26 LED Parallel Circuit

[mferna14]

Dear Electronics Friends.,
I have 26 LEDs (Rating 3v 20mA) in my garden attached all in Parallel Circuit. I am using a 12v 5amp DC power adapter. I calculated the value of Resistor which was nearly 13ohms 1 watt resistor. All LEDs light up very well.
My question is after 4 ~ 5 days the first 2~3 LEDs (starting in the circuit) nearest to the power adapter get burnt or just do not light up & the rest 22 LEDs makes no difference, they glow very well. Why is this so? This is the 3rd time I have replaced the 1st 3 LEDs in the start of the circuit. Am I doing something wrong, or the 1st 3 LED require a resistor each? Can anyone help me in this circuit design? Thanks in advance.

[eccerr0r]

Re: 26 LED Parallel Circuit

LEDs are current controlled devices. Wiring them in parallel will not get them the same current and by luck of the draw, the ones that draw more current will draw more, overheat, and burn out.

LEDs need to be connected in series with other LEDs or resistors and control their current for longevity.

You could just keep replacing them and find 26 LEDs that match but it may take a while and a lot of replacements...

[stj]

Re: 26 LED Parallel Circuit

or put a seperate resistor on each led

[eccerr0r]

Re: 26 LED Parallel Circuit

Since you have a 12V PSU, the cheap solution is to try to wire a few in series in groups of three with a resistor per group. 26 isn't a multiple of 3 so you'll need to recalculate a resistor for the stragglers.
The optimal solution is connect all in series and have a 20mA CC power supply (which will get to 90+ volts, but who's looking?)

[momaka]

Re: 26 LED Parallel Circuit

Since you have a 12V PSU, the cheap solution is to try to wire a few in series in groups of three with a resistor per group. 26 isn't a multiple of 3 so you'll need to recalculate a resistor for the stragglers.
The optimal solution is connect all in series and have a 20mA CC power supply (which will get to 90+ volts, but who's looking?)

+1

Both of these are good solutions, or wire each LED with a resistor... in which case, you can even swap out the PSU for a 5V one to waste less power with the resistors (less voltage drop across them.)

I'm also curious what LEDs you're using. Care to post a link where you bought them or datahsheet for the LEDs? If the LEDs are cheap no-name stuff from Amazon, eBay, Ali, or similar, forget that they will do 20 mA in the long term and not burn out. Cheap LEDs don't last at all at high power... and sometimes not at all, regardless of the power being fed. I find SMD LEDs to be the worst offenders when it comes to die separation (and thus the LED starting to flicker randomly.) But even the regular "oldschool" 3 mm, 5 mm, and 10 mm clear epoxy lens LEDs are not safe from this anymore.

So in short, if you have cheap LEDs, don't plan on pushing more than half of their rated current... in this case, 10 mA if they truly were rated for 20 mA. And if they were rated for 20 mA absolute max, I'd say 5-7 mA would be the most you can push through them to have them last a reasonable amount of time (a few years, fingers crossed.)

[mferna14]

Re: 26 LED Parallel Circuit

Thank you so much guys for all your input & tips. I think putting them in series, (5 LEDs per line) will be fine. Surely have to redo all of them. I am so grateful to have so helpful electronics techs all across the world. A BIG THANK YOU ONCE AGAIN.

[redwire]

Re: 26 LED Parallel Circuit

The 13Ω resistor seems wrong.
3V LEDs on 12V power is 9V drop, 26 LEDs at 20mA is 520mA. That's 17.3Ω required. Using 13Ω you'd get 692mA for 6W and 26.6mA per LED.
Seems too much.

[stj]

Re: 26 LED Parallel Circuit

https://ohmslawcalculator.com/led-resistor-calculator