Booting the Prop from low voltages, 1 of 3: Single Solar Cell @ 0.56V

TubularTubular Posts: 2,743
edited July 2011 in Propeller 1 Vote Up0Vote Down
Finally had a chance to fire up my low voltage booster based on the LTC3105.

The LTC3105 is a 'solar energy harvester' that features maximum power point tracking, has low quiescent current, and a switch rated at 400mA.

It can start up from voltages as low as 0.25V, which makes Parallax's single solar cell a good match not only when its sunny, but also when overcast, and even indoors with a bit of window light.

This successful test was completed in dappled sunlight with the single cell producing 0.56v, an output setpoint ~ 3.2v, booting the prop and flashing a led.

LTC3105 links:
Video
Datasheet
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Comments

  • 34 Comments sorted by Date Added Votes
  • BeanBean Posts: 7,801
    edited July 2011 Vote Up0Vote Down
    Great experiment. I can't wait to hear more...

    I'll have to check out the LTC3105.

    Bean
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  • LeonLeon Posts: 7,617
    edited July 2011 Vote Up0Vote Down
    I've been experimenting with one of these ALD EH300 energy harvesting units:

    http://www.aldinc.com/ald_energyharvesting.htm

    I tested it with my bench supply, powering a PIC board flashing an LED, but that only goes down to 1.25V; I should have used have used a pot for a proper test. I've got a solar cell somewhere that I could try.
    Leon Heller
    G1HSM
  • TubularTubular Posts: 2,743
    edited July 2011 Vote Up0Vote Down
    Leon, interesting module, but whats with the min charging voltage of 4.0 volts? ( to attain a 'cycle range' between 1.8 and 3.6 volts ). . a capacitor will do that easily enough with suitable clamping circuit.

    My question, and perhaps you could test this, is if you feed it say 0.6 volts forever, does it ever manage to reach its 3.6v target and switch on its output? Or does its internal storage just stay at 0.6 volts waiting for a higher voltage to advance...
  • LeonLeon Posts: 7,617
    edited July 2011 Vote Up0Vote Down
    It'll charge from 0.0 V up to +/- 500V, AC/DC! See the data sheet.
    Leon Heller
    G1HSM
  • Dr_AculaDr_Acula Posts: 5,480
    edited July 2011 Vote Up0Vote Down
    What a clever experiment!

    One thing about solar panels is that if you use the standard circuit with a reverse protection diode, with say 36, or 10 or whatever number of solar cells, one of your cells is wasted with the voltage drop in the diode.

    But with one solar cell, there is no wastage. And with single solar cells, you can parallel them up to as many as you like. I've picked up broken solar cells in the past for great prices, but one problem with putting broken cells in series is that the total output amps is limited by the worst cell in the group. But put single cells in parallel, and nothing is wasted - the amps just add together.

    The spec sheets also mention thermoelectric generation. Grab a peltier device, hook it up as a thermoelectric generator and run your prop from warm water?
    Answers: 1) A quadcopter. 2) Very high. 3) The internet. 4) A lot. 5) No.
  • mindrobotsmindrobots Posts: 6,483
    edited July 2011 Vote Up0Vote Down
    I'm not smart enough to figure this out (yet?) but do any of the power harvesters have a way of indicating how much power they can supply or the quality of their input power?

    For example:
    Case1: I have a solar powered prop application and it's a nice sunny day, the prop can check its power source and spin off all its cogs and functions without worrying about a brown-out.
    Case2: It's a partly cloudy day, I'm at 50-75% of power output on my solar cells. I can run most functions but a few things my prop does may not be started/running. The prop application is functioning with diminished capacity.
    Case3: Cloudy/Indoor, I'm at less than 50% power output. Start up one cog to run minimal housekeeping and application functions. Check the power every so often to see if the situation is improving.
    Case4: Go to sleep to wait for more light. minimum power usage, waiting on a pin for a signal from the power harvester.

    You could tailor your code/application to provide functionality based on the power being harvested.
    MOV OUTA, PEACE <div>Rick </div><div>"I've stopped using programming languages with Garbage Collection, they keep deleting my source code!!"</div>
  • Dr_AculaDr_Acula Posts: 5,480
    edited July 2011 Vote Up0Vote Down
    I'm not smart enough to figure this out (yet?) but do any of the power harvesters have a way of indicating how much power they can supply or the quality of their input power?

    That ought to be possible. I think you need a voltage reference - something that in itself uses minimal power and always outputs the same voltage. If the prop measures that voltage (say it is 1V, or 0.1V - it does not matter), it can compare this with the solar cell output. Put a large capacitor in parallel with the solar cell(s). Presumably it is running Case3. Now load it up a bit more and see if the solar cell volts drop too much. The capacitor adds a delay so there would be a few seconds to do this. Input still stable at say, >400mV? Then load it up a bit more.

