How can I measure DC current with the MMS3000 T6V4?

Submitted byglx25v onFri, 08/17/2018 - 17:29
  • It is possible to measure current with the T6V4 by placing a shunt resistor in the current path, and measuring the voltage over the resistor.

    For example see the diagram below:

    Motor Example

    Note this technique can only be applied to DC currents, not AC mains currents!

    The value of the shunt resistor must be chosen carefully, as follows:

    Step 1. Find the maximum current
    You may know this value (in Amps) already, but if not it can be found from the power rating of the motor (or whatever the load is):
    I (Amps) = Power(in Watts) / Voltage
    In the example above:
    I = 300W / 24V = 12.5 A

    Step 2. Find a suitable value for the resistance
    If the resistance is too high:
    Too much voltage will be dropped over the resistor, taking power away from its actual purpose (in this case driving the motor). As a guide, try to avoid dropping more than 1% of the available voltage over the shunt.
    In the example above, 1% of 24V is 0.24V

    If the resistance is too low:
    The voltage seen by the T6V4 will be too low, so the current measurement will be less accurate, and noisy or stepped. Avoid this by ensuring that at least 0.1V appears over the shunt, at maximum current.
    So in our example, the voltage over the shunt should ideally be between 0.1V and 0.24V, when the maximum current is flowing. Experimenting with resistance values R in the formula:
    Voltage(V) = I R
    leads to the choice of 0.01 Ohms, which will develop 0.125V at 12.5A.

    Step 3. Calculate the Wattage required for the resistor
    We don't want the resistor to burn out, so fit a suitably high wattage one using the formula:
    Power(Watts) = I