Introduction: Repair/ Reuse Dead LED Bulbs for USB Power
The LED household bulbs (A-lamps) are here to stay. They brought in Very high efficiency (Compared to stupid Incans), Less heat output; and more importantly, Longer operating life.
However there are still times where an LED bulb fails. Interestingly, the usual failure mode of LED bulb is just the busted driver. LED chips themselves usually survive. Even if the LED chip fails, just just 1 or 2 from the entire array. This phenomenon makes the LED A-lamps a good candidate for salvage and reuse.
Here I shall guide you how to salvage an busted LED bulb, Remove the driver and trace out the good LED chips. These chips then, can be hooked up a low voltage convenient power source such as USB or AC-DC adapter.
Step 1: Crack Them Open
These bulbs are usually glued shut, which no access to components from outside. Help yourself to a hammer and smash away. Faint hearted folks may try to saw the lens off. Use gloves & Eye protection.
Step 2: Multimeter Multimeter! Here to Help
Discard the LED driver. Its more than likely the component to fail.
We just need the LED array now.
Use the Multimeter continuity to figure out the circuit path of designed array. Each lamp manufacturer has their unique way. Some designers put all the LEDs in series. While some prefer a Bunch of Series-Parallel matrix. Some Manufacturers also use Multi chip LEDs in a single package. 3030 is one of them, Having 2 LEDs in Series inside the package, with an effective VF of about 6v.
More likely Manufactures today use 2538, 5730, 5670 Chips. Some older deigns do use 5050 or 3528 style Chips. All these chips are about 3.2v DC.
One neat way to test the LEDs is to use 3 AA Cells in series (effective 3.6v for Rechargeable), Hooked up to some thin probes ( I used needles). Test each LED with the probes. Mark the Polarity of Each LED. Also mark out the dead LEDs. We need to remove these out.
Step 3: Convert to Parallel
That was fun, Wasn't it?
Now that you've removed the bad LEDs (this is important or they'll short the array) and Identified good ones, Its time to re-design the array. If you are using low voltage source like USB 5v, you can use LEDs in parallel only. If you are using a higher voltage like 12v Adapter or a car battery, You can use a series string of 4 LEDs.
For my Project I Converted all the good LEDs to Parallel by soldering thin Telephone wires on them. You will have to cut the circuit traces to make each LED individual & Isolated from others. Coat the whole mess in Hot glue for safety and longer life. Keep LED emitters open though.
Step 4: Add USB Cable & Resistors
Finally, Add some length of wire depending on your application. I used an USB cable from Old Printer. Cut off the 'B' end and solder one lead to LED array. Other lead will have a series resistor to limit the current. I decided to use 12 ohm, 1 watt resistor. That kept the current comfortable while being plenty bright.
Here's a very neat LED resistor calculator-
Full credits to the website owners, Admins and engineers respectively.
Step 5: Enjoy
With this neat little LED USB light, the possibilities are endless. Here I am using it to light my Laptop Keyboard and workspace. The Light is plenty bright to write or read by.
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