Rescue working LEDs from "dead" bulbs | Hacker Day

2021-11-25 10:22:23 By : Mr. Buffon Liu

Of course, the box says that they can be used for years or even decades, but anyone who has bought cheap LED bulbs knows that the actual situation is more complicated. Sometimes several LEDs in the array will burst, reducing the overall light output. More commonly, the power supply starts to malfunction and the light bulb starts to flicker or buzzes. In either case, you will eventually pull the bulb and replace it.

But [Bifferos] thinks we can do better. Instead of blaming it on poor QA and throwing away the bulb, why not do some exploratory surgery to identify salvable LEDs in otherwise "dead" bulbs? After disassembling a few burned out bulbs (brand names and others), he was able to pull out an astonishing number of convenient LED panels, which can be easily reused. Naturally, with more coaxing, a single SMD LED can also be liberated and put into use.

As you might expect, there are too many different LED bulbs on the market to create a comprehensive disassembly guide, but [Bifferos] does provide some tips to help turn on the bulb without hurting yourself or destroying objects in the process. Once in, the design of the bulb will determine what happens next. Bulbs with multiple LED arrays on their own PCB are easily damaged, but if you only have a single board, you may need to pull down the LEDs individually. For this reason, this article shows an effective method of peeling off the LED using hot air or a pair of soldering irons.

Compared to the noble claims of the manufacturer, we have previously discussed that the performance of modern LED bulbs is rather mediocre. We would rather see that these bulbs are designed well enough that they actually use their full potential, but the ability to save useful components from malfunctioning lamps can at least mitigate the blow of having to throw them away early. Although this is not the only reason you should disassemble the LED bulb before putting it in the trash can.

I think the better way is to take precautions...Modern LED bulbs are usually not made of inferior components, but since these components are driven to the absolute maximum amount of light that the manufacturer can push, they are indeed greatly affected and cause overheating And breakage. Buying a light bulb with more light than you need seems to be a better idea, turn it on and change the power supply current setting resistor so that it runs at only half of the rated current. The heat should drop and your LED will not only run longer but also be more efficient.

BigClive has a lot of videos on this topic, especially videos about LED failure due to overdrive...

And how the Dubai government requires the bulb to last longer, so manufacturers install more LEDs in the bulb, but drive them much less often. marvelous.

When I was in Dubai recently, I decided to check the LED manufacturing section of a hardware store. There is only a single Dubai bulb on the shelf, with hundreds of "normal" bulbs around

I like his video about this design, which usually appears in bulbs in dollar stores, where two resistors are connected in parallel to set the current limit. Most of them are set at the limit that the LED can handle, and they will fail prematurely. Just cut off a resistor, it can run with less power, and may extend the entire life of the LED chip. Sometimes there is only one resistor, which requires more work, but I have some 0603 resistors, which are mounted diagonally on the pads. It reduces the light to 2W and is a less harsh light for close-up use.

They also seem to have less silicone to hold the bulb cover, making them easier to eject than more expensive bulbs, while still maintaining good condition.

"Change the power supply current setting resistance so that it runs only at half of the rated current."

This is the first question. LED bulbs should include a constant current power supply, but usually not.

I took apart a few dead ones and none of them had a constant current regulator.

All they have is a capacitive dropper circuit. That is, the capacitance that reduces the current.

Any change in input voltage will cause a change in LED current.

I did this for a car light, and I want to use it to replace the 5W bulb in the car headlight. Its rated power is 2.5W. When I first bought it, I expected its power to be about 1/3 of this power, which is the same as many Chinese LED lights. Surprisingly, it did consume 2.5W-after running in free air for a few seconds, my finger was burned. The thermal imager confirmed this, and the temperature on the LED was >100°C. Nothing can be put in a closed car headlight. So I reduced the current to 50%. The acceptable temperature is about 60°C with sufficient light. It has worked in the car for more than 1 year.

The problem is that they make it impossible to disassemble these things peacefully most of the time these days. When you get something that can be taken apart, it is a rare treat.

I have several Tradfri lights from IKEA. The warm white LED lights have failed, but the cool white LED lights are still bright. It took several years, but they all had the same failure mode. However, they are good and cheap. I will buy more.

Another good source of truly bright white LEDs is the old LED TV backlight. You can remove individual LEDs or just arrange light bars for things like understage lighting.

Or use the entire TV backlight assembly as the area above the workbench to cover the light source -> hardly any shadows.

Although the processing (CPU) board lacks an "on" signal, it is basically the original TV, with only the LCD panel and modified power supply/driver circuits removed.

Haven't tried it yet, but most of them should be dimmable by PWM circuit.

Put a diffuser on it.

I only removed the LCD panel and the 1-2 mm thick diffuser. The cable light bending/polarization/any foils and sheets are preserved, they are enough/enough for the three TVs I have converted so far.

For some time, I have been saving all the malfunctioning LED lights. I need to study disassembly techniques because I used to break the power supply when opening them.

But because I’m a manufacturing engineer, I’m always interested in how things are made (that’s why I shred everything before throwing it away, and why hammers and chisels are actually part of my office kit Part).

I have also been saving people who have failed. Destroying the power supply is a matter of course, most likely the part that fails anyway.

Before I threw it away, I also tore almost everything to pieces. Just out of pure curiosity about how it works. But let's not forget to clean up / hoarding :)

According to my observations, usually those with discrete circuit boards tend to burn the capacitors first, and then the silicon will start to work. I recently pulled an integrated aluminum plate and the entire driver, as well as a push connector for a single large capacitor; the fault at that time was not on the capacitor, but on the current limiting resistor of the entire unit fed from the Edison screw base

I found that a common failure mode of these cheap LED bulbs is that a single LED in the series string will have an open circuit failure. Simply short-circuiting a malfunctioning LED will usually revive the bulb, although the light output is slightly lower (or even not noticeable). Depending on the current regulation scheme used, this may cause the remaining LEDs to fail prematurely (if a simple resistor is used instead of an actual regulator), but you can at least extend the life of the bulb.

A lamp reminiscent of Dubai

What is the failure mode? I tend to use them at fairly low settings and haven't failed...

Coincidentally, I just replaced the faulty power supply with a cheap LED flame bulb. After disassembling the faulty bulb, I found that the voltage of the LED part was 5 volts, so I replaced the cheap and compact faulty power supply with a spare USB power supply.

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