We use Faraday's law of electrolysis to calculate the cell run time to make the specific amount of Colloidal Silver at the desired PPM. It provides a run time in minutes.
For Faraday's law of electrolysis to work the current through the cell MUST be held CONSTANT. Given a constant current, a PPM, the amount of water, Faraday's law tells you how long to run the cell to create the PPM you desire.
Without the current limiter, knowing exactly what PPM you made isn't exactly easy to figure out if even you could.
The above, of course is only one part of the process, temperature, the current setpoint, whether or not you're gel-capping, whether or not you're choosing to stir,... and other factors all play a part in making good quality Colloidal Silver.
The current limiter really can't be bought given the operating point we use it at, however, if you use the LM317LZ limiter, its all of 2 parts if you want to build it for a single fixed current or 3 parts if you want the current setpoint adjustable. This is about as simple as it gets.