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Solar Panel Charger Project

  1. Feb 5, 2013 #1
    The Maker

    I saw a slew of discount solar panels and I want to use one to power my iPhone or possibly netbook.

    I’ve researched this but it seems the more I learn the more I realize how little I actually know. There appears to be a wide variety of charging circuits and methods out there. Some use big bulky capacitors and through hole. I have come across some circuits that use SMT for 15W of power though.

    I am wondering how a modern solar controller works. I’ve learned how old school solar panel charging works with diodes. But I don’t know how “smart chargers” work. My goal is to end up with a project that I can plug my iphone or possibly netbook into and charge it up while not in use, contribute to the battery power when in use, and possibly allow for a backup battery (I haven’t decided if that makes any sense yet).

    Should I choose an external battery, are the battery types interchangeable?
    Solar panels found here http://www.goldmine-elec-products.com/prodinfo.asp?number=G18569

    What can you tell me about modern charging?
    What do you think of my project?
  2. jcsd
  3. Feb 6, 2013 #2


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    The charging is taken care of by your Phone. All you can do is to supply it with the requisite volts (same as it would get from the supplied mains charger). If you try to give it too high a voltage then it can damage the phone and if you give it too little, it just won't charge. They all, afaik, use 5V, or a bit more on the appropriate pin on the USB connector.

    There is little point in buying a massive PV panel if you only want to charge a few devices at once. You'd be wasting your money. If you allow 0.5A for each device, that should be easily enough capacity. Of course, a bigger PV area will allow you to get more current as the sun starts to disappear; panels tend to be rated for full sun and pointed directly at it.
    Those 22V panels would hardly be suitable because you would need to drop the volts to well below 12V to avoid damaging your phones. You need something up to 12V. There is a fair choice on that site, I see. The essential thing is to protect your phones or you risk costing yourself a lot of dosh. Use a 5V voltage regulator to be on the safe side.
    Are you familiar with making proper connections between circuit components - soldering to the correct numbered pins etc?
  4. Feb 6, 2013 #3

    Thank you for the reply. I thought modern chargers would be very complicated like modern AC DC converters.

    I have seen some simple circuits that are nothing more than a diode and regulator. ( http://www.robotroom.com/Solar-Recharging.html )

    So to recharge my iphone / charge while in use, all I need is the panel, a diode, and a 5V regulator? That's pretty exciting. I'm not sure why the solar panel controllers cost so much online.

    Correct, once I get the parts I will be able to dentify + and - for 2 pin parts. For something with many pins like an IC I will look up the datsheet to determine which pin does what, and I do know how to orient the IC based on the datasheet or the little half circle indent.

    I am okay at soldering.
  5. Feb 6, 2013 #4


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    The online ones can be expensive, partly because they are usually handling much higher powers. Plus, it is a separate box and you always pay for each box and phones have be reasonably priced whereas solar panels and chargers are for a different market. Etc etc.

    There is another difference and that is that the chargers in phones are designed to work from a USB type source and they are not interested in efficiency. In your system, your regulator will not be getting the optimum out of the panel to suit the phone battery - the phone's charger is in the way.
    But you are giving yourself an extra facility so you can put up with a bit of inefficiency.
    Good luck with the soldering and check about which panel would be best for you.
  6. Feb 6, 2013 #5
    By phone's charger are you refering to the wall wart or the phone's internal charging components?

    My iphone has a 3.7V 1420 mAh Li-Polymer battery. I'm going with the 8V 130ma solar panel.

    If I understand my electrical engineering, it'll take (1420/130)=10.9 hours of peak output to recharge the device. Rough estimation not including ineffiency of the voltage regulator. It will also garaunteee the device charges at non peak times such as sunset.

    5V regulator from Jameco or Digikey plus a schottky diode to protect the circuit. I assume the phone has more diodes inside for when it charges normally.

    I'm going to try to charge an old cell phone.
  7. Feb 7, 2013 #6


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    I'm referring, at all times, to the internal charging regulation - because nothing outside the phone can be relied on to do anything but a bit of voltage regulation (USB spec is not a battery charging spec, is it?) and the phone is the final arbiter.
    There's no doubt that you could do better than the battery's internal charging circuit (taking the battery out of the phone) but you would need to be very careful not to overstress the battery. You would need to follow the maker's advice to the letter.

    Good idea to use an old phone first but you may find the battery's knackered as they don't like being uncharged for long periods in your desk drawer! There is an internal switch (in the LiIon battery itself) which can disconnect it from a charger permanently, although there are ways of dealing with that, I believe. Another layer of complexity - but life's like that.
  8. Feb 7, 2013 #7
    I've purchased the panel! (8v 6"x6")

    I'm going to see if I can find the right parts from my scrap bin tonight and order whatever else I can't find from Jameco.

    Shipping is a week at minimum (2 weeks in my experience).

    So until it gets here, I want to explore the buck boost circuit and MPPT. I've been reading up on MPPT and I don't understand how the controller affects the dc-dc converter.

    I've read much literature but I don't understand how it works. Namely, a buckboost is a DC DC converter. It is a very simple circuit. Yet it is somehow controled by a chip. I also don't understand how the buck boost is able to increase amps at the cost of volts.

    Could I use a small through hole or smt inductor with my application? I've seen $1.5 smt inductors rated for 3 amps :eek: !
  9. Feb 7, 2013 #8


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    One possible way the unit could work would be by using an oscillator to generate AC at a high voltage and use a transformer (or equivalent) to give you more current at a lower voltage. As long as you don't hope to exceed the input Volt Amps then there is no reason it wouldn't work.
  10. Feb 8, 2013 #9
    Are you implying the occilator steps the voltage up higher than input before going to a transformer?

    I suppose that's what the buck boost does, it has an inductor and capacitor and rapid on off switch. Wikipedia is not very clear.

    I have a camera flash circuit that does the opposite of that. Turns a battery into AC current to use a transformer to step up the voltage.

    What other ways are there? All my google search turns up is buck boost wikipedia. I have the feeling that turning DC into AC into DC again AND running through a transformer is bound to cost me more $ than adding additional solar panels lol. Or am i wrong?
  11. Feb 9, 2013 #10


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    I just meant that the voltage of the AC at the transformer primary would be the 'higher' value, governed by the higher supply voltage. There are many alternative circuits that can give 'step-up' or 'step-down' but a simple transformer is more familiar and, possibly, easier to understand - especially when it comes to talking about what happens to currents and volts.

    Ideally, you would be choosing a panel with the appropriate voltage, from the start. That would be the cheapest solution - unless you found one with the wrong voltage but at a knock down price. In which case, you could have fun (but probably not too much expense) doing a DC-DC conversion. Actually, I just remembered that, recently, I bought a DC-DC converter (cost<£10) from this family of circuits. As far as I could see, it did just what was needed (I didn't investigate it further than connecting it up as the spec sheet said and it worked.). I have no idea about the efficiency though, which may be relevant to your use.
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