how to determine the right voltage for led lamp?

[pharaon]

ok today i tried with 0.04 current and 2.6 voltage for 5 leds
1- connected for only one led and the 5 light up together


2- connect the first and last led and the 5 light up


then i tried to light up 10 leds same current at 0.04 but i had to rise up the voltage to 5 V

 

[Alec_t]

That's a much clearer image and points to the LEDs being arranged as a series of 18 groups, each group having 5 LEDs in parallel. So I reckon you'd be looking at a power supply of at least 18 x 3V = 54V, capable of supplying a constant current up to 5 x 60mA = 300mA.

 

[BobK]

Ah, this finally makes sense. At least I was right before I was wrong!

Bob

 

[Martaine2005]

Yes Bob, you guessed about 60v ages ago!. So you were right!.

Martin

 

[pharaon]

capable of supplying a constant current up to 5 x 60mA = 300mA

how did you calculate this part?

 

[Alec_t]

how did you calculate this part?

See posts 10 and 12. If 66mA is the maximum rated current, it is always advisable to run things at less than maximum to prolong their life, so 60mA per LED seems reasonable.
I'm still puzzled by your assertion that "they all share the positive line but the negative is every 5 leds". If 18 groups of 5-parallel are indeed in series then they can't all share the positive line.

 

[pharaon]

I'm still puzzled by your assertion that "they all share the positive line but the negative is every 5 leds"

yeah sorry about that, it's the opposite

 

[Alec_t]

it's the opposite

You mean they all share the negative line? That still leaves the puzzle.

 

[pharaon]

see that top thin line that all each group of leds share

 

[Alec_t]

I think you'll find that the light-coloured line is an insulating strip, not a power rail, and the darker areas are conducting paths connecting the groups in series. Can you confirm with a meter?

 

[pharaon]

and the darker areas are conducting paths connecting the groups in series.

yes that's true

 

[Harald Kapp]

This is what the circuit looks like (the polarity of the diodes may be reversed, I can't see that from your photos):

Each of these meandered sections has 5 LEDs in parallel. The sections themselves are in series.
All else has been said.

 

[Alec_t]

Conclusion: you'll need a ~300mA constant-current ~60VDC supply.

 

[pharaon]

thanks every one