To keep your LED strip project glowing brightly with the appropriate power, you will need to know how much current your project draws and it's operating voltage. Once you know those two things, you can choose a power supply. Keep in mind that current draw can be a tricky thing to figure out. Here we will take information from the datasheet and plug it into some simple equations to get the max current needed, since the information from the datasheet are if the LED is on at full brightness.

To calculate the needed power supply, we will need the following info:

length of strip

number of LEDS per meter

current draw per LED OR power consumption per LED

OR operating voltage

LED strips are commonly powered on 5V, 12V and 24V. The number of LEDs per meter (lpm) factors in the power calculation as well. Strips can be 30, 32, 60, 144 or more per meter.

Using Current Draw Per LED

As an example let's look at the white strip's datasheet. We can see the operating voltage is 12V, which should also be screen printed on the strip itself at the cut line of each segment. What we are looking for is the current draw measured in milliamps (mA). It tells us that each segment made up of 3 LEDs draws 60 mA. To make the calculations easier, the current draw can be divided by 3 totaling 20mA per LED. If one meter is being used with 60 LEDs per meter we have this information:

length of strip = 1 meter

number of LEDS per meter = 60

current draw per LED = 20 mA

Equation:

(Length of LED Strip x LEDs per Metre x LED current draw)

Plug in info:

1 (meter) x 60 (lpm) x 20 mA = 1,200 mA

1,200 mA / 1,000 = 1.2 amps.

Using Power Consumption Per LED

Another way of calculating current draw is using the power consumption per LED. The power consumption can also be used to find current draw if the power consumption, measured in watts per LED is known instead. The datasheet tells us .72 watts for 3 LEDs. First divide .72/3 = .24 watts per led

length of strip = 1 meter

number of LEDS per meter = 60

power consumption per LED = .24 watts

operating voltage = 12V

Equation:

(Length of LED Strip x LEDs per Meter x LED Power) / 12

Plug in info:

(1 x 60 x .24) / 12 = 1.2

We now know that we want to use a a power supply that can provide 1.2 amps and 12 volts. Keep in mind that the current draw per LED is at full brightness. If the strips are dimmed through a PWM pin on the Edison, it will take less current. Going by the max amount is still a good guide to know if you have enough to begin with.





Battery Life

Battery life is based on current draw of, again it will fluctuate, especially with the digital RGB strips when patterns and colors are dancing along it. Current draw will fluctuate dependent on the color and brightness the LED is outputting. The way to accurately get the current draw is to hook it up to a multimeter and watch the amps change per pattern cycle, take note and do some calculations.

Another way to find out battery life with a dynamic project, hook up a battery at full strength and see how long it takes to drain.

This aside a general calculation can be made by looking at a batteries mAh rating. Let's stick with the white strip, 6 AA batteries are being used to power the example circuit. AAs roughly have 1500mAh, the 8 batteries are in series so the current stays the same at 1.5 amps. Divide this with the current draw of our project, which is 1.2.

1500 mah/1.2 amps = 1.25 hours of full brightness