Why haven't manufacturers started putting PWM fans in PSUs?

[JoostinOnline]

They do.  It just doesn't connect to the motherboard.  By connecting it to the motherboard, you're hurting efficiency.  The PSU temperature and the motherboard/CPU temperature aren't usually the same, so you can have the PSU fan high when it doesn't need it, and low when it does.

[Mick Naughty]

1 hour ago, H0R53 said:

I don't even need a profile, the fans in PSUs are generally around 1500RPM anyway, and I have the fan on 1 of 2 CPU headers anyway so as soon as the power consumption goes up from a game and the CPU fan spins up the PSU fan will spin up as well.

Well nothing in my main rig will see over 1k rpm. Max the psu sees is 800 so I could add it to the hub id like to put a quality fan in there before I do that.

 

[H0R53]

3 hours ago, Mick Naughty said:

Well nothing in my main rig will see over 1k rpm. Max the psu sees is 800 so I could add it to the hub id like to put a quality fan in there before I do that.

 

Don't get the SickleFlow, they aren't the best, but they're not the worst. My best fans are these ones. They take a while cause they are from China but they're super quiet even on 2000RPM you can't hear them. They are better than the fans on the 212 evo and are made of very good plastic.

[flibberdipper]

TLDR is they're already temperature/load controlled (or a combination of both), so there's no reason to waste money on shit it doesn't need. And some PSU's come with a normal 2 prong connector, so you can just buy another 2 pin fan and plug that in (I plan on doing it with my CX750M at some point to replace the 650G1 my "HTPC" uses, since right now I just have an AF140L shoved in it wired to my mobo).

[H0R53]

2 hours ago, tmcclelland455 said:

TLDR is they're already temperature/load controlled (or a combination of both), so there's no reason to waste money on shit it doesn't need. And some PSU's come with a normal 2 prong connector, so you can just buy another 2 pin fan and plug that in (I plan on doing it with my CX750M at some point to replace the 650G1 my "HTPC" uses, since right now I just have an AF140L shoved in it wired to my mobo).

Some 2 pin fans don't light up or have some features I don't like, and a lot of them are wobbly and low quality so I'd rather replace it with something I know works. Most likely I'll start just stripping the wires and connecting that to the existing 2-pin lead and using the remaining pin on the MB for monitoring. If not including a PWM MB header they should at least include a modular cable you can plug in that fits on a PWM header pin.

[flibberdipper]

9 hours ago, H0R53 said:

Some 2 pin fans don't light up or have some features I don't like, and a lot of them are wobbly and low quality so I'd rather replace it with something I know works. Most likely I'll start just stripping the wires and connecting that to the existing 2-pin lead and using the remaining pin on the MB for monitoring. If not including a PWM MB header they should at least include a modular cable you can plug in that fits on a PWM header pin.

I don't know what crappy PSUs you're getting that have crappy fans in them, but the only one I've gotten with a bad fan is my 650G1, and that's just a one-off case.

[mariushm]

On 3/26/2017 at 7:54 AM, H0R53 said:

I started doing something not too long ago. When I get a new PSU off Amazon without a warranty, I take it apart and replace the stock fan with a decent PWM fan, if it's 70, 80, 92, or even 120mm, I replace it with something like a CM SickleFlow. It looks nicer and when the motherboard controls the fan from ambient temps the PSU generally maintains efficiency. I have not done this with my Corsair CX600 because it's still under warranty and it's a pain in the ass to take out of my case...

 

That's not a good idea.

 

Manufacturers often choose a fan model based on the amount of air flow it produces at certain rotation speeds, which they control by adjusting the voltage going into the fan.

So it's something like this... they know the fan produces 40 CFM of airflow (cfm = cubic feet per minute) at 12v and they know the fan produces only 15 CFM of airflow at 5v. They also how much the heatsinks they use will cool down depending on the amount of CFM moving across them, so they can maintain the temperature of those heatsinks at let's say a maximum of 80 degrees Celsius.

If you replace the fan with another one that has only 30 CFM at 12v and only 5-10 CFM at 5v, the heatsinks may heat up to 90-100 degrees celsius or you may end up having hot spots inside the case, which may cook up (age prematurely) certain components like electrolytic capacitors. Also, at lowest voltage the fan would produce too little CFM keeping the psu constantly warmer than the engineers desired.

 

Also .. while less importat in power supplies, there's fans optimized for static pressure (for pushing air through fins of heatsinks) or fans optimized for moving air (for placing on computer cases) .. power supplies usually need the later.

know as it's often cheaper than producing a pwm pulse to the fan. 

