The CC SINK was created as a testing and validation tool. After the failure of the first POWER PAK, I needed a way to quantify the performance of a power supply. The way you do that is with a variable load. You set the load to specific parameters to repeatably test the power output. This kind of load sets a current limit, which is useful for testing the maximum current of power supplies and the discharge characteristics of batteries (and probably other things I haven't done).

While you can find many kinds of these off the shelf, I was inspired (nay, implored) by Dave Jones demonstrating his home built design. The CC SINK is a more or less direct implementation of the theory presented in that video. It turned out to be quite useful for validating the POWER PAK v2, and other power supplies since.