Convert old Christmas lights to LED

Thread Starter

Ivan Iceheart

Joined Dec 17, 2023
4
Hello all,
I’m a complete newbie here but hope to get some constructive advice.
I have a set of aging Christmas lights with fancy shades that I would like to resurrect.
They are a set of 12V incandescent bulbs (x20) wired in series straight to the 240V mains supply, as was very common before LEDs took over.
The question is how easily, with a bit of cutting and soldering, etc. could I convert the set to e.g. 20x 12V LEDs? I’m looking at some 10mm diameter 12V LEDs.
OR
Would I be best using a 12V DC transformer and probably new wiring to put the 20 LEDs in parallel?
Thanks in advance for any advice.
 

BobTPH

Joined Jun 5, 2013
8,957
I would try to find a string of 20 lights that operate from your line voltage and just fit the shades to them. I do find such strings for 120V.
 

Thread Starter

Ivan Iceheart

Joined Dec 17, 2023
4
Yeah, that was my first thought, but after a couple of purchases, nothing is quite doing the trick and I was hoping to end up with something a bit more reliable with extended life.
 

Dodgydave

Joined Jun 22, 2012
11,302
You would need to put a bridge rectifier in the mains supply, because the leds will only work on one half cycle, i presume they have a series resistor.
 

Tonyr1084

Joined Sep 24, 2015
7,899
The reason why 20 twelve volt lamps in series works on 240VAC is because each lamp drops 12 volts across its filament. LED's don't quite work like that. To use 20 LED's in series would require a lot more effort than you think. For instance, each LED has its own forward voltage drop (Vf) Red colored LED's tend to have the lowest Vf while blue and white the highest. And with different manufacturers those numbers change. You can't compare one red LED to another if they are not manufactured at the same time, same place, same machine. Those variances will make a huge difference in the way the LED's perform. And since the primary difference in voltage requirements for incandescent lamps versus LED lamps means, and this is purely a guess, running 20 varied colored LED's in series means you can have a Vf of between 40V and 60V. That depends on how many of what colors you have. This means your 240VAC supply will blow out a bunch of LED's frighteningly quickly.

OK, so you think you can put a resistor in series to limit the current. Yeah, that's a possibility. But not recommended. That resistor is going to get hot. Without knowing specifics I can't guess at how many watts the resistor would need to dissipate. THEN there's the complexity of making sure all the LED's are polarity correct. Once you've overcome all that - there's yet another devil in the details. LED's don't like reverse voltage. They will tolerate a small amount of voltage but at 240VAC, they're going to go the way of the devil in hell himself.

LED's are current driven devices whereas standard lamps are voltage driven. It takes 12 volts to light a 12 volt incandescent lamp whereas an LED can be driven from a greatly varied voltage. As long as you limit the current to what the LED is rated for you can (in theory) power it from thousands of volts. Running a red LED with 2Vf at 12 volts (DC) with a current of 10mA means you're going to need a 1KΩ resistor. That will limit it to 10mA. That same LED can be run from 24VDC at 10mA using a 220Ω resistor. And again, with 48VDC and 10mA, the resistor is 4.6KΩ. While you can do the same thing with incandescent lamps the resistors required will have to be different values and higher wattages. That means you're wasting more current as heat energy.

Sadly it's not so straight forward as simply replacing an incandescent bulb with an LED bulb. The lamps you use in the home for light are designed to operate on their respective voltages with the internal electronics providing the proper current for the LED's inside the lamp. There is no electronics inside an incandescent lamp. It works on its rated voltage and that's it.

I foresee a lot of rewiring of your string of lights in order to get the effect you want. And all that rewiring might be far more unsightly than using some hot melt glue to glue on those fancy shades you want to use.

I miss Christmas of old. When I was a child. The colored lamps, their warm glow, their soft colors. LED lights attempt to achieve the same thing but they're just not the same. They lack the charm I grew up with. For my grandchildren it's a different story. What they're growing up with will be dear to them when they're in their old age. Life moves on. Change is the only thing I've observed to be a constant.
 

