CrystalFontz CFA-635

by Matthew Harris on April 11, 2006 in Peripherals

With the cornucopia of fan controllers and temperature monitors on the market today it’s not very often that you run across one that brings a whole lot more to the table. Today we’re taking a look at one that brings more than just fan speed control and simple temp reporting.


Since modding hit the mainstream back around 2002 we’ve seen a literal explosion in modding related products for the PC. One of the most popular areas covered is cooling and temperature monitoring. At first we had simple 12V-0-7V mod based fanbuses followed by knob controlled rheobuses for user controlled fan control. For temp monitoring we had the venerable Compu-Nurse followed by the Digidoc which bundled multi channel temp monitoring with rudimentary fan control based off a set trip point.

Sadly the Digidoc had several shortcomings. First there was an annoying high pitched alarm that went off whenever your user set fan trip point was reached. I know that I’m not alone in pulling my Digidoc apart and crushing the little speaker element just to shut the stupid thing up. Secondly the fans came on only as long as the temp was above the point you’d set. Not at a percentage of full speed either, full bore. Once the temp was below the trip point the fan would shut off so you couldn’t set an ideal temp, instead you set a temp that was either a panic state or a temp that was unrealistically low which negated the point of having it.

Since then there have been many fan controllers that bundled user controlled fans via rheobus with temp monitoring and a handful that allow the fans to be controlled via temperatures. Today we’re taking a look at one such controller provided by the kind folks at Crystalfontz, the DB635AK-TMF-KU3. This unit is based on the CFA-635 and comes user configured with the drive bay kit of your choice. You have the choice of Black Aluminum (AK), Black Plastic (BK), Beige (BG) and Silver Aluminum (AL). The display unit comes in your choice of 2 types Black on light Yellow-Green Backlight (YYE) and White on light (Blue) with Blue Backlight (TMF).

To have it configured as a fan controller and temp monitoring device you can only choose USB (external + internal) including SCAB and cables. SCAB stands for System Cooling Accessory Board and is the heart of the system. Without it the CFA-635 is nothing more than a 4 X 20 LCD display that fits into a single 5.25″ bay and includes 6 buttons. With the SCAB the CFA-635 becomes more than that, much more. With the SCAB you can configure the CFA-635 to control fans based on one (or more!) of the four included temp sensors and not just off/on either (although that is an option if you wish) but starting at a preset level and ramping up to any level you choose. You can even plot a power curve with as many points as you want.

There are a few downsides to the SCAB, it doesn’t work as most normal fan controllers do by adjusting fan voltages instead it’s a PWM controller. PWM or Pulse Width Modulation means that to achieve the speed control the voltage going to the fans is split up into pulses. Instead of a steady stream of power going to the fan at whatever voltage you set it to the SCAB instead splits the voltage up into 18 pulses per second. The pulses are full voltage and if I’ve read the documentation (Which BTW is only downloadable as is the software) correctly there are reversed polarity pulses in there as well. What this means is that your fans speed is set by varying the number of pulses going to the fans.

What this means is that if you have high torque fans your fans will slam from a braking mode (when you apply resistance to the leads of a DC motor it brakes the motor, PWM apparently does this during the “off” pulses to stop the fans from freewheeling) to a powered mode and this creates an annoying clicking or rattling sound. I’m personally running a Delta AFB 1212VHE 120CFM 120mm fan as my single exhaust fan and running it at the same RPM level I was with my venerable PC Mods (Circa 2001) rheobus I got bad rattling.

At this point I’ll interject something here. Crystalfontz has a forum dedicated to end user support. If you have an issue or a question you can go post it in their forum (after registering naturally) and you can normally expect an answer ASAP. I have seen a few posts go unanswered though so that’s a bit of a turn-off. Anyways, I’d run into a bit of a problem with the CrystalControl 2 software and needed a bit of help which was quickly sorted out and I mentioned in passing that the fan noise was driving me nuts since it was increasing the sound my system made by nearly double and that’s when I found out about the PWM issue with high torque fans. The long and short of it is that running the fans (for bigger high CFM fans) under 30% is going to lead to troubles with noise from the pulses and can potentially lead to premature failure! Oh man, that’s not good.