    I see some cool experiments ahead...
    Answers: 1) A quadcopter. 2) Very high. 3) The internet. 4) A lot. 5) No.
  • TubularTubular Posts: 2,743
    edited July 2011 Vote Up0Vote Down
    Leon wrote: »
    It'll charge from 0.0 V up to +/- 500V, AC/DC! See the data sheet.

    Leon, the very same data sheet tells me its min charging voltage is 4.0 volts, which would be consistent with a "managed supercap" arrangement, rather than some kind of charge pump that is able to boost 0.6v to 3v3. When its storage cap is fully depleted I don't doubt that it starts charging from 0v!

    ALD make some nice parts, but that is certainly not the clearest datasheet I've ever read. Block diagram? Efficiency curves or even typical values?
  • TubularTubular Posts: 2,743
    edited July 2011 Vote Up0Vote Down
    You can certainly check the voltage level on your storage reservoir to know how much is in the tank, and decide what to do accordingly.

    The LTC3105 has an open drain 'power good' signal which floats up to whatever rail you tie its resistor to, once the main output hits its preset value determined by its feedback resistors. This can be used to release the prop from reset for example. The datasheet also shows a way to LTC3105 to go back into shutdown (thus preserving what is left in the reservoir for the next cycle..)
  • Tracy AllenTracy Allen Posts: 5,985
    edited July 2011 Vote Up0Vote Down
    I'm doing something in that new area too, for a job that harvests thermal energy from a TEG at mostly low temperature differences. This uses the LTC3108, which has a step-up transformer instead of an inductor and can operate down to 0.05 Volts. Unlike the LTC3105, it does not do MPPT and is very limited in the current that it can supply (like 4mA max!). My design includes an LTC4070 Li-ion shunt charger (210mAh battery).
    LTC3108_4070_72.jpg
    Input  mV....... Volts into 10k load
    50                0.0
    60                0.248
    70                1.58
    80                1.60
    90                1.59
    100              2.94
    110              2.63
    120              3.00
    130              3.52
    140              3.68
    150              4.00   ' LTC4070 current shunt in operation.
    160              4.00
    
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  • TubularTubular Posts: 2,743
    edited July 2011 Vote Up0Vote Down
    Tracy,
    That shunt regulator is a nice solution to the 4mA limit. I actually started with the LTC3108 (here) , then moved on to the LTC3105 for more current and the MPPT feature. The LTC3108 is amazing, starting off such a low voltage as it does.

    Also those LPR6235 coupled inductors (transformers) are great for several applications.
  • Cluso99Cluso99 Posts: 12,530
    edited July 2011 Vote Up0Vote Down
    Tubular: Have you tried a solar cell from those garden led lights?
    They can be had for $2 from Coles or Woollies and include a 500mA rechargable AA battery. On my boat, I replace the LED with a superbright blue LED, and replace the battery with a 2500mA one. They then run for the whole night for about 3 weeks, at which time I recharge the battery manually (tops it back up).
    My Prop boards: P8XBlade2, RamBlade, CpuBlade, TriBlade
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  • Tracy AllenTracy Allen Posts: 5,985
    edited July 2011 Vote Up0Vote Down
    I'd missed your earlier '3108 post. Good stuff. It is a completely different animal from the '3105, and you're right, it is terribly inefficient. But it does provide at least a little battery charging from a TEG even at the lowest possible potentials, which is what we need. That will be less than 7 °C temperature difference. Higher temperatures happen, but not reliably. Now Linear Tech also offers the LTC3109, which extracts energy from both positive and negative fluctuations, basically two '3108s hooked up back to back internally. Also inefficient, but something.

    The '3105 seems to be a much better match for a solar cell and for extracting a lot more power. (relatively and maximally speaking!)
  • TubularTubular Posts: 2,743
    edited July 2011 Vote Up0Vote Down
    Cluso, I ordered a few cheap single cells from Futurlec to try, but they haven't arrived yet. But yes, you should be able to use those cheap garden lights as long as the solar doesn't go too far above 5v DC ( I think the abs max is 6V on the input).

