Stealing wasted EM energy from other devices - Page 1
Forum section: electronics / projects

author: Stonent
author_rank: Super Contributor
timestamp: January 01, 2014, 02:40:42 am
content: About a month or so ago, I connected my oscilloscope to an inductor and it was pretty good at picking up the hum from a spiral fluorescent light bulb. It was getting about 100 to 350mV depending on where I moved it to. So I then ran it through a small transformer of unknown ratio and was able to get about 3 to 4V AC. I then put in a small bridge rectifier and a few ceramic caps and was able to keep a 5mm LED lit continuously.So I got to thinking, this energy I was picking up, is it otherwise just wasted or am I adding an additional load somewhere?I started having ideas about energy stealing devices to power small devices or maybe charge a phone.We've already got wireless charging phones, so why not some kind of one that just tries to harvest any kind of EM energy it can find? Perhaps just sit it on top of your laptop's power brick to pull some charge, or maybe even just lay it on top of a PC case or DVD player.Maybe even throw a Joule Thief in there for good measure.I hope you don't think I'm trying to turn this into a "free energy" idea, just trying to find ways to suck up any energy that's just otherwise being wasted through the general inefficiencies.I read an article about a year or so ago where a company was using some kind of heat exchanger with a turbocharger to boil water and spin a small turbine and added maybe an additional 1% efficiency to an engine. So the otherwise wasted heat was being collected and being put to another use.

author: Zero999
author_rank: Super Contributor
timestamp: January 01, 2014, 02:54:39 am
content: You won't be able to harvest much energy.If I connect the earth on the circuit attached to a radiator or tap and hold "VAC" in my hand, the LED lights dimly from the mains hum picked up by my body. It acts as a voltage doubler so the LED will light from low voltages. I've found high efficiency transparent green LEDs work best.

author: SArepairman
author_rank: Frequent Contributor
timestamp: January 01, 2014, 03:06:29 am
content: look at ultra low boost converters. there is one that has a 0.02 volt minimum threshold from linear tech, i believe you can use it for this purpose ( i think i saw one app note hooking it up to a copper plate near a fluorescent light fixture)

author: AlanR
author_rank: Regular Contributor
timestamp: January 01, 2014, 11:19:10 am
content: I just looked up the LTC3109, and all I got to say is that chip seems AWESOME. Man could you imagine someone out there applying for a patent for a TRUE power down device that would GREATLY exceed the EPA requirements for energy efficiency when said device is in standby mode? I plan to add this to my 30 watt amplifier theater system that I built. I placed a sample order for these little beauties. Thanks for this post. If it wasn't for you, I would not have known about such devices in existence.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 01, 2014, 11:28:00 am
content: Shahriar did a tutorial about energy harvesting ic's:http://thesignalpath.com/blogs/2013/01/03/tutorial-and-experiments-on-energy-harvesting-ics/

author: SArepairman
author_rank: Frequent Contributor
timestamp: January 01, 2014, 01:00:15 pm
content: copper plate app note:http://cds.linear.com/docs/en/design-note/DN483.pdflast paragraph

author: Stonent
author_rank: Super Contributor
timestamp: January 02, 2014, 02:54:20 pm
content: I just now remembered that Dave got that energy harvesting kit a few months back too.I read about that really low power LT chip the other night. I saw it has a .1F capacitor in the example circuit.

author: qno
author_rank: Frequent Contributor
timestamp: January 02, 2014, 08:07:54 pm
content: It is my experience that the energy you can regain is much less than you put in.

author: edavid
author_rank: Super Contributor
timestamp: January 02, 2014, 08:24:53 pm
content: Quote from: Stonent on January 01, 2014, 02:40:42 amI believe the answer is yes, you are adding an additional load to your power line. I think you are drawing extra energy from the inductor in the CFL power supply. I could be wrong though - it could be that the same amount of energy is normally absorbed by the room environment - and it would be hard to measure such a small change in the energy use of the CFL.

