Solar Mac Wireless keyboard project help.

Discussion in 'Mac Accessories' started by Mattyb91193, Apr 20, 2012.

  1. Mattyb91193 macrumors newbie

    Joined:
    Apr 20, 2012
    #1
    Well I am trying to install a solar panel on my wireless keyboard so that it would be not self sufficient but not as bad on my batteries. I put a small 6.7V one on it with 20 ma. But it is barely drawing any power, maybe I have it hooked up wrong to the solar panel? But I know that I have the right wires for the keyboard power, because it powers a led light.

    Any help at all would be sweet, this would be an awesome project.

    thanks.

    and heres a link to the solar panel I have hooked up now.

    http://www.hobbyengineering.com/H2202.html
     
  2. aComicBookFan macrumors member

    Joined:
    Feb 26, 2012
    #2
    Keyboards don't normally use a lot of power. There's not a lot of data to transmit or stream compared to a mouse or trackpad that is constantly streaming motion. You probably have everything hooked up right.

    Have you seen the Logitech solar powered keyboards? They work pretty well.

    -=- Boris
     
  3. Mattyb91193 thread starter macrumors newbie

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    Apr 20, 2012
    #3
    Not working

    Well I may have everything hooked up correctly, but it doesnt work at all. It still needs the batteries in it to work at all.
     
  4. fhall1 macrumors 68040

    fhall1

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    #4
    My guess without seeing your setup...The batteries are completing a circuit inside the battery compartment. With nothing in the compartment the circuit it open....you have to bridge a piece of wire from the positive to negative end of the battery compartment that completes the circuit.
     
  5. Mattyb91193 thread starter macrumors newbie

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    Apr 20, 2012
    #5
    Well when i hook power up directly to the wires that i have hooked up to the solar panel without any batteries. It works perfect, without the batteries in it. So im thinking that my solar panel may not be powerful enough. Do any of you know of any solar panels that would work for it? Be powerful enough?
     
  6. Mattyb91193 thread starter macrumors newbie

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    Apr 20, 2012
    #6
    Pictures of it.
     

    Attached Files:

  7. fhall1 macrumors 68040

    fhall1

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    #7
    That panel only supplies 20mA current draw...I don't think that's nearly enough to power the keyboard
     
  8. Mattyb91193 thread starter macrumors newbie

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    Apr 20, 2012
    #8
    Ok, so if I get a new solar panel what should I be more worried about, MA, or Voltage? If somebody could give me an example of one that would work that would be great.
     
  9. ljonesj macrumors 6502a

    ljonesj

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    #9
    well my energizer rechargable batteries i use in my bluetooth keyboard are 2 2000mah and 2 2200mah batteries
     
  10. fhall1 macrumors 68040

    fhall1

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    #10
    Both....you need to find the voltage/current specs of the wireless keyboard and make sure your solar panel will meet those. I did some quick Googling and didn't find any specs online for the keyboard - so you'll need to do some digging....or find someone with a keyboard and a digital multimeter that can give you actual measurements....then work from there.
     
  11. marzer macrumors 65816

    marzer

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    Colorado
    #11
    I'm no EE, but two AA batteries provide 3V and the cell you're using generates 6.7V. Also, I would roughly estimate my 4400mah (2200x2) rechargeable last me about 1.5 to 2 months. Again, VERY roughly, I would estimate the draw to be approximately 70-100mah/day, that would be combined operation of on and low power mode.

    Of course the 3 battery keyboard would require 4.5V input.
     
  12. Mattyb91193 thread starter macrumors newbie

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    Apr 20, 2012
    #12
    well the funny thing about that is I am a freshmen CE. lol. not that far off from EE, but we havent covered much electrical yet. I just thought that this would be simple enough to do. Ill try to find a multimeter.

    If this works it would be real awesome. Ill see what it needs, order a couple more cheap panels, wire them together in series, and go from there.
     
