How do I calculate how long a battery will power an LED?

Asked by pallen123 (1519

) December 1st, 2013

I want to power an ultra-bright LED for a science project with my son and the product description says “At about 3V, the LED draws ~200 mA, so connect two Alkaline batteries up directly with no resistor for a basic bright lamp”. From this information is there any way to determine approximately how long the batteries will last?

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5 Answers

AA Alkaline batteries have between 1800 and 2500 mAh and C Alkaline batteries up to 8000 mAh.

mAh/mA = hours

Calculation is batteries mAh divided by load 200 mA, for AA 9 to 12 hours and 40 hours for C.

Tropical_Willie (31656

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Thank you @Tropical_Willie!

pallen123 (1519

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mileage may vary ;>)
You may want a simple switch between the bulb and battery pack.

Tropical_Willie (31656

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@Tropical_Willie Don’t forget the low voltage cutout, LED’s usually last a long time, but a 3v 200ma one sounds like it might have a bit of a higher minimum voltage.

XOIIO (18360

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@XOIIO that is true ^ ^ ^ . That was the reason for mileage may vary add-on.

Tropical_Willie (31656

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