Fun with Fans

I’ve been running a Dell PowerConnect 5324 as my secondary switch at home that connects all the rooms together. The switch is rather loud in the location it’s sitting so I’ve decided to replace the fans in it to something quieter.

The switch uses 2 40mm high speed fans that exhaust air out of the enclosure. I had several 40mm fans that I could try to get the best noise/cooling ratio. I’ve used a digital multimeter with a thermal probe to measure the efficiency of the fans, my simple SPL meter to measure noise level and a simple Android app to measure the sound spectrum. The switch was ran for 30 minutes in each configuration to let the temperature of the switch settle.

Testing Methodology:
Ambient Noise: 23.3 dbA
Ambient Temperature: 23C

Configuration Temperature Sound Level
Stock Fan 26.2C 59.2 dBA

In the stock configuration the switch blasts out almost 64 dbA.

What would happen if I invert the fans so that they blow air into the switch?

Configuration Temperature Sound Level
Inverted Stock Fan 26.5C 63.7 dbA

Wow. Definitely not an improvement. Not only this configuration is slightly louder. The fans emit a noise 1.5Khz range that’s very, very annoying.

The new fans are significantly thinner and operate at lower RPMs. They do not move quite as much air as the original fans.
A quick note about the fan pinout on the Dell PowerConnect 5324. The fan pins are actually non-standard and have to be swapped around. The Dell PowerConnect fans use Positive-Sense-Negative pinout as opposed to the standard Negative-Positive-Sense pinout. Connecting the fans incorrectly doesn’t seem to have any detrimental effect on the fans themselves (as I found out) but the fans will simply not operate.

Once the fans were installed. I ran the test.

Configuration Temperature Sound Level
New Fan 27.4C 50.9 dbA

A 9.1 dbA drop is quite significant, that’s almost half as noisy as the original fans and the switch is now quieter than the ambient noise in the room the networking equipment is in. The temperature with the new fans running only went up a few notches.

Unfortunately the switch did not like the reduced RPM on the fans. The Fan LED now blinks alternating red/green. However there doesn’t seem to be any performance degradation of the switch.

Even though this was the configuration I was most likely stick with, just for kicks, I’ve went ahead and tried the inverted fan configuration.

Configuration Temperature Sound Level
Inverted New Fan 27.9C 46.5 dbA

Even though in the inverted configuration the fans were quieter, the temperature went up a few more degrees and once again, the fans exhibited a noticeable whine 700hz range.

In the end I ended up going with the smaller fans in the same configuration as the stock fans, blowing air out of the switch. While slightly louder than the inverted configuration, it was lacking the whine which was quite noticable.

4 thoughts on “Fun with Fans

  1. Hi Tom,

    I got crazy with the noise of my 5324 today and disconnected both fans.
    The fan led is red but it works.
    I’ve read of a few people that did so and had no reliability problems after months of use.
    My 5324 is under little load, SOHO use during daytime with only 5 ethernet cable connected.
    Do you think it is really risky?

    Thank you for your advice

    Thomas

    • Depends on the ambient temperature I suppose. The room my switch is has a temperature that’s a bit toasty, so some air movement is a good precaution. I don’t imagine the switch will get really hot with moderate/low usage as it’s got a pretty substantial heatsink.

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  3. Hi,

    I bought my Dell 5324 a few months ago brand new out of the box and just got it fired up today

    I must say the fans are noisy and hence made some effort to Google info about it which led me to your blog

    I’m so thankful for your research and investigation into the matter and have made me decide to retrofit the fans as well to less noisier units

    I’ve done this with my old Dell 2748 with favourable results other than the fact that I get a fan fault warning LED blinking

    However after running the switch almost 3 years trouble free, I must say its well worth the effort

    I don’t load the unit so much and is just commissioned the device as a SOHO switch running less than 10 client computing devices at any one time.

    Again thank you for your invaluable help to my efforts in finding a solution for my Dell 5324 fan noise problem.

    With your data, you have confirmed to me my observations from my Dell 2748

    Any other tips you can send my way regarding first use and configuration of this Dell 5324, I would very much appreciate.

    Marlou Jasmin Madrio – Singapore

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