Christmas LED lights wiring

KeenPensioner · Dec 11, 2022

Can someone explain how these are wired - a diagram would be great. I have stripped a few bulbs just to see how they are wired. One continuous wire goes all the way back to the source and that leaves some bulbs with 2 wires connecting them and others with one wire connecting them. I have tried to follow the current path and can't see how it works. Any help would be appreciated

Avo Mk8 · Dec 12, 2022

Take your pic!
Is it possible that your first pair of diodes are in parallel but opposite ways round, a bit like B1 below, but then with another identical pair in series?
It's unusual to put individual diodes in parallel (the same way round), more usual to have strings of say five or more, and put those is parallel. This allows for differences in diode forward drops to average out.
Maybe the examples below will help you get your head round what you have.
I can't offer any further explanation of your incomplete circuit as drawn.

[ElectriciansForums.net] Christmas LED lights wiring

Lucien Nunes · Dec 12, 2022

Are these powered direct from the mains, possibly with a capacitor ballast in a little box, rather than from an ELV power supply? If so, each pair of adjacent LEDs are in anti-parallel, with all pairs in series. The string is then fed with AC - one half cycle flows through LEDs 1, 3, 5... and the other through 2, 4, 6...

It might be possible to prove this by waving a pair of LEDs fast through your peripheral vision where you eyes respond fastest, to space the individual light pulses out in space. You might see the pulses of light emitted by alternate LEDs are staggered rather than simultaneous.

KeenPensioner · Dec 12, 2022

Thanks for your replies. I'm sorry for my poor circuit diagram. The lights re powered by a 36V transformer.

Lucien Nunes · Dec 12, 2022

Presumably that's a wirewound transformer with AC output rather than an electronic one supplying DC? If so, the principle could be the same. Try the wave test.

KeenPensioner · Dec 12, 2022

Thanks again, the output is 36V DC

Avo Mk8 · Dec 12, 2022

KeenPensioner said:
Thanks again, the output is 36V DC

Do they work, and all light up?
How many led's?
Sorry for more questions! Does the adapter state it's output current, and presumably no flashing effects etc!!

Lucien Nunes · Dec 12, 2022

In which case, presumably the individual lamps have some internal ballasting resistance so that they can be connected in parallel pairs and share the current equally. The total amount of resistance is sufficient to absorb the total variation in forward voltage (e.g. due to temperature) and make the series / parallel string voltage-driven overall. The number of series / parallel groups will have been decided based on the forward voltage of each LED+resistor, vs. conveniently available transformer secondary voltages such as 36V.

KeenPensioner · Dec 12, 2022

Avo Mk8 said:
Do they work, and all light up?
How many led's?
Sorry for more questions! Does the adapter state it's output current, and presumably no flashing effects etc!!

Thanks for taking the time to reply. It's quite a complicated set up (for me). It's one of those outdoor Christmas tree effect decorations (see pic) with a central pole and 11 strands coming from the top - each strand has 23 LEDs. I'm not at the location of the lights at the moment so can't say what the output current is. I got half of them working - every second LED. It does have several "effects" but none of them work.

DPG · Dec 12, 2022

Nice lights, I like those.

Christmas LED lights wiring

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