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The_LED_Museum said:
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If the lights are regulated, the LEDs should run correctly.
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I, likely, would have said the same thing until I really thought about the consequenes. It was brought home to me when I was trying to find some answers for
this thread about the Pelican Sabrelight. If you look in the reviews this light is very well regulated, but it uses a simple circuit rather than one of the many special ICs designed for this purpose. One of the facts of life is rechargeables can deliver very high current levels even when their voltage is extremly low. Alkalines cannot do this. With any regulated design we are trying to feed the LED with a constant amount of
power. Power, in watts, is voltage times current, in amps. This particular flashlight uses a regular 1.2 W Luxeon and 3 "C" size cells. Lets call the efficientcy of the regulator 50%. So we would be trying to draw 2.4 W from the battery. OK, fully charged rechargeables (3 x 1.35 V) 4.05 V and we will be drawing (2.4 W / 4.05 v) 0.593 A or 593 mA. No problem! But a real flashlight has real resistance. In battery contacts, wiring, the switch, the traces on the circuit board. Also, since this is regulated, we don't know that our battery is running low. Let's call the resistance 1/2 an ohm (actual would just change the point were the problem occurs, acutal point in time wouldn't be much different). Another permutation of Ohm's law tells us that
power is resistance times the current squared. So at full charge we are lossing 0.176 W in wiring. No problem. When rechargeables reach a point their voltage starts dropping fast, but remember they can still deliver high current. Lets pick a point in time were we have a voltage of 0.2 V per cell giving a current draw of (2.4 W / 0.6 V) 4 A! Wiring loss, which becomes heat, is (0.5 ohm * 4^2) 8 W. The LED is still fine, but likely the rest of the flashlight isn't! A requlator must be designed to shutdown when the current drawn reaches a certain point to allow it to be safely used with rechargeables. Another reason for moonlight mode!
George