UPS Fan swap problem

[viktorfilim]

Hi,

I own a UPS that is very loud. So I thought I would change the fans to make it quieter.

Instead of the 2 stock fans I've installed 2 Noctua NF-A8 FLX fans.

The problem is that after a while the UPS starts to complain and starts beeping. I can't mute this alarm.

Most likely the problem is from the new fans.

Is there something I can do to trick the UPS into thinking that nothing has changed?

 

P.S. This is related to a earlier post of mine. https://linustechtips.com/topic/1282319-ups-fan-swap/

 

[mariushm]

The Noctua fans consume much less power, only 0.84 watts says the website.  That's 0.84 / 12 = 0.07 A

The stock fans say up to 0.5A ... that's almost 7 times more power consumption.

 

The UPS probably monitors the current consumption of the fans and if it's below some threshold, it triggers the warning.

IF this is the case, you have options ... either add something that consumes power (for example a led or a resistor, but a resistor would make only heat) or you could try to tweak the current sensing to trick the ups into thinking more power in consumed.

Tricking the sensor would involve replacing some resistors inside the ups.

 

You didn't post schematics of the UPS, you didn't post pictures of the circuit board, you didn't even say how many wires the fans have (i guessed 2 from pictures but who knows).  If there's a rpm wire, could be the ups complains about rpm speed being too low.

 

Also, the UPS has that high power fan for a reason, to blow a lot of air through the internals while the batteries are charged (after they discharged during a power failure)

A lot of UPSes have the charging circuitry undersized and designed to only work for short periods of times (8-12h then not work for days) and have small heatsinks that rely on the heavy air flow to keep the components within acceptable limits.

 

You changed the fan from one that probably pushes 2-3x the amount of air (at 3-6000 rpm) compared to the noctua that peaks at 2000 rpm - don't be surprised if your batteries go bad within a year due to overheating, if you have power failures often..

[viktorfilim]

7 minutes ago, mariushm said:

The Noctua fans consume much less power, only 0.84 watts says the website.  That's 0.84 / 12 = 0.07 A

The stock fans say up to 0.5A ... that's almost 7 times more power consumption.

 

The UPS probably monitors the current consumption of the fans and if it's below some threshold, it triggers the warning.

IF this is the case, you have options ... either add something that consumes power (for example a led or a resistor, but a resistor would make only heat) or you could try to tweak the current sensing to trick the ups into thinking more power in consumed.

Tricking the sensor would involve replacing some resistors inside the ups.

 

You didn't post schematics of the UPS, you didn't post pictures of the circuit board, you didn't even say how many wires the fans have (i guessed 2 from pictures but who knows).  If there's a rpm wire, could be the ups complains about rpm speed being too low.

 

Also, the UPS has that high power fan for a reason, to blow a lot of air through the internals while the batteries are charged (after they discharged during a power failure)

A lot of UPSes have the charging circuitry undersized and designed to only work for short periods of times (8-12h then not work for days) and have small heatsinks that rely on the heavy air flow to keep the components within acceptable limits.

 

You changed the fan from one that probably pushes 2-3x the amount of air (at 3-6000 rpm) compared to the noctua that peaks at 2000 rpm - don't be surprised if your batteries go bad within a year due to overheating, if you have power failures often..

I don't have any schematics.

I've attached a photo and a video of the insides. They are not very good as I took them as a reference for me when I changed the fans so I know how to assembly back all the pieces.

The original fans have 2 pins connectors. The Noctua have 3 pin and I used an adaptor supplied by Noctua so that I can connect them the the UPS.

I'm not worried about the battery life as this UPS will be used for a 3-4 hours a week. The rest of the time it won't be powered.