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Homework Help: Can I charge a solar battery very fast with a large current?

  1. Nov 30, 2014 #1
    1. The problem statement, all variables and given/known data

    The main problem is if it is safe to charge a solar battery as quickly as possible assuming that I have a large current charger. Let's say I have:

    70Ah Solar Battery
    50 F, 15 V Ultra Capacitor

    C = Q/V
    Q = CV = (50)(15) = 750

    I = Q/t
    It = Q = 750 Ampere-second

    E = 15 V
    P = 11,250 Watt-second

    so that means a fully charged capacitor has a rating of 11,250 Ws or 750 As
    I think with this current it is possible to charge a 70Ah solar battery in a few moments.

    2. Relevant equations
    I've searched the net for the formula in order to know how long will it take to charge a battery and came across this:

    h = (Ah of battery) / (A of charger)

    so if we use the data above
    h = 70Ah / 750A
    h = 0.093 hr or 5.6 minutes

    but I'm not sure if this formula is true or not, and if it is true, is it safe for the battery to charge it for a short amount of time.

    3. The attempt at a solution
    I keep on researching the net and asking people on the net.
  2. jcsd
  3. Nov 30, 2014 #2


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    Staff: Mentor

    You definitely cannot charge any secondary cell in as brief a time as suits you. To withstand rapid charge, a cell has to be manufactured with that severe treatment in mind. I think it unlikely that a cell intended for gradual solar charging would be a rapid charge type. If it is not, then your rapid charging can cause it to explode or otherwise markedly shorten its life.

    If you know the battery model and manufacturer, you should be able to find a data sheet applicable.
  4. Nov 30, 2014 #3


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    2017 Award

    Staff: Mentor

    Which current? You did not calculate any current. As is a charge, not a current.
    The capacity of your capacitor is very small compared to the capacity of the battery.

    There is no way to charge it with 750 A. No element of your battery is designed for those currents, so the question is just "which part will fail first?". If you are lucky, you just lose the electric contact somewhere and the overheated parts does not break anything else. If you are less lucky, your battery might break physically.
    Oh, and your capacitor probably cannot deliver that current either.

  5. Dec 1, 2014 #4


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    Science Advisor
    Homework Helper
    Gold Member

    That's 750 Coulombs

    A 750AH battery can nominally deliver 750A for 1 Hour. So if fully charged it must contain at least..

    750 * 60 * 60 = 2,700,000 Coulombs.

    So your ultra capacitor only contains about

    750 * 100 / 2,700,000 = 0.03%

    of the charge needed to "fully charge" the battery.

    It's not possible to calculate the current that would flow from capacitor to battery because you don't specify the internal resistance of either.

    Is it safe to connect the capacitor to the battery (with some nice thick wire)? No. There is a risk the capacitor or possibly even the battery might explode or fail in a similarly spectacular way.
  6. Dec 1, 2014 #5


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    Homework Helper

    Most rechargable batteries, if they include documentation, will specify normal and quick charge rates in temrs of a factor x capacity / hours. Typically the "normal" charge rate is 1/10 C, for a 70 Ah battery, the charge rate would be 7 amps (10 hours to charge). For a fast charge battery, the rate might be 1 C, 70 amps (1 hour to charge), but that's a lot of amps, and probably more than what that battery can handle. See if you can find documentation for that battery. You'll also need a smart charger that is aware of the battery type, Nimh, LiPo, lead acid, ... .
  7. Dec 1, 2014 #6

    rude man

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    Homework Helper
    Gold Member

    What's a "solar battery"? ',ve heard of solar cells but never a solar battery.
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