PSU manufacturers also often use those plastic sheets covering some parts of the fan bottoms to direct the air flow of the fan to certain parts of the power supply that are usually hotter than others, or to prevent the air from exiting directly through the case back instead of reaching the other end of the case first. Not a good idea to remove those sheets or to alter them.

 

In order to adjust the rpm of a fan using PWM, you'd have to have something creating that PWM pulse, a series or digital 1s and 0s at around 38kHz .. psu manufacturers would have to add some microcontroller or some custom chip that would monitor the temperature of the heatsinks inside the power supply and change the duty cycle in order to adjust the fan speed. Such chips could cost 20-50 cents, not to mention the fans may also be more expensive.

 

Controlling the fan voltage is cheaper, it can be as simple as adjusting the current flow into a 5 cents transistor. It's more inefficient, but the 0.1w to 0.25w of heat produced (or something like that) are nothing compared to the tens of watts of heat produced by the power supply (a 90% efficient psu would produce 10w of wasted heat if the computer uses 100 watts, so less of a quarter watt of heat produced controlling fan speed is nothing) 

[H0R53]

12 hours ago, mariushm said:

 

That's not a good idea.

 

Manufacturers often choose a fan model based on the amount of air flow it produces at certain rotation speeds, which they control by adjusting the voltage going into the fan.

So it's something like this... they know the fan produces 40 CFM of airflow (cfm = cubic feet per minute) at 12v and they know the fan produces only 15 CFM of airflow at 5v. They also how much the heatsinks they use will cool down depending on the amount of CFM moving across them, so they can maintain the temperature of those heatsinks at let's say a maximum of 80 degrees Celsius.

If you replace the fan with another one that has only 30 CFM at 12v and only 5-10 CFM at 5v, the heatsinks may heat up to 90-100 degrees celsius or you may end up having hot spots inside the case, which may cook up (age prematurely) certain components like electrolytic capacitors. Also, at lowest voltage the fan would produce too little CFM keeping the psu constantly warmer than the engineers desired.

 

Also .. while less importat in power supplies, there's fans optimized for static pressure (for pushing air through fins of heatsinks) or fans optimized for moving air (for placing on computer cases) .. power supplies usually need the later.

know as it's often cheaper than producing a pwm pulse to the fan. 

PSU manufacturers also often use those plastic sheets covering some parts of the fan bottoms to direct the air flow of the fan to certain parts of the power supply that are usually hotter than others, or to prevent the air from exiting directly through the case back instead of reaching the other end of the case first. Not a good idea to remove those sheets or to alter them.

 

In order to adjust the rpm of a fan using PWM, you'd have to have something creating that PWM pulse, a series or digital 1s and 0s at around 38kHz .. psu manufacturers would have to add some microcontroller or some custom chip that would monitor the temperature of the heatsinks inside the power supply and change the duty cycle in order to adjust the fan speed. Such chips could cost 20-50 cents, not to mention the fans may also be more expensive.

 

Controlling the fan voltage is cheaper, it can be as simple as adjusting the current flow into a 5 cents transistor. It's more inefficient, but the 0.1w to 0.25w of heat produced (or something like that) are nothing compared to the tens of watts of heat produced by the power supply (a 90% efficient psu would produce 10w of wasted heat if the computer uses 100 watts, so less of a quarter watt of heat produced controlling fan speed is nothing) 

I mean all in all it's a DIY project. I can connect the + and - leads of a fan to the PSU header, not that big of a deal.

[Unimportant]

On 26.3.2017 at 6:54 AM, H0R53 said:

I started doing something not too long ago. When I get a new PSU off Amazon without a warranty, I take it apart and replace the stock fan with a decent PWM fan, if it's 70, 80, 92, or even 120mm, I replace it with something like a CM SickleFlow. It looks nicer and when the motherboard controls the fan from ambient temps the PSU generally maintains efficiency. I have not done this with my Corsair CX600 because it's still under warranty and it's a pain in the ass to take out of my case...

The fan in most power supplies is already speed controlled, based on some criteria the manufacturer chooses, either temperature or power being drawn from the unit, or some combination.

 

You can control any fan's speed by varying the voltage you supply to it, you don't need a PMW fan to be able to control speed. The problem is, each type of fan responds differently to changes to it's supply voltage. Because you can install many different types of fans in your system from all kinds of manufacturers they needed a way to be able to uniformly control them, that's where PWM fans come in.

A PWM fan regulates it's own speed internally, based on the requested speed trough the PWM signal, the fan "knows" it's own characteristics and thus "knows" what it has to do to reach the requested speed.

 

Since the PSU manufacturer knows exactly which type of fan it will be installing in it's PSU and thus exactly knows the characteristics of that fan, there is no need for a PWM fan. A normal, voltage controlled, fan will suffice.