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I'm trying to reuse some old HD425Y1U51-T0L6 LED Backlight LED strips to make a light box. img1

They look like this: image 2

The closest link I found for them (but no spec sheet) is https://www.shopjimmy.com/hisense-hd425y1u51-t0l6-led-backlight-strips-3-43a6g/ My goal is to break the 8-LED strip into 2 sections of 4 LEDs each.

My question is:

  1. Can I split the 8-LED strips into 2 sections of 4 LEDs?

  2. I would also like to test each LED before and afterwards to make sure each LED is working but I can't find the specification sheet that tells me the voltage of each LED. How can I figure this out?

I have a variable power supply 0-24 volts DC, a multi-meter and 8 18650 to test with but I don't have a LED tester.

I only want to use 3 sections of 4 LEDs to create the light box

Setup example: Current LED backlight setup strips:

1st strip = LED1 - LED2 - LED3 - LED4 - LED5 - LED6 - LED7 - LED8
2nd strip = LED1 - LED2 - LED3 - LED4 - LED5 - LED6 - LED7 - LED8
3rd strip = LED1 - LED2 - LED3 - LED4 - LED5 - LED6 - LED7 - LED8

The setup I'm trying to create:

1st strip = LED1 - LED2 - LED3 - LED4
2nd strip = LED1 - LED2 - LED3 - LED4
3rd strip = LED1 - LED2 - LED3 - LED4
 
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  • \$\begingroup\$ Can you not measure them connected to the original driver circuit? Also don't use those lithium batteries without a current limiting circuit for the leds \$\endgroup\$
    – Passerby
    Sep 6, 2023 at 8:42
  • \$\begingroup\$ @Passerby unfortunately it was salvaged from a broken TV and everything else they trashed. Thanks about the Current limiting circuit information. \$\endgroup\$
    – Rick T
    Sep 6, 2023 at 11:23
  • \$\begingroup\$ @RickT Another note on the used LEDs from TV backlights: some of them may have failed, and even if you had the original circuit they might not work as they might be open or shorted. Sometimes they will work under a lower current, but not at the higher current provided by its TV backlight driver. You could also apply 24V across the whole strip with a 1kΩ resistor in series to see if all of them work, and even then some may not work at a higher current. \$\endgroup\$ Sep 6, 2023 at 13:27

2 Answers 2

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Yes, it is possible to do that.
The thin line going from the connector to the opposite end looks like the negative line. The LEDs are likely about 2.7-2.8V each (typically rounded to 3V, but don't run them directly at 3V without a resistor or other ways to limit the current), so for all 8 you need about 22+V, and 11+V for 4 of them in series.
The way to test the voltage they run at is to set your power supply to about 4-5V and use a 1kΩ resistor in series, and then test one LED by using the small copper pads on both of its sides as contacts. The voltage you measure will be slightly smaller than the full power voltage (for example, you may see 2.6V at the 1-2mA test current, and 2.7-2.8V at the full power 50-100mA current).
In fact, any time you need to test any diodes, you simply supply a voltage larger than what you expect they would need, and limit the current to 1mA or less. Also, don't forget that LEDs NEED TO BE SUPPLIED WITH A REGULATED/LIMITED CURRENT!
Supplying just a regulated voltage will easily lead to too much current which would destroy an LED, because LEDs are non-linear elements, meaning their current changes greatly with a very small change in voltage.
The simplest way is using a constant voltage above 3V with a resistor in series to limit the current, and a more efficient way is using a switching converter, typically a dedicated LED driver or merely a constant current supply.
Each LED may run at no more than 1W, but I would recommend going no more than 0.3W, which is no more than 100mA at around 3V, because larger currents overheat and destroy LEDs much faster - the lower the current you run through them, the longer they last.
If you need more light, it is better to use more LEDs than to run them at a higher current, if you want to make them last much longer.

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If LEDs are white, you can safely assume that each one of them is rated for 3V. It may as well be 2.9V or 3.2V but it should not be this much important. The proper way to power a LED is to limit the current and allow the voltage over the LED to settle wherever it feels like.

In regard to current (amperes), they are generally related to the led size and you may have some success comparing them to the spec of a known LED of the same size, but here your mileage may vary. Just looking at your picture, I would try 50mA first.

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