I work in the automotive sector and we have robotron weld controllers model s-415. Presently they are set up for primary constant current control. Sometimes due to human error the secondary loop is altered by the wrong jumpers/cables (different length) being installed. I'm lead to believe that the constant current compensation is 2-3%; would this compensate the schedule for one of a pair of guns, ie were originally set up the same (weld schedule, hardware)? We do not have the ability to go to secondary compensation presently so that is not an option.

-- Terry Cooper (Tcooper38@cogeco.ca), December 07, 2002

Answers

You should check with Robotron of course, but I had a similar problem at the Lordstown Assy Plant, which was nicely handled by Bruce Kelly of GM CRW group in the GM Tech Center. The problem was that the weld control would start out at the % setting it last used, and then compensate the current starting from there. This was a problem where different heats followed each other on the same gun, and would be a problem for you with different heats sent to different guns. I assume you mean that you intend to fire the guns one at a time, mechanically cascading them. Bruce setup the controls to fire one cycle of heat in the % mode, at a level that would produce the desired current. Then the rest of the cycles were performed in the current mode, set to the desired current. This caused the control to start heat at a value very close to what we needed, then regulate the current for the rest of the weld. This would work the same way with a situation where the guns were cascaded too. I do not know the model number of the controls at Lordstown, but it is possible that the heat routines are the same. Again, ask your Robotron representative about that, or just try it! All current regulated weld controls have the same problem, how to regulate the current on the first cycle. Some of them take a few cycles to regulate, such as the ADC control, some are able to build a history of what % equals what current at what voltage, such as the ATek control, which can hit the current within 1% on the first cycle. But they all must "learn while they work". While there are some distinct advantages to secondary monitoring, there is nothing wrong or inaccurate about primary monitoring. I don't think you need to change that.

-- David Bacon Update Technology (dbacon@updatetechnology.com), January 03, 2003.

This answer had to be split in two, as I am too "wordy". Here is the second half:

If you are running the guns in parallel, you are not going to be able to compensate for the current on one without affecting the other. If your guns aren't balanced, you must balance them. Goodrich sells a device that is like a 1:1 transformer that you can splice in the leads to the two guns that will force them to be balanced. Not too many people realize this is available.

-- David Bacon Update Technology (dbacon@updatetechnology.com), January 03, 2003.