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Noisy Cisco Fans
Replacing fans in Cisco catalyst 3500 XL
If you own any Cisco appliances you will know how loud they are. Cisco use fans that can push incredible amounts of air but make a lot of noise doing it.
It's fine if your running the equipment in a server rack in a baffled server room but if you're running it in small offices or in open areas you'll be quite aware it's switched on without needing to wander over to take a look at the flashing lights.
 As the fans in the Cisco's are constantly spinning they pick up a fair amount of dust which can lead to the fan making quite a bit of extra noise above what it originally made.
If you can catch it soon enough, just cleaning the fan (we recommend using a toothbrush to brush away the build up of grime) will save it from becoming any worse but if the fan is left to run without cleaning, the eventual build up of grime will unbalance the fan enough for it to become horrendously loud and ineffective.
The Cisco catalyst 3500 XL we looked at had four 40mm x 40mm x 20mm fans along the left hand side of the case.
 They look similar to standard video card or 486 cooler fans, but the Cisco fans are 10mm centimetres thick, double the size of a standard 40mm fan.
You can find the correct Cisco fans new and used on the web through various online shops and scrappers, but they're typically very expensive.
On eBay these 'original' Cisco fans can fetch up to as much as $50 a fan - so replacing the fans with original Cisco fans was out of the question for us.
The fans themselves aren't really that unique and if you're lucky you might find cheap no-brand versions very in a local PC an electronics store.
The only ones we could find were still fetching up to $25 a fan so we kept looking.The cheapest replacement fans we could find were approx US$3 each (delivered) from DealExtreme, the only problem was they were only 10mm wide.
The fans we received had no plugs on the end so we used some plugs from an old PC computer case. The socket pins are a little wider than the plug is meant for, but it works fine.
The socket on the Cisco switch is a standard 2 prong fan power plug, It is common in old PCs around the late 90's before the 3 pin smart fan plug we have now.
We didn't test it but it looks like you could probably use a 3 pin plug to plug into the 2 pin socket on the motherboard with a bit of force.
The fans in the Cisco don't screw into the chassis, they are held in place by two metal clips on two sides of the fan and a third clip on the bottom of the chassis.
 The 10mm fans we used were held fairly securely by the two metal clips, but because the fans were only 10mm deep they didn't come in contact with the third clip.
Whilst the replacement fans would be fine for a fairly static environment, you might like to bend the metal clips for a tighter hold or dab a bit of superglue on the bottom of the fans to hold them in place.
The noise
It was obvious from the start that the replacement fans weren't going to push the same amount of air as the original Cisco fans but we were surprised at the difference.
The replacement 10 mm fans weren't silent but were barely audible, about the same volume as a regular pc power supply but the Cisco fans seemed to push about twice the amount of air as the replacement fans!
The Cisco had gone from being the sound of a jumbo jet to the sound of a normal desktop PC.
Because this switch would raraly have any more than 10 ports in use there would be much less heat generated, and hopefuly a reduced need for cooling.
After the success with the switch, we were eagre to tackle our neighbours Cisco 2600 router which you could hear running at night!!
But be warned, when we opened up the router we found that the noise was coming from the power supply in the router and not the fan at all - This means a trip to your local power supply repair shop.
Rob (Friday, 23 January 2009)
UPDATE: The Catalyst gets hot. with or without the orginal cisco fans the case temp gets to 35-40 degrees in a rack in an un-airconditioned room. I've currently switched back to using the cisco fans to test if there is any difference. | Hamvi (Saturday, 14 March 2009)
Thank you so much to share the information. I still need some help about about opening the 3500 XL chassis. Any hint will be very appreciated. | Patrick (Wednesday, 25 March 2009)
You might try looking here http://www.excesssolutions.com I have 3 3524XL-PWR switches with bad fans (noisy). I opened it up and pulled one of the fans 40mm x 20mm 3 prong. I pulled the brand and model number off the fan and googled it, which led me to the site above. According to their website, they have the identical fan (brand / model #) for $4 each. I am about to order 15 replacements (5 per switch - 4 on one side 1 on the other) replacements.
| Glenn (Wednesday, 13 May 2009)
Was it any difference?
I'm considering removing all the 4 fans, and drill a hole in the top, to install a 80mm fan over the PSU, which gets hottest. I've seen people running this switch without fans(!).
The only drawback was that the PSU got extremely hot, that's why I consider putting a 80mm fan over, as I don't have the switch in the middle in a rack.
What do you think? | Rob (Saturday, 23 May 2009)
Mounting a fan over the top of the power is a great idea but it's going to be tough drilling/cutting vents in the case. I was thinking of taking the lid off the switch and mounting some fans in the rack above it... |
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