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Wiring 10w leds to 12 volts Answered

OK, I have some 10 watt - appr. 900 lumen leds that I want to use for a video room.  I have low voltage wiring in the walls and have a 12 volt 96 watt dimmer that I plan to power with a deep cycle 12 volt battery.  The leds are 3.4 - 3.6 forward voltage and 350ma.  I want to use 3 of these on each side of the room and was just hoping to get away with wiring each side in series and then connecting both sides to the dimmer.

Am I looking for trouble wiring them directly without any resistors?  I really don't want to get into resistors, etc. if possible.

Thanks in advance for any thoughts and suggestions. 



6 years ago

I running parallel with multiples 10 watt actinic led with a 11-13V(micro-adjustable) 20A switching power supply for my DIY reef aquarium lighting.

The led is powerful and you will feels burning if you place your finger 1 cm away the light source. Generated heat around 45C on 20x5 inch heat sink with fans.

Led Properties:
DC Forward Voltage (VF): 9.0V-11.0V DC
DC Forward Current (IF): 900-1000mA

It seem to be very hot if i adjust my current to greater then 12v. Currently I am running at 11.5v at 12 hours per day for couple months without issue.

I also having many 3 x 3watt royal blue led (fwd voltage 3.6v, fwd current 700mA) in series with 11.5v without any resistor and still running fine.

technically my lighting will draw
10 watt x 3 = 3A
3x3Watt in series = 1.4A

but when I measure my total current, it show 3.2A at 11.5v, that was a bit funny or my LED is dying?


Reply 6 years ago

The forward current figure isn't a fixed quantity, it depends on the temperature of the device. You are running these things very riskily, there is a good chance, since they have no current limiting, you will get into thermal runaway, and they will die rapidly. Once one goes, the others will take up the slack, and then another will blow a little quicker. By the time you reach the last LED it will all be over in seconds.


8 years ago

I think it is difficult to help you without knowing more about the dimmer and the LEDs. It is a bit strange that you say the LEDs are 10W when they are only dissipating ~1W according to the current you mentioned. Perhaps that 10W is referring to the equivalent incandescent output.
Can't understand your adversity to resistors; if you put 3 LEDs in series (3 x 3.6 = 10.8v) and connect to 12 volts without a resistor they will pass too much current and burn out. If you put 4 in series ( 4 x 3.4 = 13.6V) and connect 12V they will barely light up.
If your current figure is correct I would put a 6.8 - 10ohm 1w resistor in series with a test string of 3 LEDs and bring up the 12V very gradually checking to see how hot the LEDs get (don't do this in the wall). Even if you are careful you may have to heat sink the LEDs to play safe.
If you are wiring this in the walls use fuses on each run of wire to avoid fires if you have a short. If you are not completely expert with household wiring it is worthwhile having someone who is an expert check your wiring.