LED Fairy Lights

[Speedy Builder5Participant @speedybuilder5]

Last years lights don’t work, the wires have gone rusty as they are the outside variety.  The battery reads 4.65 volts (4.5 rated).

2 questions,

what detects nightfall.

What test would show that the string of lights is good or dead.

Bob

 

[Speedy Builder5Participant @speedybuilder5]

Forgot to add that they are Solar charged lights and the panel is working.

[John HaineParticipant @johnhaine32865]

<p style=”text-align: left;”>When it’s night there’s no solar…</p>

[duncan webster 1Participant @duncanwebster1]

It’s too early to be worrying about fairy lights, leave it till Advent at the earliest.

[noel shelleyParticipant @noelshelley55608]

The pins on the LEDs are steel and will corrode off ! The set of lovely blue ones in my garden taught me this. They seem to be wired parallel . The rechargeable battery was a 600ma 1.2V.  As Duncan has said FAR to early, wait till Christmas eve and then for 12 days, down on 12th night. Noel.

[Grizzly bearParticipant @grizzlybear]

Hi Speedy Builder5,

Light or dark detection is done by a LDR (Light Detecting Resistor).

It will be hiding amongst your leds, but it will be a different profile.

https://www.ebay.co.uk/itm/263460668317?mkevt=1&mkcid=1&mkrid=710-53481-19

Good luck……

[Andrew TinsleyParticipant @andrewtinsley63637]

Now that is interesting, I always thought that if there were no output from the solar cells. then that acted as the trigger to switch on the lights.

I had a string of such solar powered LEDs in the garden. One evening I put up a string of mains powered lights for a party. Switching these on, switched off the solar powered LED string. This strongly suggests that it is the output (or lack thereof) from the solar panel which switches the LEDs.

However I could well be wrong.

Andrew.

[noel shelleyParticipant @noelshelley55608]

It’s a LDR Light dependant resistor a small version of the old ORP12. and it is on the circuit board. Noel.

[Andrew TinsleyParticipant @andrewtinsley63637]

Hello Noel,

Certainly no sign of an LDR on my circuit board and the board if fully enclosed, so always in the dark. No sign of anything on the solar panel either. Checked the string of LEDs and they all light up, so no LDR there either. So it looks certain that my version does rely on the solar cell output to turn the lights on and off.

Thinking about it further, it seems hardly cost effective to add an LDR, when the switching function can be done with the solar panel.

Regards.

Andrew.

 

 

[Andrew Tinsley]

On Andrew Tinsley Said:

Hello Noel,

Certainly no sign of an LDR on my … So it looks certain that my version does rely on the solar cell output to turn the lights on and off.

Thinking about it further, it seems hardly cost effective to add an LDR, when the switching function can be done with the solar panel.

Regards.

Andrew.

 

 

My sample size is too low to be conclusive, but all of the lights I’ve looked at are switched by a separate photo-sensor as Noel says.  Almost certainly for cost/convenience reasons – the electronics are very simple.

I’ve bought pound-shop LED lights just to get the LDR.  The whole unit is cheaper than buying a new LDR retail, if you can spare the time ripping them out.

Using the solar panel is certainly possible, and would save the cost of a <50p component.  But the electronics are a bit more complicated – more components, costing more.

Two possibilities:

• Andrew’s unit breaks from tradition and exploits the solar panel.  Entirely possible.
• Andrew hasn’t found the LDR.  They’re sometimes hidden behind a black daylight filter that matches the box.

Only matters if cannibalising or attempting a repair.   Speedy has to check both possibilities, and confirm that whatever circuit is fitted to his lights is working.   Though a separate LDR is most likely in my limited experience I wouldn’t bet the farm on it!

Dave

[mike barrett 1Participant @mikebarrett1]

some use an LED as its sensitive to light and cheaper than a LDR. Connect it the wrong way round so it doesnot light and fed it via a resistor to the positive supply. The voltage across the LED changes depending on the light levels. Very   cheap and simple light sensor.
almost as good as taking the black paint of OC71 transistors to make photo sensitive devices…

mike

[not done it yetParticipant @notdoneityet]

It is also likely you have a dead battery?  It might read input volts but not pass any current.  Try a new one or load test the present one.

 

[noel shelleyParticipant @noelshelley55608]

A photo transistor may easily be mistaken for an LED. As a 9 year old boy I wondered why OC71s had black paint on then, I found out much later in life. Noel.

[Speedy Builder5Participant @speedybuilder5]

If the LDR is “hidden” as one of the lamps, customers would return the lights saying one of the lamps didn’t work.

