Energy Harvesting Chat

John So, this is a first for me, should we start with those questions in the sheet?

Shayna Yep, we'll get started with the questions in about ten minutes, @John

John OK

Shayna Usually we'll get a few more coming up during the discussion, but unless they're a pretty quick one-liner answer we generally try to save them for after the question sheet is completed.

Sophi Kravitz hi everyone!

kk.bedead @John well could you give us some field overview first?

Shayna And if you're able to stay longer, the open discussion after is usually pretty fun. :)

Sophi Kravitz @John what time is it there?

Shayna Yes, and if you'd like to introduce yourself in the meantime @John, that would be terrific

Shayna Here's the question sheet once again, for folks who just joined in: https://docs.google.com/spreadsheets/d/12pdRwse7w_fa37hgPZezdCcVQ2WvNw--9SwoBAAFy-M/edit?usp=sharing

kristina panos Hi everyone

Mike Szczys Hi @kristina panos

Zalán Meggyesi Hi!

kristina panos :)

ecomer Hi

Shayna hello

Audi McAvoy Hello everyone

John Ah sorry, closed the chat for a couple of minutes

John Alright it's now 9pm in Rotterdam

John (where I'm based)

kk.bedead is there any kind of command interface available here? #help

John As a background, I'm one of two founders of a R&D company (TWTG) based here.

John You might know us from the Things Network (LoRa WAN) hardware

Andrey is the chat getting recorded?

Jordan Bunker I'll be posting a transcript of the chat afterward :)

Zalán Meggyesi oh cool!

Zalán Meggyesi thanks in advance!

Sophi Kravitz hi @kristina panos !!

Shayna Excellent

John As a company focusing on embedded connected hardware we are working with different forms of Energy harvesting

John We definitely don't know everything, but will try to share some experiences

John insights etc that we gatherd

kristina panos Hi @Sophi Kravitz !_!

John So i guess that's it in short,

John are we ready to start this madness?

Shayna Ready to start with the questions, @John ?

Shayna :)

John Yes sure

kk.bedead \o/

John Should we start with the sheet?

kk.bedead give us some overview of existing methods pls

Shayna First question is from @Charlie Lindahl : "What reference(s) do you recommend? I would like your opinion on two:

(1) https://www.energyharvestingjournal.com/

(2) https://spectrum.ieee.org/consumer-electronics/gadgets/three-technologies-for-harvesting-ambient-energy"

John I think both are usefull

John read them earlier, great to get to know what's happening in the area

John (we prefer hackaday ofcourse)

John Next question I liked

Shayna Here's @Charlie Lindahl again: "Similar queston: have you looked at the RuuviHarvester platform yet? (see GITHUB archive at https://github.com/ruuvi/harvester). "

John We love the opensource Ruuvi platform

John It's a nice platform to start thinkering,

John tinkering

Todd Pollman Thinkering is what I do before tinkering.

Shayna Hehe

Shayna Next up from @zakqwy : "Any recommendations for [economically] measuring the extremely low currents present while developing energy harvesting devices?"

John Let me combine this with the next question

Shayna That would be from @Josh Cole : "Do energy harvesting devices require special software/firmware that can withstand the volatile amounts of voltage that may or may not be available?"

John Sorry meant the one after that

Shayna From @Shantam Raj : "What are some good practices in ultra low power design that implement energy harvesting so that the leakages at various points in the circuit is minimum?"

John In a ultra low power solution it's good practice to switch off a lot of subsystems with loadswitches

Paul Crouch Low current measurement: Dave's uCurrent?

https://www.eevblog.com/projects/ucurrent/

John SO to measure the current in the easiest way you could actually use a lot of default solutions, but just make sure to disconnect them completely

John A lot of the default energy harvesting IC's normally have these build in anyway

zakqwy So the IC has switches built in to switch loads.. but how do you measure total draw, other than (a) an expensive bench meter or (b) a uCurrent from Dave?

John As a bench setup we use the uni-T UT61E

John It's quite affordable for these kind of applications

Shayna Back to @Josh Cole : "Do energy harvesting devices require special software/firmware that can withstand the volatile amounts of voltage that may or may not be available?"

John More expensive, but more accurate is a Brymen mb869s

John https://www.youtube.com/watch?v=Bz6CYDRl1M8

YOUTUBE MJLORTON

John bonus points

John Firmware, correct

John You will need something different than your normal approach

kk.bedead well, obviously

John We use a scheduler approach

John This will take the available amount of energy in account

John "Energy based scheduler" (time for a project page)

Josh Cole interesting!

John Should we finish the questions and then circle back to this if interested?