author: Bloch
author_rank: Unknown
timestamp: January 02, 2014, 08:53:15 pm
content: Quote from: qno on January 02, 2014, 08:07:54 pmIt depends the you live

author: peter.mitchell
author_rank: Super Contributor
timestamp: January 02, 2014, 10:52:20 pm
content: Quote from: edavid on January 02, 2014, 08:24:53 pmGenerally, it will have no impact, the SMPS will spew out the same amount of crap, it's just instead of it disappearing into the world of inverse square law, you pick it up on your antenna.

author: edavid
author_rank: Super Contributor
timestamp: January 02, 2014, 11:55:50 pm
content: Quote from: peter.mitchell on January 02, 2014, 10:52:20 pmWell, I disagree, since the OP doesn't really have an antenna, I don't see how it could be RFI. I think it's inductive coupling. I guess it would be possible to confirm that with copper vs. mu-metal shielding.

author: Spikee
author_rank: Frequent Contributor
timestamp: January 02, 2014, 11:59:20 pm
content: A friend of my and I have been developing a resonably inexpensive energy harversing development board using the BQ25504 from ti as nano-power battery monitor.The dev board focuses on building / room monitoring. Thus it has the following features:-Barometer (ULP) to measure temperature / detect air flow (is a window open ?)-Low power light sensor (detect presence)-ULP rf transceiver-Cypress psoc 4 device which has sole interesting low power modes (~20nA in "frozen mode)The processing unit will be in some kind of low power mode for the majority of the time, as it waits till a certain battery level /charge is achieved. so it can resume taking measurementsand transmit them via the rf chip.Your input can be a solar cell , or EM energy , vibration , heat etc...I actually went to a TI seminar some time ago and they actually told that it is illegal to harvest rf energy (GSM etc) in some country's.*ULP = ultra low power

author: amyk
author_rank: Super Contributor
timestamp: January 03, 2014, 08:07:08 am
content: Quote from: edavid on January 02, 2014, 08:24:53 pmHere's another situation to consider: does a radio transmitter use more energy when there is a receiver somewhere receiving its signal?

author: peter.mcnair
author_rank: Contributor
timestamp: January 03, 2014, 11:13:33 am
content: Cool...a deep question!For what it's worth: I think that a receiving antenna is not vacuuming up the transmitted energy: photons from the transmitting antenna either hit the receiving antenna or they don't...at leastif the antennas are far enough apart(i.e. in each other's so called far-field). If the antennas are not far apart then there is a mutual interaction (so called mutual coupling) between the antennas. In this case then, yes I think, the loading of the receive antenna would be 'felt' by the transmitter antenna (the system has become a transformer!). I guess this is always the case (at least at some - possibly vanishingly small - level), unless the antennas are infinitely far apart. I have a natural tendency to think in terms of currents flowing on the antennas when they are close together and in terms of photons coming off the transmitter antenna (and being picked up or not by a receiving antenna) when they are far apart.Can’t resist throwing in this thought: (assuming everything is passive) the receiving antenna is simply a transmitting antenna going backwards in time...

author: peter.mitchell
author_rank: Super Contributor
timestamp: January 03, 2014, 11:20:55 am
content: Quote from: edavid on January 02, 2014, 11:55:50 pmI doubt it, magnetic field strength drops off so quick that even products designed to do this kind of thing have a stupidly limited range.

author: Jon86
author_rank: Frequent Contributor
timestamp: January 03, 2014, 11:27:21 am
content: I don't think this energy is necessarily 'wasted', I'm pretty sure you're just inductively coupling to the source.Oh and that video was quite funny, anything that people don't understand is now inherently deadly

author: edavid
author_rank: Super Contributor
timestamp: January 03, 2014, 05:19:43 pm
content: Quote from: peter.mitchell on January 03, 2014, 11:20:55 amAnd the efficiency of a tiny antenna is very low.

