What is a “Demand Charge” and how do you lower the power bill for resistance welding?

Resistance welding professionals understand the delicate balance between weld quality, production throughput, and operational costs. 

While optimizing weld parameters for metallurgical integrity is paramount, energy consumption (particularly demand charges) often represents a significant, yet sometimes overlooked, expense. 

Due to resistance welding machines utilizing high peak power demands, these demand charges can balloon a manufacturer’s operating costs. Demand-related charges can be upwards of 30% to 70% of a commercial customer’s utility bill.

In this blog we will discuss the impact of demand charges on resistance welding operations and how adaptive control technologies can mitigate these costs while enhancing weld consistency.

The Significance of Demand Charges in Industrial Power Consumption

First, we need to understand what a “demand charge” is and how it works in relation to your energy bill.

Your current electricity bill is split into two parts:  Energy and Demand. You’re likely familiar with the energy charge, which is based on the total amount of electricity you use over a billing period, measured in kilowatt-hours (kWh). A demand charge, however, is based on the highest amount of power you use at any one time (the rate), measured in kilowatts (kW).

This is where the demand charge comes in. Beyond the standard kilowatt-hour (kWh) charge for total energy consumption, industrial power users are billed for the maximum “peak power” draw within a defined billing period (typically 15-30 minutes). These demand charges are the fees levied by the utility company to offset their cost of maintaining sufficient infrastructure (power plants, transmission lines, etc.) to meet the peak power demand of all their customers at any given moment. 

Said another way, demand charges are not about how much energy you use overall, but rather how quickly you use it at any given moment. In essence, a demand charge is a fee for having the capacity to use a large amount of power at once, regardless of whether you consistently use that much power throughout the billing period.

Resistance Welding and Peak Demand: A Direct Correlation

The fundamental principle of resistance welding—Joule heating (Q = I²Rt)—dictates a direct relationship between current (I), resistance (R), and time (t) in generating weld heat (Q). 

Traditional resistance welding controls, which use fixed weld schedules, can lead to inefficient energy use and demand spikes because welding requires high-current, short-duration pulses. While resistance welding uses relatively little energy overall (kWh), these short bursts of high power usage create spikes in demand, leading to higher demand costs.

The peak demand can be further exacerbated by factors that increase current or weld time to achieve acceptable weld quality:

• Electrode Wear: As electrodes wear, the contact area changes, affecting current density.
• Material Variations: Differences in material thickness, surface condition, or coatings can significantly affect weld quality.
• Fit-up Issues: Poor fit-up between parts can create inconsistencies. 

Inverter Technology Solves Demand Charge Mitigation and Enhanced Weld Quality

Fortunately, resistance welding controls that use inverter technology provide a solution to these challenges. In resistance welding, inverters provide precise control over the welding current, resulting in more consistent welds and reduced energy consumption.

How Inverter Technology Reduces Demand Charges

Resistance Welding inverter controls offer a solution to reduce the peak power required in some manufacturing operations. This technology efficiently converts alternating current (AC) to direct current (DC), and then delivers the precise current and voltage required for the welding process.

So how does this impact demand charges? Inverter technology is able to help manufacturers achieve:

• Reduced Power Consumption: Inverters allow for precise control of the welding current, reducing the overall power consumption of the welding process. This leads to lower peak demand and, consequently, lower demand charges.
• Improved Energy Efficiency: By optimizing the welding process, inverter systems can reduce energy consumption, leading to lower overall energy costs.
• Better Weld Consistency: By providing a consistent welding current, inverters reduce the number of failed welds and scrap. This improves production efficiency and reduces the need for rework, which further lowers energy consumption.  
• Power Factor Correction: Inverters can improve the power factor of the welding machine, reducing the reactive power drawn from the grid. This can lead to lower demand charges, as some utilities include power factor in their demand charge calculations.  

Additional Benefits of Inverter Technology

In addition to reducing demand charges, inverter technology offers several other benefits for resistance welding:

• Improved Weld Quality: Inverters produce more consistent and reliable welds with optimal nugget formation, superior joint strength, and excellent surface appearance.  
• Shorter Weld Times: Inverter technology produces heat more efficiently, decreasing weld times by as much as one-third. This increases production throughput and reduces energy consumption.  
• Reduced Heat Affected Zone (HAZ): The shorter weld times and precise control offered by inverters cause a smaller HAZ, minimizing distortion and improving the quality of the weld.  
• Welding of “Hard-to-Weld” Materials: Inverters improve the welding of materials such as coated steels, aluminum, brass, and copper. This expands the range of applications for resistance welding manufacturers.

WeldComputer’s Inverter Technology

WeldComputer’s inverter technology specifically addresses the issue of demand charges by providing advanced control and monitoring capabilities. Our controls are designed to keep power steady, increasing welding performance while saving energy.  And if you’re retrofitting to an existing AC welding transformer, the savings can be even greater.

Additionally, WeldComputer controls using Adaptive technology can continuously monitor and adjust the weld current throughout the weld, compensating for variations in workpiece resistance, worn electrodes, shunting, poor part fit-up, and other sources of variation. This results in utilization of just the right amount of energy for each weld to ensure it’s good, further reducing energy consumption and demand charges.  

If you’d like to see the WeldComputer control in action in your own facility, we offer a proof-of-concept evaluation so you can see how much you’ll save on your energy bill and reduce your demand charges without needing to make a significant capital investment.

Customers like McCorvey Sheet Metals were able to quickly achieve the same weld sizes while increasing the Power Factor to 85-90% from 50% and reducing power demand by over 80kW solely by switching to the WeldComputer evaluation control. By leveraging the WeldComputer trial, McCorvey was able to nearly half their energy use, justifying an upgrade to WeldComputer controls.

Conclusion

Demand charges can represent a significant cost for resistance welding operations. By understanding the factors that contribute to peak demand and implementing effective strategies to mitigate them, manufacturers can significantly reduce their energy costs. 

Inverter technology, when combined with intelligent control systems, offers a powerful solution for optimizing resistance welding processes and achieving significant cost savings. Resistance Welding Controls using inverter technology, like those from WeldComputer, can be a valuable tool for companies looking to reduce energy costs and improve welding performance.

To learn more about how WeldComputer’s inverter technology can help your business reduce demand charges and improve welding performance, contact us today for a consultation.