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Can a nokia bl-5j 3.7 volt battery be used to power LED's safetly and how?
Wiki User
∙ 13y ago
A: It sure can but what is voltage iof the LEDS 3.2 V then you need to drop 3.7 to 3.2 v at ~20ma .5v / 0,02=27 ohms in series the LEDS are 1.8 you need 3.7- 1.8/.02= 100 ohms in series. The warning is the life of this setup is going to be short lived after the battery drain off the battery needs recharging if so it is better to supply the LEDS from the charger directly will last until the LEDS QUIT FUNCTIONING
Wiki User
∙ 13y ago
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Trying to make some indicators for a bike and am going to use 1.5 volt leds and a 12 volt 11ah battery by putting 8 leds in series was wondering whether resistors are needed not to short the leds?
Resistors will be needed in all cases when driving LEDs from a voltage source, unless you are using LEDs that already have a built in current limiting IC inside the package (a few do these days, for example I have some blinking LEDs that need no resistor they have a blinker IC built in that also limits current).However you have another problem that you obviously are not aware of. 8 LEDs rated at 1.5V in series totals exactly 12V. But your battery is only rated at 12V. As the battery discharges its voltage slowly drops, the moment it drops under 12V all the LEDs will turn off! I strongly recommend that you use no more than 7 LEDs rated at 1.5V in a circuit powered by a 12V battery, so that the battery can actually gets a chance to discharge beyond its knee voltage. In this case the resistor will drop the remaining voltage, whatever it is depending on the charge state of your battery.
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Trying to make some indicators for a bike and am going to use 1.5 volt leds and a 12 volt 11ah battery by putting 8 leds in series was wondering whether resistors are needed not to short the leds?
Resistors will be needed in all cases when driving LEDs from a voltage source, unless you are using LEDs that already have a built in current limiting IC inside the package (a few do these days, for example I have some blinking LEDs that need no resistor they have a blinker IC built in that also limits current).However you have another problem that you obviously are not aware of. 8 LEDs rated at 1.5V in series totals exactly 12V. But your battery is only rated at 12V. As the battery discharges its voltage slowly drops, the moment it drops under 12V all the LEDs will turn off! I strongly recommend that you use no more than 7 LEDs rated at 1.5V in a circuit powered by a 12V battery, so that the battery can actually gets a chance to discharge beyond its knee voltage. In this case the resistor will drop the remaining voltage, whatever it is depending on the charge state of your battery.
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