How to make string LEDs?

[ahsrabrifat]

I see long string LEDs at wedding venues. I also see the small ones at homes for decorative purposes. I would like to make one by myself. But I don't know how to proceed. My main concern is, do I have to connect the LEDs in series or parallel? Another question is, normally, an LED runs at approximately 3V DC. But these LED strings that I am talking about run at 220V AC. What makes these strings capable of running at AC? Can anybody explain? Any suggestions are welcome.

 

[Diver300]

LED strings are almost always in series to get the total voltage of the LEDs near the supply voltage.

For instance, 12 V strings will have three LEDs in series, and a resistor to control the current.

LED lamps that run at 220 Vac contain rectifiers and many, many LEDs in series to get a large voltage. There are various different methods used to control the current. It is rare to have 220 Vac directly connected to LED strings. There is often a control box somewhere.

 

[ahsrabrifat]

LED strings are almost always in series to get the total voltage of the LEDs near the supply voltage.

For instance, 12 V strings will have three LEDs in series, and a resistor to control the current.

LED lamps that run at 220 Vac contain rectifiers and many, many LEDs in series to get a large voltage. There are various different methods used to control the current. It is rare to have 220 Vac directly connected to LED strings. There is often a control box somewhere.

Does the control box consist of only one rectifier circuit that runs 100 LEDs?

 

[Nigel Goodwin]

Does the control box consist of only one rectifier circuit that runs 100 LEDs?

It depends entirely on the specific design, many such strings use NeoPixels so are multicoloured, fade-able, and can run patterns. Even plain single coloured LED strings could well have a switch-mode driver.

 

[shokjok]

A closer look inside the LED strings reveals flat or low-profile LEDs connected as Diver300 described. I don't know who supplies flat LEDs, and this project will be time consuming. I made name-in-lights displays in 1988 using regular domed LEDs, CMOS ICs, and a 9VDC wallpack - unknown how many still exist.

 

[Nigel Goodwin]

A closer look inside the LED strings reveals flat or low-profile LEDs connected as Diver300 described. I don't know who supplies flat LEDs, and this project will be time consuming. I made name-in-lights displays in 1988 using regular domed LEDs, CMOS ICs, and a 9VDC wallpack - unknown how many still exist.

Everyone?, they are simply surface mount LED's - probably far more common now than through hole ones.

However, if you want an LED string, then just buy one - it's cheaper than buying the individual LED's.

 

[ahsrabrifat]

It depends entirely on the specific design, many such strings use NeoPixels so are multicoloured, fade-able, and can run patterns. Even plain single coloured LED strings could well have a switch-mode driver.

Sir, I am not thinking about using Neopixels. I will use 5mm generic LEDS. (Red or yellow).

 

[ahsrabrifat]

A closer look inside the LED strings reveals flat or low-profile LEDs connected as Diver300 described. I don't know who supplies flat LEDs, and this project will be time consuming. I made name-in-lights displays in 1988 using regular domed LEDs, CMOS ICs, and a 9VDC wallpack - unknown how many still exist.

Is there any picture of schematic of your project?

 

[ahsrabrifat]

Do I need to use diodes?

 

[Galgso]

What makes these strings capable of running at AC?

They either run on rectified AC or directly off mains with a current-limiting capacitor (like in a capacitive dropper supply). If they run on unrectified AC they will only conduct on one half of the cycle and there will be noticeable flicker. The LEDs are placed in long strings so that their forward voltages add up so they can run more efficiently off of mains. If they were not wired this way the control circuitry would have to drop the extra two to three hundred volts that are not dropped by the LED.

If you want to run the LEDs straight off mains, you may find this link useful: https://www.talkingelectronics.com/projects/30 LED Projects/30 LED Projects.pdf (see page 28)

Except as an exercise in circuit design, running the lights directly off mains is however highly unrecommended because you would not have any galvanic isolation between mains and your lights and there is no reason to take such risks in the 21st century. A better idea would be to use a switching supply (e.g. 12v DC) and then drive multiple strings of series-connected LEDs in parallel.

 

[ahsrabrifat]

Thank you all. I look forward to posting my updates in this thread.

 

[ZipZapOuch]

Thank you all. I look forward to posting my updates in this thread.

Didn't you recently post, in another thread, about how someone in Bangladesh was electrocuted by mains power and ask, "how could this happen?" Well, one way some of the 8000 people that are electrocuted in Bangladesh each year is because people cobble together mains powered projects without proper isolation or enclosures.

Be careful. For yourself and anyone who may come in contact with your project while it is connected to mains power.

 

[ahsrabrifat]

Didn't you recently post, in another thread, about how someone in Bangladesh was electrocuted by mains power and ask, "how could this happen?" Well, one way some of the 8000 people that are electrocuted in Bangladesh each year is because people cobble together mains powered projects without proper isolation or enclosures.

Be careful. For yourself and anyone who may come in contact with your project while it is connected to mains power.

Yes, I posted that thread. For the time being, I am planning to make a battery-operated LED string. Like the ones used in fairy light jars. I will not work with AC now.