12v fan on 5v supply?

Just received my pair of Noctua NF-A4x20 FLX fans I intended on replacing the stock ones to reduce the noise of the refurbished switch I've just bought, which I waited until I received it to check the fan size and voltage before ordering these.


Just connected the Noctua in them, fired it up to check which way the fan blew, and it didn't turn at all, plugged the original back in and that works fine.  Maybe the pin config is different, so I checked the volatge polarity only to find 5V's on the pins?  How can this be?12v fan12v fan 

Model: M4100-50G-POE+ (GSM7248P)|ProSafe 50 ports gigabits fully managed L2 switch with PoE+
Message 1 of 7

Re: 12v fan on 5v supply?

Hey did you ever get anywhere with this? I have the same switch and did the same thing - opened it up, saw the 12v fans and ordered the 12v noctuas which spin up for a second or 2 then stop.

Checked the voltage and it's putting out around 6v.

Opened up a GSM7248 and it had one of the exact same stock fans but that switch was putting out 12v from the pins. If I try that one in the M4100 it runs no problem.

If I try the noctuas in the GSM7248 they run and stay running and no fan fault light.

Should I just try the 5v versions of the noctuas instead?
Message 2 of 7

Re: 12v fan on 5v supply?



wouldn't recommend the 5v Noctua either.  I think where your getting the 6v is that the switch is just sending a lower voltage to have the fans run at a minimumal speed.


I even went to the expense of getting another set of 12v fans, think they were noiseblockers, and they didn't work! I got so frustrated, not only having to disconnect, take the switch out of the rack, take apart, that I sensed the wiring colours differentiate from all the others from the stock fan that Netgear phase reverse somewhere, anyway, cut a long story short after many variations I think I blew the 12v power rail.


so bought another switch off eBay, probably easier and cheaper than sending this for repair.  Noticed an American eBay seller selling fans for the Netgear switch.  He wasn't very forthcoming as to what voltages were where and what fans he's using and his prices are expensive and cost of shipping and import fees, I headed over to Aliexpress and have bought a selection of 3 or 4 fans that maybe suitable and should cost the same if not less than our US eBay guy.  When they come in from China, I'll let you know, may have spare fans available!

Message 3 of 7

Re: 12v fan on 5v supply?

Let me know how you get on. The noctuas spun up in the GSM7248 when the positive and negative were reversed. I've ordered some 5v noctuas to try the same thing with reversing the pins.

Have seen the US seller on ebay as well but the cost plus shipping seems extortionate and no mention of what the noise output may be with those fans fitted.

I have so much Netgear kit I'd prefer not to have swap out equipment for other manufacturers and spend even more money, but the way they use fans in each device seems pretty strange.

I've made the same mods with other dell, hp and cisco switches and not had any problems like this.

Would be very interested to hear what results you get with the new fans.
Message 4 of 7

Re: 12v fan on 5v supply?

Ordered the fans after i bought the latest switch on eBay, fans were shipped on 9th Jan via Aliexpress shipping, so in theory should be here at the end of the month.  I'm now living in Dublin, so opted for the eBay "International shipping", even though its shipping from the U.K., I reckon the parts from China will be here before that gets here.


The Netgear switch replaces a Ubiquiti PoE switch which went bad not even after two years, never going to buy Ubiquiti again (had a Unifi G3 filter stick as well!).


id be interested in what you consider the pin (voltage) configuration, am so confused with Netgear and Noctua differing configurations?

Message 5 of 7

Re: 12v fan on 5v supply?

Can't see anything strange - except of that people try to put in replacement fans able to create a light airflow (40% less than the 5000 min^-1 Delta fan variant, max rotation speed 5000 vs. 13000 making less than 25% of the max airflow, and some 85 of the max air pressure). How easy it is to build a "silent" fan at these limitations (lower fan tip speed - this is whee most aerodynamic noise is coming from). In my opinion a fan not fit for replacing in any of these switches, even if it rotates, and the Fan error LED does not go on.


If an amateur aircraft builder would ask me if this engine and propeller combination ("hey I found a sooo silent solution and my Piper L-4 with it's Conti A-65 flies great") would fit his next project designed for a much bigger engine and better prop, he will hear that the takeoff run over 50 ft obstacle will be much longer, the max rate of climb will be nuts, and last but not least the cruise speed will be poor. Overall, doing so would be a major safety risk, and I'm most likely unable to sign-off his project powerplant. 


The FFB0412SHN nominal 12 V models have a rated operating voltage range from 4.5 to 13.8 V as per the specs - so 5 or 6 V voltage is OK. As @DigitalVT mentioned, this lower "cold switch" fan voltage is certainly implemented this way to allow lower minimum rotation speed - and it will come up to higher voltage if required. Depending on the Noctua fan motor design, it's well possible that the fan does rotate easier in the non-intended rotation direction. For example small classic DC brush engines (think of what Mabuchi builds in zig millions of and millions of one model every year) are timed to rotate in one direction for ideal power output including the torque. To let them rotate backwards, a much lower voltage is sufficient, but power out and efficiency will be ways below. And yes, several Mabuchi can be ordered from the factory for alternate rotation direction, and many can be re-timed by bringing the brushes for it. Enough said on this excursion here. 


Note: There is absolutely nothing wrong with the Noctua fan design and specifically the NF-A4x20 (FLX just designates the add-on electronics for interfering even more) - if is deployed where the massive lower cooling capacity of the airflow is acceptable - they just can't replace any FFB0412 variant.

Message 6 of 7

Re: 12v fan on 5v supply?

Am sure the stock Netgear fan is great for switches in an enterprise scenario where the switch is under full load, speaking for myself, just want a switch with enough ports that can accomodate various connectivity around the home without additional switches elsewhere or having to manually repatch, thus the device itself wouldnt be under much load, therefore a slight breeze from these quieter fans may be enough to keep the Netgears internals cool enough to be accpetably quiet in a home environment?


I've got 8x PoE cameras, 3x PoE AP's, a PoE Cloudkey and multiple wired ethernet devices.  My thoughts that a Noctua or other "quiet fan" running at 100% capacity keeping the internals cool when the switch is not busy and then may take longer to cool for the "short" busy times, is an acceptable useage, giving a quieter environment?

Message 7 of 7
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