Induction Heater Shunt

I Have a 1800 watt induction heater that i am feeding with a 48VDC 50 amp power supply. I am Pulling 44 amps on start up for about 20 seconds then quickly dropping down below 40 amps. I am trying to figure out my amps between the output side of the induction heater and the coil. I am trying to use a 50 amp 75mv shunt to determine this but it appears as if the shunt is not functioning correctly. Could this be due to the oscillation of the induction heater. Hopefully someone can determine if this is possible to do with a shunt or not. I was using #8 wire but its getting very hot. I switched to #6 and its still getting fairly warm but its not too alarming. I would just like to know my amps.

Hello Jon,
Thank you for the request.
Do you have a model number of your induction Heater so we can try and find some specs. Also Have you measured the Voltage output to the Coil? That is a spec you did not have.