Battery capacity: Difference between revisions

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Revision as of 15:50, 10 December 2010 (view source) Brted (talk \| contribs) m (moved Measures of Capacity to Battery capacity: better description) ← Older edit		Revision as of 19:23, 10 December 2010 (view source) Brted (talk \| contribs) No edit summary Newer edit →
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	There is more to a good battery than its measured capacity. An LED might draw 1 amp of current at 3 volts. So that is 3 watts or 3000 milliwatts. If you have a 2400 milliwatt-hour NiMH battery (whose 1.2 volts of power are being boosted to 3 volts to run the LED) then you can figure that you could run the LED for 2400mW*hr/3000mW=0.8 hours, or 48 minutes. But you're having to provide a lot of current (I=P/E) of 3/1.2=2.5 amps. That's a lot for any battery to deliver and it will at least get very hot and may only be able to drive the LED at something less than 3 watts. So the ability of a battery to deliver a high current is also important. "High drain" devices require more current.		There is more to a good battery than its measured capacity. An LED might draw 1 amp of current at 3 volts. So that is 3 watts or 3000 milliwatts. If you have a 2400 milliwatt-hour NiMH battery (whose 1.2 volts of power are being boosted to 3 volts to run the LED) then you can figure that you could run the LED for 2400mW*hr/3000mW=0.8 hours, or 48 minutes. But you're having to provide a lot of current (I=P/E) of 3/1.2=2.5 amps. That's a lot for any battery to deliver and it will at least get very hot and may only be able to drive the LED at something less than 3 watts. So the ability of a battery to deliver a high current is also important. "High drain" devices require more current.

	Cells that have high internal resistance will not be able to deliver the same current as ones that have less internal resistance. Alkaline batteries have higher internal resistance than NiMH batteries~~. This is why NiMH batteries are designed to deliver only 1.2 volts. If they were 1.5 volts, they would deliver more power than a device designed for a 1.5 volt alkaline could handle~~.		Cells that have high internal resistance will not be able to deliver the same current as ones that have less internal resistance. Alkaline batteries have higher internal resistance than NiMH batteries.