I have a bunch of these 12v automotive festoon led lamps. They are quite bright and contain 16 of the 3528 smd leds that will use 0.06w each when properly driven as per the manufacturer's datasheet.
When the fixture is powered from 12v it's power consumption is 3.3w when in fact the leds only consume a rated 0.96w. I think it's time to fix this mess of wasted power.
Step 1: Preparing the Leds.
First the stupid tabs came off then those power hog resistors I unsoldered. Now the array is ready for the next steps.
Step 2: Driving Them Right!
I have a couple of these 1.5watt, 350mA led micropuck drivers from years ago. This is a neat way to give them a new life!
I configured the micropuck to act in buck mode to allow powering from a Lithium "9v battery" (which is actually 7.2v) and also be the most efficient in this configuration.
Step 3: Connecting the SMDs in Parallel.
Once the nasty resistors were off, I wired all 16 LEDs in parallel. With the micropuck output current of 350mA, this arrangement will be perfect for driver and LEDs.
Step 4: Initial Testing.
The factory power consumption was 3.2W. With the efficient driver, parallel LEDs arrangement, the power is 0.816W. This is 4 times less power usage! Amazing! Goes to show those cheap car LEDs are power wasters!
Step 5: Fitting Into an Enclosure
I used an old 220v heater switch to put the battery and drivers into. The 2 modified leds went into the outside. The big red switch is the on off control for the portable light.
Step 6: Completion.
I used black silicone to stick the leds onto the pvc enclosure. The 4.3Wh battery can provide 2 hours of lighting with the new efficiently driven leds!