Controls & Transformers

Questions and Answers

Current monitors usually allow one to set high and low limits around the desired set current. These can be used as an alert that the process is changing and action might be necessary to maintain good weld quality.

Selection of the initial desired set point is determined by the desired quality and the general philosophy of the manufacturing facility. Some facilities prefer to operate near expulsion and others prefer to run midrange in the weld window.

 Low Carbon Steel Weld Lobe

Any point inside the weld window/lobe should produce a good weld. If one chooses to operate on an extreme near expulsion there is little room for error. The alarm would be set very tight? If the current raises on the top side expulsion and overheated burned product could be expected.

Conversely if one operates on the low end. One is risking producing small or a “NO WELD” situation. One never wants to be at the low end and produce small or no welds. Current must exceed this.

The answer is the choice of the operating current setting and any monitor setting alerts around this setting are determined by the individual plant their individual need to meet the manufacturing requirements.

This is beyond the scope of this blog.

Another related article on this subject is:
WHEN SHOULD A WELD MONITOR BE SET UP TO SAMPLE DATA DURING RESISTANCE WELDING?

Reference: RWMA – Resistance Welding Manual 4th Edition

This question was generated from another article in this blog:
HOW DO YOU MEASURE THE INSULATION VALUE OF A RESISTANCE WELDING TRANSFORMER?

?Meggar Tester

            MEGGAR TESTER

The original article describes how to measure the insulation condition of a transformer. This is very important since the insulation is very thin and its failure makes the machine inoperable.
The question is how do you test without causing the damage. The answer was in the original article in the last sentence.

This type of testing should be performed by personnel trained to test transformers. Transformer manufactures can perform this test.

Reference: RWMA Resistance Welding Manual 4th Edition

After reading the article “WHAT IS MFDC WELDING” a reader asked for more detail on how the transformer performs in this process. This blog does not go into specific equipment detail but there is another article which has more detail of the functions of the MFDC control and transformer:

IS THERE A DIFFERENCE BETWEEN MFDC AND AC RESISTANCE WELDING TRANSFORMERS?

This articles answers the question of how the MFDC transformer functions and how it handles the voltage and current.

Inverter Control Transformer Schematic

   Schematic of Power Conersionin Control and Transformer of Mid Frequency Inverter

 

Reference: Entron Controls, LLC

The amperage capability of a cable depends upon its size in diameter/conductors and its length. It is also cooling dependent. The cable must be cooled at each end or water cooled its entire length. Its ampacity varies depending upon each of these variables. Most cables are cooled at each end. The chart below gives amperage for cables of this type.

Cable Air Cooled Sizing

Based on the above chart a 750 MCM air cooled cable is rated at about 1400 – 2700 amperes depending upon length.

 Cable Water Cooled Sizing

For comparison a water cooled 750 MCM Cable is rated at approximately 12,000 to 37,000 amperes at the above lengths.
Water cooling increases the ampacity substantially.

Sizing of the cables is discussed in the article:

HOW DO YOU SIZE THE PRIMARY CONDUCTORS FOR AN AC RESISTANCE WELDING TRANSFORMER?

Reference: National Electric Code
                   RWMA Manual Chapter -21.7
                   Roman Manufacturing Inc.

After reading the article:

COMPARE MFDC VS AC IN RESISTANCE WELDING?

 

Inverter Control Transformer Schematic

SCHEMATIC AND POWER CONVERSION IN CONTROL AND TRANSFORMER OF MID FREQUENCY INVERTER

A reader requested a full manual and description of how to use an inverter control. This is a very logical and important step to learn the features and operating procedures of the various MFDC controls in the marketplace.

This blog is devoted to the basic science of resistance welding and does not deal with the features and operation of the machinery in the marketplace. For this important information contact local distributors or manufacturers. They are fully prepared to supply this information.

Reference: RWMA – RWMA Resistance Welding Manual 4th Edition

Have a Question?

Do you have a question that is not covered in our knowledgebase? Do you have questions regarding the above article? Click here to ask the professor.