Hello I have a problem regarding my MMA welding inverter. The model of the inverter is ST Weld mini 160.
When I make a short circuit on the output using a bolt for example, then the measured current is about 30-40 Amps higher than the value indicated on the display. I measure the current using a DC clampmeter. For example if I set the output current to 100A, then the measured value during output shortcircuit is 130-140A.
Is this normal ?

 

It is reasonable that the direct short circuit current will be greater than the actual arc welding current. In actual welding there iare a number of resistance elements in the connections that reduce the current, AND there is a resistance in both the actual spark of the arc, and in the steel welding rod. And every bit of resistance reduces the current some.
Besides that, putting a direct short circuit across a welding supply is an abuse that may cause it to fail. There is a big difference between a welding load and a deliberate shorted circuit.

 

I measure the current using a DC clampmeter.

I've never heard of a clamp meter that can measure DC. Not unless there's one out there that is probably very expensive.

 

Hall effect Clamp meter -UNI-T UT207B $90 at Amazon DC current up to 1000 amps.

 

I've never heard of a clamp meter that can measure DC. Not unless there's one out there that is probably very expensive.

not all clamp meters use same sensor. ones with current transformer and Rogowski coil are only for AC.
but if sensor is using hall effect, it can measure both AC and DC. many ICs use that too (ACS7xx).
one of the advantages (compared to using shunt) is complete galvanic isolation from test circuit.

 

OK!! I CAN imagine a clamp-on hall effect ammeter performing as described, and costing $90 USD.
But it may not be quite as accurate as an expensive ammeter and shunt system.In addition, it may be that the welder power out is not perfectly noiseless DC In fact, some welder supplies add AC to improve the weld quality. ( Understand that I claim NO welding mastery at all.)

 

agree... it is plausible that clamp-meter reading is off. inverter type welders use high switching frequency, probably too fast for the low pass filter (may be not decay fast enough).

 

I am thinking that an inverter supply welder has harmonics and noise that would cause errors in a current reading. BUT it might not.