    It may also be possible to break up Parallax's huge cell and get multiple cells out (at lower currents!). Mine already has a small crack across one corner, perhaps I should help it along :)

    Tracy what kind of voltage do you get from your TEG with a 7 degree difference? I am thinking about adding a TEG to give at least some kind of gradual power source for when the solar panel gets covered with dust / grain.
  • Hi Tubular !
    I ´m interested by your small board with the LTC3105, you use in your experimentation.
    If you can tell me where you buy, I search this kind of board since 3 weeks and nothing
    only one board for evaluation and it ´ s huge. I search something small .
    Thanks
    stongej
  • Hello!
    To Tubular, and you as well, Tracy.

    Where did your completely amazing boards come from? I've got about six different ideas taking shape, and two of them involve running a Prop off of a solar cell array.
  • TorTor Posts: 1,699
    edited October 2015 Vote Up0Vote Down
    Ah, a thread from 2011.. the new forum software took me to the first post, although it should have been marked as read already. So I went looking for the datasheet for the 3105 and got a 404.. that's when I went back to the thread and looked at dates! :)
    Anyway, it's very interesting and matches something I've had in my mind for some time. Glad I found the thread, even though it's old.

    Anyway, I collected some current links:
    LTC3105fa data sheet Updated Linear link (the 404 from post #1, new location)
    LTC3105p data sheet
    Various Linear LTC3xxx chips

    -Tor
  • I laid out my own pcb for that. I'll think about making some available for sale, either as the pcb, or an essential parts kit, or assembled. In the photo below, two of the resistors set the output voltage and one resistor sets the MPP control point. The sandwich attached to a 3V solar panel is one of the '3105 boards along with an LTC4071 LiPo charger.
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  • I laid out my own pcb for that. I'll think about making some available for sale, either as the pcb, or an essential parts kit, or assembled. In the photo below, two of the resistors set the output voltage and one resistor sets the MPP control point. The sandwich attached to a 3V solar panel is one of the '3105 boards along with an LTC4071 LiPo charger.
    Hello!
    That'll work. Please keep us posted.
  • Buck RogersBuck Rogers Posts: 1,119
    edited October 2015 Vote Up0Vote Down
    Strangely enough our friends at Sparkfun sells a related part from LTC. It also according to them will allow people to power stuff from a panel.

    They show one of their redbots, (A bot powered by an Arduino clone of their making.) wearing a big cell of their design on its back.

    Now I'm curious if this individual https://www.sparkfun.com/products/9946 can be confused into running say the Prop version of the BOE bot, or its relative the Activity Bot. (Its possible they are the same gizmo, but the company does sell a Prop version of the BOE set.)

    Now that would be interesting, and throw a big heap of stuff at the Arduino robot builders.

    EDIT: It turns out that the bot shown in the learn portion of their site has since retired from normal lists. They do not list a replacement.
  • Linear Tech put a lot of thought into their line of energy harvesters optimized for different energy sources and sinks. The data sheets and the efficiency curves are rather complex and require careful reading. But it all comes down to energy input * efficiency factor needs to be greater than energy out. Given that, any of these should be able to operate a Propeller as well as anything else. They store energy on a capacitor or charge a battery, and that then powers the project.

    Looking around, I found these breakouts for the LTC3108 and LTC3105.
    https://forum.crispytronics.com/.

    Buck, I tried your signature link but it timed out. Send me an email at tracy@emesystems.com and I'll hook you up with one of my boards. The connections on the edge are for the power, status and control. You'll have to swap the 0603 resistors if you want to change the output voltage and MPPC point.


  • Linear Tech put a lot of thought into their line of energy harvesters optimized for different energy sources and sinks. The data sheets and the efficiency curves are rather complex and require careful reading. But it all comes down to energy input * efficiency factor needs to be greater than energy out. Given that, any of these should be able to operate a Propeller as well as anything else. They store energy on a capacitor or charge a battery, and that then powers the project.

    Looking around, I found these breakouts for the LTC3108 and LTC3105.
    https://forum.crispytronics.com/.

    Buck, I tried your signature link but it timed out. Send me an email at tracy@emesystems.com and I'll hook you up with one of my boards. The connections on the edge are for the power, status and control. You'll have to swap the 0603 resistors if you want to change the output voltage and MPPC point.

    Hello!
    Okay I'm writing one now. Don't know why the site was ignoring you. And thank you in advance.
  • I'm doing something in that new area too, for a job that harvests thermal energy from a TEG at mostly low temperature differences. This uses the LTC3108, which has a step-up transformer instead of an inductor and can operate down to 0.05 Volts. Unlike the LTC3105, it does not do MPPT and is very limited in the current that it can supply (like 4mA max!). My design includes an LTC4070 Li-ion shunt charger (210mAh battery).

