What size solar panel needed?

Discussion in 'General Electronics Chat' started by mrel, Oct 23, 2012.

  1. mrel

    Thread Starter Active Member

    Jan 20, 2009
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    Hello
    Have 6 volt 1.3 ah gel cell .
    what is smallest amp size solar panel can use to full charge this battery?
    mrel
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    6V X 1.3 Ah= 7.8 Watt panel, so a 6V 10W would do.
     
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Might want to boost V to about 10 OC, 7.5 V / .7 @ about 100 mA. SC. This assumes a light or no load and no time limit stated.
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    Ther output of a solar panel is rated on when it is outdoors pointing at (or following) the sun at noon on a sunny day in summer.

    In the morning and in the afternoon and evening the output is much less.
    Guess what happens to the output on a cloudy day or at night?
    Even a window reduces its output.
     
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    You want to put in as much (or more really due to charge efficiency) as you take out. Is this a daily load? What percentage of capacity are you using each charge/discharge cycle? How long is the sun available?

    AFAIK a gel cell is based on the lead-acid type. Even "deep discharge" types should not be drained completely each cycle, if you want them to live. 50% is max, 25% is more reasonable.

    So, assuming your daily load is 25% of capacity, your charge efficiency is 80%, and you have 5 hours of daylight to charge you'll need:

    (1.3 AH ) * 25% / 80% / 5 hours = 0.8 Amps

    Again, derate the current a cell produces by 80% so that brings us back to a 1 amp output.

    I hope I've spurred some thoughts about how your system is being specified.
     
  6. mrel

    Thread Starter Active Member

    Jan 20, 2009
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    1
    So are you saying to full charge this battery 6 Volts @ 1.3 ah battery need .800ma solar panal ,what is solar panal voltage need to full charge ths battery.
    mrel
     
  7. mrel

    Thread Starter Active Member

    Jan 20, 2009
    97
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    So are you saying to full charge this 6 volt 1.3 AH battery is to get a solar panel that is 7.5 volts at 100 ma solar panel is that right.
    mrel
     
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    People have give you good numbers and calculations but YOU need to give more info, mainly; how much current your devices uses up and how fast you need to charge the battery!

    You can charge a 1.3Ah battery at 60mA, but it will take a few days and won't be a perfect "full" charge. And that is if nothing else is draining power (like your device). Personally for a 1.3Ah battery and low current drain device I would use a panel of about 300mA to 400mA. But then, I live somewhere very sunny. :)
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    No, I said 10 V, OC, which will drop under load. Or a panel that will hold 7.5V under a load of 100 mA; this is bare bones- re read THE_RB's post.
     
  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Nope, use the 1 amp number. The reason being the current is typically spec'd with an Irradiance 1000 W/m2, but 800 W/m2 is something typically expected. I omitted this point.

    What is your expected load?

    How many amps for how many hours?

    Is the load draw during daylight (just draws from solar cell) or night (needs to figure into the charge efficiency)?
     
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