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.

 

[betwixt]

In series, add enough LEDs at 3V each to make up a little more than 220V. A few more ensures they do not run at maximum current and all burn out simultaneously! For AC, the LEDS are wired the other way around in short chains, for example 10 LEDS in series one way then in parallel with 10 LEDs wired the other way and the pattern repeated until enough are there to make up just over 220V.

That is how cheap LED strings are wired but if you want to do it properly and more reliably you must understand that LEDs are current operated and (almost) constant voltage devices. You should ideally run them from a constant current source. The problem with the cheap method is there the current is only limited by the applied voltage and spikes in the 220V AC can, and often does, destroy them.

Brian.

 

[ahsrabrifat]

In series, add enough LEDs at 3V each to make up a little more than 220V. A few more ensures they do not run at maximum current and all burn out simultaneously! For AC, the LEDS are wired the other way around in short chains, for example 10 LEDS in series one way then in parallel with 10 LEDs wired the other way and the pattern repeated until enough are there to make up just over 220V.

That is how cheap LED strings are wired but if you want to do it properly and more reliably you must understand that LEDs are current operated and (almost) constant voltage devices. You should ideally run them from a constant current source. The problem with the cheap method is there the current is only limited by the applied voltage and spikes in the 220V AC can, and often does, destroy them.

Brian.

Thank you. What should I use as a constant current source?

 

[Hattles1973]

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 space waves? 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.

These LED strings run on AC because there’s circuitry inside (usually hidden in the plug or sealed unit) that either rectifies the AC to DC or limits the current to a safe level for the LEDs. That’s what ‘makes them capable’ of running on 220V AC.

 

[betwixt]

These LED strings run on AC because there’s circuitry inside (usually hidden in the plug or sealed unit) that either rectifies the AC to DC or limits the current to a safe level for the LEDs. That’s what ‘makes them capable’ of running on 220V AC.

That's what SHOULD be there but in most LED strings the AC is applied directly to the LEDs and they are wired 'anti-parallel' in short chains. Being wired across each other but reversed means half of them conduct on one half cycle and the remainder on the other half cycle. Wiring them in short chains is done to limit the reverse voltage to the forward voltage of the other LEDs. It also helps to disperse the differences between individual LEDs.

Ideally, they should be driven from a constant current source, easy with DC, a little harder with AC because the voltage drops through zero each half cycle so keeping the current up is harder. The better chains use an AC to DC power supply then current control it so the output is constant then they use a H-bridge circuit to reverse the voltage on the wires at high speed to avoid flicker.

Brian.

 

[KlausST]

Hi,

safety first:
Your question regarding serial or parallel connection of LEDs tell me you are not experienced with basic electronics at all.
Now it seems you want to deal with lethal high AC voltage. To do so you not only need founded knowledge in electronics design (physics, math ...)
but additionally nou need to know and fulfill the safety regulations. This is a whole other level.

My recommendations: don´t deal with high AC voltage at all. Use a suitable DC power supply instead.
I´ll come back as soon as I see you know / care about safety regulations.

Klaus

 

[ahsrabrifat]

Hi,

safety first:
Your question regarding serial or parallel connection of LEDs tell me you are not experienced with basic electronics at all.
Now it seems you want to deal with lethal high AC voltage. To do so you not only need founded knowledge in electronics design (physics, math ...)
but additionally nou need to know and fulfill the safety regulations. This is a whole other level.

My recommendations: don´t deal with high AC voltage at all. Use a suitable DC power supply instead.
I´ll come back as soon as I see you know / care about safety regulations.

Klaus

It's true that I have very limited experience in working with AC. Ok sir. I will start with a battery-operated one. Like the ones they use in fairy light jars. Any suggestion?