Project Background

A well-known domestic welding equipment manufacturer specializes in the research, development and production of MF inverter welding machine, which is widely used in automobile manufacturing, steel structure, shipbuilding, pressure vessel and other industries. Compared with the traditional frequency welding machine, MF inverter welding machine has the advantages of small size, light weight, energy saving, good welding quality and so on.

Welding quality depends directly on the precise control of the welding current, requiring high-performance current detection solutions. At the same time, the harsh working environment of welding machines and frequent high-current shocks place high demands on the overload capacity and long-term reliability of the shunt.

Product range and technical requirements:

• Product Series: 200A/300A/400A/500A inverter welding machine
• Work system: 60%
• Current control accuracy: ±2%
• Overload requirement: 2.5 times the rated current for 3 seconds (at the moment of arc initiation)

Technical challenges faced

1. High overload capacity requirements

Welding arc instantaneous current can be up to 2-3 times the rated current, the shunt needs to withstand frequent high-current impact. Take 500A welding machine as an example, the arc current can be up to 1250A or more, and the instantaneous power consumption of the shunt can be more than 6 times of the normal operation.

2. Harsh working environment

Welding machines generate a lot of heat, metal spatter and strong electromagnetic interference. The shunt and its signal conditioning circuit need to have good protection and anti-interference ability.

3. Rapid response requirements

Accurate control of welding current requires fast current feedback, and excessive delays in the control loop can affect welding arc stability and weld quality.

4. Long-term durability

Industrial equipment requires high reliability, and shunts need to withstand tens or even hundreds of thousands of thermal cycles to maintain stable performance throughout their service life.

Technical Solutions

1. Shunt sizing

For different specifications of the welding machine, the FL-2 type series shunt is selected, and the 75mV rated voltage drop specification is adopted uniformly:

2. Overload capacity design

The FL-2 shunt has excellent overload capability:

• Continuous overload: 1.2 times rated current
• 5 seconds overload: 5 times rated current
• Transient shocks: can withstand higher multiples of short-term shocks (<100ms)

The electron beam welding process ensures the strength and reliability of the solder joints between the resistor body and the copper terminals, with no false soldering or cracking under frequent thermal cycling.

3. Thermal solutions

The shunt is mounted on an aluminum heat sink base plate that is bolted down to ensure good heat transfer. The welder's built-in fan provides forced air cooling. The temperature of the shunt is stabilized at less than 75°C under 500A/60% operating conditions.

4. Signal conditioning

• Wide bandwidth operational amplifier with small signal bandwidth >1MHz and large signal swing rate >10V/µs
• Signal Response Time<10µs for fast control loops
• Add TVS protection and RC filtering on the input side to prevent the surge generated by the welding arc from damaging the back-end circuitry

Project results

• Control precision:Welding current control accuracy reaches ±2%, to meet the requirements of various types of welding processes
• Reliability:The shunt passed 100,000 thermal cycle tests (room temperature ↔150°C) with no significant change in performance
• Security Protection:Overcurrent protection response time<1ms, effective protection of the welding machine and operator safety
• Application Scale:More than 50,000 welding machines have been used, covering the full range of products
• Market Feedback:Extremely low failure rate, good customer feedback, has established a long-term strategic partnership