Power from an LED to "Solar" Power a Clock?


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Thanks to Sean (SeanB) in South Africa for this one!
I demonstrate how an LED can produce “solar” power and run a digital clock.
This is a practical solution so that I can monitor and log the run time of solar powered lights I’m testing with my Fluke 287.
I show some lights I’m testing: Console solar glass jar, d.light S20 Solar Lantern and the Energizer Solar Rechargeable 9-LED Lantern.
Some kit from Adafruit – MintyBoost, Solar Lithium Ion/Polymer charger…and more.
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42 replies
  1. koala central command
    koala central command says:

    the electricity in ontario, canada is clean, but it's becoming very expensive, and i'm trying to figure out ways to reduce costs. i'm in a basement with some air quality issues (i'm slowly figuring them out, but detroit is just a dirty city.), so about 40% of my electrical costs are about moving the air in the apartment around. if i could offload the fans to solar, i could cut my bill nearly in half – useful because they just increased it by 55%.

    i've purchased a usb fan that has the same dimensions as the one i'm using. i think the one that's running is about 40 W/day, something that wasn't previously a problem, but is now. the specs on the fan i purchased, which is supposed to be the same size, are 2.5-3 W. so, it's a much more efficient device, and we'll have to see if it moves the air around the same way or not.

    but, i'm thinking that i should be able to get a few watts from the sun, right? the thing is that i need this running 24/7, and i'm trying to save costs, so i want to get an older battery, the kind that's in a bargain bin and somebody is otherwise just going to throw away. if i'm only getting 5-6 hours a day of sun here in the winter, through the window, i need a lot of storage capacity, and it might not even be enough.

    and, it kind of hit me – could i just put the diode in the lamp? i sleep with the lights on to keep the roaches out. and, it's running a fairly strong led. i know it's a different wavelength of light, but is there enough in there to run a fan? i just need a few volts…

    maybe you could do the video with a capacitor rather than a store bought battery, but it seems like there is.

    so, if the fan is a little weaker, maybe i'll just get a couple of them, and string them up on the different lights. and, that's 20% of my electrical bill cut out by recycling the light from the bulbs…

    maybe, i can find some way to recycle the heat from the heaters, too.

  2. Steve Fox
    Steve Fox says:

    I was curious if the larger LED's would produce more amperage as it didn't seem to effect voltage in my own testing. Thanks for the info on that. I also found you can use this to meassure light wave lenghts. I found this out by the fact I was only getting voltage from a UV led when my light source produced UV. Same deal with IR. Using white led's as a torch is great for most colors, as it does produce something from the middle spectrums just not the far ones or IR and UV. You will notice that a white led does not produce any UV light though. A UV led does and if you use it to produce the light you will then get voltage! They say the sun changes spectrum from more blue to red in the winter and red back to more blue in the summer. I how ever noticed no change in voltage. Amperage might change though, have not been able to test that either. When it comes to color. I have found red is the best for not needing to be directly aimed at the sun. Blue produces more voltage but needed to be directed. In the end, to make this technology useful I am finding higher wattage red LED's are where I will be going now. 

  3. rockradio928
    rockradio928 says:

    Regarding getting the clock to work without voltage slowly increasing from zero, my first though was to put a zenner in series with the clock. Not in the conventional way using a resistor, but putting the zenner directly in series with the clock. Ring towards the supply voltage. Not tried it yet, but have a feeling it will only conduct when the zenner approaches its breakdown voltage so only present the clock with voltage above the zenner's operating voltage. But will loose 0.6V across zenner

  4. stonent
    stonent says:

    Martin, around Easter I picked a few solar powered LED garden lamps at DollarTree for $1 each. A month later they had some that used a metal tube instead of plastic so I picked up a few of those. I really only cared about the device but the tube could be useful. One ran for several days on a single charge. Inside is a small chip, a AAA NiCd and LED. Obviously NiCd is not ideal because of charge memory, but they are cheap for any solar hobbyists. I plan to connect a 10KuF cap and try it out also.

  5. stonent
    stonent says:

    For anyone interested in learning more, do a google search for the "Mims effect" it was named after electronics hobbyist and author Forrest Mims. There's a picture of him on Wikipedia demonstrating an obstacle avoidance device for the blind when he was stationed in Vietnam in 1967.

  6. EcProjects
    EcProjects says:

    Wow, I've heard about this phenomenon before, but I couldn't believe my eyes when you hooked up that ammeter :O .. I thought it would be a uA or two at best..
    Very nice video, keep it up ! 😀 Hehe
    Indeed something I need to play around with. Thanks for sharing 🙂

  7. birrbert
    birrbert says:

    Very nice video! Thanks for coming back to more practical and fun little projects/experiments. 🙂
    I, personally, like these video the most.

    And Sean, the wizard. A great and knowledgeable character, providing many good ideas and suggestions. I'd love to meet him, but the distance is sooo big (~9000 km from where I live).

  8. Spag The Maker
    Spag The Maker says:

    Anyone want to hack up a light version of RFID? So an IR led gets illuminated by a reader. That illumination charges up a cap, which powers a tiny microcontroller just long enough to use the same IR led to send a message. Just like RFID tags using their coils as both a power source and an antenna.

  9. SeanBZA
    SeanBZA says:

    Note that if you use a red LED no matter how bright the light a blue led will give zero output. Other way you get voltage as the wavelength is shorter and provides enough energy per quanta to drive the electrons through the valence gap of the material.

  10. SeanBZA
    SeanBZA says:

    Voltage depends on the band gap of the material in the LED. IR diodes are the only ones made from silicon, the red,green and yellow leds are made from Gallium Arsenide or other similar materials, with a larger band gap. Thus they will generate a higher voltage with incident light, providing it has a wavelength shorter than the band gap. The blue and white units are made from silicon carbide, just white has a phosphor coating.

  11. twjonckheere
    twjonckheere says:

    One could then use a single LED for one of those LED night lights. It would detect when it became dark (low voltage) and then kick on the same LED when it's dark to light it up. Now and then it would turn off quickly, detect if it's dark or not, and then switch back on accordingly. I think the human eye would never catch the check since it could be done quickly. This will be a fun Arduino project. 🙂

  12. Cool Joule
    Cool Joule says:

    10 leds could charge a battery during the day and a joule thief could in turn run the leds at night. Like you said, you just need the right switching ckt.
    I look forward to your methodical approach – very nice video!

  13. Pulsed Neutrino
    Pulsed Neutrino says:

    if you only use a lithium ion battery between 3.7v and 3.9v it will last for 4000 or more charge cycles vs 300 from 3v- 4.2v and 1000 at 3.4v to 4.1v. admittedly 3.7 to 3.9v gives you very little capacity but if longevity is the goal then you cant go wrong.


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