Power supply output voltage

Thread Starter

Sundoo

Joined Jul 21, 2021
15
Hello. Complete electronics newbie here.
i bought a Led driver off Aliexpress.
input: AC100-240V
Output: DC30-57v / 600mA (constant)

i connected it to a led strip, they flashed several times then switched off (i suspect they died).
i then took the multimeter and measured the Output voltage, and it was around 74V.

i suspect this is what killed the leds.
My question is: am I missing something ? This power supply is supposed to output max 57V. Why does it show 74?
is the power supply faulty? Or did I measure it wrong?
 

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bertus

Joined Apr 5, 2008
21,534
Hello,

Is the ledstrip for 600 mA constant current?
Constant current drivers can have a higher clamp voltage as the working voltage.
Most ledstrips are only fixed voltage.
The driver is likely for a COB led.

Bertus
 

Dodgydave

Joined Jun 22, 2012
10,050
It's a Constant Current output , so measure the current instead , the voltage will vary depending on how many leds are connected.

Your leds need to be able to withstand 600mA otherwise they will blow..
 

dl324

Joined Mar 30, 2015
13,111
Welcome to AAC!
i suspect this is what killed the leds.
My question is: am I missing something ? This power supply is supposed to output max 57V. Why does it show 74?
is the power supply faulty? Or did I measure it wrong?
As its name implies, a constant current supply is designed to provide a constant current. If the LEDs you connected are rated for 600mA continuous current, the output voltage will be whatever the LEDs require to conduct 600mA; providing that voltage isn't higher than what the source is rated for.

You measured a higher maximum output voltage because your voltmeter wasn't drawing 600mA.
 

Thread Starter

Sundoo

Joined Jul 21, 2021
15
ok, Let me try to explain what happened.
I had this ceiling lamp, composed of 2 LED strips ocnnected in paralel to a led driver (A):

Model: EIP030C0600LX
PRI: 100-240VAC
SEC: Constant Current: DC 600mA, 34-50V

Suddenly the led strips started flashing (please see the video attached)
So I assumed that the LED driver is faulty, and ordered another one. (B)

input: AC100-240V
Output: DC30-57v / 600mA (constant)

I made sure that the output current is respected (600mA). However, I couldn't find the exact voltage specs, so took the approximate ones.
When I connected the new power supply to one LED strip, the LEDs flashed (maybe 10 times) then switched off.

Then I connected it back to the old power-supply (A), and the leds didn't flash either.
However when I connected the second strip to the the old supply (A), they started flashing.
I didn't connect the second strip to the new supply (B), cause I'm afraid they will die like the first ones.

When I measured the output voltage on the new power supply (B) - it showed 74 V
When I measured the output voltage on the old power supply (A) - it showed the right voltage (around 46V if I'm not mistaken)

I've attached the photo of the old supply,
And here is the flashing video: https://drive.google.com/file/d/17ZYYLUM0Gk9tdt32N7OiH-nyw9m-Sbwk/view?usp=sharing
Hopefully someone can clarify this
IMG-4899.jpg
Thanks
Alex
 

LesJones

Joined Jan 8, 2017
3,494
What was the voltage and current rating of the LED strip ? Even if it's current rating was greater than 600 mA if it's voltage rating was less than 30 volts the you would be forcing the power supply to work outside it's design specification so it is probable that it would give greater than 600 mA when it's output was clamped to less than 30 volts. to test the power supply you would need a load resistor of between 50 ohms and 95 ohms. (The resistor would need to have a power rating of at least 35 watts.)
Edit . I have just read your post #5 I have seen LEDs fail in a mode that they cause the whole string to flash. They become open circuit when they reach a certain temperature which cause the whole chain to switch off. When the faulty LED cools down down it goes back to conducting. so is comes back on. This process repeats causing the flashing. To identify the faulty LED you need to measure the voltage across each led and note the voltage when the LEDs go out. The voltage across the faulty one will rise to a higher value than normal.

Les.
 
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Thread Starter

Sundoo

Joined Jul 21, 2021
15
What was the voltage and current rating of the LED strip ? Even if it's current rating was greater than 600 mA if it's voltage rating was less than 30 volts the you would be forcing the power supply to work outside it's design specification so it is probable that it would give greater than 600 mA when it's output was clamped to less than 30 volts. to test the power supply you would need a load resistor of between 50 ohms and 95 ohms. (The resistor would need to have a power rating of at least 35 watts.)

Les.
There are 2 LED strips of 30 LEDs each. This is what is marked on the strip:

unnamed.jpg

I assume the current rating was 600mA, as the old power supply was the original one. That lamp worked several years, before it died

Unfortunately I don't have any resistors I could use to test the power supply.
 

