Power supply monitor

Projects General Guidance
1

Hello,

I've been working on a project to convert a server power supply into a power supply for my RC helicopter battery charger. I've got that working well, but I like to add a couple of fans and a fan speed controller.

The server power supply has circuitry that controls the speed of the fan based on the current flowing through the power supply. Is it possible for me to split the speed sensor line so that it continues to feed the supply but also feeds the Arduino?

I've measured the voltage of the sensor line of the fan at low speed it is 5.2 V. I'm hesitant to plug that directly in the Arduino for fear that when the fan goes full speed the voltage will overload the digital input.

Any input would be greatly appreciated.

Loren

2

The fact that it is a speed sensor line suggests to me that it is not a source of volts for the arduino.

If it is an actual sense line it is an input to the supply and loading it with the arduino would effect the sensing. If it is an output to the fan, I expect it to vary and hence not be suitable.

Weedpharma

3

weedpharma:
If it is an actual sense line it is an input to the supply and loading it with the arduino would effect the sensing.
Weedpharma

Does anyone have any recommendations on how to wire the Arduino so that reading the pulses does not affect the server power supply's performance?

4

On re reading the OP, I am wondering if "feed" refers to powering the arduino or simply being used as in input to the arduino powered elsewhere.

Does the voltage change at higher speed?

If being used as input only and is a series of pulses, (PWM?) the simplest way of conditioning the input is a resistor/Zener clipper. Use 1k/10k divider with a 4.7v Zener across the lower resistor. This will limit the input voltage to less than 5v but be high enough to be read as a high.

Weedpharma

5

weedpharma, thanks for the input!

weedpharma:
On re reading the OP, I am wondering if "feed" refers to powering the arduino or simply being used as in input to the arduino powered elsewhere.

Exactly, sorry that I wasn't more clear in my description.

weedpharma:
Does the voltage change at higher speed?

I think so but I need to verify this

weedpharma:
If being used as input only and is a series of pulses, (PWM?) the simplest way of conditioning the input is a resistor/Zener clipper. Use 1k/10k divider with a 4.7v Zener across the lower resistor. This will limit the input voltage to less than 5v but be high enough to be read as a high.

Weedpharma

does the attached picture depict what you described?

Screen Shot 2014-11-19 at 5.38.25 AM.png

6

Yes.

The top resistance is current limiting into the Zener while the lower one is tying the input to ground.

If this effects the power supply, it may be that the circuit is loading the power supply. In that case, raise the values but keep a similar ratio.

Weedpharma