Tuesday, July 23, 2013

Repairing And Understanding A Zalman Fanmate-2 Fan Speed Controller

UPDATE: I made an assumption...that was wrong. The regulator is a 7805, the resistor is a 710 ohm (708 ohms measured) and the potentiometer is 1K ohm. It turns out that reading resistor color bands is difficult without good lighting and measuring components in circuit can introduce errors. See here for an updated analysis. Although some of this post should be useful still.
I picked this up at a yard sale a year ago. A Zalman Fanmate-2 computer case fan speed controller. For some reason the 3 wire connector for the motherboard had been cut.
Not the most exciting thing to look at.
I pried the housing apart. Surprisingly it did not break.
A neat little layout. The heat sink covers up a resistor and what I presume is an LM317T variable voltage regulator (could be something else I suppose but it’s behaving like one). Read the datasheet!
You can see the three legs of the LM317. It’s bolted to the heatsink (which also means that its live with the output voltage).
Some LM317Ts from my parts drawer.
My general impression of the circuit which seems to follow the classic LM317 voltage regulator, without any capacitors. It was nearly impossible to take a picture of the resistor, but it has bands (red, none, black, black, red, purple) that indicate it’s a 200 Ohm, 2% resistor. The potentiometer has a variable resistance between 637 Ohms and 1721Ohms. Plugging those values into an LM317T calculator it shows a voltage 5.23V and 12.01V. Because there is a voltage drop from supply voltage on the regulator (that depends on mumble, mumble, mumble, more math than I want to do), the maximum voltage it can produce from 12V should be about  10V. In real life I get a voltage of between 5.13V and 10.5V with a fan hooked up. the power supply voltage, resistor, potentiometer, load from the fan and my consumer grade voltmeter all conspire to make this less than an exact science.
Oh yeah, I soldered on a connector.
Running it out of the case to measure temperature on the heatsink (90 deg. in a 78 deg. room)
Just running a fan at different speeds. Fun.

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