Replace noisy 80 mm fan in Socomec UPS

[toriam78]

Hello everyone,

At home I have a 42U rack which stores my network components and at the bottom of it I have a Socomec Netsys U1700 UPS (https://www.socomec.com/files/live/sites/systemsite/files/UPS/PDF_catalogue/pdf_web_GB/2016/cat_netysrt_EN.pdf)

 

My challenge is that my computer room is in the middle of the house and the UPS fan is audible into my living room which is on the same floor. There is one fan from delta (http://www.delta.com.tw/product/cp/dcfans/download/pdf/FFB/FFB80x80x25.4mm.pdf) ( FFB0812SH ) at the back of it and is quite noisy but in turn pushes a lot of air.

 

I am debating with myself to replace this fan with one from Noctura (https://noctua.at/en/products/fan/nf-a8-flx/specification) although it has half the CFM of the Delta one.

 

Power distribution here in Norway is excellent and I don’t experience outages that last long and I use the UPS to prevent systems going down in short "blinks" in power.

 

I haven’t found much information on line about this but one comment has been that a too low CFM fan in an UPS causes the UPS to overheat and shut down in cases where it is discharging power via the batteries.

 

Should I be worried about UPS overheating with the chosen fan? Has anyone any experience with replacing their UPS fan(s) with quieter fans and how the UPS is after?

[Tabs]

@toriam78

 

I wouldn't recommend just replacing the delta fan, but there are options I can think of.

 

Rather than replacing the fan, would it be possible to add some kind of control for it? For example, adding an inline variable resistor. That way, you can keep the fan at low RPM most of the time when it isn't needed, and if you have a power outage, you can manually increase the fan speed to ensure the ups doesn't overheat.

 

If the UPS came with a delta fan, it's likely it gets super hot under load - probably not the batteries specifically, but the actual discharge circuitry. I know from experience that even at really low loads, half an amp at line voltages (~110w/220v) can push those kinds of circuits way above 125C, which is bad news for longevity.

 

Alternatively, assuming the UPS is already out of warranty, you could replace the fan, and add more fans inside the chassis to ensure airflow through the device in the event of a power failure and a full-load discharge scenario.

 

 

[toriam78]

@Tabs

Thank you for your answer.

The challenges with adding a resistor is that iit effectivly reducing the speed and thus resulting in less CFM. This would do the same as replacing it with a lower CFM fan. I am out of my depth on this subject. I've found this papst fan (https://www.digikey.com/product-detail/en/ebm-papst-inc/8412NGH/381-2338-ND/441670) which has 46,5 CFM (37 dB) compared to 67 CFM (48,6 dB) on the Delta fan in the UPS today.

 

As you say the cicuitry will get super hot when the line power drops and the batteries take over. I am no thermal engineer but how far down in CFM would be adviseably to reduce to (with tradeoff in less fan noise) before compromising batteries and circuitry?

 

The UPS is out of warranty and I've opened it up. There is not space for mutiple fans and no extra 12V fan points onthe PCB so either I live with the fan noise or figure out somehow how much minimum CFM performance the fan needs to be and replace it.

 

Your comments are appreciated.

[Tabs]

3 hours ago, toriam78 said:

@Tabs

Thank you for your answer.

The challenges with adding a resistor is that iit effectivly reducing the speed and thus resulting in less CFM. This would do the same as replacing it with a lower CFM fan. I am out of my depth on this subject. I've found this papst fan (https://www.digikey.com/product-detail/en/ebm-papst-inc/8412NGH/381-2338-ND/441670) which has 46,5 CFM (37 dB) compared to 67 CFM (48,6 dB) on the Delta fan in the UPS today.

 

As you say the cicuitry will get super hot when the line power drops and the batteries take over. I am no thermal engineer but how far down in CFM would be adviseably to reduce to (with tradeoff in less fan noise) before compromising batteries and circuitry?

 

The UPS is out of warranty and I've opened it up. There is not space for mutiple fans and no extra 12V fan points onthe PCB so either I live with the fan noise or figure out somehow how much minimum CFM performance the fan needs to be and replace it.

 

Your comments are appreciated.

Just to clarify - I suggested using a variable resistor, not a permanent, static resistor. It's sometimes called a potentiometer, a potential divider, or a rheostat. In such a way, you could have it set to a high resistance value for 24/7 operation, which will slow the fan, reduce the noise (and yes, the airflow) and in the event of a critical power failure (where the higher potential airflow capacity of the fan is needed), you can manually adjust the resistor down to return the fan to standard operating conditions.

 

I fully expect the fan can be run at 50% or less of it's current capacity for standard usage without any deleterious effects to your hardware. To confirm, you can use thermistors to check the temperatures of the battery packs and the charging circuitry now, and compare it to after you make the modification. It should be easily reversible for an inline unit.

