luxeon headlamp

[tidos76]

first off let me say this is not going in a car. Its going on a atv.
I make a headlamp using 4 luxeon III's and a 1000ma buckpuck. by the specs the buckpuck can handle 5-32vdc.

i wired everything up and it works,blindingly!.lol but when i turn my power supply up to around 9-10v the leds actually get dimmer. is this normal? at 7v they seem to work normally without any flicker or anything. I need these to be able to run on 11-13v. that is what the stator on the atv produces. any ideas or suggestions will be greatly appreciated.

 

[crutschow]

The problem is overheating of the LEDs which will cause the light output to drop, so yes the dimming is normal. It's not very clear from the data sheet but the LEDs need to be mounted on a heat sink. At 1A each diode dissipates over 3W which is way more than the small diode package can dissipate to the air without overheating. If you touch them when operating without a sink you'll probably burn your finger.

The white diodes have a thermal resistance of 17C/watt junction to board. The derating curves show that the thermal resistance from junction to ambient should be about 20C/watt if the diode is operated at 1A. This means each LED needs to be mounted on a heatsink with 3C/watt to air thermal resistance.

Also note that the aluminum case of the diodes is electrically connected to one terminal of the diodes thus you can not mount them all to the same heat sink. The heat sink for each diode must be electrically isolated.

As you can see high power LEDs are much more complicated to use than a plain old incandescent light bulb.

 

[tidos76]

the leds are mounted on a heat sink. and i used thermal compound to isolate them. the dimming above 9v occurs immediatly, even before the leds have time to heat up. they also did it before i attacked them to the heat sink. I am almost positive they are not overheating.

 

[crutschow]

Have you measured the current into the LEDs?

 

[tidos76]

6.36V 1.76A from the buckpuck to the leds. I have a switch inbetween the power supple and the buckpuck. if i turn the supply up to 12v then turn the switch on, the led will stay bright for about 10 sec. if i lower the voltage, or turn the switch off and back on the will become bright again.

 

[tidos76]

**broken link removed**

I'm basicly using this except i'm only using one resistor with a switch between the control and ref. and i'm using a 1000ma buckpuck with luxeon III's

 

[crutschow]

You shouldn't connect LEDs in series-parallel. One branch will tend to hog the current. All four LEDs should be placed in series and the current should be adjusted to 1A or less. Didn't the buckpuck wiring diagram show them wired in series?

After you rewire the LEDs, turn down the intensity control pot on the buckpuck until the LEDs do not dim at 12V input.

 

[JBrock]

Caution! NEVER exceed the rated current for your LEDs! They can become permanently impaired!
Are those 3-Watt Luxeons? Do you have some kind of colimater (reflector) ? Can you show us a picture? How are they mounted physically?