The two current measurements are fundamentally different.

The supply (input) current measurement is the value most people are familiar with, since that’s what was measured by Talon SRX. It’s the value of the current being drawn at the input bus voltage (which matches the current drawn through the PDP channel).

The stator (output) current is a measure of the current being drawn by the motor, which is usually at a *different voltage* (whenever you’re not at 100% output).

Since power in has to equal power out, the current values are also usually different.

## Math on why they're different (Click to Expand)

Couple of examples:

I’m ignoring heat and assuming power in is perfectly power out, it makes the numbers nicer.

Also, I completely made these numbers up for math purposes - they’re not real-world numbers at all.

Assume you have a Falcon that’s running at 100% output. The supply current is measured at 15 amps. Because the output is 100% the input and output voltages match, meaning the stator current will also be 15 amps.

Now assume the Falcon is running at 50% output. The supply current is measured to be 20 amps and the input voltage is 12 volts. The output current would be measured at 40 amps.

How?

Since Power(Supply) = Power(Stator), 12V x 20A = (12V x 50%) x (Stator Current).

ie, since the output is at 50% (half), the output voltage is half the input voltage which means the output current is double the input current.

Now which current should you limit for which situations?

We cover this piece in our docs (https://phoenix-documentation.readthedocs.io/en/latest/ch13_MC.html#new-api-in-2020), but I’ve paraphrased it below.

The stator current limit is what limits the motor. So if you want to limit acceleration, motor heat, etc. you should limit the stator current.

The supply current is the same as the current being drawn through the PDP, so this is what you should limit to prevent breaker trips.