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Project 1 : Battery pack / charger

Discussion in 'Power Electronics' started by TheZink, Oct 28, 2014.

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  1. TheZink

    TheZink

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    Oct 25, 2014
    Hello all. New user , first project log...


    I'm doing this , so that I can look back and see where I went wrong. Probably A:Overthinking , and B: Lack of Action ... as always...

    My intentions , are to make myself a portable battery pack / charger. I have a solar cell , and will pick up another of the same sort , and sleve them so they can fold closed for transport. They are from RS , so if they break , local replacement is available. I use an e-cig , so this will be a mostly usb device , with whatever connector I end up choosing for the box... The other half of the project , is a mobile breadboard'n bits box... Basically a small plano/hobby box , with the solar/battery unit that would fit/attach on top of the box , to stay together . The lid of the box would stow inside to seal the compartments... Basically like any other bit-box you see , just with a more mobile specific set of components.


    Will sketch some things out , make some diagrams , put some datasheets up here , and just put my crap here for the most part. Anyone is welcome to post and tell me how silly I am... or otherwise...



    Thanks
    -j
     
    Last edited by a moderator: Oct 28, 2014
  2. TheZink

    TheZink

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    0
    Oct 25, 2014
    Battery charger ic : mcp73213
    running two of the largest LiPo's I can get my hands on that fit the back of the panels...
    what are the largest single cell flatpacks you can get without paying huge money? I cant seem to find much more than a 3"x1.5" pack... these panels are probably 5x7 ...


    Features :
    5v 1A
    3.3v 500mA
    Integrated logic probe , votlage/current meter...more I'm sure...
     
  3. TheZink

    TheZink

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    Oct 25, 2014
    Day 3 : Making progress...


    Settling in with the datasheet from the mcp73213 , and I figure out a couple numbers... My solar panel (in hand) is a RS:2770053 ; discontinued. The specs are 9v , 1.5w . Works out to .16667 ma . A bit low for the mcp* . I need to look at a booster (buck?) . Indoor , the panel is putting 4.8v , so even with a boost converter , and a second cell , i will still only be half the required input current just for the mcp...

    anyone have some insight or suggestions?
     
  4. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    9V and 1.5W is .167A nor mA. That is 167mA.

    And a boost converter raises voltage and lowers current, a buck converter lowers voltage and (possibly) raises current. Both lose a little in the process.

    From the microchip site:

    So 167mA is within it's range.

    But I should also ask if you looked at the package. it is a square of 3mm (less than 1/8 inch) with 10 leads and a thermal pad. The only practical way to solder this is by reflow soldering, which is not beginners stuff (I have never done it myself).

    Bob
     
  5. TheZink

    TheZink

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    Oct 25, 2014
    The supply current while charging is 700mA . So the 167mA is not enough , even with two panels , so I am looking into the tradeoff boost/buck issue. I have seen breakout boards for the dfn package , and have heat guns at work that will handle solder paste on a breakout.
     
  6. BobK

    BobK

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    1,688
    Jan 5, 2010
    To charge a LIPO at 700mA you will need 4.2V * 0.7A = 2.94W. You cannot get this from a 1.5W solar panel. In fact, you cant get it from a 3W solar panel except under ideal conditions. You need probably 3X the size of solar panel that you have.

    A buck-boost converter does not help. They can increase voltage at the expense of current or they can increase current at the expense of voltage. The power out is always less than the power in.

    Bob
     
  7. TheZink

    TheZink

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    0
    Oct 25, 2014
    Thanks Bob. I have been considering the actual output of the panels , and the chances of optimal conditions is minimal at best , so I am looking around for something that wont need a breakout , that can just do a single cell and I can manually balance the cells. I also figure that for most breadboarding , a single lipo will suffice , with minimal regulation... maybe even need to step up to 5v for some stuff...

    I am going to keep it very basic to start. I overcomplicate things , and dont follow through , so tonight's mission is to get one of the batteries charged and carry out some tests , then re-populate my ATmega board , and get her up.
     
  8. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    You should not be charging LIPO batteries without at least a voltage limited (4.2V) constant current power supply. This type of battery is very intolerant of overcharging and can catch fire or even explode, and both current and voltage must be limited to prevent that.

    Bob
     
  9. TheZink

    TheZink

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    Oct 25, 2014
    I understand that part of charging Lipo's. I meant that I will use a battery management IC to control the current and voltage , but charge each cell individually , then if I need two to power a device , I can just ruse two fresh cells. I have not looked into it , but would I need to use a special controller if using two independent cells?
     
  10. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Okay, good. I thought you were going to try to charge them without the IC.

    You would need 1 controller for each cell. There are many single cell LIPO charger ICs out there.

    Bob
     
  11. TheZink

    TheZink

    12
    0
    Oct 25, 2014
    Are you talking about the protection circuits , or the actual controller? I have been looking around , and a commercially available lipo charger should suffice until I need in-circuit recharging...if ever...
     
  12. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    I thought you were trying to charge batteries from a solar cell.

    Bob
     
  13. TheZink

    TheZink

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    0
    Oct 25, 2014
    I was looking at using the solar panel , but it's just not going to happen with this panel . I have to keep myself on track with this and not go off on a tangent... My goal is to get prototyping and working out the numbers to get the theory drilled till it's second nature. I have been thinking about things , and I also need to work on sharpening my basic and intermediate math skills.

    Sorry for not making it clear that I had decided to just use a commercial charger and protected cells.
    Thanks for the heads up though.

    -j
     
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