๐ฌ The Harvester: ultimate power supply for the Raybeacon DK
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Hi @NeverDie,
I also have the strong feeling that a couple of voltage detectors could make it much easier, yet โ due to picoamps leakage โ more effective.
Such, in the couple of last days I've tried to reproduce the UB40M circuit with real transistors. Perhaps, when you build a die you can construct every transistor with the parameters you need, but I admit it was not a trivial task to pick anything suitable from a catalogue. I defined no strict constraints to the application, rather tried to be opportunistic and use whatever works. There were some assumptions though:
- Input voltage is defined by the solar cell and is somewhere between 2V and 3V. In the deign below it's set to 2.5V.
- The short circuit current for the cell should not extend 50 nA. I've limited it down to 25 nA with the Rcell = 2.5V/25nA = 100Mฮฉ.
- The harvester should be able to charge 22ยตF storage capacitor - this capacity should be enough to send a single non-connectable BLE advertisement.
I haven't bothered to find the low leaking MOSFETs and chose something small, handy to solder, cheap, and in stock. That turns out to be power MOSFETs in PowerPAK SC-70 package from Vishay. The nomenclature is SiAxxxDJ where the xxx is what you may see in the circuitry below. For example, 421 stands for SiA421DJ.
The core of the circuit is the pretty much of the UB40M reference design. The series of MP5-MP7/MN6-MN8 triggers will pull Reset line high when VREF will become low. This will happen when MN5 will pull it down, and depends on the Vdet voltage. At the same time, the MP4 will be turned off by VoutL (Reset) thus preventing VinL from being unintentionally pulled to the GND. The MP3 is used as a diode there.
I failed to create the VREF voltage in the way it was defined in the Bristol paper. With the circuit powered by the very low-power source, it suffers from transient processes a lot. To address that, I went for more complicated solution with couple of triggers controlled by Rdet1+Rdet2 divider. The divider also allows to tune the circuit to better match source and storage capacitor.
Finally, there is a 1k load attached to the Vin line. It discharges the Cstore capacitor as soon as the Reset will be set high. Upon discharge, the voltage detector will went reset the Vdet and the Cstore will be charged back.
In my KiCad ngspice it looks as follows. With Vcell=2.5V, Icell=25nA the Vin oscillates between 1.4V and 1.95V. Although this is way below required 1.8V for most of sensors and MCU, raising solar cell voltage to 3.5V will shift the voltages to the usable range.
Discharge current is limited solely by the Rload=1k. At the same time, average current consumption of the harvester is about 3nA - the blue line I(Rharv). Solar cell load is below 10 nA - the yellow line I(Rcell). However, due to non-linear nature it's hard to predict how the line will look like with a real cell. Probably, it's better to simulate it with a current source, I don't know. The red line Vdet shows how the voltage detector works.
To be honest, I'm quite unhappy about the circuit.
First of all, it uses a lot of transistors, please compare this to the BJT harvesters you're working on. Also, many of them work on subthreshold voltages, and this makes it relatively hard to to tune. But worse, real devices will likely to suffer from the voltage interference which makes the whole circuit too fragile. Taking in account the money to build it (even with $0.40 per FET), it turns out the circuit shall be considered rather impractical.
:man-shrugging:You may be unhappy with your circuit at the moment, but to my eyes it looks like you've got some traction and you've made a good start.
@Mishka said in ๐ฌ The Harvester: ultimate power supply for the Raybeacon DK:
I haven't bothered to find the low leaking MOSFETs and chose something small, handy to solder, cheap, and in stock. That turns out to be power MOSFETs in PowerPAK SC-70 package from Vishay. The nomenclature is SiAxxxDJ where the xxx is what you may see in the circuitry below. For example, 421 stands for SiA421DJ.
