Led light bar form tv?

[TheDrunk]

I had just parted out a led tv, where the screen part was ruined, and it cost more to replace the screen, yet while salvaging the tv. i found a LED bar with aprox 6 11 led lights.
how can I find the voltage on them ?
I plan on using them to light up my work station and curio cabnit.

Here is a picture of the light bar.

 

[S0ULphIRE]

You've got 11 white LEDs which have a forward voltage of around 3.2-3.4v usually

If they're in series, the voltage adds and you'll need a ~36V power supply.
If they're in parallel, the input voltage will be about ~3.3V

Unfortunately they could also be a mix of series/parallel I think usually they pair 2 of them in series then connect all the pairs in parallel, meaning input voltage of around ~6v or so would be required.

From the pics it looks like you should be able to see how they're all connected
Can you either confirm how they're connected or post a clearer picture of a few links in the strip?

You can also always work backwards too; start with a ~3.3v source (e.g. a coin cell battery, a couple AA's strapped together, etc) and connect two wires to the pos/neg outputs. Put a potentiometer in series with one of the wires, then connect the wires to each side of 1 of the LEDs. Start on the highest resistance setting for the pot, then slowly lower it until the LED turns on to what looks like a good brightness. Measure your voltage drop across the pot with a multimeter, then turn off power and measure resistance across the pot and bam you'll have found teh current you need to supply as well.

 

[TheDrunk]

I will post a picture lining out the traces.

 

[TheDrunk]

I belive it is Paraell I hope this picture can help make sence of it.

 

[S0ULphIRE]

I actually think it might be in series, but it's really hard to tell from your pics lol. I need a high res pic of as many segments as you can fit into a single shot, so that I can see where the traces are going in full, or at least for 4-5 segments.

Here's something you can try that might make this whole thing easier
1. Get 2 AA batteries and connect one side of positive/negative terminals together, then attach wires to the remaining two terminals (e.g. same way that this does: https://cdn.solarbotics.com/products/photos/42b6d3bead98a923fe9fc289c3ff0af1/bholdaa.jpg)

2. Connect the two output wires from the batteries directly to the input of those boards. If the lights all turn on, then yay you've got a bunch of LEDs in parallel. If they don't turn on, they're probably in series.

3. If they *don't* turn on in step 2, then try connecting 3 9V batteries just like you did with the AAs, then do the exact same test. IMPORTANT though, don't leave it connected. Just quickly touch/tap the wires coming from the battery to the circuit. Reason being, you'll likely need some sort of current limiting in place (e.g. a resistor or potentiometer) and without that your LEDs could draw too much power and blow.

But yeah, see how you go with the above or with taking some clearer pictures and let me know

 

[TheDrunk]

Okay I found this video, gave me some idea. https://www.youtube.com/watch?v=4O37rHsk-20

Now, this is the lights I have


LG Innotek 50" L Type REV0.0 2014.03.05 50W12S1P Left Backlight UDULED0GS045

Same as his.
so they are series. now he says 24V and reduced to 12V I do not want to split the light bars I have. What would be a good way to provide 24V

 

[S0ULphIRE]

His are slightly different to yours, there's only 7 lights on his bars.
They also looks like much simpler strips than yours, but lets assume for now that yours are in series (they probably are tbh).

As I said before, forward voltage for white LEDs is usually 3.2-3.4V, so lets say 3.3 for now.
3.3v * 7 LEDs = 23.1V required to power the full strip. That's why he says he needs 24V in his video.
In your case, 3.3 * 11 LEDs = 36.3V, so you'd need a 36V source to power the full strip.

 

[TheDrunk]

Okay, tomorrow, I will see what I can salvage to make a tester. And see what I have laying around power supply wise.
I do thank you helping me figure this out.

 

[TheDrunk]

Okay, so I got the stuff I believe I need as now to test. I am still looking for the power source,
How hard is it to take a power brick from a TV and convert it so it has the nessary voltage for each led strip

 

[S0ULphIRE]

Just get any 36V DC power adapter, off a junk pile or an old laptop charger or whatever. It's a pretty common output voltage so you should be able to find something pretty easily.

Then all you need to do is put a resistor in series to limit the current: https://www.sparkfun.com/tutorials/219

e.g. their example, they have a 3.8V power supply and an LED that needs 3.1V and 30mA of current.
So to find out what resistor value you need, you take your input power (3.8V), minus the voltage that your part needs (3.1V for the LED), then divide that by the amount of current your LED needs (0.03 aka 30mA)
So the whole equation is (3.8V - 3.1V) / 0.03 = 23.3
They will need a ~23.3Ohm resistor in their circuit to limit the current to 30mA and ensure they don't blow the LED.

In your case, you have a string of 11 LEDs that need 3.2v and probably 20mA of current.
3.2 * 11 = 35.2V
If you have a 36V power supply, your equation is:
(36v-35.2V) / 0.02 = 40
You need a 40 Ohm resister in series with your 36V power supply to make sure you don't blow up the LED strip.