New PWM FAN controller design

[unevent]

3-wire fans power the hall (tach) sensor using the input voltage.  So if you control a 3-wire fan with PWM you get PWM back on the tach line which will interfere with speed reading.  3-wire fans are best voltage controlled and 4-wire PWM controlled (constant voltage and a PWM signal sent on the 4-wire to control the fan speed).

[NAS]

It feels odd to me that we are supplying this type of information to a PWM fan controller designer.

[S80_UK]

3-wire fans power the hall (tach) sensor using the input voltage.  So if you control a 3-wire fan with PWM you get PWM back on the tach line which will interfere with speed reading.  3-wire fans are best voltage controlled and 4-wire PWM controlled (constant voltage and a PWM signal sent on the 4-wire to control the fan speed).

 

True.  Three wire fans also can give very inaccurate outputs from the sensor as the voltage is lowered.  This behaviour varies a lot from one fan type to another, and also according to the hardware of the speed monitor (depends on voltage thresholds when looking at pulses, etc.).  Such fans are often fine at or near their nominal supply voltage, but may read double speed, not at all, or some random speed when supplied with low voltages.

 

It feels odd to me that we are supplying this type of information to a PWM fan controller designer.

 

Me too.

[Golfonauta]

Hello NAS,

 

we know the specs, and voltage regulation can be done with PWM with a bit more of electronics to ramp it up to the 12V line for example.

 

What I want to ensure is that the product we are designing fits your needs, I only wanted this kind of feedback.

 

We don't want to design a product that ends up only good for our needs and not other users

 

 

Regards.

[NAS]

Hello NAS,

 

we know the specs, and voltage regulation can be done with PWM with a bit more of electronics to ramp it up to the 12V line for example.

 

What I want to ensure is that the product we are designing fits your needs, I only wanted this kind of feedback.

 

We don't want to design a product that ends up only good for our needs and not other users

 

 

Regards.

 

Understood. I think we went a bit off topic for what you need then

 

So essentially we have two use cases:

 

1. Server, primarily HDD, cooling

2. Cabinet control

 

both also require the ability to add physical temperature sensors and you have seen the requirement for "fail to open" and "full speed on boot" along with "groups of readings driving specific fan settings".

 

What is not clear though is the physical layout of your device. The forma factor, cabling options, mounting, external sensor options, power options along with how it would scale beyond one device might help us come up with more comments.