Not sure if what I'm finding out about my Vishay SiRA80DP mosfet might be similar to your Vishay mosfet, but I'll mention it anyway as a possible "heads up": I'm finding evidence of a pretty wide discrepancy between Vishay's SPICE model and what's physically true by measurement. Although I don't yet have a picoammeter (I'll be building one soon) for a more definitive test, I was able to do a relevant measurement with the voltage follower I built (see picture in previous post). The test circuit, to indirectly compare leakage of two different mosfets, was this:
If the mosfets were ideal and there were no leakage in either mosfet, then presumably the voltage measured at VF1 and VF2 would both be 3.3v. But, of course, they're not ideal: simulation shows that VF1 would be 3.12v an VF2 would be 1.59mv. I built the circuit and the actual measurements, taken with my voltage follower and a DMM, were almost the complete opposite: VF1=280mv and VF2=3.01v. i.e. the Vishay mosfet measured as far more leaky than predicted by TINA TI spice simulation of Vishay's SPICE model, and the other N-Channel mosfet (one of two mosfets on Diodes Incorporated DMC2700UDM-7) measured as far less leaky than predicted. It's a very easy test to perform... ahem, that is, if you are in possession of a 10 gigaohm resistor and a buffer (voltage follower) with a picoamp input bias. :wink:Edit1: Come to think of it, a better way to test would be to use no resistor and just measure how much leakage there is with the gate set to GND. The leakage would likely be in the nanoamps, so it could be measured with a uCurrent Gold, or equivalent, which maybe you already have in your possession. Setting the DS voltage to whatever is listed in the datasheet for the leakage value would then give a number that can be directly compared to the leakage entries in the datasheet. Much easier and doesn't require high value resistors or exotic buffers! :grin: Obvious in retrospect. May or may not require a picoammeter, depending on the mosfet. To cover all the cases, I'll try these measurements after I build my picoammeter (soon!). I'll be building the inexpensive picoammeter designed and already vetted by an EEVBlog user named "Gyro":
https://www.eevblog.com/forum/beginners/static-control-requirements-for-picoamp-measurements-using-ucurrent-gold/msg3068708/#msg3068708
For anyone interested, you can find photos and all the details here: https://www.eevblog.com/forum/projects/picoammeter-design/msg790045/#msg790045
Rather than reduced to a nice simple PCB, the critical parts are air-wired, which is deemed the superior method according to the op-amp's datasheet. In addition, to better ensure accuracy, the DUT and all the measurement instruments should be enclosed together within conductive shielding as a countermeasure against external interference when measurements are taken. -
I tried soldering wires directly to some femtofet's, but I've concluded they either need to be locked down to a larger substrate with glue or else properly reflowed in an oven. Otherwise, they behave like super energetic tiddly-winks: even the slightest bump when attaching the first wire will make the femtofet jump great distances, most likely never to be found or seen again. :face_with_rolling_eyes: I lost 3 in a row that way, so my next attempt will use glue and very fine wire. I have an idea on how I might pre-align the wires prior to soldering, which is probably necessary in order to hand solder such a tiny thing.
My first attempt at a picoammeter is almost built. Unfortunately, it might might work well only with a DMM and not so well with an o-scope. So, I may have to build something different for that.
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Regarding the hand soldering of itty-bitty components, this inspiring video shows it can be done:
https://www.youtube.com/watch?v=edERx4x5eY0 -
I tried soldering wires directly to some femtofet's, but I've concluded they either need to be locked down to a larger substrate with glue or else properly reflowed in an oven. Otherwise, they behave like super energetic tiddly-winks: even the slightest bump when attaching the first wire will make the femtofet jump great distances, most likely never to be found or seen again. :face_with_rolling_eyes: I lost 3 in a row that way, so my next attempt will use glue and very fine wire. I have an idea on how I might pre-align the wires prior to soldering, which is probably necessary in order to hand solder such a tiny thing.
My first attempt at a picoammeter is almost built. Unfortunately, it might might work well only with a DMM and not so well with an o-scope. So, I may have to build something different for that.
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I have a working picoammeter now:
Because it's a very sensitive measuring instrument, I'm working out how to automate the collection of measurement data so that all measurements of a DUT can be made within a shielded secondary enclosure. -
XC6190 is a voltage detector (1.47v trigger voltage) with what it claims is just a 10na quiescent current. Sounds pretty good to me:
https://www.mouser.com/datasheet/2/760/XC6190-837296.pdf -
Here's a courtesy heads-up.
I just now stumbled across a circuit:
published here:
https://www.edn.com/solar-powered-motor-runs-on-10-na/
that allegedly can operate on as little as 10na while collecting energy, which it then uses to power a small pager motor once a threshold voltage is reached.It also has the virtue of utilizing inexpensive jelly bean parts and not relying on gigaohm resistors, which in the Dave Johnson circuit turned out to be so large that I lack the means to verify their specs through measurement after they are delivered.
