Hi & Goodday to all! I just bought a Luxeon 1 Watt LED & intend to replace it with my old aluminum 6-LED flashlight case, intended to DD it (resistored) by 3x AA batteries (4.5V). But I am not sure about the value of the resistor (omh & watt) I should put in, any advice appreciated! /ubbthreads/images/graemlins/smile.gif
Resistor Value
- Thread starter DIYLite
- Start date
andrewwynn
Flashlight Enthusiast
the problem is.. the lux will run at a wildly different Vf depending on which it is... the best way to figure out how to do a DD light like you describe is to get a nice 5W wire-wound resistor that is in the sub-100 ohm level so you can dial it up and down and measure the current and voltage (two meters at once is best)..
the 'poor mans' way would be to do some quick ohms laws calculations and start with a resistor like 10ohms in series to start with and decrease the resistance 'til you get the brightness (current level) you desire.
Lux1 i believe is designed for 350mA and about 3.5V.. so you need to drop 1V at 350mA.. resistance x current =Volts.. so 1V divided by 350mA = 2.85ohm.. however.. the Vf can vary a lot so i'd probably start with 8 or 10 ohms.. measure and bump it down... i've seen a lot of 3-cell lights with about 1 to 2 ohms.. my LiON drive lights like to have 1/2 ohm with a lux3.
have fun! good luck.. ask questions.. you'll love the lux!
the 'poor mans' way would be to do some quick ohms laws calculations and start with a resistor like 10ohms in series to start with and decrease the resistance 'til you get the brightness (current level) you desire.
Lux1 i believe is designed for 350mA and about 3.5V.. so you need to drop 1V at 350mA.. resistance x current =Volts.. so 1V divided by 350mA = 2.85ohm.. however.. the Vf can vary a lot so i'd probably start with 8 or 10 ohms.. measure and bump it down... i've seen a lot of 3-cell lights with about 1 to 2 ohms.. my LiON drive lights like to have 1/2 ohm with a lux3.
have fun! good luck.. ask questions.. you'll love the lux!
The L1s and most of the L3s I've used have been 'K' forward voltage (Vf) which is about 3.5v, IIRC. I've been using 2 ohm (they usually test at 2.1 ohm) resistors for about 500ma with lux 1s and 1 ohm for around 1000ma for Lux 3s. One 6v lantern I modified for a friend drew 540ma running on 4 nicads (about 4.8v) and 2.2 ohms resistor. I prefer to use 1 or 2w resistors but I had to put several in parallel to get the right value for this one. He wanted to keep his Lux1 under 600ma even with a massive heat sink in this plastic housing. A 1w resistor dropping 1/2 volt at 500ma is 1/4 watts, so it shouldn't get too hot. I try to stay below 1/2 the resistor rating since they get REAL hot (150C?) at the rated wattage.
Just for an example, 3 different 3C NiMH (3.6v) DD lights with Lux 3s (no resistor) draw 950ma to 1200ma and it varies about +/- 50ma depending on temp(?) or other environmental influences. It could vary more but usually doesn't. Current tends to go up as the light warms up. Using the resistor doesn't drop the current much but makes it more stable. I mention this because you may want to use a smaller resistor if you stick with rechargeable batteries. You might start with 5 ohms and then parallel another (2 5ohm in parallel for 2.5ohm or 3 for 1.67 ohm)
Just for an example, 3 different 3C NiMH (3.6v) DD lights with Lux 3s (no resistor) draw 950ma to 1200ma and it varies about +/- 50ma depending on temp(?) or other environmental influences. It could vary more but usually doesn't. Current tends to go up as the light warms up. Using the resistor doesn't drop the current much but makes it more stable. I mention this because you may want to use a smaller resistor if you stick with rechargeable batteries. You might start with 5 ohms and then parallel another (2 5ohm in parallel for 2.5ohm or 3 for 1.67 ohm)
