welder current adjustment and measurement

Question

Hello everyone, over the past few months I have been interested in building ARC welders from microwave transformers, after my prototype version I decided to add more features to my second model one of which would be adjusting and displaying current output. The problems I have been facing are developing an accurate way to vary the amps and to locate a high amp digital meter. If any of you have any methods for varying current and or know a device that can measure high current your help would be greatly appreciated.Thank you

jw0752 · Answer

The best way to control the amps of your secondary is to control the voltage of your primary. For this you could use a triac or even a commercial light dimmer control of sufficient current handling capacity. I do not know how many amps you are talking about and I do not know what your circuit looks like but since you are talking transformers I will assume you are trying to measure AC amps. You can make your own ampmeter by winding a coil around one of the transformer secondary wires and using the induced voltage to drive a milli or micro volt meter with a shunt resistor. Set up a resistive load on your secondary so you have a known current, say 10 amps, flowing. Add or subtract winds of the coil around the wire until your meter reads 10 accross the shunt resistor. Then you will have a correspondence between the Amps of your secondary and the millivolts of your meter. As I am fairly old school I will not be the least bit surprised to find out there is a better way to do this but this should get the discussion going.

D_Hersey · Answer

Hall effect - Wikipedia, the free encyclopedia Allegro MicroSystems - ACS714 and ACS715 FAQ We are measuring the magnetic field that the current produces, this allows us to take out less energy than the CS resistor approach. From Wiki: The charge carriers of a current carrying conductor placed in a transverse magnetic field experience a sideways Lorentz force; this results in a charge separation in a direction perpendicular to the current and to the magnetic field. The resultant voltage in that direction is proportional to the applied magnetic field. This is known as the Hall effect . The Hall effect is often used to measure the magnitude of a magnetic field. It is used as well to find the sign of the dominant charge carriers in materials such as semiconductors (negative electrons or positive holes). ========== The other fellas in this thread are hinting you in the right direction: It would be far easier to sense current on your low-current primary and infer secondary side current. Transformers are pretty efficient in this regime, probably.