PWM fan confusion.

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H4X0R46

H4X0R46

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Sep 25, 2016
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Hello guys! So I got a new fan today, an Enermax TB Vegas with red LEDs. I installed it as a front intake and it's working fine so far! Better temps than I was originally getting! Now I have a question about PWN fans. Do you HAVE to control their speed to use them properly? Or do they auto adjust when the machine is under heavy load?

Here's a link to the fan I bought: https://www.amazon.com/Enermax-T-B-Vegas-Twister-Technology-UCTVS12P-R/dp/B00HWQUJ24/ref=sr_1_1?ie=UTF8&qid=1493329078&sr=8-1&keywords=enermax+tb+vegas+red
 
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If you connect that fan properly to a mobo 4-pin header, the mobo will (in its default settings) control the speed of the fan for you. It does this by monitoring the mobo temperature and adjusting fan speed according to that temperature to keep it under control.

A PWM fan (which this is) has its speed controlled by the PWM signal sent to it on Pin #4 of the mobo header. Pin #2 of the header sends it a fixed 12 VDC supply, and then a chip inside the fan motor alters that voltage according to the PWM signal to adjust fan speed.

There are a few wrinkles you should know. This fan comes with red LED's that are powered also from that 12 VDC supply line. Further, its description says it has a small 3-position switch on the motor used to...
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H4X0R46

H4X0R46

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Sep 25, 2016
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I have it connected to the motherboard directly into a 4 pin header. So in my case it is adjusted automatically? When the computer is under load, it will kick up the rpm?
 
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Paperdoc

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If you connect that fan properly to a mobo 4-pin header, the mobo will (in its default settings) control the speed of the fan for you. It does this by monitoring the mobo temperature and adjusting fan speed according to that temperature to keep it under control.

A PWM fan (which this is) has its speed controlled by the PWM signal sent to it on Pin #4 of the mobo header. Pin #2 of the header sends it a fixed 12 VDC supply, and then a chip inside the fan motor alters that voltage according to the PWM signal to adjust fan speed.

There are a few wrinkles you should know. This fan comes with red LED's that are powered also from that 12 VDC supply line. Further, its description says it has a small 3-position switch on the motor used to limit its maximum speed. I recommend you leave that switch always set to High speed, and allow the mobo automatic control system to do its job properly. Setting the switch to a lower speed will prevent the fan from high cooling rates just when it is needed.

A true 4-pin fan header uses what is called PWM Mode to control its fan. That means it always sends 12 VDC out on Pin #2, and sends the PWM signal on Pin #4. Older 3-pin fans are controlled in a different way - there is no PWM signal, and the voltage on Pin #2 is reduced to slow down the fan when needed. These days there are a couple of variations of 4-pin fan headers on mobos that do not always do it the true PWM way. SOME mobos allow you to set an option in BIOS Setup for each fan header whether it uses PWM Mode of Voltage Control Mode (aka DC Mode). If your mobo has that choice, set it to PWM Mode. SOME other mobos do not actually use PWM Mode even though they have 4 pins on the headers. They use Voltage Control Mode only. For fan operation, this is a small matter, because a true PWM fan CAN be controlled in this manner although it is slightly less that "optimum". But in your case this would have another effect. The LED's on the fan are fed from that same DC signal on Pin #2 that powers the fan motor. So if the mobo is using reduced voltage on Pin #2 to slow the fan, it may cause the LED's to glow more dimly also.
 
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Karadjgne

Karadjgne

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For the most part, I don't find led pwm feeds to be an issue, just means in idle, the leds get dim, but when gaming they brighten up. Mobo temps are unlike cpu temps, case/mobo temps are really not subject to the almost instant changing temps that happen with cpus, it's usually quite gradual, both up and down. So you really don't get a strobe affect.

The fan speeds are subject to user settings, be it in bios or mobo software or 3rd party software such as SpeedFan, so they can be set where the light barely changes, staying at a higher rpm etc. All depends on where you want temp ranges, fan volume etc.
 
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Paperdoc

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The effect on LED brightness with fans is due to use of Voltage Control Mode, in which the voltage supplied to the fan is altered to change the fan motor speed. But in a PWM fan there is always the option in its design to have the LED's fed directly from the fixed 12VDC supply on Pin #2 and avoid that effect. I assumed that the Enermax TB Vegas fans were designed that way, but maybe I'm wrong. As I pointed out, though, if such a fan designed to avoid varying LED brightness is connected to a header using Voltage Control Mode, the LEDs' brightness WILL change as fan speed changes.
 
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H4X0R46

H4X0R46

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Sep 25, 2016
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Thanks for breaking that down for me. I DID notice that the lights get a lot brighter when I'm gaming, when the fan is spinning faster. It's a great fan! Moves a lot of air! Thanks again guys for all your answers! :D
 
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