AC Resistance Welding vs CD Welding: Which Technology Is Right for Your Application?
The Two Main Resistance Welding Technologies Explained
Both AC resistance welding and CD (capacitive discharge) welding create joints by passing electrical current through metal at the weld interface — resistance at the contact point generates heat, the metal melts and fuses under electrode pressure. That's where the similarity ends.
The energy delivery mechanism is completely different: CD welding stores energy in capacitors and releases it in a millisecond burst; AC welding draws power from a transformer continuously for as long as the trigger is held. This difference in energy delivery determines which applications each technology handles correctly — and using the wrong technology for the wrong application produces consistently poor results.
Watch this overview of AC resistance welding and CD welding technologies:
How CD (Capacitive Discharge) Welding Works
Energy Storage and Release
A CD welder charges a bank of capacitors to a set voltage level between weld cycles. When triggered, the stored charge discharges through the tungsten electrode in a single controlled pulse. The total discharge takes 1–10 milliseconds — far shorter than any transformer-based welding process.
The energy per weld is defined by the capacitor bank charge state, set in joules by the operator. Because the energy comes from a pre-charged capacitor bank rather than live mains power during the weld cycle, each pulse delivers the same energy regardless of mains voltage fluctuations. This gives CD welding its characteristic weld-to-weld consistency.
For a deeper explanation of the CD mechanism and physics, our what is a CD spot welder guide covers the capacitor discharge process in detail.
Pulse Shape and Duration
The CD pulse is essentially a single-discharge event: high peak current in a very short duration, then rapid decay as the capacitor exhausts its charge. The pulse shape (current vs time curve) is largely determined by the capacitor bank characteristics and the circuit's inductance. In advanced systems (Sunstone CD with Tru-Fire Technology), electronic control of the discharge characteristics improves consistency at very low joule settings.
Dual-pulse CD systems fire two sequential pulses — the first conditioning the interface surface, the second completing the fusion. This is the professional configuration for battery tab welding where surface oxide variation is a significant source of weld inconsistency.
Best Applications
CD welding is the correct technology for:
- Battery tab welding (18650, 21700, pouch cells): The millisecond pulse duration keeps cell surface temperatures within safe limits during the weld
- Electronics and PCB component joining: Fine wire termination, thermocouple assembly, component lead welding
- Permanent jewelry welding: The 1–30J or 1–60J energy range of professional CD welders covers jump ring fusion in fine precious metal chain
- Precision spot welding on thin and heat-sensitive materials: Any application where thermal damage to adjacent material is a concern
- R&D and prototyping: Quick setup, repeatable results, wide material compatibility
How AC Resistance Welding Works
Continuous Wave vs Pulsed Energy
AC resistance welding uses a transformer to step down mains voltage to high-current, low-voltage output. Unlike CD, the current flows continuously from the mains through the transformer to the electrodes as long as the trigger is active. The weld duration is measured in line frequency cycles (50 or 60Hz), not milliseconds — a 5-cycle weld at 60Hz is 83 milliseconds; a 10-cycle weld is 167 milliseconds.
Sunstone AC Resistance Spot Welders can be adjusted down to weld times as low as 1/100 second, providing fine control at the short end. The AC welding systems are primarily used to create seam welds using the continuous flow of energy from the AC Power supply — the unit will continually flow weld energy as long as the trigger is pressed.
This continuous energy delivery is the defining characteristic that separates AC from CD. It's not a limitation — it's the feature that makes AC uniquely suited for seam welding and mesh welding applications.
Seam Welding Capability
AC resistance welding can create continuous seam welds — an unbroken fusion line along a joint — by maintaining current through a rolling electrode (roller electrode / EL-Roll) as it travels along the workpiece. CD welding, with its discrete discharge-per-trigger mechanism, creates a series of overlapping spot welds rather than a true continuous seam.
For applications requiring hermetic seals, continuous filter seams, or mesh welding where every wire intersection must be fused with consistent and maintained current — AC's continuous energy delivery is not just better, it's the correct technology.
