything meaningful.
Charging a battery with a couple microamps per hour. Would probably negates things like self-discharge? But certainly wouldn’t recharge a battery that you have in use with a device. And if that device has radio or storage attached to it, you definitely aren’t gaining enough electricity.
A few years back some farmer living in Droitwich, England (where the Radio 4 longwave transmitter is situated) lit his barn by connecting an antenna to fluorescent light tubes.
It worked, but also created a “not-spot” in the radio reception which the BBC really didn’t like (its part of critical national infrastructure!) - officers from Ofcom turned up at his door, made him take the lot down and ordered him to use more “normal” power sources…
I’m skeptical of the “not-spot” claims here. This would suggest that radios also create “not-spots” when being tuned to as well, or that somehow the florescent light tubes were able to “pull” more electrons from the air that were destined to other radios.
@rarely a radio receiver uses *much* less of the power than lighting up the fluorescent tubes would (it wasn’t just one lamp) and this incident happened close enough to the TX that it could upset the SWR of the transmitter output stages - if it /was/ possible to do this without creating problems elsewhere then every tall transmission tower would use the RF to power their aircraft warning lamps rather than a separate power supply…
@rarely if the link below federates correctly, here is a receiver that uses just the power of the signal, but from a 4kW transmitter 32km away there are only a few tens of milivolts, enough to be amplified by the line in of a desktop PC to listen to the audio but certainly not enough to light any lamps (even an LED). Maybe I could light an LED from our wifi signal close to the access point, but I don’t have any RF detector diodes to hand that work at 2,4 GHz
That is the most plausible explanation I have heard but I still have questions. Say there’s an MW tower down the road and I have a 160m tower in my backyard. If I understand correctly, my tower may cause the signal coming from the AM tower to be re-resonated back to the AM tower so the AM tower needs to be detuned. But say I want to harvest the signal and I have tuned my tower to be resonant with the AM tower. Maybe in this case the SWR reading at the AM station is different because it is getting some of that re-radiated power back, and maybe the radiation pattern of the am station has changed slightly, but wouldn’t the main AM tower cover any gaps just like how waves spread out in the double slit experiment once they hit my resonant tower?
I get that a tower excites another tower, and I can understand that the AM engineers will likely hate me, but I don’t understand how radio reception could be affected. If anything, I might have made the station more directional (like a reflector in a yagi) but probably not.
@rarely if you are /that/ close to the antenna an extra tower, or any large amount of metal making the station more directional will definitely be unwanted, both by tradio station engineers and the Communications Ministry (licenses often require a particular directional pattern). But this is more an issue with LF and MF where waves are larger. At UHF/SHF frequencies for wifi harvesting could work but at present the component count required makes it less viable than other power sources.
@rarely this is why things behave differently when very close to the TX (how close will of course depend on the TX power and frequency/wavelength)
It may surprise you to know that in the US as a ham, I have the legal right to hoist an antenna or build a tower so long as it doesn’t fall on a power line.
But even then, I don’t think this setup will create nulls. Say the antenna is 400 meters away which I think is still in the far field but I could be wrong. Even if I erected an almost resonant tower (160m) and assuming the regulatory bodies gave me the permit to do so, assuming it’s not powered and simply is resonant, maybe the radiation pattern changes but not so dramatically that my neighbors on the opposite side of my antenna (from the tower) will get poor reception.
Is the direction of the radiation pattern changing what was meant by the “not-spots”?
@rarely the historical reports of issues I’ve read about are from mid-late 20th century in areas near high power LF/MF stations that would be in the nearfield - from the Wiki article
> absorption of radiation in the near field by adjacent conducting objects detectably affects the loading on the signal generator (the transmitter).
so it would be noticeable, and viewed as an undesirable thing. Harvesting (small) amounts of power in the far field would not cause issues.
Yeah, exactly. This isn’t how radio signals work at all. This is a tall tale and never happened. When I searched for such a story, none came up. When I removed the location and searched for the same type of story, thousands of them are floating around the internet. Powering military tents from radar emissions, powering homes from radio tower emissions, all of them are re-tellings of stories someone once heard from the 1930s, 1940s, and so on. They’re effectively chain letters for the confused.
I’ve heard teachers telling the same story, but so it happened locally in a different country entirely. Sounds like a scare legend.
A couple things stick out in your story. first off, there’s no such thing as a “not spot” when it comes to radio. That’s not how RF energy works at all. Second, zero news stories show up when I search for such a story. So my guess is that this tall tale has spread in legend form and relies on people not realizing how radio signals work.
https://www.iloq.com/ for example does a lot of parasitic energy stuff. Most of the advertised things now seem to be RFID, but I think they also had locks that are powered by the key insertion.
There’s plenty of places where infrastructure power is not available and a flat battery would be a disaster. Door lock is one mundane one. Space is one more extreme one.
