Why I didn’t choose a Noctua replacement fan

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We’ve all been there, we’ve picked out a new router, switch, or other device for our home lab and the fans are LOUD. First thing we do is to replace those fans with something a little more quiet. We hit up our favorite online store, maybe read some reviews, and choose a fan that fits. Sometimes that fan is an expensive Noctua fan because its promise of being quiet is so alluring. After the fan is replaced it is a bit more quiet but now the fan error lights are on or it malfunctions. Clearly it’s the wrong fan for our device.

In this blog I’ll go over some of the items you should look for when buying a replacement fan for your devices that can help you find a better fit and not break your wallet. Fair warning, the stock fans in these engineered devices were designed to be optimal for said device. Altering them in any way can be harmful to the device plus working on electronics without proper training is never advised.

First, identify the stock fan in your device and find its datasheet. You may need to remove the fan from your device. I recently replaced some fans in my Mellanox IS5022 InfiniBand Switch. The stock fan was made by Delta, the make #EPB0142VHD Subtype -R00, it has 3 wires, 12 Volt DC Brushless, and draws .18 AMPS. I underlined Subtype as it is very important when identifying your stock fan. In this case if I just search for the make I’ll get the wrong fan information. In fact EPB0142VHD with no subtype only has 2 wires.

Second, I review the stock fan specification datasheet. I already know the Voltage and Amp rating but here are the things I also need:

  • Fan Size – 40mm x 40mm x 20mm
  • Hole Mount Size – 32 mm between mount points
  • Hole diameter – 3.5 mm diameter.
  • Length of Wires – 330 mm
  • Identify the 3 wires and their purpose – 12v, Ground, and Lock Rotor
  • Db Noise rating – 32-36 Dba
  • RPM – 9000 RPM
  • CFM – 10

Not sure if you caught it but identifying the 3 wires on the stock fan is critical if you want to resolve these error lights. Most 3 wires fans are going to have 12v DC and Ground. It’s that 3rd wire that makes them unique and its one of the more important items you must find out to select the correct replacement fan.

The 3 most common types of 3 wire fans are:

  • Step RPM Speed – think of this like gears on a bike. The fan speed steps from one RPM to another. Most have between 3-5 steps in RPM.
  • PWM – Pulse Width Modulation, allows for granular speed control. Instead of instantly stepping to the next speed it is gradually sped up and down.
  • Locked Rotor (sometimes called alert) – This is a fan spin error detection. Normally, the fan will spin at one speed. 40 mm Locked Rotor fans seem to be the most common for routers, switches, and other similar devices.

Another item is the length of the wires. The datasheet shows 330 mm (+-10mm), however the fan you order could be shorter. It’s best just to measure the stock fan, and make sure the replacement fan you ordered has enough length or room to stash the wires if they are too long.

Third, now that I understand my stock fan I’m ready to choose a replacement fan that meets with my goal of reducing fan noise. In most cases, fan noise is reduced by slowing the RPM. Additionally, there are fans specifically designed to reduce noise but they can be expensive. I thoroughly looked at 40mm Noctua fans but none of them matched the voltage and Locked Rotor requirements. However, I still see a lot of folks buying Noctua 40mm fans and then complaining about the fan error lights or issues with it malfunctioning. Most just ignore these errors or alter the fan wires to send a false message to the device. Both I don’t recommend.

In this case I choose the Sunon MagLev KDE1204PKV3 MS.AR.GN 40x40x20mm 3pin Low-Speed 5200RPM 6.3CFM (Locked Rotor Alarm Signal). Cost is about $6.50 US, compared to a non-compliant Noctura $14 US

How do the stock and replacement fans compare:

Item (recommendation)Delta EPB0142VHD-R00Sunon KDE1204PKV3 MS.AR.GN
DC Volts (match)1212
Amps (do not exceed stock)0.180.03
Fan Size (match)40mm x 40mm x 20mm40mm x 40mm x 20mm
Hole Mount Size (match)32 mm32 mm
Hole Diameter (close match)3.5 mm4 mm
Length of Wires (match)330 mm300 mm
3 wire purpose (match)12v, Ground, Lock Rotor12v, Ground, Locked Rotor
Db Noise rating (reduce)32-36 Dba18 Dba
RPM (close match)90005200
CFM (close match)106.3

Fourth, Prepare the fan to be installed. One item I didn’t mention was the fan edge connector. Most data sheets do not come with information on the edge connector as device manufactures may customize this. In this size of fan the edge connectors seem to be a standard size with some variants.

Some fans will need their wire order changed to match the circuitry on the device. Aligning these pins is critical, if they are wrong you could damage your device. For example your replacement fan came with Pin 1 12v Red, Pin 2 Ground Black, and Pin 3 Motor Lock Yellow (Sometimes White or Blue) you might need to reordered them to match your device. Simply use a wire pin removal tool, light pressure down, and push the pin out. Then, reorder the pins to match your device and you are good to go.

Next the replacement fan mount hole might be a factor. Some replacement fans come with screws or bolts that you may be able to use. If not, you may be able to use the stock hardware or hardware you provide. Either way, depending on the hole size you may have to work this out a bit. In my case, the stock fan screws worked perfectly. Tip – Don’t over crank or force in screws, it may damage your fan.

If your stock fan had a protection sleeve over the wires you may want to reuse it as some devices have sharp metal edges that may cut into your wires. Fan vibration may also cause this too. As an alternative, you may want to consider adding heat shrink when you re-pin the fan.

Lastly, how did my selection perform? Basically, the Sunon is a very close replacement to the Delta. It has a reduced RPM and CFM which drops its Db noise by 20 Db. Since I choose a replacement fan that is not an exact match, I’ll need to monitor the device and ensure its temps are within normal thresholds.

Very unscientifically, I used a Db meter app in my smartphone to measure the Db for the Delta and Sunon Fans. The noise reduction was notable and best of all no fan error lights.

Summary, there is no doubt that Noctua makes a quality fan product but they can be expensive and sometimes do not meet the requirements of your stock fans. If you can find one that does, it may be worth the extra spend. However, by doing just a bit of research you are sure to land on a replacement fan that will meet your goals and not break your wallet. My goal was to reduce fan noise for my home lab and by doing my homework I hit a home run with the first fan I chose.

Thanks for reading and do feel free to leave a comment or suggestion.

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