0
\$\begingroup\$

My prelit tree has strings of LED lights and each bulb has three wires going to it. Looking on the web there are a number of sites that describe how to repair strings wired in series that have two wires per bulb. However I cannot find any reference to strings with three wires per bulb.

\$\endgroup\$

closed as off-topic by laptop2d, ThreePhaseEel, duskwuff, uint128_t, Dmitry Grigoryev Dec 19 '16 at 12:20

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the repair of consumer electronics, appliances, or other devices must involve specific troubleshooting steps and demonstrate a good understanding of the underlying design of the device being repaired. See also: Is asking on how to fix a faulty circuit on topic?" – laptop2d, ThreePhaseEel, duskwuff, uint128_t, Dmitry Grigoryev
If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ Dimmable lights? We need images or a bit more info to answer this... \$\endgroup\$ – 12Lappie Dec 16 '16 at 16:07
  • \$\begingroup\$ There should be a site for how do I search with intelligent keywords google.ca/… \$\endgroup\$ – Sunnyskyguy EE75 Dec 18 '16 at 3:04
3
\$\begingroup\$

I took a string apart and traced the circuit. It's interesting- pairs of LED's are in parallel and these pairs are wired in series. The string uses a full-wave rectifier (improves flicker) and splits the diodes between the plug end and receptacle end (so both plug and receptacle are not too large). So for an extra wire per bulb this design gains redundancy- one bulb of any or multiple pairs can be missing or open and the string still lights. However if both bulbs of a pair are missing or open the string is dark.

Of course a parallel string is better for reliability but I think that would require four wires per bulb and a brick power supply of some type.

So as far as repairing it seems best to replace burned out bulbs immediately. This is because if the other bulb paired with a burned out bulb goes then the entire string goes. Then tracing which bulb is bad requires special effort. Of course I've read that sometimes LED bulbs fail shorted instead of open. So this helps.

Here is a schematic:

enter image description here

\$\endgroup\$
1
\$\begingroup\$

Typically one of the wires would be parts of the series string and the other two would be connected to each side of the power. That allows sets of series strings to be daisy-chained. Below diagram from here:

enter image description here

\$\endgroup\$

Not the answer you're looking for? Browse other questions tagged or ask your own question.