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DotStar (144/m) safe operating temperature
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DotStar (144/m) safe operating temperature

by RobbieKatz on Tue Jan 16, 2018 7:13 am

I'm busy with a project where I am using about 600 dotStar LEDs. I'm concerned about how hot they are getting whilst being run, and what effect this will have on the lifespan of the LEDs. I want to keep the brightness to a maximum while staying in safe operating temperature.

At the moment (dimming 50%), the leds are reaching a temperature of 50˚C. On the webpage - https://www.adafruit.com/product/2241 - for the dotstar leds it says the operating temperature is a maximum of 40˚C. But the datasheet of the APA102 https://cdn-shop.adafruit.com/datasheets/APA102.pdf says that the max is 70˚C. Can anyone explain the discrepancy? and can someone suggest a safe temperature for the LEDs?

RobbieKatz
 
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Joined: Tue Jan 16, 2018 7:07 am

Re: DotStar (144/m) safe operating temperature

by empewoow on Fri Jan 26, 2018 5:22 pm

Hi, I am also very interested in this topic. What about lifespan anyway for this product..? There is nothing in the datasheet about it.

How are you planning to configure the 600 LEDs? All in one "line" as in a LED strip? Or is it a matrix? What about the data line, 600 LEDs after each other? Does this work? What is the limit anyway, data/clock signal wise?

And how did you measure the temperature by the way? What is the temperature when you have them at 100% brightness?

empewoow
 
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Re: DotStar (144/m) safe operating temperature

by RobbieKatz on Mon Jan 29, 2018 11:01 am

Hey thanks for the interest :)

I actually did not measure the temperature at full brightness, but just touched it and knew it was too hot. at 50% brightness I used a multimeter with a temperature setting (and probe) to measure.

The LEDs were constructed in the shape of a logo (but effectively in a single line). Because the DotStar leds (APA102 chipset) run on SPI, they can be run with a super fast clock, 10 plus MHz. I'm not sure what the max speed is. Because my RAM usage was really high, I used a Raspberry pi Zero to run the LEDs, which is possible because of the SPI interface. PIs cannot run normal Neopixel LEDs. So the script was just written in Python. I comfortably get a 20 frames per second frame rate with 600 leds. I'm sure you can go much faster but for my application I don't want to.

As far as I understand you can run as many LEDs in a line as you want. Your data transfer rate will limit your frame rate and you must ensure that you insert power at multiple points to ensure the voltage doesn't dip too low.

RobbieKatz
 
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Joined: Tue Jan 16, 2018 7:07 am

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