Voltage, Wire speed, no amperage??

Date 06-30-2008 05:00 Edited 06-30-2008 05:36

This may seem like a simple/dumb question but here goes: I learned to Mig weld with a Lincoln 3200HD which had a 4 setting amperage control and wire speed control. I've recently picked up a Millermatic 250X and it only has Voltage and Wire speed controls. How is the amperage figured out? Does a lower wire speed and higher voltage simply put out more amperage as opposed to a higher wire speed?

By DaveBoyer (*****)

Date 06-30-2008 05:26

Not a dumb question, but here is an explanation:

In wire feed constant voltage [CV] machines the settings are voltage and wire speed. This applies to Your Lincoln as well. The amperage will change relative to the wire speed up to the capacity of the machine. This is because the transformer is trying to maintain the set voltage and arc length, and the more wire You feed in the more amperage it takes to melt it all.

The transformer is wound differently in a stick welder, You set the maximum amperage, and the voltage varies with the arc length, this is called constant current [CC].

These are theoretical descriptions, in actuality both machines have slope to the volt amper curve if You plot it on a graph, but the ammount of slope is extremely different on a CV [MIG] machine than on a CC [stick/TIG] machine.

There are charts published that show the amperage based on the wire diameter and feed rate, You read the amperage from the chart if the machine has no instrumentation and You have no external way to measure it.

By phaux

Date 06-30-2008 05:39

Thanks. So what about things such as the Miller suitcase welders that run off of a stick welder? Would they be CV or CC because of the power supply?

By aevald

Date 06-30-2008 07:09

Hello phaux, Dave gave you a very concise explanation of the workings of voltage versus amperage concerning a Constant Voltage power source. If you use the search function on the forum and type in suitcase wirefeeders, voltage sensing feeders, or other such topics, I believe you will come up with a wealth of information to answer your questions on how these particular feeders work and the differences between the Constant Voltage and Constant Current. Very quickly, the Constant Current power sources have to be used with a voltage sensing feeder in order to work and most of these feeders also have the ability to be used on either CC/CV depending upon how they are set-up. Generally any sort of code work needs to be performed in the CV mode with a CV power source unless a WPQR has been done to support it otherwise. Enjoy the reading. Best regards, aevald