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Old 01-24-11, 11:07 AM   #32
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I am making some cheap LED lights for a boat project. I purchased 1000 warm white 5mm LEDs for $65, taking advantage of a quantity discount.

This project will use an incredibly high tech and innovative system of voltage regulation: I am using old batteries that previously were used for an electric bicycle and are pretty much worn out. The batteries do not allow the voltage above about 12.8V. So a series of 4 LEDs needs no regulation at all. The batteries do not have the capacity that they used to have, but I am now pulling less than an amp where the electric bike used to pull close to 20 amps, maybe more on startup.

The 20 LED lights will pull about 0.1 amp, since each 4-series pulls 20 ma. The 32 LED light will pull about 0.16 amp. In practice, actual amperage changes quite a bit with voltage. This has the happy situation that as battery voltage drops, amperage drops so the battery will last longer. Yes, the light output drops but it is still usable even at lower voltages.

My battery system has a 10W solar panel with charge controller. I never expect to add an alternator to the system, which means it is fairly sure that that there will never be voltage spikes.

The LEDs are rated 3.0V to 3.4V. Four in series would be rated at 13.2V. I don't expect my old batteries to allow the voltage to rise above 13V, even under charge from the solar panel.
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