The Sunstone Wave AC is an outstanding welding solution for continuous seam welds, foil welding, pouch cell welding, mesh or screen welding, hermetic sealing, and filter production applications.
Best Applications
AC resistance welding is the correct technology for:
- Wire mesh and screen welding: Every wire intersection across the mesh grid welded in a single seam pass
- Continuous seam welding: Hermetic package seals, filter body seams, battery pouch seals
- Foil welding: Very thin metal foil joining where the sustained current creates consistent fusing
- Pouch cell sealing: The seam around the perimeter of lithium pouch cells
- Filter basket and strainer body assembly: Mesh-to-frame joins in filtration components
- Heat insulation blanket fabrication: Stainless steel insulation assembly in industrial and nuclear applications
Head-to-Head Comparison
Heat Input and Material Sensitivity
CD welding: Very low heat input. The millisecond pulse deposits energy at the weld interface and ends before significant heat can conduct into the surrounding material. Heat-affected zone (HAZ) is minimal. Appropriate for heat-sensitive adjacent materials (lithium cell chemistry, PCB components, gemstones in jewellery).
AC resistance welding: Moderate heat input sustained over milliseconds to tens of milliseconds. The HAZ is larger than CD, but for AC's target applications (mesh intersections, seam joining, foil) the sustained energy is necessary and appropriate. Typical welding applications range from sheets as thin as 0.05mm up to 1.2mm, depending on metal and orientation.
Speed and Throughput
CD welding: Extremely fast per spot — each weld takes milliseconds. For single-spot applications (battery tabs, jewellery jump rings), individual welds are very fast. Throughput for a large mesh grid (requiring hundreds of intersection welds) is limited by the need to trigger and position for each spot.
AC resistance welding: Slower per spot (multi-cycle weld), but the continuous seam mode enables high-throughput mesh and seam applications by welding every intersection in a single continuous pass. For mesh welding, the AC seam mode is dramatically faster than discrete spot welding.
Material Compatibility
CD welding: Excellent for nickel, gold, silver, platinum, and most ferrous metals. Copper requires a professional high-joule CD system. Aluminium is limited. Highly suitable for dissimilar metal joining where each metal can absorb the rapid pulse differently.
AC resistance welding: Designed for thin steel, stainless steel, nickel alloys, and similar materials in sheet, foil, and mesh form. Sunstone AC resistance spot welders are ideal for a broad range of complex alloys and applications commonly used in the aerospace, automotive, electronics, jewellery, medical devices, batteries, military, laboratory and many other industrial sectors.
Weld Types: Spot vs Seam
CD welding: Spot welds only — each trigger press produces one fusion point (or two spots for dual-probe). No true continuous seam capability. Overlapping spot pattern is possible but not equivalent to a genuine seam weld.
AC resistance welding: Both spot and continuous seam welding. The seam mode, combined with roller electrodes, creates an unbroken fusion line. This is the technology's defining advantage for seam applications.
Equipment Cost
CD systems: Sunstone CD range from approximately $500 for entry single-pulse through $1,200–$2,000+ for the CD200DP/CD400DP dual-pulse professional systems.
Wave AC: The Sunstone Wave AC is a professional-tier product positioned for manufacturing applications. Pricing is not published publicly; it's marketed to semi-automated manufacturing environments and industrial-scale filtration, battery, and medical device manufacturers. Contact Sunstone for pricing.
For the complete CD buyer's guide, our best battery spot welders guide covers the full CD range with pricing.
Ease of Setup and Use
CD welding: Digital joule setting; calibration on scrap material; parameter setting is straightforward once the joule range for the material is established. Sunstone's CD interface is intuitive for operators familiar with the application.
Wave AC: The heart of the Wave AC's performance is absolute digital energy control via a 10-inch color touchscreen display. The 10-inch color touchscreen provides real-time updates, transforming welding parameters into a dynamic waveform — as operators make changes, they can see exactly how these adjustments impact the welding process. The waveform visualisation is the standout feature for operators managing complex seam welding parameter profiles.
