utorok 14. mája 2019

fixing interior 41mm festoon leds from china

as in previous post, here I am modifying china made festoon leds, 41mm in this case. After few month of using as interior lights they start blink.  So I order new one (1st were from banggood, 2nd from aliexpress) all of them failed. I have last set which I am going to try with lower current. Original these leds are driven at ~160mA with 4 paralel set of 3 leds this mean each led is driven at 40mA each.

Pictures of module


Removed heatsink.

Removed heat transfer compound.

useless CAN-BUS resistor

1st I removed stupid "can-bus" resistor, it is there just to generate heat. It's marked as 271 which mean 270Ohm so current which this resistor generate in 12V environment is 40mA (12/270). As original bulb are 5W they run at 416mA on 12V so this resistor is really just heat source ....


Using PT4211 current is defined by Rs resistor value, manufacturer value is 0.82Ohm, based on datasheet current is calculated as 0.2/Rs so ~250mA (0.2/0.83 = 0.2439A). This mean 60mA over each led. I try 2R2 and 4R7 resistor which mean 90mA or 42mA.

Light output

I use my samsung to measure output of these modules with changed resistors

Rsens = 0.82Ohm (original) 9500x at 220mA (170 with removed 271 resistor)

Rsens = 2.2Ohm 3800lx at 66mA

Rsens = 4.7Ohm 1400lx at 27mA

Pictures of instaled modules

original modules with 0R82 sens resistor (i cant remember if this is 1 or 2 modules in car)
1 module with 2R2 sens resistor
1 module with 4R7 sens resistor

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