Homework Help: Car Batterys and A*h

1. Feb 16, 2004

Magna1

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. Feb 16, 2004

Staff: Mentor

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?

3. Feb 16, 2004

Magna1

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?

4. Feb 16, 2004

Staff: Mentor

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.

5. Feb 17, 2004

Magna1

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????

6. Feb 17, 2004

Staff: Mentor

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.

7. Feb 17, 2004

NateTG

Now it's time to bring in the Ragone (spelling may be incorrect) plot.

8. Feb 17, 2004

Staff: Mentor

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