This other guy instantiated the circuit as a PCB, and he made the gerber for it available as a free download: https://hackaday.io/project/159691-electron-bucket-extreme-power-management-module
If it turns out to be true that the circuit can both collect the current and trigger at a threshhold voltage all with just 10na of overhead, then on its face it sounds better than the David Johnson circuit turned out to be and possibly also better than many/most/(all?) of the commercial chips that we've reviewed on this thread if paired with an appropriate amorphous solar panel.
Edit:
But wait! There's more. There appears to exist an equivalent single chip voltage detector that also consumes a mere 10na of current: https://www.akm.com/content/dam/documents/products/power-management/power-ic-for-energy-harvesting/ap4405aen/ap4405aen-en-datasheet.pdf
It's itty bitty, so it's probably a great fit for your uber-compact design."But I want more!" I can hear you say. "I want a total step-up solution! And I want one that doesn't use a transformer!" Well, of course you do. Who wouldn't? Apparently, a 0.2v transformerless step-up solution does exist as well. I'm just not sure where. They developed it for a customer who wanted to harvest energy from... bacteria. Actually, the official term is "microbial fuel cell." The chip is the AP4470, and thankfully it can also be powered by solar, without bacteria.
https://solutions.akm.com/us/en/applications/energy-harvesting/
But can we buy it? Or is it just another inaccessible research project? I don't yet know. Can you read Japanese? The trail of bread crumbs written in English seems to run cold after the above link, but there's more about it that's written in Japanese. Argh. -
Gah! I've lost the ball :disappointed:
No progress on discrete harvester, sorry. Also, the PV panels I got earlier were shelved until better times.
I still monitor a couple of the SPV1050 devices though. They're running from various PV panels that I switch from time to time. The load is an nRF52833 beacon and sometimes an IMU broadcasting every one second at 0dBm to 8dBm and reporting voltage of attached ML2032 battery to my phone.
My experience is that a tiny PV panel cannot sustain the device working online. By online I mean that both the device and the harvester power consumption exceeds the panel capabilities, so the battery slowly decays. A bigger panel can address the issue. I still unsure how much we will win if a more efficient online harvester like AEM10941 or even more efficient R1800K will be used. A batch harvester is definitely the way to go.
But how about you? Have you had a chance to build anything yet?
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Gah! I've lost the ball :disappointed:
No progress on discrete harvester, sorry. Also, the PV panels I got earlier were shelved until better times.
I still monitor a couple of the SPV1050 devices though. They're running from various PV panels that I switch from time to time. The load is an nRF52833 beacon and sometimes an IMU broadcasting every one second at 0dBm to 8dBm and reporting voltage of attached ML2032 battery to my phone.
My experience is that a tiny PV panel cannot sustain the device working online. By online I mean that both the device and the harvester power consumption exceeds the panel capabilities, so the battery slowly decays. A bigger panel can address the issue. I still unsure how much we will win if a more efficient online harvester like AEM10941 or even more efficient R1800K will be used. A batch harvester is definitely the way to go.
But how about you? Have you had a chance to build anything yet?
@Mishka Nice to hear from you again!
When you left I decided to take a break from solar, and so I shifted my attention back to PCB milling, to take advantage of some technological progress now at fruition which resulted in inexpensive, high precision magnetic encoders that have since made cheap closed-loop stepper drivers possible.
As for solar, not sure if you caught it in the news, but worthy of note was the breakthrough announced a few months ago of 6-layer solar cells capable of 39.2% efficiency at 1 sun illumination. For solar PV, that's a monumental breakthrough. The work was done at NREL. So, although that's a very recent breakthrough and not something we can yet buy, I do think we'll be seeing more efficient than usual solar cells within a year that will be hybrid silicon and perovskite, and those will have better efficiencies than what's available now. IIRC, Oxford PV plans to launch production of 400w solar panels at year end, and those will be things that anyone can buy, and so the solar cells in them should be available as well.
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@Mishka Nice to hear from you again!
When you left I decided to take a break from solar, and so I shifted my attention back to PCB milling, to take advantage of some technological progress now at fruition which resulted in inexpensive, high precision magnetic encoders that have since made cheap closed-loop stepper drivers possible.
