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Q & A: LED plus battery

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Most recent answer: 08/01/2016
I am working on a project in which I am lighting a 12Volt light bulb off a 12 Volt battery. Works great for 20 minutes and then light dims...I need to get hours out of this not minutes...5 hours would be ideal but I don't want a huge battery. I am using a 12V 3.3AH AGM; would I get this extra time using a 12volt 4watt LED bulb- or am I out of luck to get a bright light for more than 20 minutes...
- Kristem (age 16)

Your LED bulb will let the battery last maybe six times a long as the old incandesent bulb.  Actually if you calculate its current draw, 4 W at 12V is only 1/3 A. (1/3 A *12V=4W) So if you can really get 3.3 AH from the battery, it would last 9.9 hours. Probably it won't really last that long. You might get 5 hours though.

Mike W.

(published on 08/01/2016)

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