# 12V LED strips in series with a 24V power supply?

I am purchasing 50x - 1Meter / 12V / 72 LED /Rigid SMD 5730 strips directly from china. I don't know the LED manufacturer, nor the resistor being used. (yes, this is a gamble)

The strip is one that could be cut at every 3rd led. So, it seems that every 3 LEDs is wired in series, and there are 24 groups of 3 wired in parallel.

Each strip is specked out at 12V/18W. I would like to take 2 strips, and wire them in series with a 24V 18W power supply.

(By series, I do not mean chaining them in parallel and calling it series like the billion articles polluting my google searches)

My question is, can I wire two 12V strips in series using a 24V power supply? It seems like I can, but am worried I am overlooking something that I don't even know to ask, or I do not have enough information without the LED spec sheet.

Thanks!

• You've got it right (the pic on the right). Any time two 12v loads are wired in series, it's now a 24v load. But what your sixth sense is telling you is correct - the supply is not big enough. It's only good for one strip. V x A = W – user57849 Nov 9 '14 at 4:00

Well, yes and no. On the one hand, connecting 2 in series ought to work. On the other hand, you will need 24 volts at 36 watts.

Since each string takes 12 volts at 18 watts, its current must be 1.5 amps. Connecting them in series will still take 1.5 amps, but the total power will be 1.5 x 24, or 36.

• 24 volts at 36 watts what? You must mean 24 volts with 1.5 amps – Funkyguy Jul 25 '14 at 0:32
• As long as power equals volts times amps, I fail to see the difference. – WhatRoughBeast Jul 25 '14 at 1:36
• Yes, sorry, I had a brief moment of duh. Of course adding a second fixture will double the wattage demand on the power supply regardless of voltage. – Cody Jul 25 '14 at 16:57
• Heh. Let's hear it for brain farts, our constant companions :) – WhatRoughBeast Jul 25 '14 at 17:00

This is an old post, but i just wanted to contribute my observation. Both your parallel and series would work, however that is if we assume that none of the LEDs would ever burn out.

If half of the leds on the 24V would have burned out on the left side (see image).

The result would be catastrophic because the remainder leds on the burned side would receive an increase in voltage (about 16 V) and on the right side the voltage would drop to about 8V.

In conclusion, as the led burn out the voltage increases on the same parallel side and if your LEDs are rated at 12V it would be just a matter of time until all lights in the same parallel burn out due to high voltage.

That is why it is recommended to always connect led strips in parallel.

• Excellent point! Hopefully people read this and understand the theory vs the reality that LED invariably burn out prematurely. Of course the longer the individual (smallest serial) runs are the worse this can get since most LED strips in series act like old christmas tree string lights, when one goes out, they all go out in that small serial run. (Which would correspond to the each of the rungs of the ladder in the original post...those rungs are each 3 LEDs wired in series...so the more LEDS in those rungs...the more impact each LED burnout will have on the overall misbalancing you discuss) – Questor Jun 11 '18 at 14:11

This is of course correct and a real problem as long as you have only a few LEDs on each side. However, if you connect 2 X 2 meters with 2 X 120 LEDs, a burnt unit (3 LEDs and a resistor) will increase the voltage only about 0,6 Volt on the other side. This will not do any harm especially if you turn down the power supply a little bit (if the power supply can be adjusted). Furthermore you can balance the systen anew by cutting of 3 units as soon as 2-3 units are burnt on the other side. Sorry, no native speaker of English.

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