As for solar, not sure if you caught it in the news, but worthy of note was the breakthrough announced a few months ago of 6-layer solar cells capable of 39.2% efficiency at 1 sun illumination. For solar PV, that's a monumental breakthrough. The work was done at NREL. So, although that's a very recent breakthrough and not something we can yet buy, I do think we'll be seeing more efficient than usual solar cells within a year that will be hybrid silicon and perovskite, and those will have better efficiencies than what's available now. IIRC, Oxford PV plans to launch production of 400w solar panels at year end, and those will be things that anyone can buy, and so the solar cells in them should be available as well.
Hi @NeverDie,
The 39% is a HUGE!
I think there is must some fundamental limit on how much we can get from these oscillations of the, well, Ether. Or is it the quantum vacuum? Or the strings? Well, the very last name to this kind of shit is the time crystals. And, no matter what the name is, the shit can oscillate, and these oscillations are the essence of the energy. So, while currently most of electronic devices employ electrons as drivers, I'm wondering would it be possible to build an electron-less system where the oscillations (aka waves) may be passed through a number of transformations, and this will bring us to some useful things.
Actually, there is RF and optics which works exactly like that. There is also a number of RF harvesters to collect the energy, but the energy is used mostly to push electrons forward, i.e. produce direct current. That's understandable - most of devices are DC. But creating some kind of a microwave transistor would be just rad.
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@Mishka Nice to hear from you again!
When you left I decided to take a break from solar, and so I shifted my attention back to PCB milling, to take advantage of some technological progress now at fruition which resulted in inexpensive, high precision magnetic encoders that have since made cheap closed-loop stepper drivers possible.
As for solar, not sure if you caught it in the news, but worthy of note was the breakthrough announced a few months ago of 6-layer solar cells capable of 39.2% efficiency at 1 sun illumination. For solar PV, that's a monumental breakthrough. The work was done at NREL. So, although that's a very recent breakthrough and not something we can yet buy, I do think we'll be seeing more efficient than usual solar cells within a year that will be hybrid silicon and perovskite, and those will have better efficiencies than what's available now. IIRC, Oxford PV plans to launch production of 400w solar panels at year end, and those will be things that anyone can buy, and so the solar cells in them should be available as well.
Regarding the PCB milling, I found myself thinking fairly often about full-cycle manufacturing too :-)
I usually do small boards, up to 4x4 inch. For this size it should be possible to build an affordable, but highly capable machine. Some thoughts on it:
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High precision. The machine must be able to cut tracks and pads as thin as 6 mils (0.15 mm), but 5 mils would be really nice to achieve. Because of this I'm more inclined to laser cutting. On a milling machine 6 mil gaps between tracks will be hard to do. Another advantage of laser cutting is that it won't tear tiny tracks off the board. Perhaps, even a copper foil can be laser cut. But there's also a spoon of tar: the copper is known to be very reflective and imposes higher requirements to the laser cutter - the price may increase. Another thing to note is that the laser may be not so good at removing large surface areas.
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Kapton tape for solder mask. For sticky mask to apply, I'm also thinking about some kind of a pallet - this would allow to use cheap polyimide tapes from eBay. Alternatively, non-sticky masks can be laminated. Laminated masks will stick stronger and can be two sided - think of it as about three and more layers. Again, laser cutting is preferred here.
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Engraving of the silk layer. Laser could be also used for high-res silk layer over the kapton tape. With laser used, the difference in distances from the head to surface because of the copper layer is not an issue. Engraving on both copper and substrate is also possible.
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Interchangeable heads? Probably, no. The cost of the working head, either laser or milling, will likely dominate over the cost of other components - the machine is small. Seems it's more reasonable to have different machines.
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Assembly machine. This would be my favorite, but first things first.
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Regarding the PCB milling, I found myself thinking fairly often about full-cycle manufacturing too :-)
I usually do small boards, up to 4x4 inch. For this size it should be possible to build an affordable, but highly capable machine. Some thoughts on it:
-
High precision. The machine must be able to cut tracks and pads as thin as 6 mils (0.15 mm), but 5 mils would be really nice to achieve. Because of this I'm more inclined to laser cutting. On a milling machine 6 mil gaps between tracks will be hard to do. Another advantage of laser cutting is that it won't tear tiny tracks off the board. Perhaps, even a copper foil can be laser cut. But there's also a spoon of tar: the copper is known to be very reflective and imposes higher requirements to the laser cutter - the price may increase. Another thing to note is that the laser may be not so good at removing large surface areas.
