Forcing a variable speed fan to full speed

[denisbaldwin]

As I've said in other posts, I replaced all the fans on my Antminer S5s with Scythe Slip Stream 120mm 3-Pin Case Fan SY1225SL12SH units. I like how much air they push for the sound level.

What I've noticed is the fans, while advertised at 1900 RPM, are running at a variable range of 1300RPM to 1680RPM. Is there a way anyone is aware of to force them to run all the way to 1900 RPM by modifying the controls in the web interface? Or something similar? I was considering getting an inline fan controller, but I would think this is something that could be controlled with software.

Any ideas?

Denis

[quakefiend420]

I believe if you were to disconnect the other wire and leave just red and black that it would run at full speed.  Could probably pop them right out of the connector, no need to cut them.  Not a software solution, however.

[padrino]

I believe if you were to disconnect the other wire and leave just red and black that it would run at full speed.  Could probably pop them right out of the connector, no need to cut them.  Not a software solution, however.

That definitely works..

[windpath]

Cut the blue wire!

[alh]

I am confused as to why "cutting the blue wire" would alter the RPM of a 3-pin fan. My understanding of a 3-pin is as follows:

- Ground: The black wire in all cases I have seen.
- +12V: Usually yellow, maybe Red on some fans?
- Tachometer: Blue wire? This is a signal FROM the fan TO the controller. It allows the controller to "sense" what what the speed of the fan is. Originally used to detect a stalled/broken fan. This is how you can get the RPM on the GUI.

Usually most variable speed fans these days have a 4th wire, which carries pulses TO the fan to control it's speed. Prior to the PWM (aka 4-wire) fans, the controller would have to adjust downward the actual voltage on the +12V line to slow it down.

I'd swear the S5 had 4-wire PWM control logic and connectors for it's fans.

It seems to me that if you want a 3-wire fan to always at full speed, you connect the +12 and Ground wires directly to the power supply, and call it a day. No need to have the controller board get involved at all. This seems particularly attractive if you add a 2nd fan to the S5.

I've read that the S5 can in some cases lower the fan speed and still run the hashing hardware at near full speed. A fan directly wired to the power supply will continue to run at full speed even in this case.

[OgNasty]

I am confused as to why "cutting the blue wire" would alter the RPM of a 3-pin fan. My understanding of a 3-pin is as follows:

- Ground: The black wire in all cases I have seen.
- +12V: Usually yellow, maybe Red on some fans?
- Tachometer: Blue wire? This is a signal FROM the fan TO the controller. It allows the controller to "sense" what what the speed of the fan is. Originally used to detect a stalled/broken fan. This is how you can get the RPM on the GUI.

Usually most variable speed fans these days have a 4th wire, which carries pulses TO the fan to control it's speed. Prior to the PWM (aka 4-wire) fans, the controller would have to adjust downward the actual voltage on the +12V line to slow it down.

I'd swear the S5 had 4-wire PWM control logic and connectors for it's fans.

It seems to me that if you want a 3-wire fan to always at full speed, you connect the +12 and Ground wires directly to the power supply, and call it a day. No need to have the controller board get involved at all. This seems particularly attractive if you add a 2nd fan to the S5.

I've read that the S5 can in some cases lower the fan speed and still run the hashing hardware at near full speed. A fan directly wired to the power supply will continue to run at full speed even in this case.

Your misconception seems to be the "Tachometer" wire.  This is the wire that lets the controller control the fan speed.  Cut it, and it should be 100% all the time.  You probably already know that, but I'm confirming for you. 

[aarons6]

um this fan appears to be a 3 wire fan..
http://www.newegg.com/Product/Product.aspx?Item=N82E16835185060

no blue wire to cut.

it has only - + and sense.

it should already run at full speed..

they do have a 10% variance tho.. which is about 200 rpm.

not quite sure these are suitable for a s5, even with 2 in push/pull.

[dogie]

There is 2 methods of controlling fans which is why you're getting confused.

1) The first is by variable voltage, where instead of a constant 12V being fed, somewhere between 5-12V is fed. This slows down the fan.
2) More powerful fans will use a constant 12V but with a PWM signal. This signal determines how quickly the motor should flash on or off. So if you want the fan to run at ~half speed, the PWM signal tells the motor to be off for ~50% of the time. That signal usually determines the off part of the cycle, and so a lack of any signal means 100% on (full speed).