Intermittent fan for intermittent LED, or steady? Thermal question for 100W system

jwhildeb

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Joined
Oct 27, 2017
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1
I have an unusual system with three identical projector-type devices that I have retrofitted each with 100W LED modules and drivers. Basic AliExpress stuff with big 4in aluminum cube heatsinks and massive 120v fans. Two of the three projectors have been running without failure for hundreds of hours now. The third one has failed twice.

The only difference between them is that the two reliable ones are on steadily for 8 hours every day. The one that keeps failing is run intermittently on a timer: on for 15seconds, off for 45 seconds, on for 15, etc for 8 hours a day. I have to assume that the LED chips are dying because of the thermal stress of turning on and off like that all day.

Currently, I have my cooling fans wired in parallel with the LED drivers, so they are cooling only when the LEDs are on. Do you think this is best, or should the fan be on constantly? My original thinking was that having the fan on all the time would be worse, as it would cool the turned-off chip faster and give it a harsher temperature curve. But now I'm second guessing that.

Any thoughts on which fan arrangement would be best? Alternate theories on failure? Thanks!
 

wizardg

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Oct 18, 2017
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Oregon
I build high power LED lighting systems for ....indoor gardeners, and my advice would be to run the fans 24/7. Keep the LEDs as cool as possible.
 

brokenmonitor

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Joined
Nov 6, 2017
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5
I build high power LED lighting systems for ....indoor gardeners, and my advice would be to run the fans 24/7. Keep the LEDs as cool as possible.

Agreed. I don't know why you'd want the fans to be intermittent, you might as well keep them as cool as possible all the time in order to avoid any degradation. Fans are cheap, efficient and generally reliable, so this seems like an easy win (unless you have noise/power constraints)
 
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