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Kapton tape for solder mask. For sticky mask to apply, I'm also thinking about some kind of a pallet - this would allow to use cheap polyimide tapes from eBay. Alternatively, non-sticky masks can be laminated. Laminated masks will stick stronger and can be two sided - think of it as about three and more layers. Again, laser cutting is preferred here.
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Engraving of the silk layer. Laser could be also used for high-res silk layer over the kapton tape. With laser used, the difference in distances from the head to surface because of the copper layer is not an issue. Engraving on both copper and substrate is also possible.
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Interchangeable heads? Probably, no. The cost of the working head, either laser or milling, will likely dominate over the cost of other components - the machine is small. Seems it's more reasonable to have different machines.
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Assembly machine. This would be my favorite, but first things first.
@Mishka I wouldn't say 6 mil is easy to achieve, but some people claim they can get it on even a sub $200 machine. That was the premise for this other thread that started here: https://forum.mysensors.org/topic/7836/what-did-you-build-today-pictures/161 and then became its own thread here: https://forum.mysensors.org/topic/8735/cnc-pcb-milling
I think for just about everything I do though being able to etch at a 0.4mm lead pitch (that's 0.4mm center to center on the pads) is good enough, and that's a lot easier to achieve. For instance, that's the pitch on an SPV1050 or an nRF52832.
There is industrial equipment that can etch copper PCB directly using a laser, but it must be pricey because I have not read of any hobbyists using it. It would likely require a fiber laser.
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Regarding the PCB milling, I found myself thinking fairly often about full-cycle manufacturing too :-)
I usually do small boards, up to 4x4 inch. For this size it should be possible to build an affordable, but highly capable machine. Some thoughts on it:
-
High precision. The machine must be able to cut tracks and pads as thin as 6 mils (0.15 mm), but 5 mils would be really nice to achieve. Because of this I'm more inclined to laser cutting. On a milling machine 6 mil gaps between tracks will be hard to do. Another advantage of laser cutting is that it won't tear tiny tracks off the board. Perhaps, even a copper foil can be laser cut. But there's also a spoon of tar: the copper is known to be very reflective and imposes higher requirements to the laser cutter - the price may increase. Another thing to note is that the laser may be not so good at removing large surface areas.
-
Kapton tape for solder mask. For sticky mask to apply, I'm also thinking about some kind of a pallet - this would allow to use cheap polyimide tapes from eBay. Alternatively, non-sticky masks can be laminated. Laminated masks will stick stronger and can be two sided - think of it as about three and more layers. Again, laser cutting is preferred here.
-
Engraving of the silk layer. Laser could be also used for high-res silk layer over the kapton tape. With laser used, the difference in distances from the head to surface because of the copper layer is not an issue. Engraving on both copper and substrate is also possible.
-
Interchangeable heads? Probably, no. The cost of the working head, either laser or milling, will likely dominate over the cost of other components - the machine is small. Seems it's more reasonable to have different machines.
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Assembly machine. This would be my favorite, but first things first.
@Mishka On the other hand, as I just posted on the CNC thread, using a regular etching laser to remove black solder mask above copper pads might be an awesome solution: https://forum.mysensors.org/topic/8735/cnc-pcb-milling/801
At least notionally, it sounds more bullet proof than using a spring bit to grind off the solder mask in those locations without damaging the copper underneath. Maybe even a lower power etching laser (relatively speaking) would suffice for doing it, as long as the beam spot was sufficiently small and sharply defined. -
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@Mishka On the other hand, as I just posted on the CNC thread, using a regular etching laser to remove black solder mask above copper pads might be an awesome solution: https://forum.mysensors.org/topic/8735/cnc-pcb-milling/801
At least notionally, it sounds more bullet proof than using a spring bit to grind off the solder mask in those locations without damaging the copper underneath. Maybe even a lower power etching laser (relatively speaking) would suffice for doing it, as long as the beam spot was sufficiently small and sharply defined. -
I had thought these energy harvesting chips were kinda pricey, but then I went shopping for a good buck/boost MPPT 12v SLA battery charging chip. I found one that I like called the LT8491 (https://www.analog.com/en/products/lt8491.html#product-overview), but it's priced at $25/chip on both digikey and mouser. The same is true for the somewhat simpler LT8490, which is buck/boost MPPT but without the built-in 12v SLA battery charging features. What's surprising is that aside from those two chips, I haven't found any other MPPT buck/boost chips that seem suitable for charging a 12v battery. At best the other chip solutions are MPPT buck, and far more commonly PWM buck, but in neither case with any boost capability. I wonder why would that be? I bring it up on this thread as a datapoint because it's a similar set of issues, just at 12v instead of the much lower voltages we've been considering. That said, there do exist some MPPT buck/boost solar charge controllers on offer from various vendors, but those prices are around $80 and up, which doesn't make sense for my application, which is keeping my car battery fully charged: during the covid19 apocalypse I'm not doing enough driving to keep it charged in the regular way. At $80+ I' reckon I'd be better off just adding another solar panel behind the windshield and not worrying about MPPT.
