Hello forum,

I bought a second hand  SMX2200RMHV2U where the fan noise is constant when it's on. According to this FAQ, the SMX should use variable speed fan.

I opened up my unit and found the following fans:

-  Sunon EE80252B1-0000-A99 41CFM
-  Y.S.TECH NYW08025024BSS  59.2 CFM

I have a feeling the fans are replacemen fans, as they only have GND and +24DC cable going to a 3 pin connector. The control board has 3 pins, I haven't yet measured what the third pin is for, but I would think it's a tach input signal?

Does anyone know what the original fans are for this unit? Schneider support doesn't want to comment on it.

Or if anyone knows if the third pin is for Tach, then I will obtain fans that match the CFM but also provides tach.

Thanks in advance

Hi NB-23, 

Thanks for taking the time and helping me!

I've gone for this fan: https://uk.rs-online.com/web/p/axial-fans/2025435, 60CFM, and it seems to be a tiny bit more quiet.

However, my confusion is why the fans are running at full speed, continuously even when there is less than 70W load and batteries are fully charged. They never change speed, from my understanding, the SMX units should adjust speed depending on demand, but this doesn't seem to be the case.

Have you come across SMX units that use the third fan pin on the controller board? This must be tach signal right?

Thank you!

That's so strange, I wonder what's causing my unit to have the fans blow at full speed.. I wonder if bad batteries can cause this?

I haven't seen any configuration which would change this behaviour either

Hi zdave

I did not, I believe it's due to a fault that this situation occur. Internal temperature wasn't high for the fans to trigger, nor was the load levels or charging. So most likely something to do with the sensor or inverter? 

I ended up buying a core UPS without bezel, battery etc from ups trader which tested the unit to ensure fans were not running at full speed. This unit has been working fine for me since I bought it. 

I did the same for my POE+ rackmounted switch, swapped out the fans to Noctua, triggered the low fan speed alert but temperature has been stable even under heavy load. Which is why I also thought this would be a good idea for the UPS before I decided it's actually just more practical to change the core unit as they aren't that expensive and saves me hassle in the future.

There was a Sunon EE80252B1-0000-A99 and Y.S.TECH NYW08025024BSS in my unit from my notes. I believe the YS TECH was mounted infront of the inverter board. The Sunon has 41CFM while YS TECH is at 59.2CFM (might be wrong, just checking my notes from when I tinkered with this last). The YS TECH spins at 4500 RPM and produces 41 dB. 

Looking at for instance Noctua NF-A8 PWM, it has 32.67 CFM which is essentially half of what the YS TECH is, which is a significant decrease.  Also, the fans in my unit are 24VDC, which I doubt Noctua would produce (as they are targeted PC market which runs 12V rails)

In my unit, I could fit a bit thicker 80mm fans, and the one I was eyeing up was Sunon ME80252V1, 41CFM at 33 dB.  Still a reduced airflow but for my usecase it would work.

However, to manually manage expected load and permanently reducing air flow throughput is a bit of a gamble, specially when dealing with batteries of this nature. A user would have to consider the temperature, load and test charging from empty every time they make a significant change to what devices are plugged in to the UPS. I don't think this is reasonable but someone might consider this as a acceptable operational cost if their infrastructure doesn't change much. 

Though, the problem here is more there is something triggering the units to place the fans on full speed rather than variable rate based on need, I never managed to get an answer to this and my old unit won't be helpful as I managed to brick it as well. 

Is this 59 degrees celcius? That's quite warm and it should be expected that the fans run att full speed. I would expect fan's to rnu at full speed at 40 degrees celcius. 

What is the room temperature the unit is in?