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I have led string lights outside (6 sets) that each have their own 3.6v power supply. The power supply's are not weatherproof and are failing. In addition the 6 separate power supply's are not ideal required a few extension cords. I would like to directly connect these lights to my 12v low voltage outside lighting system. How would i drop the voltage? Would i connect them in parallel or serial?

Thanks for any help.

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2 Answers 2

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You might get away with connecting sets of 3 LED strings in series. At 3.6 V each, that would drop a total of 10.8 V. By measuring the current drawn by a string, you can calculate what resistance to add in series to drop the remaining 1.2 V.

Depending on what kind of electronics is actually in each string, they may be OK with connecting 3 in series to 12 V. That would supply each with 4 V. Or, that could seriously overcurrent the LEDs, causing them to blow out or have severely decreased lifetime. Without a datasheet there is no way to tell from your description.

Another option is the 12 V supply with a couple of diodes in series instead of a carefully calculated resistance. Each diode would drop about 700 mV, leaving 10.6 V for the three strings, or 3.53 V for each. Again, without a datasheet for the LED strings, it's impossible to say what is acceptable.

You also need to look carefully at this "12 V" supply. Is that 12V±100mV, or something unregulated like a transformer and four diodes? If the latter, and the LEDs need a tight voltage, then you can't use your 12 V supply directly anyway.

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LED emitters are current devices. They want a constant current. They are highly non-linear and applying a fixed voltage may work in some conditions and make magic smoke in others.

How do you know they are a 3.6 volt power supply? They may be an x-amp constant-current power supply, which just happens to be at 3.6 volts in your bench testing conditions, and with x amps being correct for the emitter they use. 3.6v is a typical voltage to see.

I would dig deeper. Find out what emitter(s) specifically are used by the lights, or just measure current, and figure out which constant-current supply suits them.

Then hit eBay, Amazon, Mouser, Alibaba, etc for ones with 12v input. I would expect these items to be commodity items widely available cheap. Light makers, especially the Chinese ones, aren't engineers, and generally knock these things together using COTS subassemblies like this.

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