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Homework Help: Car Batterys and A*h

  1. Feb 16, 2004 #1
    A battery has a rating of 250AH What is the total amount of charge this battery can supply to a cct? And What is the max current this battery can provicde for 5 min?
    I don't know what formula's to use?
    I have C=QV I=q/t
    but I don't which ones to use or even worse where to apply for these
     
  2. jcsd
  3. Feb 16, 2004 #2

    Doc Al

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    I assume that "AH" is Amp-Hour, which means that the battery can provide: 250 Amp-Hours of charging. By definition, 1 Ampere is 1 Coulomb of charge per second. So how much charge does a 1 Amp current provide in 1 Hour? In 250 hours?

    That 250 AH can be delivered over 250 hours (at a current of 1 Amp) or it can be delivered in 1 hours (at 250 Amps). (The greater the current, the quicker you use up the battery.) So what's the maximum current it can deliver for 5 minutes?
     
  4. Feb 16, 2004 #3
    Lets see If I got this right

    250 AH/60min = A/min x 5min= Amp@5min=20.83333 But 1c x 300secs= ???? This again is a sticky point. What is the charge in Coulombs? Do I multiply 20.833 by something?
    Am I at least on the right train of thought?
     
  5. Feb 16, 2004 #4

    Doc Al

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    Re: Lets see If I got this right

    Separate the two problems. First find the total charge delivered by the battery:
    Q = 250AH = 250 Amp-Hours = 250 (Coulombs/sec)Hours(3600 sec/hour) = ??

    You take it from here.

    For the second problem, realize that 5 minutes is 1/12 of an hour.
     
  6. Feb 17, 2004 #5
    In that case 250AH x 3600=900 000 Then 900 000/300= 3000 A is the answer to the max current?

    I think that this is what you were talking about ..... yes????
     
  7. Feb 17, 2004 #6

    Doc Al

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    Excellent. You found the total charge that the battery could supply (Q = 900 000 C), then used I = Q/t to find the max current. Perfect.
     
  8. Feb 17, 2004 #7

    NateTG

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    Now it's time to bring in the Ragone (spelling may be incorrect) plot. :wink:
     
  9. Feb 17, 2004 #8

    Doc Al

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    I think it best if we just skip over that one, NateTG.
     
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