1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Solar battery charger

Discussion in 'Renewable Energy' started by knarf180, Jun 2, 2013.

  1. knarf180

    knarf180 New Member

    Joined:
    Jun 2, 2013
    Messages:
    3
    Likes:
    0
    Location:
    USA
    Hello all,

    I'm attempting to figure out how to charge a Ni-Mh battery with a solar panel.

    Battery: 10.8v 3.8Ah

    Panel: 22.25 Open circuit voltage, 1.5 watt

    The panel is likely too large for trickle charging the battery. I assume my amperage should be no higher then 380ma to prevent over charging.

    I'm trying to keep the circuit as simple as possible. Any suggestions on how I should be controlling the incoming power before delivering it to the battery?

    Thanks much for any input
     
  2. Joe G

    Joe G Member

    Joined:
    Dec 18, 2009
    Messages:
    506
    Likes:
    16
    Location:
    Florida. USA
    unless I'm really tired, that panel works out to an output of only 0.068+/- A, or 68mA? 1.5/22=0.068
     
  3. knarf180

    knarf180 New Member

    Joined:
    Jun 2, 2013
    Messages:
    3
    Likes:
    0
    Location:
    USA
    Hmm.. True. I'm a bit new at this.

    The amperage should be fine then. Do i need to worry about the voltage at all?
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. Joe G

    Joe G Member

    Joined:
    Dec 18, 2009
    Messages:
    506
    Likes:
    16
    Location:
    Florida. USA

    the voltage is a bit high, someone may give you a good answer tonite, its way past my bedtime..
     
  6. MikeMl

    MikeMl Well-Known Member Most Helpful Member

    Joined:
    Mar 17, 2009
    Messages:
    11,048
    Likes:
    541
    Location:
    AZ 86334
    I would need to know something about the usage pattern of the batteries. Are they mostly discharged over night, and then recharged during the next day, or are they more-or-less fully charged at the beginning of each solar day? If the latter, then the panel will dry out the battery due to chronic overcharge, and you will need a regulator.

    Be aware that terminating charging for NiMh batteries is very complicated.
     
  7. Mr RB

    Mr RB Well-Known Member

    Joined:
    Jul 22, 2008
    Messages:
    4,716
    Likes:
    194
    Location:
    Out there
    The 22v open circuit voltage is a typical 12v solar panel, peak power will be around 17v (so is 17v at 88mA).

    Directly connected to the 10.8v battery it will deliver a fraction more, maybe 92 to 95mA. Considering that 90+mA will only be achieved for a few hours around noon, on very sunny days, it looks to be underpowered for charging a 3.8Ah battery.
     
    • Like Like x 1
  8. knarf180

    knarf180 New Member

    Joined:
    Jun 2, 2013
    Messages:
    3
    Likes:
    0
    Location:
    USA
    Thanks Mr. RB.

    So directly connecting the panel to the battery (with the addition of a diode to prevent reverse voltage) I shouldnt really have to worry about over charging if the battery is fully drained overnight. Am I correct in my understanding?
     
  9. MikeMl

    MikeMl Well-Known Member Most Helpful Member

    Joined:
    Mar 17, 2009
    Messages:
    11,048
    Likes:
    541
    Location:
    AZ 86334
    In our part of the world, the panel would output near 1.5W for 6h per day, and about 0.7W for another 4h per day for a total of 12Wh per day. Because the MPPT voltage for the panel is somewhat higher than the battery voltage, due to inefficiency, say we get ~8Wh into the battery per day. That is twice the capacity of the battery, so clearly some regulation is needed.
     
  10. Mr RB

    Mr RB Well-Known Member

    Joined:
    Jul 22, 2008
    Messages:
    4,716
    Likes:
    194
    Location:
    Out there
    Sorry to argue Mike, but the battery capacity is 10.8v 3.8Ah or 41.04 Wh.

    Wiki says the charge efficiency is only 66%, so to get the rated 40Wh out means 40/0.66 or 60.6Wh needed from the solar panel. :)
     
  11. MikeMl

    MikeMl Well-Known Member Most Helpful Member

    Joined:
    Mar 17, 2009
    Messages:
    11,048
    Likes:
    541
    Location:
    AZ 86334
    Wh ≠ Ah! Brain Fart.
     

Share This Page