Electronic – arduino – Help identifying a motor and how to control it with an Arduino

If this is the type of fan you are using: http://www.formfactors.org/developer/specs/REV1_2_Public.pdf

-then the output sensor claims it is an open collector or open drain. (Meaning it only pulls down.) It also says "Motherboard will have a pull up to 12V, maximum 13.2V". Written this way I would take this as a recommendation. If the output is truly just an open collector/drain then you should be able to add your own pull-up resistor as needed. For the Arduino input you would have the resistor pulled up to +5 only. (You could add the 5k resistor as shown, or if you know how to enable the internal pull-up on the Arduino port pin use that, in which case you would not need the 5k resistor shown.) With a resistor in place the fan sensor pulls down (to 0v) then releases the pin, so it then climbs back up to what ever voltage the pull-up is connected too.

The hook up should look like this:

^{simulate this circuit – Schematic created using CircuitLab}

But just as a precaution, before connecting the Arduino Speed input pin to Sense, you should measure the voltage on the Sense fan pin while the fan is slowly rotating (with 12v on the fan power input).

The spec lists the Fan's Control input to be a 5v PWM signal. So coming from the Arduino no extra driver circuit is needed.

Also the spec says the pulses from the Sense pin is 2 per revolution, so measure the pulses per second then divide by 2.

Here is a guess as to what the diagram might be. It might be possible to figure out which wire is which and whether or not this diagram makes sense by careful measurement of resistance. I think I have the L-M-H sequence backwards.

More re resistance measurements etc.

To figure out which winding is which and which speed and voltage taps are connected to each winding, you need resistance measurements that distinguish very small resistance differences, perhaps 0.1 or even 0.01 ohms. If you can verify which wire is neutral and which winding is which, you may be able to run the motor, measure current and estimate speed to help determine the rest. Accurately (and inexpensively) measuring low ohms is a good subject to research.

If you can't find detailed information on the motor, you will also need to guess at the capacitor value. You will be able to find tables that give ranges based on motor power and voltage.

You might consider taking the motor housing off and carefully examining the lead wire routing, the connections to the windings and the winding wire size. Be careful doing that. The windings are somewhat fragile and there may be several washers on each end of the shaft that need to be in the right order. Those tend to stick either on the shaft (good) or on the bearing in the housing where they might drop off when you are not looking (bad). The bearings themselves may stay on the shaft or in the housing.

Without knowing the motor current rating, it may be difficult to know if you have everything right if you get the motor running. If you don't know why this motor was taken out or why the air handling system was scrapped, you don't have any reason to assume this is a good motor.