Magnifying light voltages

[Martaine2005]

Try and work it out. You can’t really have more than three LEDs for 7V. 2V each plus current limiting. Could be higher of course depending on current.
But more than likely a DC to DC buck is involved.

 

[bushtech]

The 3 resistors on the bottom is all she cried

 

[Martaine2005]

You have a black pen ( if I can still say that). You must have a mixed colour to make red.
Just join the dots, anode to cathode. It will become obvious. Or take a high res image and link to it. Zooming in is better than scrolling left and right with a phone.

Martin

 

[bushtech]

Anode to cathode marked. And yellow jobbie is the battery that drove it 500mAh 7.2V

 

[Martaine2005]

Sorry, with my scrolling. It looks in cases, you have two in series. Let me draw this out .

 

[Martaine2005]

so Far, you have three in series. That’s probably it. So 1.7 or 2V each .

 

[Martaine2005]

Forget what I just wrote. I think I have it. I hate a phone screen sometimes.

 

[bertus]

Hello,

On the PCB I see 30 leds.
15 strings of 2 leds in parallel.
There is also a standby led that is separatly wired.

Having leds in parallel is a bad practice.
I would give each string its own current limiting resistor.

Have a look at the attached PDF.

Bertus

 

[bushtech]

Thanks Bertus
Trying to get my head around this. With leds in parallel the cathodes will be connected and also the anodes. Here the 2 leds of the 15 led series are connected anode/cathode/anode/cathode

 

[bushtech]

Using an online calculator from the resources section I get:
Source Voltage = 12V (Assumed)
Diode forward voltage = 2.5V ( Guess)
Diode forward current = 20mA
30 Leds
3 x 10 arrays + 270Ω resistor on each array
Circuit draws 200mA

I know nothing about these leds so all guesses
Does this look correct?

 

[bertus]

Hello,

You could measure the voltage accross one led on your board, when you power it with the battery.
That way you might have a better estimation of the forward voltage.

White leds can have forward voltage upto 3.5 Volts.

Bertus

 

[bushtech]

Hi Bertus
Thanks
Unfortunately I have already started stripping leds off the board.

 

[bertus]

Hello,

For the calculation you could take 3.3 Volts.
The attached chart shows 3.3 to 4 volts for white leds.

Bertus