martinsliquidlab.org

Potentiometer (Variable Resistor) Control DDC-3 (Blue)

So we got standard voltage control testing out of the way, but the real treat to this controller is it’s built in ability to control speed.  Through the guidance in the XS thread and help of fellow members, it was suggested that a 50Kohm potentiometer would be just right.  I stopped by radioshack and picked up a few different flavors, and can confirm that 50K is just right.  I tried a 100K and found that it had the ability to reduce speeds below startup, but 50K was just about perfect giving a nice large range of control.  I used a larger .5watt pot, but you could easily use one of the mini .1watt pots as well if you can find them.  I could only find the mini in a 100K size from the shack.

To install, you first need to break the bridge trace on the PCB between the VSP and VREF, then install wires from the PCB to the pot.  Those details can be seen below:

Speed Controller Installation

The potentiometer basically reduces voltage that is supplied by Vref to about 2.4V variable to 5V.  One meter said 2.44V minimum, while another multimeter said 2.35V which is partly due to the meters and wiring themselves.  I then proceeded to retest a few settings starting at the minimum and working up to the maximum.  The pot controller really worked well in giving the pump a very broad range of pumping power.  The low setting feels similar to a D5 setting 1, and the high setting like a D5 strong at 24V.  It’s really quite impressive.  The hardest part of this was removing the bridge between VSP and Vref, it’s very small and hard to see, and I simply used a knife to scratch the trace away creating a break between the two points.

50K Pot, lowest setting VSP=2.35V

Med/Low VSP=3.0V

Med/High VSP=3.5V

At high speed, the pump works and tests the same as the 12V analog test where VSP and Vref are both 5.0V.

50K Pot speed control comparison

The potentiometer really gives it a nice large speed operating range, much larger than voltage control is capable of.  As high of a speed as these pumps run with these controllers at 12V, I would highly recommend doing the potentiometer mod as part of the package.  You could also mount the potentiometer controller just about anywhere for easy access.

Share this:

• Email
• Print
• Facebook
• Twitter
• Pinterest
• More

• Google +1
• StumbleUpon
• Digg
• Reddit
• Tumblr
• LinkedIn

Pages: 1 2 3 4 5