LED aren't lighting up in series

Thread Starter

Tridibeshhh

Joined Jun 25, 2022
10
IMG_20220705_134642.jpg
4 little LED lights were connected in series using this power supply. I tested each led with a 9v step down transformer they worked perfectly, but when I'm attaching them in series none of them lighting up. Using the Power supply (image) isn't lighting up the leds either. What might be the issue?
 

Thread Starter

Tridibeshhh

Joined Jun 25, 2022
10
What is the rated input voltage of this power supply?
Extremely sorry can't see anything written on the board, but im connecting it to my wall socket 230v ac.
But why the LEDs aren't working in series (using transformer not the power supply). I double checked the anode cathode and they are all connected properly.
 

Alec_t

Joined Sep 17, 2013
13,226
What resistance do you have in series with your LED string?
What colour LEDs? White LEDs would need about 12V to drive a 4-LED string.
Is your "transformer" the old-school heavy iron type with an AC output, or is it a light-weight switch-mode type with a DC output?
The power supply shown is a capacitive voltage-dropper type and is dangerous when powered directly from the house mains, as it provides no isolation from the mains.
 

Ian0

Joined Aug 7, 2020
6,677
Extremely sorry can't see anything written on the board, but im connecting it to my wall socket 230v ac.
But why the LEDs aren't working in series (using transformer not the power supply). I double checked the anode cathode and they are all connected properly.
If you operate it with no load, then the voltage on the electrolytic capacitor will rise to the mains voltage. If you subsequently connect the LEDs across the electrolytic (although that’s where they should connect) then they will probably fail due to the current surge. Make sure that everything is discharged, connect the LEDs and only then connect to the mains.
(I would recommend an isolating transformer whilst you are experimenting with it)
What output voltage do you measure across the electrolytic cap?
What is the value of the (large orange) film capacitor?
 

LesJones

Joined Jan 8, 2017
3,897
The power supply in your picture is a transformer less design. This will not provide any isolation from the mains supply SO BE VERY CAREFUL as the output will be at mains potential. Are you sure that you have connected the LEDs with the correct polarity ?
Is there a zener diode across the output of the power supply to limit it's output voltage ? If so it may be limiting the voltage to less than that required by the string of LEDs.

Les.
 
View attachment 270774
4 little LED lights were connected in series using this power supply. I tested each led with a 9v step down transformer they worked perfectly, but when I'm attaching them in series none of them lighting up. Using the Power supply (image) isn't lighting up the leds either. What might be the issue?
They use a cap as a resistor to down size the current. You must work like in dc with the R of the cap is 1/120*3.14*c if you use 3 led in serial you have to change the value of the cap to have the same curent with a larger voltage.
Your leds aren't burned, it's easy to burn with a 9V batt.
You could search supply without transformer in google, my english is too bad
 

Pyrex

Joined Feb 16, 2022
24
They use a cap as a resistor to down size the current. ...... if you use 3 led in serial you have to change the value of the cap to have the same curent with a larger voltage.
Same capacitor will work fine with one LED and four LEDs in series. Voltage drop on the LED is far less than mains voltage, so the "orange capacitor" works as a current source. You may calculate the needed capacity for 2 volt output and for 2x4=8 volt output, it will be almost the same value
 

Ian0

Joined Aug 7, 2020
6,677
Because the voltage and current on the capacitor are in quadrature, the LED voltage makes very little difference to the current. No real need to change the capacitor value up to about 50V of LEDs
 

Thread Starter

Tridibeshhh

Joined Jun 25, 2022
10
What resistance do you have in series with your LED string?
What colour LEDs? White LEDs would need about 12V to drive a 4-LED string.
Is your "transformer" the old-school heavy iron type with an AC output, or is it a light-weight switch-mode type with a DC output?
The power supply shown is a capacitive voltage-dropper type and is dangerous when powered directly from the house mains, as it provides no isolation from the mains.
IMG_20220705_152427.jpg

These are the rgb ones, im just connecting them into series and powering them with a 9v DC (uses diode bridge rectifier) step down. And they are not lighting up. But testing each of them individually and they're working fine.

I am about the ditch that power supply and turn it into a battery operated one. But i Dont know why they aren't lit togather in a series connection. Double checked polarity.
 

Thread Starter

Tridibeshhh

Joined Jun 25, 2022
10
The power supply in your picture is a transformer less design. This will not provide any isolation from the mains supply SO BE VERY CAREFUL as the output will be at mains potential. Are you sure that you have connected the LEDs with the correct polarity ?
Is there a zener diode across the output of the power supply to limit it's output voltage ? If so it may be limiting the voltage to less than that required by the string of LEDs.

Les.
No such diodes, and these are the led im using..... multicolourIMG_20220705_152427.jpg
 

Ian0

Joined Aug 7, 2020
6,677
They can’t be RGB because they don't have enough pins.
They could be red-green, so the polarity can’t be wrong because one polarity gives red and the other polarity gives green.
How much voltage are you measuring across them when you think that the should be illuminated.?
 

Thread Starter

Tridibeshhh

Joined Jun 25, 2022
10
They can’t be RGB because they don't have enough pins.
They could be red-green, so the polarity can’t be wrong because one polarity gives red and the other polarity gives green.
How much voltage are you measuring across them when you think that the should be illuminated.?
Yes there a constant multicolour light while connecting each of them to a 9v dc
 

Ian0

Joined Aug 7, 2020
6,677
If they are what @Danko suggests, then they probably need a stable supply. Try putting a 9.1V zener and a decoupling capacitor across each LED
 
Top