author: edavid
author_rank: Super Contributor
timestamp: January 03, 2014, 05:24:47 pm
content: Quote from: amyk on January 03, 2014, 08:07:08 amWhat we are discussing is whether it's the same situation or not... whether the energy transfer is via RF or via inductive/magnetic coupling.Anyway, the answer to your question is not so straightforward. It doesn't matter if the signal is being received or not, but an object in the near field, such as a receiver, changes the impedance seen by the transmitter, and therefore can change its energy use.

author: SeanB
author_rank: Super Contributor
timestamp: January 03, 2014, 06:05:10 pm
content: If the antenna is absorbing power that would otherwise be radiated out it will have little effect on the power supply/transmitter. If however it absorbs energy that otherwise would be reflected back to the antenna it will have a detectable effect on the transmit side. Stealing wasted energy simply means the transmit unit is not very efficient, as you really should design for lowest power use, radiated power is wasted power, unless you are doing a deliberate radiator.

author: SArepairman
author_rank: Frequent Contributor
timestamp: January 03, 2014, 07:25:47 pm
content: is it reasonable to go under the assumption that no energy is lost by the antenna from far field effects while energy is sapped from the antenna by near field effects?assuming you have an antenna and a transmitter separated by miles of free space with no planets around.i mean on a purely theoretical level, how does this work?

author: SeanB
author_rank: Super Contributor
timestamp: January 03, 2014, 08:03:48 pm
content: In a simple sentence, very poorly.

author: AlienRelics
author_rank: Unknown
timestamp: January 03, 2014, 10:46:50 pm
content: Passive RFID works by loading the transmitting coil more or less to communicate with the base. So such a device could be drawing a little extra power not otherwise lost.

author: Stonent
author_rank: Super Contributor
timestamp: January 04, 2014, 04:43:03 am
content: I wonder if you could get a better transmission of power by wrapping a length of wire that's equal to the wavelength of the AC frequency? (50/60/100/120hz) whatever the fluorescent tube uses?Thought the wavelength of 60Hz is 4.9965e+6 meters, I guess that would have to be cut down.

author: Tinkerer
author_rank: Frequent Contributor
timestamp: January 04, 2014, 05:06:51 am
content: If its picking up RF, then no, you arnt adding any load. If its inductive, than yes. If you can move the thing around a room without a drop in power, its probably RF since an inductive field rapidly disapates with distance.On a side note, I have a circuit where I have a 100uF cap connected behind two diodes(and ground). Connected on the other side is a transformer. You can imagine my shock(no pun intended) when I am fiddling around and get a major spark to fly after the circuit had been disconnected for a day or more. Shocked(not literally), I do some measuring and here I see the cap charging up while the circuit is not physically connected to any power source.(and the nearest outlet is 2-3ft away) After leaving it for a while I end up with the cap being charged to 25V and get a pretty good spark to fly from it.

author: SArepairman
author_rank: Frequent Contributor
timestamp: January 04, 2014, 08:38:09 am
content: Quote from: Tinkerer on January 04, 2014, 05:06:51 amhow were the diodes setup? I guess it was rectifying the RF and charging the capacitor with HF DC?i wonder if anything dangerous ever happened because of a parasitic diode (some kind of oxide or w/e) on a big capacitor near a radio transmitter)

author: Tinkerer
author_rank: Frequent Contributor
timestamp: January 04, 2014, 09:32:36 pm
content: Quote from: SArepairman on January 04, 2014, 08:38:09 amThe two diodes were to rectify to DC from the transfomer. It was not originally just a cap sitting at the end by itself, I stripped some stuff out and happened to leave it like that. I imagine had I left the original 16V cap in there something bad may have happened.(the cap is 100V rated now)

author: SeanB
author_rank: Super Contributor
timestamp: January 05, 2014, 08:31:05 am
content: 16V capacitor would just have had increased leakage as the voltage went over around 25V, and would have stayed charged to around that voltage with no problems. energy being added is integrated by the capacitor, you would have other worries if the RF field was adding enough energy to increase pressure in the cap to blow out level, like that you would also be burning.