SR2148P Fans running at full speed

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We have a couple of closets of SR2148P switches that run there fans at full speed nonstop. The switches are located in an enclosed hoffman box with a fan kit installed. Wondering if anyone else is experiencing this issue.
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Jeff Turley

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Posted 4 years ago

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Mike Kouri, Official Rep

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Hi Jeff,
I vaguely recall the name Hoffman, didn't they sell tons of printer enclosures to schools back in the days when greenbar paper was king and dot matrix printers were loud?

If the Hoffman enclosure you are using is at all like what I recall, the several inches of sound deadening materials they use will turn it into an oven. I would expect any networking equipment installed in one of those to end up with their fans running full speed and/or going into thermal shutdown after a while.
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Jeff Turley

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Not sure what type of enclosure you are talking about but these are just standard enclosed network boxes that would be hung on the wall in an office. I have used them in various locations for years with and without the fan kits and I have never seen a switch installed in one behave like this. The fans are rated to move 100 CFM and the air leaving the vents at the top of the enclosure is not hot.
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Jeff Turley

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Here is a picture:
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Jeff Turley

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The air leaving the vent at the top of the box is reading 34 degrees Celsius which is within the operating range of the switch. 
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Mike Kouri, Official Rep

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Jeff,
Those are nice looking enclosures. Your switches are operating fine, right? Just noisier than you expect? And air at 34C leaving thru the top of the enclosure was when the door was closed, not open like in the photo, right?

The airflow thru the switches is from left to right, not front to rear, and it looks like that's the most constrained dimension inside your little mini-rack. I am pretty sure the air temperature measured inside the switch skin is higher than that leaving the enclosure. 34C leaving the enclosure would be, at a guess, over 40C inside the SR, which is warm enough to drive the fans to their top speed.

Did your fans slow down after a few minutes when you opened the door?
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Jeff Turley

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The fans do not slow down with the door open. I will concede that the enclosure is not thermally optimal. However switches located within the access layer of a network are often put in locations that are not thermally optimal. Under desks, in classrooms and library spaces that do not have great climate control and in enclosures such as the one we are using. Unfortunately for us and I am sure other customers that would like to use your switches these locations also happen to be spaces where workers work and students learn.  If the SR2148P is designed is such a way that it runs its fans at full speed when it is placed in these types of environments that is a serious problem for us and I would think most of your other customers.
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Nick Lowe, Official Rep

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The thing to bear in mind is that, for a particular generation of semiconductor fabrication, the better featured silicon will get hotter and will need more aggressive cooling.

That heat has to be dissipated for the device to function correctly and for longer term reliability reasons. If the cooling is not sufficient when the fans are at a lower speed, they have no choice but to speed up to increase the airflow.

Yes, there are various design decisions that influence dissipation efficiency, often with a cost implication, but If your enclosures aren't suitable, perhaps you should consider changing them for something more appropriate?
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Jeff Turley

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You are correct that design decisions influence heat dissipation. However when you have a switch mounted in a 2 post rack in a room with an ambient air temperature of 75F you should not have to do this to keep the fans from running at full speed. 
(Edited)