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
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..
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.
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.
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.
@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...
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.
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.
@rarely Temporarily lighting small lamps from nearfield RF with a TX power of some kW is definitely possible, a family friend who was the engineer at Radio Caroline in the 1960s did it on board the ship as a demonstration to visitors; but didn't use any antenna nor leave the lamps around to light up the deck (it would have created hassle with unwanted stray RF, and there was plenty about already!). Its not common these days as TX sites are designed to keep people out of the nearfield for safety.
@rarely the claims of "poor reception" caused by "large scale" nearfield power harvesting are from Communications Ministry officers from some decades ago (I mistakenly referred to modern Ofcom rather than the British Post Office which investigated these things until the 1980s), it is possible they just wanted to discourage this practice for the safety of those involved whilst not also opening a can of worms about human exposure to RF (it was Cold War era and much info was classified)
Hold the phone! You’re telling me now that the government lies to people?!
I have also heard of this tale of “not-spots” but have found no evidence myself. The SWR and near field antennas stuff you mentioned makes a lot of sense, I just didn’t understand how I could be stealing electrons meant for others. I mean, if it worked that way wouldn’t trees also creat not spots, especially if they get to a certain height?! Anyway, thanks for the info, and… 73?
@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
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.
That does actually exist, it’s called a toroidal transformer. Instead of a tube shape though it’s a donut shaped piece of ferrite with the primary and secondary wound one on top of the other. The different types have different use cases though, as far as I remember the toroidal ones have higher leakage current. Marco Reps has a good video on his YouTube channel where he explains some of the differences if you’re interested, although he mainly focuses on what’s important for precision electronics.
I’m not sure I understand your proposed solution, but the ferrite core guides the magnetic flux, there are very few losses, and both circuits are perfectly electrically insulated from each other. How would your solution be an improvement?
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.
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.
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.
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.
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