Pyrex

Joined Feb 16, 2022
267
Hi,
for safety reasons, use of a step -down isolation transformer is highly recommended. As i know, those incandescent lamp garlands , say 12Vx20, were used in past only, unfortunatelly, it's easy to get an electric shock, if a bulb is cracked and you touch it.

12V LEDs are easy available. As well as 240VAC/12VDC constant voltage drivers, called as a "transformers". Use a conventional transformer and KBU810 is not the best idea. LEDs will work reliably , if powered from a regulated constant voltage source, not from a source with pulsating voltage at the output
 
So called 12V LEDs are supplied with a series resistor which controls the current, possibly to 20mA when connected across 12V. The actual voltage drop across the LED varies according to the colour, from around 1.8V to 3.3V.

You might want to consider buying LEDs without the series resistor and string maybe six or seven in series with a resistor connected to a surplus laptop charger. Experiment with one series resistor to adjust the current/brightness. Three such strings connected in parallel would give you the 20 total you are looking for and you are working with a safe low voltage
 

MisterBill2

Joined Jan 23, 2018
18,484
Even if the TS was able to get 20 of the 12 volt LED lights and provide a DC source, there is an unmentioned additional problem of POLARITY!! LED devices are very much polarity sensitive, and also reverse voltage sensitive. So getting one backward would surely destroy the LED in an instant. The same challenge will exist if the connections are changed to put all 20 in parallel across an isolated safe 12 volts DC.
So the quite significant effort to adapt the housings to the replacement LEDs will be the way to go. It might work out to find someone with a 3D printer to produce adapter pieces to allow the smaller diameter LEDs to mount where the previous bulb assemblies were fitted. Definitely tedious but a safe choice.
 

Tonyr1084

Joined Sep 24, 2015
7,899
THEN there's the complexity of making sure all the LED's are polarity correct. Once you've overcome all that - there's yet another devil in the details. LED's don't like reverse voltage. They will tolerate a small amount of voltage but at 240VAC, they're going to go the way of the devil in hell himself.
Even if the TS was able to get 20 of the 12 volt LED lights and provide a DC source, there is an unmentioned additional problem of POLARITY!! LED devices are very much polarity sensitive, and also reverse voltage sensitive. So getting one backward would surely destroy the LED in an instant.
WHY DO YOU DO THIS? DO YOU NOT READ OTHER PEOPLE'S POSTS? You are very plagerizistic. Stop taking credit for other people's posts. You really seem to do this a whole lot to me. STOP it. Form your own thoughts or quote the person who said it before you, then declare that you either agree with it or disagree with it. Or if you wish to add additional details. But stop trying to look like the genius of the website!

I'm going to catch heck from the moderators for this. But enough is enough!

there is an unmentioned additional problem of POLARITY!! LED devices are very much polarity sensitive, and also reverse voltage sensitive.
UNMENTIONED? Where did you learn to read? Or maybe Bill has me on the iggy button. Whatever!
 

MisterBill2

Joined Jan 23, 2018
18,484
Upon occasion it appears that I may become a bit distracted . Thins and stuff happen around my end of the wires here, I do not live in a vacuum. Others speak and need attention right away.
And occasionally some posts seem
 

Thread Starter

Ivan Iceheart

Joined Dec 17, 2023
4
Thankyou to all who have answered my query.
I now understand that there is no easy/reliable/safe way to convert what I have, that was the crux of the question.
Having reviewed all posts, I am now considering using ‘standard’ (3.3V or 5V) LEDs and new parallel wiring with a suitable regulated DC power supply, as I have many old ones.
I can then cannibalise the original set with the intention of housing the LEDs in the original bulb holders, as that is what the shades attached to.
Thanks for all the advice.
Best for the season.
 

