This post is an update to the really interesting discovery I ran across and detailed in this post:
In short, the Phobya Maxguide6 dual bay controller has a really unique output, whereby once turned above the minimum or OFF position, (where there's only a few tenths of a volt output) there's a 4VDC base voltage, and an 8V PWM rider that starts at about 10% and increases to 100% as you turn the control to maximum position.
It's a very low PWM frequency, only 45.4Hz, but it is PWM.
I thought it might be interesting to see if I could pick off 5V of the PWM and use it as the control signal to control a regular PWM controlled fan or pump that takes its power from a PSU molex.
I posted here that I had pretty good luck with my initial attempt to do so, but some refinement was needed:
The one issue was that the Maxguide6 needs a significant load before it produces a decent looking pulse shape, which prompted a RadioShack run this morning.
With a minimal load, the trailing edge of the pulse drags out instead of cutting off cleanly which effectively makes it behave as a wider pulse width percentage than it is.
That yields a higher effective output voltage and higher speeds on whatever it's running.
One of the prime reasons for using PWM devices is to gain lower operating speeds and better low speed control and start up.
With that concept in mind I worked up a little adapter board that takes the Maxguide 6 output, picks off 5V of PWM and conditions the pulse shape by adding a resistive load, which then can be used as the PWM control signal for normal 4 pin PWM fans or pumps.
To give you some more details, here's the pics:
These first few show the actual output of the Maxguide6, before splitting out the PWM component.
Basic test bench setup;
The scope is showing the 4V base with the 10% duty cycle 8V PWM rider. The effective voltage is 4.6V on the yellow meter and the fan rpm is 750. . . . With the 3W fan and a 7W resistor pack attached, the wave form is pretty fair.
Now here's the same setup with the load resistor plugged out:
Fan is at 1020RPM, voltage is showing at 5.7V, PW showing at 19.5%, The trailing edge of the pulse is badly drawn out, not nicely cut off.
Here's a close up to show the details:
And here's a close up with the load resistors plugged back in:
The effective voltage is back where it should be, along with the PW percentage and the fan RPM
These next few pics show the picked off PWM component of the output.
The little board loads the output to shape up the PWM pulse, and then a zener diode is used to drop out the first 5.1V, so all that's left is 7V of pulse, which a resistive divider then gives me the 5V needed.
Here's the little board:
Here's the 5V PWM signal; The shape is nice and clean, 11% duty cycle, and an effective voltage of 4.6V
The PWM cpu fan speed is 1260RPM, which is really close to the 1200 RPM minimum that it gives from an actual 0% pulse width.
Since it seemed like everything was working surprisingly well, controlling well at 45Hz where the norm would be 25KHz, I plugged up the Maxguide6 and the little board to one of my dual 35X setups, hoping like h3ll that I wasn't blowing $200 down the tubes . . . . .
Damn this was an awesome hack, works fine, with the lowest I can get at ~1600RPM . . . and of course it maxes out easily.
The really cool thing here is that with one controller, you could control all your rad fans (36W per channel) and with one little board, you could use another channel to control a PWM 35X or D5.