Cutting and re-wiring X-mas LED garlands (not strips)

Hi,
Has anyone had to deal with cutting LED Christmas garlands into shorter pieces and then rewiring-powering them?
What should I keep in mind when doing so?

As far as my electrical knowledge goes I should first inspect the voltage which is provided by a standard converter already on a garland and then measure the voltage with the load (garland) on in several spots to determine a single LED voltage drop. Then cut the garland to desired lengths and power it with appropriate converters. Is this right?

What I don't understand completely however is the voltage drop. Given that this is a series circuit and the voltage(resistance) sums up - should I add all the single LED drops to find out the total drop and therefore subtract that from my supply voltage to find out the LED working voltage?

Oh, and maybe I am simply wrong about the circuit being in series?

Thanks!
Raitis

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Wired_Mist2 years ago

If they are 12v-DC lights, looking at the converter you mentioned, they are most likely wired 3-4 Led's in series, and those groups of 3-4 Led's wired in parallel. If this is the case, your question got a bit easier to answer. It is really unlikely that a DC system like that will be wired Totally in Series. At 3.2v drop per Led, You would need a 40v supply just to drive a dozen lights.

Similar to 12v led light STRIPS, You should be able to cut them apart at certain spots. NEED A PICTURE before you get a solid answer

120v-AC led light strings (least the 2 I have hacked apart) are wired in series; Personally I wouldn't mess with them. I imagine you could compensate with a resistor or maybe a Triac. You would have to offset the missing voltage drop or you will fry you LED's with Great Efficiently !

Regarding your question about Voltage drop; YES. Add the voltage drop from Any Device wired in series and subtract it from your supply, Compinsate with a Resistor or even a Voltage regulator.

Pardon my Verbal Diarrhea; Hope it hellped !

Raitis (author)  Wired_Mist2 years ago

Thanks for the answer! I've ordered a longer string and will see how it's wired. The short one I have and don't need to cut has 20 LEDs and the power converter is 230Vac in 230Vdc out, and every light has 1 wire in 1 wire out, so the only logical way is they are in series. I don't want to cut the wires, but should probably do so and test what's going on with a multimeter.

If by any chance the 80 LED one I've ordered is powered by the same 230Vdc just wired in a way you mentioned, i.e. 4 segments of 20 LEDs in series then it should be pretty simple and a diode bridge should do?

Regarding the voltage drop - do I need no remaining voltage in a circuit? Let's say I wire 3 leds of 3V drop in series fed by 12V. Does this mean, that I should compensate for the remaining 3 volts by either a resistor or another LED? And if the other way around, say 12V supply with 4 LEDs of 3.2V drop means that they will be a little dim compared to max power?

So, I'll take a WILD Guess, and say your in Europe :P

Double check The Transformer; are you sure it converts to DC and not AC? (Can you send a Pic?)

I know that 120v-DC supplies are rare were I come from. But if that is the case the YES, it must be wired in Parallel. 240v(Max) / 80 LED's = 3v each; right about were it should be.

"4 segments of 20 LED ("groups") " Would have to be powered by 12v(ish). AC or DC wont matter if you send it through a Diode Recip; AC is just a bit dimmer.

Yes, @ (4x 3.2v) they will be a bit dim due to the lack of voltage. and Yes you need to minimize, if not Eliminate the voltage differential..A fraction of a volt Might be over-looked; Really depends of the device. For a 12v device were it will most likely be regulated down to a operating voltage, it's less important. For basic electrical components I like to set my tolerance for 0.25v.

Now to answer the Actual question,...

For DC light check back to my Last Post.

If you insist on using a string, that is wired in series, You may be able to buy a new transformer. A lower rail voltage may be easier to deal with. Just add the Voltage drops together. Remember that a straight up transformer will be unregulated, I Can't help you with a AC regulator (I do mostly DC Lighting)

Raitis (author)  Wired_Mist2 years ago

Europe it is.

The transformer converts it to DC. I took it apart to have a look what's going on in the short garland I have (20 LEDs) and it seems like it's all good. There are 4 resistors in series (total 33kOhm). Since it's written that the LEDs are 60mW each there's a way to do some calculations. I assumed that they are 3V LEDs (white) so it's a total of 400mA and 60V drop for the garland which leaves us with 160V to 180V to drop with the resistors. After calculation that leaves us with a fact, that a resistor capable of 770 to 975mW power is needed. Those in there look pretty big and there are 4 of them so I doubt they even get hot. I suppose using a single 2W 33kOhm resistor would suffice.

I'll just wait for the longer garland I've ordered to arrive, inspect the wiring and then try to hack it into shorter ones. Should be good with the wiring info you provided. Thanks!

Garland_converter.jpg

Well I'll be dammed, lol. No doubt it's DC/Series.

It does seem really strange that the resistors are wired in series. Like you said a 2W 33Ohm resistor could Work. My though is why didn't they? (Using 4X the components to do the job of 1 costs more to produce; not great for business right?) Even if the resistors don't fit horizontally, a single resistor and a jumper would be cheaper.

One last thought, Look around for a transformer, It could bring the line voltage down to something that you could run through a voltage regulator ( less then say 32v Difference, Preferibly Less then 12-ish. The Regulator will allso remove that flickering effect you may see.

Even If you Stick with the stock supply, You'll have a decent chunk of Lights left over. Can't let them go to waste right? :P

Right on buddy; Have fun !

Raitis (author)  Wired_Mist2 years ago

Thing is, I'm not going to use this particular supply anywhere else than this garland it's already on. I simply need relatively cheap garlands of preferably 20 LEDs to use in Festive bottles which I'm selling rather actively around this time of a year. The place I've bought them earlier (and the importer) doesn't have them any more, but still has other garlands at same cost per LED from the same manufacturer, just that they're longer. Other places and even eBay are around 3 to 4 or even more times expensive for the same length of garland, so I've decided to hack away and re-wire them myself.

Yhea I saw that, Kinda cool Idea with the Darker bottles !

Check www.DX.com. Nice and cheep, IF you can wait for the shipping1.5-2.5 months.

I suggest the transformer for the remaining lights; you could get two or more bottles out of a string !

While you wait for the garland to arrive, Why not experiment with some Straight-up Led's? You could Wire say, 3 Led's in series and power them with a cheep 12v wall-wart (from a second hand store) + a 150-Ohm resistor. Then Add more groups in parelell.

Raitis (author)  Wired_Mist2 years ago

The maximum I could wait is like 2 weeks and then only if I 100% knew, that something's going to work, that's why China is not an option. I will probably go for aliexpress next year ahead of time, simply didn't expect the local shop not to stock the ones I used anymore - oh, the naiveté!

No point in experimenting with 12v supplies right now and probably at all. I expect the solution to cost me 2$ or less per strip and it's not exactly clear how the longer strip will be wired, so I'll just work on other things while the stuff arrives and see what happens. And at this time of the year there's no time for waiting, it's making gifts/orders/something else all the time.

EDIT: If you insist on using a **AC** string, that is wired in series,