Tonyr1084

Joined Sep 24, 2015
7,899
Thankyou to all who have answered my query.
I now understand that there is no easy/reliable/safe way to convert what I have, that was the crux of the question.
Having reviewed all posts, I am now considering using ‘standard’ (3.3V or 5V) LEDs and new parallel wiring with a suitable regulated DC power supply, as I have many old ones.
I can then cannibalise the original set with the intention of housing the LEDs in the original bulb holders, as that is what the shades attached to.
Thanks for all the advice.
Best for the season.
We're here to help.
Perhaps because your comments tends to be rather (ehh... extremely) verbose?
Well, maybe so. I've been accused of having the engineering mentality which comes with a lot of thorough explanation. And since we're dealing with potentially 240VAC, clarity and thoroughness may be well advised. To simply say "Do this" or to say "Do that" without imparting a thorough understanding of what's being suggested could lead to damage, injury - or worse. I just don't want to be the guy who says "Go ahead" and have someone end up hurt because of it.

As for my posts not being fully read before someone makes comment - I get that. I'm somewhat guilty of that too. But it seems like most often it's one person who says what I said, sometimes virtually with the same words. From my viewpoint it sucks to be overrun by someone who boasts their superior knowledge. Me? I'm happy to admit to my limitations. When I don't know - I say so.

To avoid being ignored any further I'll end my comment here. And this thread is no longer being watched. So say what you will. G'Day mate.
 

MisterBill2

Joined Jan 23, 2018
18,484
T1084: sometimes your comment is so important that it bears repeating. Probably also attributing to you, Sorry if I omitted that part. One option that could be added to these forums is, in addition to "Like", the option of "CONCUR COMPLETELY", or something similar.
 

MaxHeadRoom

Joined Jul 18, 2013
28,685
I have a set of aging Christmas lights with fancy shades that I would like to resurrect.
They are a set of 12V incandescent bulbs (x20) wired in series straight to the 240V mains supply, as was very common before LEDs took over.
The question is how easily, with a bit of cutting and soldering, etc. could I convert the set to e.g. 20x 12V LEDs? I’m looking at some 10mm diameter 12V LEDs.
Probably just as easy to use the $8 - $10 strips of LED lights that are multi coloured and include a remote control for displaying in many different shades, fading up & down , several other effects.
I got one set free with a keyboard from my local store.
 

Tonyr1084

Joined Sep 24, 2015
7,899
T1084: sometimes your comment is so important that it bears repeating. Probably also attributing to you, Sorry if I omitted that part. One option that could be added to these forums is, in addition to "Like", the option of "CONCUR COMPLETELY", or something similar.
I know I said I wasn't going to follow this thread any further, but since I was quoted I figured I'd take a look. You said "sometimes your comment is so important that it bears repeating." I've quoted you in the past and said "I agree with this statement". But in your repeat of my comment you showed that you didn't read it, let alone it being worthy of repeating. You said "there is an unmentioned additional problem of POLARITY!!" UNMENTIONED. Perhaps you meant to say "Unnoticed" because you went right past my comment with your own. Maybe you had the same thought. Not the first time people here reached a similar conclusion at the same time. But you said it was unmentioned when it was. The truth is that either you didn't read it or you DID read it then forgot where you saw, heard or read it and just repeated it as it was your own thought.

Look! This is public. I don't want to disrespect anyone. I'll grant that somehow you got the same idea I had regarding polarity and reverse polarity and voltage destroying LED's. But I felt like I was rolled over. Ignored. That's why I wondered if maybe you had me on your IGGY list.

I still see you as an equal. Nobody is better than anyone else. And nobody should feel superior either. I sure don't. There's LOTS and LOTS I don't know. I don't even know how much I don't know. But at least I admit errors and show respect to others who may have said something that I inadvertently repeated because a thread has gotten many pages long, and my retention isn't what it used to be.
 
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