Controls & Transformers

Questions and Answers

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

All RWMA resistance welding equipment is designed on a maximum 50% duty cycle. All power calculations are based upon this premise.
An article has been written which builds upon this premise and determines the power usage of a 150 kva welder.

Power calculations can be found in the article:

HOW MUCH POWER IS USED RESISTANCE WELDING ON A 150 KVA WELDER?

The calculations for duty cycles can be found in another article for AC & DC:

WHAT IS DUTY CYCLE?

Reference: RWMA – Resistance Welding Manual Section 19.3

Duty cycle for all RWMA equipment is designed to operate at a maximum 50% duty cycle. For each new resistance welding application one must confirm this value will not be exceeded.
The AC and DC duty cycle calculations can be found in another article:

WHAT IS DUTY CYCLE?

Power calculations can be found in the article:

HOW MUCH POWER IS USED RESISTANCE WELDING ON A 150 KVA WELDER?

Reference: RWMA – Resistance Welding Manual Section 19.3

An MFDC or AC weld gun is just a working tool that does what it is told to do by one or more controls. The robot puts it in place to make the weld and the resistance welding control makes all of the decisions for the welding schedule. The gun is not adaptive. The robot positioning is not adaptive but can be repositioned. The weld control in some cases can be adaptive.

     SERVO ACTUATED GUN

SERVO ACTUATED WELD GUN

The amount of adaptability and diversity depends upon the control. A discussion of adaptive controls is beyond the scope of this blog. One should contact your local supplier and control manufacturer to expand your knowledge on adaptive controls.

RWMA could be a source of equipment manufacturers with knowledge in this area.


Reference: RWMA - Resistance Welding Manufacturing Alliance

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