Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Christmas Light string repair

jack0987

Member
If you have a string of 50 or 100 led lights and one goes out the whole string goes out. It is very hard for me to find the one to replace.
If 2 led light have gone out it is even harder.

Near as I can figure, the led lights are in series. How that is done with DC leds in an AC circuit I have no idea.
An explanation of how this circuit works in the first place would be helpful in understanding how to make a better mouse trap so to speak.

Anyway, could a simple detection device be built using the continuity of my ohm meter to run along the wire until I find the point where the voltage is no longer present then that would be the led that needs to be replaced.
 

Pommie

Well-Known Member
Most Helpful Member
Didn't think that was how LED lights worked but, if so, if you can measure the voltage across each LED then the highest reading is the blown one.

Mike.
 

audioguru

Well-Known Member
Most Helpful Member
One rectifier diode in series with all the LEDs will cause all to flash at the supply frequency. Or half the LEDs can be all facing one direction and the other half facing in the other direction.
 

jack0987

Member
Didn't think that was how LED lights worked but, if so, if you can measure the voltage across each LED then the highest reading is the blown one.

Mike.

That is kind of the thing, Mike. Most likely it is not the led that is blown but a loss of connection through corrosion and plus the leads break easily and it is a pain to get at them one by one. Also, the light strings are poorly made at best. I just spent over an hour fixing one string only to have it go out again when I set it down.

Making my own light strings with the leds in parallel would be best I think but then using a 5 volt power supply I thing I would have to add a resistor for each led.
What may be the best way to do that I do not know.

Any Ideas?
 

jack0987

Member
One rectifier diode in series with all the LEDs will cause all to flash at the supply frequency. Or half the LEDs can be all facing one direction and the other half facing in the other direction.

Are there any circuit diagrams of these?

All my leds seem to have the same polarity on my strings as I can interchange them since they are keyed.

I do not know of any diode in the circuit and do not see one. I'll take a second look.
 

jack0987

Member
You want them in series - parallel is far too wasteful - just make them decently.

As crazy as it may seem, I'll take wasteful over trying to fix them and trying to fix them in the field is next to impossible.

I put them up outdoors in mid November and by New Years a quarter of them have dropped. By the end of the season (late March), about two thirds are gone.
 

jack0987

Member
You want them in series - parallel is far too wasteful - just make them decently.

Wait a minute. I just had an idea that may work.

On the strings, if one goes out, the rest are supposed to stay lit.
Maybe I could just remove the leds and the wiring from their sockets and then solder them since corrosion and poor connections seem to be the main problems.
However, I may have to get new strings since the ones I have do not boast the "one out rest lit" slogan on the box labeling.

Is there a way to tell?
What do you folks think?
 

jack0987

Member
They look like this.
The reason I use them is to be able to create my own color combination.

lights.jpg
 

jack0987

Member
Indoor only I hope?.

The box says "indoor/outdoor".

With all the trouble I have had, I still think a parallel setup would be the safest choice.
We are not talking hundreds of stings here. I only use six or seven of fifty lights each.

If I could do them in parallel without resistors and at line AC voltage that would be a big plus.
 

audioguru

Well-Known Member
Most Helpful Member
One red LED uses 1.7VDC to 2.2VDC. Hundreds of red LEDs in parallel also use 1.7VDC to 2.2VDC. 120VAC to 230VAC line AC voltage would cause a huge explosion.
Usually a few LEDs in parallel will have the one with the lowest forward voltage very bright and the others dim or off. To be in parallel the LEDs must all be tested and grouped with exactly the same forward voltage. Since different LED colors have different forward voltages then you cannot have different colored LEDs in parallel.
 

EE World Online Articles

Loading
Top