Where CD Welding Wins
Battery Tab and Pack Assembly
CD welding is the industry standard for 18650, 21700, and pouch cell battery tab welding. The millisecond pulse duration is the reason it's used rather than AC: the energy is deposited and the weld completes before meaningful heat conducts to the cell interior. Lithium cell manufacturers specify cell surface temperature limits (typically 60–80°C) during assembly — CD welding meets these limits; AC welding's sustained current would exceed them for direct terminal contact.
Dual-pulse CD (Sunstone CD200DP/CD400DP) adds conditioning pulse capability to address nickel oxide surface variability, producing consistent welds across a full pack build session.
Electronics and Precision Micro Welding
Thermocouple assembly, fine wire termination, sensor leads, and electronic component joining all benefit from CD's minimal HAZ. The surrounding circuit board, adjacent solder joints, and heat-sensitive components remain at essentially ambient temperature through a correctly executed CD weld.
Prototyping and R&D
CD welding's wide material compatibility, adjustable energy range, and single-trigger-per-weld operation make it the flexible workhorse for laboratory and prototyping environments where material types and specifications change frequently. Setting up for a new material is a calibration exercise on scrap, not a machine reconfiguration.
Where AC Welding Wins
Wire Mesh and Screen Fabrication
Wire mesh welding — fusing every intersection point across a grid of crossing wires — is one of AC welding's most distinctive applications. The continuous seam mode with roller electrodes can traverse an entire mesh panel, welding every intersection with consistent current in a single pass.
The Wave AC Welder's ability to discharge weld energy continuously to seam weld a length of filtration material quickly and efficiently makes it the preferred tool for filtration manufacturers. A CD welder performing individual spot welds at each grid intersection would take many times longer for the same panel, and the results would lack the consistency of a continuous seam pass.
For detailed guidance on welding wire mesh and screen materials, our mesh and wire welding guide covers the AC welding process for these applications specifically.
Foil and Pouch Cell Sealing
Very thin metal foil — 0.05mm and below — requires the sustained, controllable energy delivery of AC welding. The continuous current can be precisely modulated to fuse foil without burn-through, which the high peak current of CD pulses makes more difficult at these thicknesses.
Lithium pouch cell sealing around the perimeter of the cell casing is a key application. AC Resistance seam welders are ideal for creating a continuous seam weld, foil welding, pouch cell welding, and mesh or screen welding. The primary applications include the creation of hermetic seal with a pouch or package.
Filter Basket and Hermetic Seal Assembly
AC Resistance seam welders create and build filter assemblies, filter bodies, and attaching mesh screen to a strainer basket. Additional applications include filter baskets, battery cells, and any metal filter or screen.
The combination of mesh welding and seam welding capabilities in one AC system makes it the logical choice for filter and strainer manufacturers. The ability to weld the mesh to the basket frame and seal the basket seam using the same machine, with different electrode configurations, streamlines the production process.
Can You Use One Machine for Both Applications?
In practice: no, not effectively. The two technologies have fundamentally different energy delivery mechanisms, and these translate to different physical machine architectures.
A CD machine cannot produce a true continuous seam weld — it can produce overlapping spot welds that approximate a seam, but the discrete discharge-per-trigger mechanism cannot replicate the continuous fusing of a roller seam weld.
An AC machine cannot deliver the sub-millisecond energy pulses that make CD welding safe for lithium battery terminal contact. The transformer-based sustained current would exceed cell temperature limits for direct terminal welding.
Some applications sit in overlap — pouch cell sealing is listed as an AC application (using seam sealing around the cell perimeter) while battery tab welding is a CD application (spot welding tabs to the cell terminals). A battery manufacturer producing pouch cells may genuinely use both in the same production line for different stages of the assembly.
For labs and manufacturers serving both application categories, the practical answer is two machines: a CD system for precision spot welding and a Wave AC for seam and mesh work.
The Sunstone Lineup: Which Technology for Which Bundle?