Thread Starter

Sundoo

Joined Jul 21, 2021
15
perhaps someone can explain why it started flashing ? I've read somewhere that this may happen if the power supply is not powerful enough.
However, why this happened after several years ?
 

Martin_R

Joined Aug 28, 2019
101
If there were 2 LED strips wired in parallel then the assumption is both strips are rated at 300mA. If one of the strips failed then the remaining strip would have to take the full current, causing it to overheat. Would that cause it to flash?
 
maybe. generally a power supply tries to only supply the load given. The 3 mega-watt plant supplies your house and th ehouse use what it needs.

If constant current was 600 mA and the load dropped to 300 mA, then the volage would go up trying to supply 600 mA that it couldn;t. The voltage then maxed out and the strip didn't like it. This is where OVP or Over Volatge Protection would help.
 

Thread Starter

Sundoo

Joined Jul 21, 2021
15
Thanks guys. This actually makes sense now.
each 30-led strip is composed of two 15-led circuits in parallel. So i guess each 15-led strip is rated for 150mA.
Now, I remember that when the lamp started flashing, first, one of those 15-led segments died (switched off for some reason). This is when the flashing began. So I assume the fix for this is simply to replace the faulty leds and it should work all again.

just need to figure out where to get this kind of strip (aluminium bar with this particular density)
 

Dodgydave

Joined Jun 22, 2012
10,050
Thanks guys. This actually makes sense now.
each 30-led strip is composed of two 15-led circuits in parallel. So i guess each 15-led strip is rated for 150mA.
Now, I remember that when the lamp started flashing, first, one of those 15-led segments died (switched off for some reason). This is when the flashing began. So I assume the fix for this is simply to replace the faulty leds and it should work all again.

just need to figure out where to get this kind of strip (aluminium bar with this particular density)
If your leds are rated at 150mA then they will blow up as the driver will try to maintain 600mA, so you will need 4 sets at least or different leds , or a different driver that will suit your leds.
 

LesJones

Joined Jan 8, 2017
3,494
Looking at the datasheet for 5730 LEDs gives the maximum current rating as 150 mA. Most of the data is given with a current of 120 mA. It is not good practice to run components at their maximum ratings so that when you repair the lamp I suggest running them at 120 mA.

Les.
 

Thread Starter

Sundoo

Joined Jul 21, 2021
15
Ok, so based on these statements, If I connect the 4x15Led strips to the power supply in parallel, it should provide 150mA to each strip.
If I want to further limit this current to, say 120mA, can I connect a resistor in parallel to the whole thing ? Or something else? If so, any tips on how to calculate its value?
 

dl324

Joined Mar 30, 2015
13,111
If I connect the 4x15Led strips to the power supply in parallel, it should provide 150mA to each strip.
Only if the voltages for the LED strips are matched. In the real world, one will likely draw more current than the rest. Theoretically, this could cause that string to fail. Then the current would be divided among 3 strings and the one drawing the highest current will fail. That continues until all strings have failed.

If you use ballast resistors for each LED strip, you can avoid this cascading failure.
If I want to further limit this current to, say 120mA, can I connect a resistor in parallel to the whole thing ? Or something else? If so, any tips on how to calculate its value?
It's not a wise thing to do, but you'd determine the output voltage with the 4 strings and use Ohm's Law to calculate an appropriate value.
 

Martin_R

Joined Aug 28, 2019
101
If I want to further limit this current to, say 120mA, can I connect a resistor in parallel to the whole thing ? Or something else? If so, any tips on how to calculate its value?

Do you have the space to have another LED string? That would be 120mA per string. Still a good idea to have equalising current sharing resistors per string of LEDS.
 

Thread Starter

Sundoo

Joined Jul 21, 2021
15
If I want to further limit this current to, say 120mA, can I connect a resistor in parallel to the whole thing ? Or something else? If so, any tips on how to calculate its value?

Do you have the space to have another LED string? That would be 120mA per string. Still a good idea to have equalising current sharing resistors per string of LEDS.
No, unfortunately I don't. There is only room for 2 bars (2x LED strips each)
 

Thread Starter

Sundoo

Joined Jul 21, 2021
15
Thanks for your comments. Does something like this make sense ?
led_diagram.jpg


Sorry, I haven't done these things before. I'm not sure which is the right way to do these Resistor ballasts. This just looks like 4x R1 and 4 LED Strips in parallel with each other.
However, if we put them in series, then the current will be the same.

Any hints would be highly appreciated
 

Martin_R

Joined Aug 28, 2019
101
You've shown the resistors in parallel with the strips ,they need to be in series with them. IE: one resistor Inn series with each strip.
 
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