Circuit
ZX7-250 Current Display vs Real Welding Current: Shunt Measurement and 75mV Metering
A circuit and measurement page explaining simulated current display, external 24V board testing, real output current measurement with a 250A/300A shunt and 75mV meter input.
Why current display can mislead
During signal-board testing, the current display can change when the current potentiometer is adjusted, even though the welder is not delivering real welding current. This is a control-side or simulated value. It proves that part of the board responds, but it does not prove that output current exists.
Measurement diagram
How to measure real output current
Real current must pass through a shunt in the output path. The notes mention 250A and 300A shunt examples. A common 300A shunt produces 75mV at full current, so the meter input must be matched to the shunt output rather than connected as a normal low-current meter.
Test table
| Check | Expected | Abnormal meaning |
|---|---|---|
| Potentiometer display change | control board responding | not proof of welding current |
| 250A / 300A shunt | installed in output current path | wrong rating gives wrong reading |
| 75mV meter input | matches shunt full-scale voltage | wrong meter input gives false reading |
| Actual welding load | required for real current verification | no load test may only prove control response |