Do you need to worry about voltage when using button batteries to power LEDs?

Question

I'm string up LEDs powered by button batteries in my room, they only need to last for a few hours if need be, but I was wondering if I needed to make sure the battery and the LEDs had compatible voltage if I'm only using them short term?

I'm so dense when it comes to electronics its unreal. Anyway, tips appreciated. Thanks in advance.

Answer 1

yes. Look up the Vf for the LED, which can be anywhere from 1.5 volts to 3.5 volts. Then add about 2 volts for a resistor, and the sum is the voltage you need.

Usually a 200 ohm resistor is OK for this use, with 2 volts it will allow about 10 mA of current.

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Answer 2

L.e.d. are current, not voltage, operated devices (unless an l.e.d, or an array of them, is packaged together with the essential series resistor, when an operating voltage will be stated by the supplier.)  

Read this http://www.davidbridgen.com/leds.htm

Answer 3

Since you're using a button battery we'll assume 3V for a Lithium coin cell.

Now you need to do two things to run the LED: make sure there's enough voltage to light it and then limit the current so the LED doesn't burn out.

First the voltage. LEDs, like all diodes have a Vf (forward voltage), which for LEDs varies by type and color. Vf for a red LED is typically 1.2V, blue ones go as high as 4V. So your power supply must be at least that much to light the LED.

Next the current. Once the LED is lit it will have an If (forward current). If varies by type, but for most LEDs it's between 5 and 20mA with 10mA being typical. Larger (higher-power) LEDs have higher If.

The easiest way to limit current is to use a dropping resistor. Its value should be set to R = (V - Vf)/If. So for a 3V battery with If=10mA and Vf of 1.2V, you get (3 - 1.2)/0.010 = 180 ohms. 200 or 220 ohms is fine, which is what most people use with a 3.3V logic supply.

You can also wire LEDs in series to increase efficiency. In this case, two 1.2V Vf LEDs would have a combined Vf of 2.4V. Then you'd use 60 ohms for the dropping resistor for 10mA forward current.