My network equipment is running hot during these days so I brought an usb to 4 pin adapter to connect a 8cm fan. It is safe to permanently connect a 12v external fan to usb connector of CRS310-8G+2S+IN?
From the specs, the port can provide up to 1 A so 5V x 1A= 5W max.
So, it depends on the power of the fan, powering a 12V fan at 5V will make it run slowly, but maybe it is enough, a typical 80 mm fan is likely to be in the 2-3 W range, so it should work.
As best practice it's generally not recommended to attach something with rotor to backbone's USB for 7x24 due to potential back EMF.
Instead you can simply patch the fan to e.g. an IKEA SJOSS with a 12V PWM controller - worst case damage would be just €10, not CRS310 at €150.
Well, a low power fan shouldn't pose any risk, see also:
https://electronics.stackexchange.com/questions/361624/am-i-unwise-to-power-a-low-draw-cooling-fan-off-my-routers-usb-port
Of course it can be over-engineered adding a diode, capacitor and resistance, but comeon, it is a small fan, I would be more worried by the thingy been able to actually turn with only 5 V, so all in all a tiny boost converter would be a good idea as it can also be used as speed regulator, there are many - really cheap - that can give 8/9/12V, example:
https://it.aliexpress.com/item/1005003203922131.html
or if you want a potentiometer to fine tune the voltage:
https://it.aliexpress.com/item/1005009554740101.html
- What kind of adapter is that? Is it just a couple of wires between USB plug and 4-pin connector or something with step-up converter that makes 12 V?
- What are the specs of the FAN (current or power)?
It's something like this connected to a 8cm 12V 0.40A fan.
Reading the comments I think I'll buy an external power adapter to stay safe.
One presumes these USB fan controller cables contain back-EMF protection as a necessary element of meeting the mission…and then one recalls, “Oh, right; China.” And then one resolves to rely on brands worthy of their reputation.
I feel no need to tear down my GeeekPi fan controller to ascertain that it isn’t going to nuke my Pi5 USB port, for instance. (Accessory to the 10-inch racks shown.)
Understood, this is a step-up converter. The FAN is ~4.8W, USB power is ~5W (but it can give more). So, I don't see any problems at all.
@tangent
The fan itself usually has back EMF protection anyway, but an "active" cable with the step up converter will act as a filter for them.
You can also find 5V FAN
if you are comfortable with a soldering station i would suggest opening the case and mounting inside a LM2596 DC-DC step-down module connected to the 24V input pins, then also add a fan on the inside, connected to the output of the LM2596 module.
Make sure to anchor the LM2596 module inside and that it does not touch / short anything in there.
That's what we did to our CRS326-24G-2S+ switches and it works beautifully.
Make sure to set the LM2596 output voltage below 12V - we set ours to around 10.5-11V for these 4cm fans: https://www.arctic.de/en/S4028-6K/ACFAN00273A
edit: oh..wait.. i see that CRS310-8G+2S+IN already comes with a built-in fan. (our CRS326 switches came without fans installed.) Maybe just swap the default fan with a higher flow one?