Catalyst 2950 fan question.

A couple of the 2950s I got from eBay have noisy fans. One in particular is extremely, annoyingly loud.

Since they're completely out in the open in a well ventilated area and not on for more than a few hours at a time, do you guys think it would be an issue if I just unhooked the fans? They cost freaking $30 on eBay and it's just not worth that to me.

Common sense and experience tells me that I'd be fine, but I figured I'd get some more opinions before doing it, as I certainly don't want to toast one of the $150 switches.

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Comments

msteinhilber

I have never had a 2950 open, but I just had a 3500 open the other day to see if I might be able to do something about the fan noise since I wanted to use it as my home switch and it was a bit loud for where it's located. I removed the cover from the 3500 and powered it up, even after 30 seconds or so of being powered, several of the components in the switch were very hot to the touch, not something you would want to keep your finger for too long. Maybe you could perform the same test with your 2950, if it's fairly hot to the touch I wouldn't advise running it without fans.

Regarding eBay fan's, most of the "Cisco" fan's that I see listed on there often look like a typical 40mm CPU fan that most certainly won't flow anywhere near what the OE fan in a switch would. You may want to check someplace such as Mouser Electronics (http://www.mouser.com/) for an inexpensive alternative.

ciscotech2007

Its funny you would mention this topic.

I have several cisco devices at work, home and heck...I even have a mobile WAP on my scion xB for wireless access where ever I go work. My mobile and home networks were causing the wife to get concerned because of the 'noise' from the fans, so my wife says. I rather enjoy the noise but there are times its distracting. Specifically when you place a switch in a NORMALLY quiet area such as an office area.

There are several items to keep in mind when it comes to changing cooling systems on ANYTHING. You must respect engineers do not put cooling systems on their products for the fun of it. Radiators on vehicles have them to cool-down coolant the engine heats up. Fans in cisco equipment provide airflow through the unit keeping system temperatures in acceptable limits.

First, if your going to investigate the possibility of 'quieting down' a cisco device. You need to open the device and identify how it's cooling is accomplished. Most cisco devices have at least (1) 40mm fan. There are units like my 2940's 8 port switches that are fanless though. Most full-size cisco rack-mounted devices have at least (1) 40mm fan. Most 2950s have (1) 40mm fan internally and my 3500's have (4) 40mm fans. The fans all connect in a similar fashion, a 3-pin connector, power, ground and RPM lead to the system board. YOU HAVE TO NOTE, WHILE THE FAN IS *SIMILAR* TO A 40mm PC FAN, THE PINOUT IS DIFFERENT. YOU MUST SWITCH THE PIN ORDER OR ELSE YOU WILL HAVE ISSUES AND COULD DAMAGE YOUR DEVICE OR FAN.

Moving on.

You need to identify the current fans on your device, most are very similar if not the same. Its important to note the power they require and the CFM=Cubic Feet per Minute. The power they require is important to make sure your replacement fan matches the same specs. The CFM is important because this is most directly proportional to how much airflow the fan can perform. Note that most cisco devices have fans that EXHAUST air out of the device. Meaning they PULL air from inside the device outside. Thus causing new cooler air to be pulled from the sides of the device into the unit, pickup the heat and then continue the exhaust flow outside the device.

Most cisco factory fans use 12v of power.

Most cisco factory fans have UP TO 37 CFM airflow.

My process was simple.

Use my decibel meter and laser infrared meter to measure factory dB level and temperature level. Those would establish acceptable baselines.

Note that packets per minute and overall device usage changes the operating temperature of te device. A device without connection to a network(a unconfigured device out of the box and plugged in) will generate LESS operating temperature than the same device processing 25% / 50% / 75% of it's total capacity.

My device is currently under 25% load which is fairly typical. Lets face it, cisco makes great products that can handle TONS of packets. The average cisco device, in a properly designed network, should be under 50% load at all times. While most can operate for years at 70-90% load....it's not recommended.

Factory dB level; 41-43dB

I researched and found this 40mm fan:

http://www.newegg.com/Product/Product.aspx?Item=N82E16835191002

Note its CFM and dB level.

I swapped in (2) of these on my 2950. It came with (1) 40mm fan and (1) space for another. Ran them in series to maintain 12v draw.

Total CFM, approximately 12-14CFM. Much lower than 37CFM factory. Using my temperature meter I would able to place the device under normal load(the same load my baselines were created off of) with case on then quickly pull case off and measure the system board chips operating temperature.

Factory Operating Temperature of System Main Processor: 108
Modified Operating Temperature of System Main Processor: 111

Factory Operating Temperature of Subsystem Processor: 107
Modified Operating Temperature of Subsystem Processor: 109

Factory Operating Temperature of System Power Supply: 106
Modified Operating Temperature of System Power Supply: 119

Factory Operating Temperature of System Exhaust: 92
Modified Operating Temperature of System Power Supply: 94

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Taking out the #2 fan causes system temperature to raise causing a system fan failure error console message, syslog message and SNMP message. Issue a 'sho env' and you will see output as well. I also confirmed higher temperatures as well. I was curious if I could go with only (1) fan but no. Because these fans are quieter....they also do not move as much air(i.e. 6 CFM). Does this mean on a 3500 with (4) fans needs to have (2X) the amount of fans....I do not know yet. The system process is 0xcalbbel. That's my next testing.

Would cisco engineers like this solution, probably not. Why? Because the factory fans were selected because although loud....they cool the system to acceptable levels.

Good luck and try not to set your house or work on fire!

info@thecisconetwork.com

/usr

Well, the problem I am having is not the "normal" noise. I can stand that. The fan blade is scraping the casing, or something is vibrating, I'm not sure.

The first 2950 I had did this so I pulled the cover and tried to take a closer look, but didn't find anything noticeable. After getting two more 2950's and placing them on top of the first one, that noise stopped.

However, one of my new 2950's is extremely loud and I haven't had a chance to pop the case yet, but I'm 99% certain it is the fan.

Eh, I'll just buy a new kit.

I'd rather do that than bother going through all the trouble you did.

tiersten

Uh. All the messing about with the temperature sensor and decibel meter is a bit overboard. I just looked up the fan specs from the model number printed on the label. Go to mouser.com like msteinhilber suggested and find one with similar specs.

dtlokee

Why not just water cool the thing? Seems like it would have been less work.

tiersten

dtlokee wrote:

Why not just water cool the thing? Seems like it would have been less work.

We apologise for the network downtime earlier. The network pipes leaked.

A silent server room would be eerie.