How to Choose a Power Supply
The first step is making sure your power supply and lighting voltage match. If you are using 12 volt LED strip lights, make sure you are using a 12-volt power supply for your input voltage. A voltage mismatch is dangerous will result in the power supply and/or lighting failure. As an example, connecting a 24-volt power supply to 12-volt lighting will cause them to overheat, burn out and worse, start a fire.
The Second step is to make sure your power supply has enough current to drive your lighting. This is a simple process. We describe how to calculate the total wattage for the lighting you plan to use below. Please contact your lighting manufacturer for their power specifications. Not all LED’s are created equal.
In our example we will be installing three segments of single color LED strip lights under the kitchen cabinets. This will require three separate runs of 6 feet, 3 feet and 8 feet.
We will install the 6 foot run on the first channel and use 12 volt single color strip lights with wattage of 4 watts per foot. So to calculate total wattage simply multiply the watts per foot by the rung length. (6 feet x 4 watts/foot = 24 total watts)
We will install the 3 foot run on the second channel and use the same 12 volt single color strip lights rated at 4 watts per foot, so total watts on the second channel is 8 watts. (3 feet x 4 watts/foot = 12 total watts)
Lastly, we will install the 8 foot run on the third channel using a different 12 volt strip of higher density LED’s that draws 6 watts per foot, so total watts on the third channel is 48 watts. (8 feet x 6 watts/foot = 48 total watts)
The next step is to divide the total watts for each channel by volts to get the necessary amps per channel. This calculation cannot exceed 5 amps for each of the channels.
In our example, for the first channel, we divide 24 watts by 12 volts which means channel one will draw 2 amps (Amps = Watts ÷ Volts).
For the second channel we divide 12 watts by 12 volts which means channel two will draw 1 amp.
For the third channel, we divide 48 watts by 12 volts getting a total of 4 amps.
Next we need to add the amperage of all three channels together and we come up with 7 amps. (2 amps + 1 amp + 4 amps = 7 amps)
A popular online calculator can be found here:
The last step is to add a 20% margin of safety and you have an idea of what size power supply is needed. So in our example, an 8.4 Amp or greater power supply will be necessary. (7 x 1.2 = 8.4)