 

There are only 2 wires leaving the solar panel/controlbox. They go to the first LED and leave that with 3 wires.  So it seems that all the LED lamps are in parallel with a third wire that goes from the first LED to the last LED (Don’t know polarity of this wire).

The first and last LEDS look like all the rest – Note  wiring comment above,

As others have said, all wire is copper plated steel,  No photo resistor on the control box but an 8 pin IC and about a dozen resistors/capacitors and on/off switch.

I will test the 4.5v cell for output on a tungsten bulb.

Bob

[DodParticipant @dod]

‘Tis the fairy light season and what joy it brings (not)

50 years ago I decided after apprenticed sparky loon and then 8 years of being demented repairing the knots of wire and screw in bulbs (no LEDs in them days) my sincere advice is to throw them in the ‘letric recycle bin and spend a meagre few pounds on a new set and to give yourself a chance of them working next year put them out, as earlier advised, on Christmas eve and take them back inside on the day after Boxing Day (shows enough of the merry spirit).

And let me be the first to wish all Forum readers A VERY MERRY CHRISTMAS. and a HAPPY NEW YEAR when it comes.

[vic neweyParticipant @vicnewey60017]

We have had a long string of these LED lights running through our veranda and out along the fence for years, long ago l cut off the dud solar panel and connected a variable voltage dollhouse transformer activated by a light sensor which works perfectly

[Engine BuilderParticipant @enginebuilder]

Not quite the same but related, I will be getting out my 73 year old family Chistmas tree. Can anyone beat that?

David

[Speedy Builder5Participant @speedybuilder5]

David – With real candles ??

Bob

[Engine Builder]

On Engine Builder Said:

Not quite the same but related, I will be getting out my 73 year old family Chistmas tree. Can anyone beat that?

David

<i>On 15 November 2025 at 14:16 Speedy Builder5 Said:
David – With real candles ??</i>

Bob,

I can’t.  But I do remember, early in the ‘50s, when we had a real tree, real candles and artificial snow (cotton wool) as well as possibly a meagre string of fairy lights, along with all the other paraphernalia.  The candles were lit – until one set fire to a piece of artificial snow!  It caused a bit of kerfuffle for a few seconds!

Those fairy lights went with the ex and she is likely still using them.

[Speedy Builder5]

On Speedy Builder5 Said:

David – With real candles ??

Bob

As a child in the 1950’s we had one dad bought in 1945 with real barley twist candles that fitted in tiny holders on the branches although they were never lit, 🤣no plastic so the baubles were glass, lt also had tiny 4″ crackers that mum said had nothing inside but in later years we discovered they had a hat, motto and little enamel brooches inside and a banger.

[Speedy Builder5Participant @speedybuilder5]

Just a tiny update,  the solar controller detects “Night Time” via the solar panel and non presence of light.  The Output to the string of LEDS is alternating DC, such that some light patterns will light up every other lamp (polarity of LEDs reversed every other lamp), allowing a chasing string of lights. Also by flashing fast alternating DC, all lamps appear to be lit at the same time. My problem is that there is a break somewhere along the string of 100 lamps !!  It’s a bin job, but keep the solar panel and battery charging side of the controller perhaps.

Bob

[Dave SParticipant @daves59043]

The Kitronik solar garden lamp uses the solar cell.

circuit explanation here: https://resources.kitronik.co.uk/pdf/2134_solar_garden_night_light_essentials_2_0.pdf

 

 

[BazyleParticipant @bazyle]

100 lamps should be able to diagnose with 7 tests – the old binary split thing. Clip your tester leads to the blades of a scalpel or craft knife that can penetrate the insulation longitudinally and will close up afterwards.

I have a 24v  led string of ‘icicles’ that has really odd collections of series and parallel and little strings of 3 leds going off to the side. That alternate polarity DC mentioned above might be useful info.

[Engine BuilderParticipant @enginebuilder]

I saw a similar tree to mine on Repair shop and was suprised to learn the the “leaves” where actualy made of died feathers.

I don’t remember candles on the tree but large screw in lamps shaped like lanterns. I still have them on the tree

but they are no longer working.

David

[Speedy Builder5Participant @speedybuilder5]

Update:-  The momentary press for on/off switch on the solar panel/control box Was duff. But before finding that, I disconnected the string of lights and could not get them to light up (Even with the lights in a dark cupboard) using the 1.5volt rechargeable battery.

However the lights still don’t work unless the press switch is held pressed and then they flash away merrily, but of course, that’s no good as they will not turn off until the battery is flat.

The more I read up on the NET, the less I can find out how these little buggers work.  If the lights CAN work by shorting out the on/off button, why don’t they work when just connected to the internal 1.5v battery.

Bob

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