  13. fhall1 macrumors 68040

    fhall1

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    #13
    Bone up on some electronics theory. You already have enough voltage (if not too much), but not enough current. Wiring the panels in series will increase your voltage output but keep current output the same. You want to wire them in parallel (keeps voltage constant - increases current output)
     
  14. marzer macrumors 65816

    marzer

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    #14
    And wouldn't you want to bring that voltage down to the 3v (or 4.5v depending on the model) to prevent damage to the circuit? A resistor or diode or something?
     
  15. Mattyb91193 thread starter macrumors newbie

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    Apr 20, 2012
    #15
    Well im going to try to get a mutlimeter here pretty soon so I can measure the actual voltage that the batteries are outputting. But as far as the solar panel goes, the 6.7 volts is the max voltage output, it isnt always going to have enough sunlight to output a full 6.7 volts.
     
  16. j-beda macrumors newbie

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    Jun 23, 2004
    #16
    Keep in mind the following is a pretty "toy" description of some of these items - don't be too rough on me.

    Roughly speaking, the voltage is set by the chemistry, not the amount of sunlight. Voltage (more accurately "electrical potential") is roughly analogous to pressure or height in a mechanical/gravity system. A 20m high water tower supplies the same water pressure as a 20 meter high dam across a huge lake. The pipe size is what determines the water flow rate, and the volume of the reservoir limits how long it will last. Thus the big fat "D" cells, the little "AAA" cells and the tiny little button cells all provide roughly 1.5V of "push". Each of them can provide surprisingly high current levels (set mostly by the specific chemicals used, and by how they are layered and things like that), while the total amount of energy roughly matches the amount of those chemicals that are in the battery - not too surprisingly the big fat "D" cells would last the longest.

    Most circuits will work reasonably well for a small range input voltages, thus you can use 1.5V alkali batteries, or 1.2V NiCad batteries pretty much interchangeably.

    For solar panels, the arrangement of chemicals (actually the electrical properties of the crystal lattices is probably a more accurate description) sets how much electrical potential (voltage) the electrons in the material gain when a photon strikes the material. If there is only a little light, only a few electrons will have this increased energy, so the maximum current will be smaller than in brighter light, but the "open circuit" voltage is pretty much the same in either case.

    For a given voltage, the rest of the circuit limits the current depending on the resistance of the circuit (through voltage = current x resistance). Thus for any electrical system, if your power supply is of the correct voltage, you can use any power supply rated at or above the maximum current your circuit would draw would work fine, with no danger of oversupply. That is why one can use the power supply for the big 17" MacBookPro to supply the tiny 11" MacBookAir with no issue, but if you try the tiny MacBookAir power supply to power the larger laptop, the powersupply gets really hot and the laptop charges very slowly.

    For your solar panel system, providing 6.7 volts of input could result in damage to the circuit that is only expecting at most 3V (two batteries) or 4.5V (three batteries) (different keyboards use different numbers of batteries). To get down to a lower voltage, I think there are various designs of "voltage divider" resistor circuits, or diodes, or transistors, or voltage regulator packages - see http://www.electro-tech-online.com/...-ideas-reviews/86779-diodes-drop-voltage.html for examples. Alternatively most individual component solar cells provide about 0.5V, so rewiring the panel you currently have (which might be essentially impossible for a sealed panel) could set it up for the desired output voltage.

    Once you have a system set up to deliver the correct voltage (or close to it), you can hook up multiple solar panels in parallel to provide the higher current needed. Basically, the max current output is set by the light intensity and the physical size of the panel capturing that light.

    What you might consider is trying to wire up the solar cells to installed rechargeable batteries so that the batteries can provide the higher current needed for keyboard operation while the slow trickle of solar power would recharge the batteries for the times when the keyboard is not demanding the high current. I don't know about energy density, but perhaps a big capacitor might be sufficient.

    It looks like Logitec uses a rechargeable button battery:

    http://www.logitech.com/en-ca/keyboards/keyboard/devices/k750-keyboard

    $60 at Amazon
    http://www.amazon.com/exec/obidos/ASIN/B005L38VRU/jbenterprises/
     

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