CD Line for Battery and Electronics Work
Sunstone's capacitive discharge line covers battery tab welding, permanent jewellery welding, electronics assembly, and precision micro welding:
- Zapp / Zapp Plus 2: Permanent jewelry, fine jewellery repair, entry battery tab welding
- Orion mPulse / mPulse PRO: Professional permanent jewelry and battery assembly, 1–60J range with Tru-Fire Technology
- CD200DP: Professional dual-pulse battery tab welding, up to 200J, independent conditioning and fusion pulse control
- CD400DP: High-power battery welding and copper tab capability, up to 400J
For a full review of the CD range, see our Sunstone CD spot welder review.
Wave AC for Mesh and Filtration Work
The Sunstone Wave AC is the current professional AC resistance welding product:
The Sunstone Wave AC is capable of delivering up to 2,700 amperes and features absolute digital energy control via a 10-inch colour touchscreen. The waveform visualisation allows operators to see parameter changes represented as a live waveform — a meaningful upgrade from dial-based control for complex seam welding parameter profiles.
Applications: continuous seam welds, foil welding, pouch cell welding, mesh or screen welding, hermetic sealing, and filter production.
The Sunstone AC range also includes earlier models available in 2.2, 5, and 15 kVA configurations with dual pulse, multi-pulse, roll-spot, foil welding, and continuous seam functions, with storage for up to 100 schedules and 10 job chains.
Frequently Asked Questions
What is the difference between AC resistance welding and CD welding?
AC resistance welding draws continuous current from a mains transformer through the electrodes for the duration of the weld (milliseconds to tens of milliseconds at line frequency cycles). CD (capacitive discharge) welding stores energy in capacitors and releases it in a single 1–10 millisecond pulse. The practical consequences: AC can create continuous seam welds (by running current through roller electrodes along a seam), while CD can only create discrete spot welds. CD's much shorter pulse duration creates a smaller heat-affected zone, making it safe for heat-sensitive applications like lithium battery terminal welding; AC's sustained current makes it ideal for seam and mesh applications where continuous energy delivery is required.
Can AC resistance welding be used for battery tabs?
For seam sealing around the perimeter of lithium pouch cells: yes, AC resistance welding is the standard method. For direct spot welding of nickel strip tabs to cylindrical cell (18650/21700) terminals: no — the sustained AC current deposits too much heat into the cell, exceeding safe cell temperature limits. Battery tab welding for cylindrical cells uses CD welding, which completes the weld before meaningful heat conducts to the cell interior.
What is the Sunstone Wave AC welder used for?
The Sunstone Wave AC is designed for continuous seam welding, foil welding, pouch cell sealing, wire mesh and screen welding, hermetic sealing, and filter production applications. It delivers up to 2,700 amperes with digital energy control via a 10-inch touchscreen, and features real-time waveform visualization of welding parameters. It's positioned for semi-automated manufacturing environments in filtration, battery, medical device, and aerospace applications where consistent seam welds are required.
What applications require AC resistance welding rather than CD welding?
Applications where the continuous energy delivery of AC is specifically required: wire mesh and screen welding (every intersection fused in a continuous seam pass with roller electrodes), hermetic sealing of filter bodies and strainer baskets (the seam around the perimeter must be continuously fused), foil welding (thin metal foil requires controlled sustained current rather than high peak pulse), and continuous seam welding generally. Any application where the weld is a line rather than a point — and where roller electrodes traversing the joint in real time is the assembly process — is an AC application.
Does Sunstone make both AC and CD welders?
Yes. Sunstone's product range spans both technologies. The CD line includes the Zapp/Zapp Plus 2 (permanent jewelry), Orion mPulse/mPulse PRO (professional precision spot welding), and the CD200DP/CD400DP dual-pulse battery welding systems. The AC line is anchored by the Wave AC, their current professional AC resistance welder for seam, mesh, foil, and filter applications. The two technologies serve different application categories and are not interchangeable — battery tab welding uses CD; mesh and seam welding uses AC.
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