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Old 02-17-2007, 02:31 PM   #11
BobVA
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Join Date: Oct 2006
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Quote:
Originally Posted by Steve Jordan
20 hours of power for 2 LEDs? That doesn't sound right. What kind of sorry batteries have they got in there? A single AA could probably do better...
I suspect they are using the 2032 to keep the cost and weight of the light down. White LED's need at least 4.5 volts to illuminate, which is pretty easy to get from two 3v lithium cells. You can either regulate it down (best) or just use a resistor (cheap).

If they used 1.5v batteries (AA or AAA) they'd need three or four (depending on the run time and LED life desired). If they only used one or two to keep the light compact they'd need a "boost regulator" to step up the voltage, which is more expensive.

The 2032's are available online for about 50 cents each in single quantities. I use a couple of flashlights that are powered by CR123 lithium batteries and it's a similar quandry; relatively cheap online ($1/battery), but Tesla help you if you have to buy one at Safeway ($7!!)

Your suspicion about AA capacity vs. a 2032 is spot on. An AA battery has around 0.9 WH (Watt-hours) of capacity vs. about 0.6 for a 2032. On the other hand an AA battery is about 8x the volume of a 2032 and 9x the weight.
The biggest thing the alkaline cells have going for them compared to primary lithium cells is relatively low cost and easy availability.

Cheers,
Bob
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