Rufusbduck
(Rufusbduck)
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The Ultrafire C3 is an example of a light that can usually use either 14500 or AA. It will say so in the description. Most small boost drivers for this purpose are designed for AA and survive the 14500 because above a certain voltage the driver goes into direct drive (no control other than the sense resistor and led Vf limiting current. Because of this it’s a good idea to use protected cells to avoid smoking the driver with a low internal resistance “hot” cell. Some are one mode and some are multi mode drivers. The common size for a AA/14500 driver is 15 mm diameter.