Doing a simple DIY project to charge my phone with a solar cell and need some help

Discussion in 'The Projects Forum' started by absoluteZro, Jun 26, 2013.

  1. absoluteZro

    Thread Starter New Member

    Nov 12, 2011
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    Me and a friend are doing this to just have some fun, learn a little about electronics, etc. We know we could just buy one that would look much nicer, but that isn't really the point of the project. So, the questions:


    1. I don't want to kill (or blow up) my battery pack. I am using a very weak solar cell (4W, 0.5V, if I'm lucky) to charge this battery. Is that too weak to even get through the Protection Circuit to charge my battery?
    2. I also would like to know how I can connect my solar cell to my battery and then my phone to the battery in one circuit. How does that work? How does the protection circuit work?
    3. I know this site has a great resource for learning about circuits, and if you look in my history I have done all the reading commenters have asked of me, so please, tell me what to read up on, and I will get to it.

    Thanks for any help!


    Products:
    Protection Circuit - http://www.all-battery.com/protectioncircuitmodulepcbfor37vli-polymerbattery8alimit-pcb1s.aspx
    Battery - http://www.all-battery.com/polymerli-ionbattery37v5500mah7552146.aspx
    Or maybe this battery? - http://www.all-battery.com/onenicdcsize3500mahrechargeablebatterybuttontop.aspx
    USB Car charger - http://www.amazon.com/PowerGen-2-4A...id=1372297992&sr=1-22&keywords=dc+usb+charger
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,128
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    Is it really just 0.5V? That's going to be tough to use by itself.
     
  3. absoluteZro

    Thread Starter New Member

    Nov 12, 2011
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    So I should buy a solar cell with a decent amount of voltage? Whats the minimum I should look for?

    Also, what is bad with 0.5V? Is that not enough driving force?
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,128
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    Assuming you want 5V delivered out of a USB port, you'll have some hoops to jump thru to get a 10X voltage boost from your panel. There are always ways to achieve that, but I think it would be WAY easier to start with a PV panel (or series of panels) that can deliver maybe 7V or more. That'll leave a little headroom for voltage regulation, allow the system to work in less-than-full sunlight, and allow the panel to deliver current at its maximum power point. The MPP is roughly where the voltage is drawn down by a current load to ~80% of its open-circuit maximum.

    You CAN continue with your current panel, but you'll need to find a boost IC and build a circuit around it. Nothing wrong with that!
     
    absoluteZro likes this.
  5. wayneh

    Expert

    Sep 9, 2010
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    Exactly. Using the water analogy, voltage is like pressure. You need to pump water up a hill, requiring 5V of pressure, and your hose is only at 0.5V of pressure. Not going to work without some trickery (that has no analogy to water pumping!).
     
  6. absoluteZro

    Thread Starter New Member

    Nov 12, 2011
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    0
    Thanks for the help on the solar cell, but I think there might be a misunderstanding. The Solar cell is not in contact with the usb port. The solar cell will only charge the battery, and only the battery will charge through the USB. Wont the delivered voltage to the USB be the same as the batteries rated voltage?
     
  7. nickelflipper

    Active Member

    Jun 2, 2010
    280
    35
    Here is an interesting starting point for a solar charging system. While this may seem like an all in one system, their is still work to be done on sizing the system to make it work. Supposedly it will do up to 1A output through the USB port. Still use protection circuit, or protected batteries, as a safeguard against over and under voltage.

    Some quality protected high capacity Li-ion batteries.

    I have used their 0.5W panels to charge 600mah 14500 (AA) LifePo4 batteries to good effect. LifePo4 is 3.3V nominal, while Li-ion, and LiPo are 3.7V. The 0.5W panels were spec'd correctly at 6V O.C. and Isc of 90-100ma, so I would expect the 2W and other panels to be correctly spec'd.

    Good luck.
     
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  8. wayneh

    Expert

    Sep 9, 2010
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    No, USB voltage must be regulated and that adapter you linked is meant to be supplied with at least 12V input. It bucks the voltage down to 5V. If you supply it with a single 3.7V battery, I'm not sure how it will behave but it's highly unlikely to output 5V. It would need a DC boost converter to do that, and there would be no need for that in its normal application.

    Do you expect the battery to ever be connected to both the solar panel and the phone (with some adapter in between the last two)? Or do you imagine two separate stations?
     
  9. absoluteZro

    Thread Starter New Member

    Nov 12, 2011
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    The first one. I want it to somehow be solar panel to battery to phone even when the sun is out and the battery is charging. How do I get a battery to charge and discharge at the same time, without allowing the solar cell to charge the phone directly?
     
    Last edited: Jun 27, 2013
  10. wayneh

    Expert

    Sep 9, 2010
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    You can prioritize the loads if you must, to direct charge current from the panel to one battery or the other. For instance an attached cellphone might be given priority.

    Or just don't worry about which battery is taking the charge. Let the respective charging circuits draw off the same supply - your panel.
     
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