Hello electronics experts. I am a uni student studying MEng in UK. Anyway i'm from Cyprus and last year i made some custom led lightning for some bumper lights of my car. I connected many leds in parallel, and each row had 4 leds in series. The leds are ebay quality;p and the listing gave the following specs:
Technical Summary
RoHS Yes
Package F 3mm
Packaging bulk
Dimensions F3mm
Lead Spacing 2.54mm
Color White
Brightness 11000 ~ 13000mcd
Wavelength 8000k-9000k
Lens Waterclear, White
Forward Voltage 3.5V
Current Rating 20mA
Reverse Voltage (V) 5
Continuous forward current(mA) 20
Peak forward Current(mA) 40
Power Dissipation (mW) 100
Operation Temperature Range() -20~80
Storage Temperature Range() -20~80
Since the voltage supply was standard 12V-14V(since the alternator of the car produces about 14V) i assumed power supply to be 14v. So with a given forward voltage 3.5V i connected 4 leds in series at each row as 14V/3.5V=4 After using them couple of days(not even 500hours of use), some started to die, others started to flickering, others sometimes from dead came alive, and finally they all died-note: I remember that they died rows by rows-not a single led died alone in a row) Then i replaced them all again, same problem, and finally last christmas when i went back to Cyprus, i replaced them again putting a resistor and a diode in the power supply...The intensity dropped but at least for the time i was there, not a single one died. What i am assuming is that the forward voltage is 3.5V and working voltage must be lower(since resistance may change with temperature increase since they were hours opened each time)..Also another thing is that despite sealing them well, when i wash the car, if water goes into the contacts and affects it somehow...
Any help appreciated(what is really weird, is the flickering and the reborn of the leds..)
Cheers, Ken
Technical Summary
RoHS Yes
Package F 3mm
Packaging bulk
Dimensions F3mm
Lead Spacing 2.54mm
Color White
Brightness 11000 ~ 13000mcd
Wavelength 8000k-9000k
Lens Waterclear, White
Forward Voltage 3.5V
Current Rating 20mA
Reverse Voltage (V) 5
Continuous forward current(mA) 20
Peak forward Current(mA) 40
Power Dissipation (mW) 100
Operation Temperature Range() -20~80
Storage Temperature Range() -20~80
Since the voltage supply was standard 12V-14V(since the alternator of the car produces about 14V) i assumed power supply to be 14v. So with a given forward voltage 3.5V i connected 4 leds in series at each row as 14V/3.5V=4 After using them couple of days(not even 500hours of use), some started to die, others started to flickering, others sometimes from dead came alive, and finally they all died-note: I remember that they died rows by rows-not a single led died alone in a row) Then i replaced them all again, same problem, and finally last christmas when i went back to Cyprus, i replaced them again putting a resistor and a diode in the power supply...The intensity dropped but at least for the time i was there, not a single one died. What i am assuming is that the forward voltage is 3.5V and working voltage must be lower(since resistance may change with temperature increase since they were hours opened each time)..Also another thing is that despite sealing them well, when i wash the car, if water goes into the contacts and affects it somehow...
Any help appreciated(what is really weird, is the flickering and the reborn of the leds..)
Cheers, Ken
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