 

The advantage of this setup is that you do not need to try to hot swap fans or risk damage to your UPS if a power failure actually occurs. If you replace the fan with a lower capacity one and it ends up not being enough - bearing in mind I have no way to know what kind of environment your UPS resides in, how much extra heat is generated from managing older batteries, what your load cycles are, how much airflow actually flows through the unit due to natural buildup of dust - then your hardware could be irreversibly damaged. As such, I can't justify recommending replacing the fan with a lower CFM one permanently, since although it would solve the immediate issue of noise, it may end up costing a lot.

 

The main issue that I'm concerned about is that as UPS units age, they tend to require more cooling during full discharge situations. As the batteries age, their ability to maintain a voltage for extended period is reduced. In consumer applications the main problem with that is reduced batter life, but in the case of a UPS, battery life is usually measured in minutes for full load scenarios. In that case, the issue becomes current draw from the cells. The unit will still try to supply it's rated current at day 1 as it will at day 3000 - but at day 3000 the batteries will need to be pushed far harder to maintain it. I fear the delta fan is there to ensure the machine lasted its full lifetime, and reducing it could be catastrophic in the event of a full power loss event.

[toriam78]

@Tabs

I appreciate your input and thank you kindly for spending the time for the extended reply.

 

I can give you some input of what the UPS is pulling:

Ubiquty 48 port 500w poe switch ubiquiti

Ubiquty Security gateway pro

Fiber modem (low power draw)

Apple tv kind of device (low power draw)

(future qnap rackmounted NAS)

 

As you can see the UPS I have is complete overkill when it comes to the maximum effect the UPS can provide.

 

The batteries are brand new but the UPS itself is perhaps 5 years old.

 

The room the rack is in is about 27 degrees as in Norway we have hot days right now with 31 degrees every day.

 

As for having a manual mechanism is not practical for me as I would have to be in the house to change the voltage from f.ex 9V to 12V. If I had the knowledge to make a rasberry PI with sensors to trigger once the temperature rises that might be an option but that is above my abilities.

 

I have pondered the challenge myself and I've come up with perhaps removing the 80mm fan in the UPS, block of that hole and instead cut a holde for a 14 mm fan (https://noctua.at/en/products/fan/nf-a14-flx) on top of the UPS close to where the 80 mm fan is mounted.

 

PIcture:

 

the 12V connector is on the PCB is right undert the plastic bracket to the left of the fan. As the fan now is pulling out air and the air is pulled in from the front I do wonder that even if the fan is mounted above the 3 copper coils that if can effectivly pull out enough air or if I would need 2 x 14cm fans to either pull out from the top or blow down on the coils and capacitors/heatsinks.. I have no idea if the 12V connectors on the PCB can pull two fans without buying them and testing it using a splitter.

 

Just so you have an idea, I would mount the fan(s) on top of the UPS as there is not enough space inside to mount any fans.

 

Another scenario would be that I make a 80 mm to 140mm funnel and bolt on in the back and drill a hole to get the power cable in.

 

What do you think of the above musings?

[Tabs]

@toriam78

 

Those are actually both really good ideas, but I think fitting fans to the top would be the better of the two - unless you decide to do both. The main part you want to worry about is the mosfets (power transistors) that are attached to the large metal heatsinks, so as long as any fan you put in has adequate airflow over the heatsinks, you'll be in good stead. The chokes (inductors), the coils at the back, they won't get warm at all (which is why they are fine placed where they are, in the flow of warm air from the heatsinks covering the mosfets), so you don't need to worry so much about those.

 

The fan you're using right now is 12 volts, at 6 watts - so that means it draws about half an amp of current. If you attach other fans to the same power connector, so long as the total combined power draw from the new fans isn't much above half an amp, you wont experience any issues. A single 140mm fan won't get anywhere close to 6 watts/half an amp at 12 volts, so if you have space in your rack to fit two 140mm fans above the mosfet and inductor area, that's a really good idea. As you suggested, if you leave the rear vent open and the fans are pulling air out of the case, the likelihood is the fan at the back will just pull cool air through the vent at the back and out the top without it cooling the mosfets. However, if you leave the vent open, and have two+ fans blowing air in it should push enough cool air through (and vent out both the front and back), or even block the back and ensure it all vents out the front. What's best depends on whether your ups location will have any issues venting out the front - if not, i think having two intakes at the top exhausting out the front will give you the best performance.

 

I didn't realise your UPS has brand new batteries, so that limits my concern somewhat about you changing your fan to one with lower cfm. I think if you're willing, the external fan idea sounds great and will be far, far quieter than the delta fan.

 

Oh, and, for what it's worth - the 140mm Noctua fan you linked draws 0.08A (0.96W@12v) - so you could theoretically attach 6 (!) to the power header and it would still be less than the single delta fan in terms of power draw.