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Preventing overcharging from solar panel

Discussion in 'General Electronics Discussion' started by Bidderswede, Oct 30, 2012.

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  1. Bidderswede

    Bidderswede

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    Oct 9, 2012
    I have a 12volt/5watt solar panel that is going to charge my 9.6volt battery pack.
    What kind of diode do i put in between, and what would be the best/easiest way to prevent overcharging the battery pack when it's full?
    The batteries are 8AA/2600mhA NiMH.
    Thanks
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    No diode can do that for you.

    Charging NiMH batteries (correctly) is very non-trivial.

    You may be able to get away with a NiMH charger that runs from 12V, the solar panel *may* be able to run that.
     
  3. Bidderswede

    Bidderswede

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    Oct 9, 2012
    I didn't mean that the diode was going to prevent overcharge, just wanted to know which kind would be best. Zener or schkotty? And what voltage it can handle?
    I have read that you can put a sensor of some kind that will sense a drop in voltage when the batteries are fully charged, and that way stop the charge?
    I also have a voltage regulator (5v) that i need to put between the battery pack and the device because it is supposed to run on 5volt, but when i measured the output from the regulator it was still showing about 9.5volts?
    Any suggestions will be appreciated.
    Thanks
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    It all depends of what you want to use the diode for. And what is that?

    There is no simple sensor that can do this, you need a reasonably complex circuit to do this.

    That means you have wired it up incorrectly (or perhaps you've damaged it)

    You need to show us some circuit diagrams...
     
  5. Bidderswede

    Bidderswede

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    Oct 9, 2012
    All i need the diode to do is preventing the batteries discharging back to the panel.
    Don't have any diagrams yet. Maybe i will make some this weekend.
    Thanks for the input so far.
     
  6. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    As Steve said you have it wired wrong, likely backwards... Did you by chance get it at Radio Shack? They are notorious for totally mislabeling their component packing...

    Pics would be helpful in determining this...
     
  7. Bidderswede

    Bidderswede

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    Oct 9, 2012
    Just getting used to using a breadboard, so i probably did it wrong.
    I'll try to get some pics and/or diagrams this weekend.
    In the mean time this is my plan to set it up so far:

    12v solar panel to diode to 9.6v battery pack to 5v voltage regulator to 5volt device.
     
  8. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    That should read "12v solar panel to diode to charging circuit to 9.6v battery pack to 5v voltage regulator to 5volt device."

    If it was my I would consider a 6 - 7.2 volt battery and a suitable low drop out regulator or a switching regulator for more efficiency... Wasting 4.6 volts dropping 9.6 to 5 is just well wasteful...
     
  9. Bidderswede

    Bidderswede

    27
    0
    Oct 9, 2012
    I need the battery pack to run the device during the night though. That is 10-12 hrs.
    The batteries are 2600mah each. Doesn't that mean it can run a 2amp device for about 10 hrs?
    Explain " charging circuit " please?
    I'm new to this, so bare with me and my "stupid" questions. Just trying to learn so i can get this project up and running.
    Thanks
     
  10. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    No, about 1 hour after you factor in the loses, possibly/probably a little less...

    1000mA = 1A so 2600mAh = 2.6Ah but that is factored at a low drain rate, if you are draining at 2A the capacity will decrease a lot!

    You need a charging circuit, you can't just pump whatever the solar panel outputs into the battery unregulated... You need a charger of the appropriate type for your battery chemistry so that you don't 'overcharge' and cause battery damage or worse cause the battery to explode...
     
  11. Bidderswede

    Bidderswede

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    Oct 9, 2012
    What if there is a 12v voltage regulator from the panel to the batteries?
     
  12. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    The regulator will likely not work as you need voltage overhead with regulators, and regardless it's not a charging circuit...

    Google NiMH chargers, that is what you need to implement in the design...
     
  13. Bidderswede

    Bidderswede

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    Oct 9, 2012
    I guess I'll put a pwm solar charge controller in.
    Any idea which one I should get?
    10,20 or 30A?
    I think the 10A should be sufficient, or maybe even less..
     
  14. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Most of them are designed to charge lead/acid batteries not NiMH...

    Different battery chemistry require different charging methods, if you can find one that support NiMH chemistry charging it should work, but it's really extreme overkill in such a small project...

    Why do you continue to ignore he advice given? Way back on the first reply Steve gave you an answer... You should be exploring a NiMH battery charger, they might or might not work because the solar cell is hardly producing any current but they are worth the try...

    But, you are still left with the issue that you will only get about 45 minutes run time and you want 10-12 hours, IMO a redesign from the ground up is required at this point...
     
  15. Bidderswede

    Bidderswede

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    Oct 9, 2012
    I will look into that some more, but couldn't find a solar panel with intergrated nimh battery charger that would do the trick. Also, i think im wrong about the 2 amps that the device was going to use. Its more like 300ma.
    The controllers i found were for nimh.
     
  16. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    You are still not going to get your 10-12 hours of run time even at 300mA... Probably in the 6 hour range...
     
  17. Bidderswede

    Bidderswede

    27
    0
    Oct 9, 2012
    If i decide to try it with a controller, would a 10amp be sufficient for this circuit?
     
  18. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    You solar panel is 5 Watts @ 12 Volts that is 0.42 Amps... A 10 Amp fuse is plenty...
     
  19. Bidderswede

    Bidderswede

    27
    0
    Oct 9, 2012
    Oh, ok. So i can go even smaller then.
    Thanks CC!
     
  20. Bidderswede

    Bidderswede

    27
    0
    Oct 9, 2012
    Why is the 5volt 7805 voltage regulator getting super hot when i put it in the circuit with a 12volt 12ah sealed lead acid battery?
    Is the battery putting out too many amps?
    Do i need to put something between the battery and the regulator?
     
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