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Old 23rd Feb 2021, 4:32 pm   #11
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,608
Default Re: Running DC brushless PC cooling fans

If you want more airflow, and to be able to control it, I strongly recommend getting some ex-server fans secondhand. I bought some from a PC parts dealer via (our local equivalent of eBay) and have found them very useful. I think rack-mounted servers are often withdrawn and scrapped/dismantled and the parts can be had at very low prices. The fans can be very powerful and high-quality units (Papst, Panasonic or Sanyo Denki). They have excellent speed control via a PWM input.

For example, I have a couple of 120mm Sanyo Denki fans which, running at full chat, will draw nearly an amp from the 12V supply and produce something like a hurricane. But the PWM control can smoothly reduce the speed to little more than a whisper. For my application I rigged up a simple PWM controller using a 555 chip which works just fine.

Trying to control brushless fans by varying the supply voltage doesn't work well at all. They're not designed for it. Get a good quality fan, more powerful than you need, and control it via the PWM input, and you'll be pleasantly surprised at the range of control possible.

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