Shayna Next up from @Shantam Raj : "With reference to https://hackaday.io/project/20523-sun-self-sustained-ultralow-power-node , what more can you suggest to extract as much energy as possible and to reduce power wastage in schottky diodes, leakage current in programming resistors, leakage in digital electronics especially the I2C bus?"

Shantam Raj Sure

John We like your project! Haven;t seen it before

John Go on!

John But on your question:

John good practise in ultralowpower design would be: choose low-power components, apply load-switches, apply high-impedances where possible, etc.

Shantam Raj Thanks a lot @John

John Seems trivial

John For your design using loadswitches could already make some difference

John Diodes with low drop helps

John In situations with sleepcurrent a DC/DC might not be ideal

Shantam Raj Already done as much as i could. If you go through the schematics and components i have used you wll realize that i made sure leakages are minimum, voltage drops are minimum etc. But i always feel there is some room for improvement. I just graduated a couple of months ago and i feel like i don't have much expertise.

John These might be good for you: HSMS-2850 250mV

John Look into them

Shantam Raj Oh, is that so? I am of the opinion that DC/DC are more efficient than LDOs

John A LDO sometimes could be more efficient

John depends on your setup etc of course

Shayna Another from @shantamraj "What are some really efficient commercial/academic products out there that implement energy harvesting and should be on our lookout to learn more about the frontiers in energy harvesting? (From the point of view of rather small digital electronics)"

Shayna (Another user posted a response to this one, "Check out bigbelly.com - they claim to be self-powered, and they make smart city products. Like connected waste bins.")

John do's and dc-dc converters have a quiescent current, if you do not require a precise voltage, you can use ordinary diodes to drop the voltage. The big advantage is that as diodes are placed in series, they can not consume a (quiescent) current.

John Enocean have great modules as well

John Answers this your questions?

Shantam Raj Yes

John Next

John How would you handle harvesting various ambient energies at once? Say for example, 60Hz, 1800Mhz, and 5GHz?

Shayna From @Soul_Est : "How would you handle harvesting various ambient energies at once? Say for example, 60Hz, 1800Mhz, and 5GHz?"

Charlie Lindahl Have you seen any energy harvesting happening on watches? I have a Pebble and was going to use their API & hardware connector for some sort of external power, but then of course Fitbit bought Pebble and killed off the platform.

John Please clarify, I think you mean RF harvesting correct? Or are you thinking about communication?

Charlie Lindahl I'd still like to find a way to "energy harvest" for my Pebble and whatever my next watch is.

Charlie Lindahl [Sorry, will get to my questions after you finish the thread you're on]

John @Charlie Lindahl Would love it. Problem will be the software platform of the pebble

Shayna Any comments on that, @Soul_Est ?

Shayna Ah sorry

Soul_Est Yes, John, I meant RF harvesting.

John it;s more focused on the battery internally, getting more of a "hybrid" solution, charging the battery

John But yeah, why not.

John use a coil for the 60 hz and a multiband antenna for 1800 and 5 GHz with a harvester

John or use a piezo and attached to a magnet near an ac source, this can yield pico to micro watts

John sorry nano wats

John watts

John But talking RF harvesting, best results are in the GSM bands

John or in the 2.4 ghz if you can control the environment

John Result is very low, but constant. Making it very interesting

John check this out: https://hackaday.com/2017/10/02/fm-snake-feeds-off-radio-waves/

John (hackaday reference bonus points)

Shayna ;)

kristina panos I still want to make one of those

Shayna From @ecomer : "Curious about ambient energy harvesting in very rural areas with little stray electronic noise, especially when solar is difficult, especially storing adequate solar energy to last through the night. Especially curious when solar is NOT an option (remember the very rural low electronic noise setting)"

Soul_Est Thank you, John. =)

John Interesting

John Care to share a little bit more about the application?

John Normally solar with a (super) cap setup could work?

ecomer Clarification: My project currently uses 2V solar with boost and AA battery storage. I'd like to eliminate the solar, if possible, but not sure what ambient energy is available in a very rural environment. Stray RF from the ether would seem to be all that there is once solar is eliminated.

John Well, if you want to go crazy: maybe get energy from temperature difference with the ground: using a peltier element?

John (try it for science, throw it away, use solar)

John Why don;t you want to use solar?

John How much do you think you'll need?

ecomer Any idea just how much energy can be harvested from the sky in a rural setting?

John Maybe a windmill?

ecomer 50ma hourly bursts, sleeping between

John bursts of how long?

ecomer ~30-50ms

John This could be done with a relative small solar panels

John We have some good experience with the ones from IXYS.

