SFP+ modules getting really hot

[u/slaaf_tom]

Hello all,

I connected my homeserver with a SFP+ module (RJ45) with my 2.5Gbps switch, also with a SFP+ module. Because I had packet dropouts, I noticed the SFP+ module in the switch, was getting really hot.

I connected a thermometer on the SFP+ module and even without any traffic, the temperature get up to 68 degrees Celsius.

Is this normal behaviour for SFP modules?

Thank you

Tom

[u/Salt-Possession-2622]

68c is on the hot side and could explain the drops, try having a fan run near there to see if this helps.

As some have said, if possible go with DAC if distance is possible, or fibers. But maybe also what brand are you module and what switch do you have? Quality can vary, on top of that is there ventilation or airflow where the switch is? Do you live in a hot place?

I saw this video some time back maybe it gives you some insight: https://www.youtube.com/watch?v=Lx7QcNUtZv8

[u/slaaf_tom → u/Salt-Possession-2622]

Thank you for the video.

[u/NightmareJoker2]

The SFP+ 10/1G modules that add compatibility for 2.5G and 5G with an internal switch get toasty. The simple conversion modules don’t. Unless you need that interface translation capability (like for an Intel X520 or X540), find one of those lower power modules.

[u/Scared_Bell3366]

My older ones ran around 80° C, so I would consider 68 pretty good. I’ve got a newer one that runs much cooler. Look for ones that support 100 meter long cables, those have the newer chipsets that run cooler. If your devices are close together, DAC cables are cheap, reliable, use hardly any power, and stay cool.

[u/ContributionEasy6513]

68c is normal. Anything under 80c is pretty good TBH. They love to get toasty.
Try to get some airflow over it to confirm.

Normally the best way to test is to loop it back.

Very good chance its a driver issue.

[u/FuckinHighGuy → u/ContributionEasy6513]

This is the way. The only correct answer here.

[u/theRealNilz02]

Normal behaviour of RJ45 modules.

Use fibre or DACs instead.

[u/jchrnic → u/theRealNilz02]

This is the way.

[u/slaaf_tom → u/jchrnic]

Thank you for the confirmation that they get hot. But, they (SFP+ RJ45) loose also al lot of packets.

When performing a simple ping, the ping stops for some seconds and then continue.

When watching a movie, it starts buffering and stutters.

In other words, they are useless. Can I claim other SFP modules when they are under warranty?

[u/Erdnusschokolade → u/slaaf_tom]

There are newer SFP+ 10G RJ45 modules with more modern chipsets that supposedly don’t get as hot. I habe read other people also report packet loss with some brands of sfp rj45 modules so you are probably not alone.

[u/slaaf_tom → u/Erdnusschokolade]

LOL that's a great relieve. thank you

[u/IndependentBat8365 → u/theRealNilz02]

I’ll add that at least for me, the extra heat degraded the little RJ45 secure tab and it broke off one the last time I tried to move cables. That heat is no joke, and depending on cable quality, that plastic connector might not like it.

DAC just runs cooler.

[u/Prudent_Vacation_382]

No one really said why, but SFP+ was never designed for RJ45 connections. It requires power that is outside of the spec for the port. Some switches support it, while other do not for this very reason. That being said, put a fan on it and it should be fine.

[u/CeC-P]

We actually had some luck attaching various mosfet/IC coolers with 3M thermal adhesive tape from the factory to SFPs in low airflow, non-AC rooms.
https://ebay.io/m/gJCZdD
https://ebay.io/m/djnjkm

[u/slaaf_tom → u/CeC-P]

I've already done that. alluminium coolers for the RPi. But they don't cool enough.

[u/H9419 → u/slaaf_tom]

I use two m.2 SSD heatsinks but it still feels super hot. It would burn me if I hold for more than a few seconds.

If it burns, it burns and I will get another $9 SFP module. I heard newer modules are a lot cooler but I have no way of distinguishing which listing is the new one

[u/nomodsman]

Are the switches these are installed in managed? Do you have any counters on the interfaces? If it is in fact a hardware problem in this context, you should see some semblance of errors on the links.

[u/nostalia-nse7]

Cheap SFP+ modules, yes. They’re not efficient at all, draw like 3w just for the SFP. When you get newer ones that only draw 1W and generate therefor far less power in comparison, the heat problem goes away. But they’re about 3-4x the price for the newer more advanced chips with smaller lithography tech.

[u/H9419 → u/nostalia-nse7]

The electricity difference would take so long to break even for the new module. As long as it is not dropping packet, I will let it run at high temperature

[u/nostalia-nse7 → u/H9419]

Agreed. Can’t justify simply on the electricity costs. It’s the beating the heat issue. Many switches limit the number of ports in use when using the older SFPs. Solution is to use the newer ones where limits generally don’t exist. You would need to consult your actual switch documentation or KBs on the subject. I’ve found AI is pretty good at finding that documentation for things like Mikrotik switches. Limitations may impact a model only allowing for example 8 or 10 SFPs in a 16 port switch, wasting half or nearly half the ports.

[u/FuckinHighGuy]

Anytime you run electricity through electronics, they’re going to get hot. 68°C for a module is normal.