Fan controller

[slepax]

Hello,

Background:
Large POE switch (24 ports) that I would like to utilise for home use. These units are normally stored in a server room so noise is not really an issue, for me however, it is. The plan was to replace the existing 3 x 40mm fans with 2 x 120mm fans using my own fan controller.

Process:
The switch has two main internal power supplies for the POE ports. I cut the cover and install the 2 fans on top. Using Arduino I have two sensors on each power supply and I can control the fans using PWM. This is an all-in-one PCB with sockets for 2 x fans, 2 x ds18b20, 1 x oled.
I control the fans PWM using Timer2 on the Arduino Nano (ATmega 328), also using interrupts to monitor fans speed. The code adjusts the timer/pwm duty cycle based on the current temperature.

This is already built and running where the idea was to mount the controller inside the switch and take power from one of old fan pins (12V). The problem I'm having is that every 20-30 one of the fans stops running for about 3 seconds and then fires up again, however:

• It works with no issues when I use an external power supply (rather than the switch existing fan pins)
• It works with no issues when I connect a multi-meter in series to check current consumption (0.5A)

I'm kind of clueless on how to resolve this. Any pointers or tips would be greatly appreciated!

Thanks

 

[Grossel]

The switch own fan controller may cut power when some criteria is fulfilled, usually that temperature goes beyond a certain point.

 

[slepax]

The switch own fan controller may cut power when some criteria is fulfilled, usually that temperature goes beyond a certain point.

I thought about that but if that was the case then the whole board would lose power including the Arduino and the oled. In my case the Arduino keeps running and the oled display is fine. Sorry I should have clarified this before.

 

[Grossel]

Then I'd assume something is overloaded, eg. the switch power consumption is already at high maximum before you connected your own fans.

What are the original fans power ratings, and the new fans?

 

[slepax]

The original fans are 0.1A, and the new ones are 0.4A.

I was hoping the power supply will have some spare capacity and a single rail for all fans (it had 3 fans before, I am running 2).

Regardless though I think you are right. I changed the Arduino code so it artificially increments the temp reading by 0.5 deg every minute, resulting with higher duty cycle and therefor higher fan RPM. With the external power supply it went from 15% duty to cycle to 100% with no issues, however with the "internal" power supply at 30% duty cycle I started having the same issue with than fans stopping, it started with just one fan and then both fans as the duty cycle increased higher.

It seems like I would have to use an external power supply after all

Thanks for your help and ideas!