# What size power supply for LED strips?

I'm not getting a clear answer to this from my reading or reviewing previous questions here. Is there a difference in the power supply requirements if LED strips are wired in parallel vs serial? Most of the examples use/imply serial wiring.

Specifically if I have a strip that is rated; 24VDC 1m = 6.8 watts 3m = 19.8 watts 6m = 34.2 watts

What if I connected three 2m strips in parallel vs one long 6m strip, what would the power supply requirement for that setup be?

Most LED strips are constructed so that you can cut them at periodic intervals so you can customize the length. What this means is that the LEDs are arranged in a parallel-series configuration. For instance, you might have a 24V strip that can be cut at every 12 LEDs. So if you have a strip of 48 LEDs it is electrically the same as four strips of 12 LEDs in series and the four strips are arranged in parallel with each other.

Now suppose you have N of these 48 LED sections and you join them end-to-end. Although it looks like you are creating a series combination of the strips, you are really joining 4*N strips of 12-LED segments each in parallel to each other.

The upshot is that connecting these kinds of strips "in series" with each other is the same as connecting them in parallel.

As far as power is concerned, it is basically proportional to the total number of LEDs. So if 1 meter requires 6.8W you should expect 6 meters to require 6*6.8 = 40.8W.

Note that you can inject power anywhere in the strip - not just at the ends. In fact, for long strips it is advisable to inject power in the middle or even at multiple points. This will reduce power loss due to the resistance in the traces that carry power to the LEDs.

Now suppose you have a 2 meter strip of LEDs. If you inject power in the middle it's the same as putting two 1-meter strips in parallel with each other. So that's another way to see that connecting segments end-to-end is the same as connecting them in parallel.

• Yes, I was talking about the strips that have cut marks. Ok, I'll go with 40W+25%, but I was hoping yo use a physically smaller transformer. Dec 3, 2022 at 10:17

If the strips are wired in parallel you will require the same voltage as for one strip, but the supply must be able to supply the sum of the currents for each strip (for 2 strips, twice the current for one strip).

Wiring the strips in series (positive of the supply to positive of one strip, negative of that strip to positive of the second strip, negative of the second strip to negative of the supply) would require twice the voltage for one strip, but the same current as for one strip. I wouldn't recommend doing this as it depends on the two strips having identical current requirements for proper operation.

If by "series" you really mean connecting the strips end-to-end, that is functionally connecting the strips in parallel.