    Tracy, this is exactly what I was wanting to do about a year ago. What are you using for a TEG? I will have low temperature differences as well.
  • Tracy AllenTracy Allen Posts: 5,985
    edited October 2015 Vote Up0Vote Down
    John, It is a standard 40mm square TEG, similar to this one from goldmine-elec.
    The output is minuscule at low temperature differentials. I'm attaching a graph of voltage output vs temperature difference and another of the milliamp output of an LTC3108. The output impedance of a TEG is very low, around 1 ohm. You can see that the '3108 with the 50:1 xfmr kicks in at around 0.1V, and that requires a temperature differential of about 20°C. The circuit maxes out at 4mA, around 1 volt from the TEG or 40°C from hot to cold side.

    For comparison, I also attached a graph showing much higher temperatures produced by a rocket stove. Around 120°C it is producing more that 3 volts and 4 watts into a 2.4 ohm load.
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  • This (uC power supply) is a good example of where a solar panel needs no converter. One is only wanting enough power to run the circuit. Just plug the right number of cells directly across the logic supply. In this case you would want a 6-cell panel to make the 3.0 - 3.6 volt useful range.

    Solar cells have a surprisingly (or maybe not) flat voltage output in their useful range. Obviously brownout detection becomes important though.


    I came across the opposite problem not long ago where people were discussing trying to wire up a small array of solar panels directly to a hot water heater. Problem here is, to heat the water you are wanting to extract peak power as much as possible. Because the light levels vary so much a straight resistive load like that will be very inefficient without a switch-mode (MPPT) converter.
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  • Tubular wrote: »
    Finally had a chance to fire up my low voltage booster based on the LTC3105.

    The LTC3105 is a 'solar energy harvester' that features maximum power point tracking, has low quiescent current, and a switch rated at 400mA.

    It can start up from voltages as low as 0.25V, which makes Parallax's single solar cell a good match not only when its sunny, but also when overcast, and even indoors with a bit of window light.

    This successful test was completed in dappled sunlight with the single cell producing 0.56v, an output setpoint ~ 3.2v, booting the prop and flashing a led.

    LTC3105 links:
    Video
    Datasheet

    Hello!
    Tubular can you point me towards your schematic after the converter? That is everything the Prop needs to operate. Oh and the program you wrote also.
  • Linear Tech put a lot of thought into their line of energy harvesters optimized for different energy sources and sinks. The data sheets and the efficiency curves are rather complex and require careful reading. But it all comes down to energy input * efficiency factor needs to be greater than energy out. Given that, any of these should be able to operate a Propeller as well as anything else. They store energy on a capacitor or charge a battery, and that then powers the project.

    Looking around, I found these breakouts for the LTC3108 and LTC3105.
    https://forum.crispytronics.com/.

    Buck, I tried your signature link but it timed out. Send me an email at tracy@emesystems.com and I'll hook you up with one of my boards. The connections on the edge are for the power, status and control. You'll have to swap the 0603 resistors if you want to change the output voltage and MPPC point.


    Tracy, the board, plus your document arrived today. It must have ran all the way here from your neighborhood. Now the interesting thing will be in convincing a Prop on a Quickstart board to blink one LED at me so I can work with your widget...
  • Tracy AllenTracy Allen Posts: 5,985
    edited October 2015 Vote Up0Vote Down
    For power savings, the first thing to consider on the Quickstart is the green LED that is connected directly across the 3.3V power. That accounts for about 10mA right away. The prop itself can blink an LED quite nicely running on RC slow. The following code gives a 20ms blink every two seconds, appoximately.
    CON
     _clkmode = RCSLOW
     MYLED = 16   ' one of the blue leds on the quickstart
    
    PUB Blink
      outa[0..27]~   ' all pins start as low outputs to minimize Iq
      dira[0..27]~~
      repeat
        outa[MYLED] := 1   ' high for about 400 clock ticks, 20ms at 20kHz
        outa[MYLED] := 0
        waitcnt(40000+cnt)  ' 2 second wait
    
  • Sorry people had been traveling and not paying enough attention to P1 forums. Let me dig out the designs and post them up later today. Can share the oshpark boards if they're not already shared, or assemble some more boards

    Tracy, neat graphs. 7 degree delta T minimum is interesting. I've often wondered whether putting a TEG (or stack of two?) on an external door (with metal liners) would generate enough power via temperature difference to be able to tweet the door open/closed status. That's starting to sound plausible with the 3109
  • LawsonLawson Posts: 870
    edited October 2015 Vote Up0Vote Down
    Just thought I'd poke my head in here. The links in my signature will be relevant. Particularly the "Propeller Limbo" thread. TLDR, the propeller runs quite well down to 1.5 volts and at RCSLOW propeller + eeprom can easily fit in a 10uA power budget.

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