John Combine these with a good supercap setup and that could work

ecomer That's what I'm doing now - small 2V panels. Seeking alternatives

John With an 3.7v 1 mA hour solar panel, there would be enough energy

John IXYS SLMD600H10L or it's bigger brother

Shayna Next up from @Richard Hogben : "Thoughts on (or alternatives to) the adafruit solar charger? https://www.adafruit.com/product/390"

John I'm vanilla

John Haven;t used it

Shayna From @Shantam Raj : "In the aftermath of a nuclear war when there is no more infrastructure, do you think energy harvesting would come to our rescue? What type of energy would be exploited more than the others? How would the world of electronics adapt to such a situation?"

Richard Hogben anything similar that might be in stock?

John @Richard Hogben Nothing comes to mind, let me check it and will update the sheet later

John » Most electronics are not rated for heavy amounts of radition. Let's hope we do not have to design our circuits for this as well.

John Vault dweller you

Shayna hehe

Shayna Another from @Shantam Raj : "When you talk of load switches, would you rather prefer dedicated ics that need a power rail to function(thereby needing a specific minimum voltage to work) or a circuit made from mosfets in such a way that it can work even with really low voltages(say below 1V) and yet be able to switch properly? I spent a lot of time with the latter but failed miserably. Do you have such a switch design in mind or have you come across one ?"

John Minimum voltage is the key point of energy harvesting, Mosfet based switches works fine

John I don;t have a default design for you in mind but it is the way to go

John we also use dedicated ic's for switching sensors, but in cases where it is non critical or a softstart is required low power p-mosfets can be used

John ic's are designed to be as low voltage as possible but voltage doubler with low dropout diodes can be implement if you want to design it yourself

John FDN306P

John might be interesting to look at

Shayna Returning to @Charlie Lindahl 's previous comments: "I'd still like to find a way to "energy harvest" for my Pebble and whatever my next watch is. The Pebble has a "port" for doing power and other interfaces, as does the Apple Watch"

John Pebble nor the Apple Watch were not designed with very low power in mind. Even the sleep current is higher than energy harvesting can provide.

Shayna Another person commented further: "Pebble nor the Apple Watch were not designed with very low power in mind. Even the sleep current is higher than energy harvesting can provide."

Shayna Or you rather :)

John Yeah liked that comment

John the problem is that you will have to step up the voltage high enough to charge the internal battery

John making it less efficient, but still go ahead, curious to see!

John mechanical design will be a challenge

John I suppose

Shayna Lastly from @Shantam Raj :

Shayna "One big problem with charging LiPo batteries using solar energy harvesting or any other source of harvesting is that the charging is intermittent. For sometime it is charging and even when the capacity is NOT full, because of environmental conditions it may start discharging. But LiPos don't like this. They want to be charged and discharged properly and undergo this cycle for max longivity. So alternative storage elements need to be looked for, like supercaps. But the problem with supercaps is its linear discharge curve that digital electronics hate. Are there other types of storage elements apart from these two?"

Shantam Raj ...apart from these two that mitigate both the problems?

John Most of Ics have overvoltage under voltage protection saving your lipoBQ25504

John BQ25504 might be a good one?

George Hahn Oops, I forgot I'm not EST anymore :P

Josh Cole If I may ask, in that same problem space, Would you say super caps are better for energy harvesting devices, or lipo batteries?

John About the alternative storages,

Shantam Raj That is fine, even i am using BQ25505 and BQ25570 for my projects. But what worries me is that a charge cycle is never completed properly. This is detrimental to the LiPo.

John We love supercaps, but they do have their downsides

Christoph what about LiFePO4?

John We haven't used them, but could work

John more cycles = more better

Shayna Thank you so much for joining us today @John

John No problem at all

Shayna If you want to stick around for open discussion, we'd love that :)

Shayna Otherwise, thank you again and twtg.io

John I;ll be here for some time, but won't be that long. If needed message me directly

John Thanks

kk.bedead wow, that's all right?

kk.bedead was not much of a use tho

John Thanks

Arsenijs Well, it's only as useful as questions asked

John @Shantam Raj About your project;

John
- I2C only consumes current when the pins are driven LOW. Every time the microcontroller communicates with I2C devices, it sends the address byte. Connecting the address pins to VDD instead of GND saves current every time you communicate with the ic.

- adding some bulk capacitance after the dc-dc converter reduces need for switching. Less switching = higher efficiency.

- increase 1kohm resistors at input of U1

- different schottky diode part numbers have different reverse current leakage

Arsenijs Thank you, John! Was a great read =)