How to Set Current Limit for Mastech CC CV Power Supply

Setting the current limit can be a bit more complex, especially in situations involving internal sources of EMF (e.g., batteries) or sensitive loads like LEDs. Follow these steps:

1. Scenario 1: Internal Source of EMF
   • Set the voltage slightly above the maximum EMF from your load (0.8V to 1.5V above).
   • Set the current to the minimum value before connecting the load.
   • Slowly increase the current limit by adjusting the current knob to the desired value.
   • For added safety, consider adding a diode in line with your load to prevent reverse current flow; for motor and inductive applications, connect a diode (that is large enough to handle the current) in parallel to the motor, but in reverse bias.
2. Scenario 2: Sensitive Loads
   • If possible, use a simple load like a power resistor or halogen lamp that can handle the desired current.
   • Set the current limit following the steps from Scenario 1. (Note: once this is set, do not touch the current knobs again!)
   • Turn the voltage down to minimum, disconnect the load, and connect your actual load.
   • Slowly increase the voltage while keeping the current setting below the safe limit for your load.
3. If Power Resistor or Lamp Is Unavailable:
   1. Before connecting your load, set the voltage limit at or slightly below your load's safely allowed voltage and set the current to minimum. The power supply should be in "CV" mode.
   2. Connect the load; the power supply should switch to "CC" mode.
   3. Gradually increase the current limit. If you reach the desired current before switching to "CV" mode, you're done.
   4. If the switch to "CV" mode occurs before reaching the desired current, slightly decrease the current to switch back to "CC" mode.
   5. In "CC" mode, adjust the current knob to find the halfway point between your desired current and the maximum without increasing the voltage setting (you do this by estimating the slope of the knob movement). This should switch the power supply back to "CV" mode.
   6. Gradually increase the voltage knob below the safe limit for your load until the power supply switches back to "CC" mode.
   7. Observe the actual current displayed. If higher than desired, reduce the current setting to the desired value. If lower, repeat the process from Step 3 until the desired current setting is achieved.