DIY LED Question

[FlyTekk]

Whats the difference between running my LEDs which have a MAX rating of 1000MA at:

1000MA but then dimmed by my dimmer/controller to 75%

or

750ma but dont dim them and run them at 100%

I ask because somepeople run them at 750ma to conserve life and tell me that im going to burn my out because i run them at max 1000ma. But i only use 25% blues and 50% whites. LoL.

So i guess im confused on what the difference is. To me im assuming im running mine cooler.

 

[stage3-S4]

Whats the difference between running my LEDs which have a MAX rating of 1000MA at:

1000MA but then dimmed by my dimmer/controller to 75%

or

750ma but dont dim them and run them at 100%

I ask because somepeople run them at 750ma to conserve life and tell me that im going to burn my out because i run them at max 1000ma. But i only use 25% blues and 50% whites. LoL.

So i guess im confused on what the difference is. To me im assuming im running mine cooler.

The problem with LEDS is that when you change the current the voltage changes as well. Say you have a cool white Cree XR-E with a forward voltage of 3.7v and a current of 1000ma. This equates to about 3.7 watts for each Led. When you dim them down to 750ma the voltage also drops, so the wattage will be different.

If you are dimming 1000ma Max LEDS by 75 percent, then they are running at 750ma not 1000ma. There is no difference.

The bottom line is you can run them at 1000ma no problem as long as you keep the junction temperature of the LED within spec. I believe the max junction temperature (Tjmax) for Cree XR-Es is 150 degrees C. I would not let them get above 100 degrees though. I run my whites at 1000ma no problem and my junction temparture maybe gets to 90 degrees c. I also have a pretty bulky heatsink with fins.

 

[FlyTekk]

I have big heats sinks and fans blowing on them. I can touch my heat sinks anywhere and its not ever warm. Its cool to the touch. So i assumeit must be below 90 degrees F. When i dont run the fans i touch the heat sink and after about 5 seconds i have to remove my finger quickly do to heat.

You confused me with the volts and watts. Not sure why they play into the equation. I dont know much about electricity.

 

[stage3-S4]

I have big heats sinks and fans blowing on them. I can touch my heat sinks anywhere and its not ever warm. Its cool to the touch. So i assumeit must be below 90 degrees F. When i dont run the fans i touch the heat sink and after about 5 seconds i have to remove my finger quickly do to heat.

You confused me with the volts and watts. Not sure why they play into the equation. I dont know much about electricity.

It was to just clarify things because people seem to concentrate on the wattage output. That doesn't really help you understanding the LEDs capabilities. It's more important to know the current limits of the LED rather than the Wattage.

The junction temperature is the temperature between the LED and the Die(the star shaped PCB under the actual LED). It's also 90 degrees C which is 194 degrees F. If your Junction temperature did in fact reach 100 degrees C, your heatsink most likely would be at much lower temperature depending on the thermal properties of the heatsink. So its hard to really tell what your junction temperature is. Usually if your heastink is cool to the touch, that should be a good indication that you're not in any danger.

 

[ming]

wattage-wise, it will be the same

but I don't recall LED's having a 750mA max

 

[FlyTekk]

So long story short, ill have 1500ma xpg cool whites and 1000ma blues and royal blues and ill run them all a little under 1000ma. Like 940-950 just to be safe.

Then i will dim each considerably. I dont think i would ever go any higher than 75% IIIIF THAT. Plus im running 28 leds off 2 MW drivers (14 each) on 2 heat sinks (again 14 leds per heatsinks) which are designed to handle 24 LEDS each. And 2 fans blowing directly onto each heatsink.

Should i be okay?

And is this setup optimal. Or am i doing anything that could be considered "not a good idea"?

Thanks for the help and great info!

 

[stage3-S4]

So long story short, ill have 1500ma xpg cool whites and 1000ma blues and royal blues and ill run them all a little under 1000ma. Like 940-950 just to be safe.

Then i will dim each considerably. I dont think i would ever go any higher than 75% IIIIF THAT. Plus im running 28 leds off 2 MW drivers (14 each) on 2 heat sinks (again 14 leds per heatsinks) which are designed to handle 24 LEDS each. And 2 fans blowing directly onto each heatsink.

Should i be okay?

And is this setup optimal. Or am i doing anything that could be considered "not a good idea"?

Thanks for the help and great info!

So you are going to have all the LEDs running at 940-950-ma? When you dim the LEDS you are reducing the amount of forward current. So if you set the maximum current output on the driver to 950ma and dim them at 75 percent by external means(Pot,PWM, reef controller,etc), the forward current for each led will be 712ma.

The amount of forward current with respect to forward voltage is not a linear relationship. This means that you will not always have the same wattage at different current levels. This is why running them at the max current level does not always give you the most light.

Sounds to me like those heatsinks should be fine. If you can find out the thermal resistance of the heatsink (usually in degrees C/Watt ), I can run a quick calculation and give you a better idea of what to expect as far as junction temperature.

 

[FlyTekk]

I have no idea how to get those specs. I bought them from RapidLeds the pre drilled ones 5.9"x9". But i think ill be okay cause i literally run my whites at 24% My Blues though i go much higher but 75% would be my max. Thats with a 24 leds 12 white 12 blue. on 2 smaller heatsinks designed for 12 leds each.

Now im getting 28 leds 10 white 12 royal blue and 6 blues. Each Leds being "better" (xp-e and xp-g) than the ones i currently have. Plus they'll be on a larer heat sink that is made to hold 24 leds each. So all that being said ill probably be okay.

Just didnt know what current to run them at. Thanks so much for the help.