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VAXman65
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How hot is too hot for CRS326-24G-2S+ ?

Mon Aug 15, 2022 9:24 pm

I have been running my CRS326-24G-2S+ for a couple years now, but I have never been especially happy with the temperature. It currently shows a CPU temperature of about 84C in a room that is not especially warm. I do have both the SFP+ ports occupied with 10Gb copper connections.

Should I be concerned about the temperature I am seeing? There are no fans in the unit, but there is the grill cutout that would, in theory, allow me to mount one. If I went down this route, is there a good power source internal to the CRS that I could reliably use for power?
 
tangent
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Re: How hot is too hot for CRS326-24G-2S+ ?

Mon Aug 15, 2022 10:35 pm

CPU temperature of about 84C in a room that is not especially warm

Temperature is relative, so saying "60°C over ambient" is more concise and more useful. If the room temp rises 1°C, so will the CPU, assuming the before and after conditions are both at equilibrium.

I don't have the same model as you, but I do have its PoE cousin, the CRS328-24P, and mine is running at 29°C over ambient with all four SFP+ ports filled and two PoE loads of around 5W each. Two of the SFP modules are unused but present, and two are actively in-use 10G modules. Here's the raw data:

Screen-Shot-2022-08-15-at-13.17.jpg

Should I be concerned about the temperature I am seeing?

80-90°C (absolute) is a pretty good threshold for getting worried. Electronics can run hotter, but it'll materially hurt the lifetime.

I like to see 60°C or less, if I can get it.

There are no fans in the unit

The CRS328 comes with two, but has spots for four, so the first thing I did on getting it was to put a full set of Noctuas in, all pointing the same direction so air comes in on one side and goes out the other.

The problem with leaving fan mounts unpopulated is that you can get eddies: air gets pulled in and is sent right back out an inch to the side, having failed to cross the heat loads. The empty spots should have blocking plates in them to prevent this.

That, or do as I did and put four fans in so there's no shortcut for the airflow.

is there a good power source internal to the CRS that I could reliably use for power?

I can't be certain of your model, but mine had headers for four fans, so MikroTik has at least one EE on staff who's thinking ahead.

It's not hard to check, and while lifting the lid technically invalidates your warranty, until you actually touch the PCB to plug in a fan, I wouldn't consider that a true violation.

After doing this mod, the warranty is, "If it breaks, you get to keep both pieces."
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Re: How hot is too hot for CRS326-24G-2S+ ?

Mon Aug 15, 2022 10:39 pm

 
VAXman65
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Re: How hot is too hot for CRS326-24G-2S+ ?

Wed Aug 24, 2022 12:04 am

@chechito Thank you for the thread references. I ended up settling on getting a 5V Noctua fan (NF-A4x20 5V)and an adapter cable that goes from a USB connections to a case fan receptacle. My idea is that I'll attach it to the exterior of the CRS and power it externally via USB. It turns out I have another device right there that provides a convenient USB port for the fan. I was impatient to see how noisy it was going to be and how effective it could be, so I just connected the cables together and use one piece of scotch tape to attach it to the switch for now. I did nothing to plug any of the nearby vents to prevent the air from just hairpining and limiting the cooling effectiveness. I'll do a proper install a little later, but consider this to be the worst case scenario.

It took only five minutes to drop the CPU temperature from 82C to 62C and continues to drop. As I write this, the temp is now flirting with 59C and still falling. SFP temperatures are also dropping.

Later tonight, I'll use the rubber anti-vibration mounts to attach the fan properly. I'll also see about taping over some of the vent holes closest to the fan to encourage airflow. I'll then see if any of these extra steps actually buy you anything.

For me, adding in a good quality 5V fan powered by USB is very simple, takes no risk with the CRS, requires no special skills and is quite effective.

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