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Art Resin tested a large number of different epoxies, and it seems that all of them yellowed to some degree over time, but some a lot more than others:
https://youtu.be/MzIxcIqCNh8Of course, since it was a test designed to make Art Resin look good, perhaps they omitted epoxies that really do never yellow. I just don't know which ones those would be. Eight weeks, which was the limit of their study, doesn't seem like a particularly long time.
@NeverDie said in ๐ฌ The Harvester: ultimate power supply for the Raybeacon DK:
Art Resin tested a large number of different epoxies, and it seems that all of them yellowed to some degree over time, but some a lot more than others:
https://youtu.be/MzIxcIqCNh8Of course, since it was a test designed to make Art Resin look good, perhaps they omitted epoxies that really do never yellow. I just don't know which ones those would be. Eight weeks, which was the limit of their study, doesn't seem like a particularly long time.
Reporting back on this: after looking into this further, it turns out there are a wide range of factors that need to be evaluated in order to pick the right encapsulate to use. Some of those factors are sumarized here: http://www.strsolar.com/UploadedFiles/Files/STR_Protected.pdf by STR, a company that has done basic research into how best to prevent yellowing. They've been running weathering tests in Arizona for over 22 years now to see what works and what doesn't. However, it's even more complicated than that: you need to test the entire assembly and also its location (e.g. on a hot roof or on open backed panels on the ground) because both strongly influence the outcome. Also, and perhaps even more significantly, and as described in this paper here: https://www.researchgate.net/publication/271553442_Discoloration_of_PV_encapsulants
they got their best results when using a particular low-iron glass known as Solite that was doped with Ce,.
In contrast, things went much worse when they tried using a low-iron glass (such as Starlight) which wasn't doped with Ce. The trouble is, according to the linked paper: neither Solite nor any other similar glass doped with Ce is commercially available anymore. As you can tell from the marketing material linked above, that fact seems to be completely glossed over, leading most people into thinking that STR had solved the problem and all you have to do is buy the STR encapsulant. As a result, I'm not sure whether any of the current encapsulant formulations will be successful in the longer-term at avoiding yellowing. Perhaps there have been further improvements since 2013, but if so, what are they? Anyhow, what's clear is that without hard empirical performance data with regard to a particular solar assembly, it becomes very easy to draw incorrect conclusions about what works best and what doesn't. -
@Mishka said in ๐ฌ The Harvester: ultimate power supply for the Raybeacon DK:
@NeverDie Cutting panels should just work. I'm unsure how do you attach wires to it though. I'll be grateful if you will share your findings.
Closing the loop on your question, it looks as though they can be cut:
https://www.ebay.com/itm/0-5W-0-5V-High-Efficiency-Back-Contact-DIY-1-6-Cut-Sunpower-Solar-Cell-36pcs-lot/291858971298?hash=item43f4267aa2:g:hsAAAOSwxp9W5tui
I've read that cutting them with a laser is the recommended method. I only just came across this, and I haven't yet found a vendor selling just one solarpower solar cell lasercut into six pieces like that yet, although the above ebay auction demonstrates that you can buy them in bulk that way.@NeverDie said in ๐ฌ The Harvester: ultimate power supply for the Raybeacon DK:
@Mishka said in ๐ฌ The Harvester: ultimate power supply for the Raybeacon DK:
@NeverDie Cutting panels should just work. I'm unsure how do you attach wires to it though. I'll be grateful if you will share your findings.
