Power an LED strip, power supply or transformer?

Question

I'm new to electricity so don't judge me too much. I need to power 5 watts of led strip. Is there a difference between a power supply and a transformer? I found a transformer in my local hardware store and it says: connecting power 10-50 watts, can I use it to power my led strip or do I need to look for suitable power supply?

This:

Or this:

Edit: The led's are 12v 7.2w per meter the power supply shown in picture is 12v 12w, I'm actually building a light pad and searching for a simple way to power led's

Answer 1

You haven't provided much info. First white thing is labelled as transformer for "LV Halogen Lamps". Most likely it's just a step down transformer which will fry your christmas LED strip during reverse polarity.

Second one is a mystery box without much info. I wouldn't go for that either.

Here is what you need to do:

Figure out what voltage is required by your LED strip - 3V, 5V, 12V or something else?

If the LED strip is 5 watts, then you can calculate the current requirement as follows:

Current = Power / Voltage required.

Ex- If LED strip needs 5V, then you will need 5W/5V = 1A of current.

Go to the market and ask for a 5V 1A(or higher) wall adapter. Modify the voltage and current accordingly. I am just giving an example.

Get something less intimidating like this:

EDIT after the question was edited:

Figure out what length of strip you want to use. I will assume 0.7 meters which will give you total power requirement:

Power = Length X Power required per unit length = 0.7 X 7.2 = 5 watts.

Voltage = 12 V

Current = Power / Voltage = 5/12 = 0.42 A

Better to go for 12V 0.5A (or higher) wall adapter or any DC power source. Make sure it's a DC power source and not just a step down transformer. If the power source is DC 12V 12W, then it will do the job without any issues.

Answer 2

LEDs require DC (direct current), not AC (alternating current). A transformer on its own will provide AC only.

If it's the standard 12 V self-adhesive LED strips which can be cut every 100 mm or so along the strip then the internal circuit is most likely similar to that shown below.

^{simulate this circuit – Schematic created using CircuitLab}

Each LED requires 3 - 3.5 V so three of them can be powered safely from a 12 V supply. The resistors limit the current to a safe value for the LEDs. The pattern is repeated along the length of the strip.

It should be obvious that each group of three LEDs forms a circuit from the positive conductor to the negative. Cutting the strip other than at the marked positions will result in the non-illumination of the LEDs in that short section.

As you have probably figured out, you need to get the voltage right to match the LED configuration. You need to get a power supply with high enough current capability to power all the LEDs. You can use a more powerful PSU provided the voltage is right - the LEDs will only draw the power they need