Closing the loop on your question, it looks as though they can be cut:
https://www.ebay.com/itm/0-5W-0-5V-High-Efficiency-Back-Contact-DIY-1-6-Cut-Sunpower-Solar-Cell-36pcs-lot/291858971298?hash=item43f4267aa2:g:hsAAAOSwxp9W5tui
I've read that cutting them with a laser is the recommended method. I only just came across this, and I haven't yet found a vendor selling just one solarpower solar cell lasercut into six pieces like that yet, although the above ebay auction demonstrates that you can buy them in bulk that way.Closing the loop even further, I received one of these 50 watt panels:
As you might be able to guess from the photo, and I'm able to confirm because I can see it up close, every single solar cell was cut in half prior to assembly. It looks as though Sunpower then used some kind of conductive tape (?) to make the electrical connections from one cell to the next. Or perhaps a flex cable of some kind? Then the whole layout was sent through a laminator. Seems as though it would be very efficient to manufacture. I'm impressed that 50 watts can be produced by such a relatively small assemblage. Hopefully Sunpower picked materials that won't yellow or brown with sun exposure and time! If so, then this might be better than most of what is commercially available, let alone the solar cell encapsulations from aliexpress that last only a few months in direct sunlight before they become so opaque as to be unuseable. -
Julien stumbled across an inexpensive PFM boost converter board which he demonstrates is able to boost 65mv up enough to light a red LED:
https://www.youtube.com/watch?v=x9_IrWipelQI can't discern from the video what the minimum start-up voltage was, but it's quite a surprising finding anyway, because on its face it would appear to outperform most of even the energy harvesting chips on the market with respect to minimum operating voltage!
Edit: In a subsequent video, Julien found that the start-up voltage was 560mv (the datasheet only promises 0.9v as the minimum, so maybe Julien got lucky with his particular device):
https://www.youtube.com/watch?v=eVXvOl7VqXIbut he's able to keep it running (albeit with just a 1.2v output and little to no load) on what he says is an input voltage of as little as 10mv. That matters because by keeping it running it sidesteps the start-up voltage requirement, and if the input voltage rises it can start being useful much sooner than having to wait for a minimum 0.56v input voltage to be reached. What would be interesting to know is just how much power is required to keep it running, even if only just for this purpose.
The switching chip is the E50D, which Julien's research indicates may be a CE8301.
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I've confirmed Julien's results. I procured a board that's inferior to his but with the same chip on it, and with no load other than its LED it can remain operational as low as 15mv. With that as the input voltage, the output voltage is around 640mv, so I think the reason my board can't survive on less than 15mv is that when the output voltage dips below about 600mv then the chip no longer has enough voltage to switch. Compared to other off-the-shelf chips, this is an impressive result, and even more so considering that these chips only cost around 8 cents each in small quantities.
Edit: This guy found another couple of possibilities as to what the E50D chip might be: https://www.electroschematics.com/pfm-module-circuit-surgery/
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I've confirmed Julien's results. I procured a board that's inferior to his but with the same chip on it, and with no load other than its LED it can remain operational as low as 15mv. With that as the input voltage, the output voltage is around 640mv, so I think the reason my board can't survive on less than 15mv is that when the output voltage dips below about 600mv then the chip no longer has enough voltage to switch. Compared to other off-the-shelf chips, this is an impressive result, and even more so considering that these chips only cost around 8 cents each in small quantities.
Edit: This guy found another couple of possibilities as to what the E50D chip might be: https://www.electroschematics.com/pfm-module-circuit-surgery/
@NeverDie said in ๐ฌ The Harvester: ultimate power supply for the Raybeacon DK:
Edit: This guy found another couple of possibilities as to what the E50D chip might be: https://www.electroschematics.com/pfm-module-circuit-surgery/
I have the same board as this guy. I removed the LED and resistor because they are on the input side, so they are almost useless anyway. For a board such as this, with a promised 0.9v startup voltage on the input side and a promised 5v on the output side, they really should have been attached to the output, not the input, to show roughly when it is that the board is producing useable output.
At a 20mv "keep alive" input voltage, the input measures 0.5ma using a uCurrent Gold. That means the keep alive energy is 10 microWatts. Offhand, for the application we've been discussing on this thread, I suspect that number is too high to be practically useful, because at only 20mv input we'd be collecting far less than 0.5ma current from a tiny panel. At least now we know.
