Every motion engineer has stood in front of a control cabinet holding two motor data sheets, trying to decide whether a job is really a 2kW job or really a 5.5kW job. Over-sizing a servo drive burns cabinet space and energy budget; under-sizing it shows up six months later as overheat trips on a hot summer day, or as accelerated bus-capacitor aging from chronic overload. The two ratings most often weighed against each other on packaging, CNC, robotics and heavy-feed assembly lines are the 2kW single-axis servo drive and the 5.5kW High Performance Servo Motor Drive. This article lines up the two ratings on the dimensions that actually decide a build - continuous load torque, peak acceleration headroom, energy draw at the AC input and thermal lifecycle - so the choice is made on numbers, not habit.
Zhejiang Tonghang E-Drive Technology Co., Ltd. is a National High-Tech Enterprise focused on full-digital high-bandwidth servo controller R&D and manufacturing. Its T3 / T3A / T3L series covers 200W–7.5kW on a single platform, so a machine builder can stay within one supplier from a 0.75kW spindle to a 5.5kW high-power axis. The 2kW single-axis drive and the 5.5kW High Performance Servo Motor Drive are the two ratings most often shortlisted side by side, and the rest of this article breaks down how they differ in practice.
Load and Torque: What the Two Ratings Actually Deliver
The first axis to compare is continuous load torque. The 2kW single-axis servo drive, paired with a 130ST-frame or 150ST-frame motor, is sized for 6–15 N·m of rated torque with peaks of 18–30 N·m for acceleration. The heavy-duty 5.5kW unit, paired with the 180AST-AM35015 motor on the T3D-H platform, is rated at 35 N·m of continuous torque - roughly 2.3× the 2kW drive's continuous figure - with the over-current and over-load protection set to handle the heavier inrush current that comes with high-inertia loads.
In mechanical terms, the 2kW drive is comfortable moving a small CNC gantry, a horizontal flow wrapper's film feed, a labeling head or an indexing conveyor. The heavy-duty 5.5kW unit is built for a vertical machining center's spindle-feed axis, a heavy gantry, a palletizer arm, a large-format slitter or any mechanism where the load inertia is several times the motor's own rotor inertia. The right question is not "which is more powerful" - it is "does the load need continuous torque within 80% of the drive's rating, or only within 30%?" If the answer is 30%, the 2kW drive has the headroom; if the answer is closer to 80%, the heavy-duty 5.5kW unit is the safer long-term match.
| Item | 2kW Single-Axis Servo Drive | Heavy-duty 5.5kW Unit |
|---|---|---|
| Drive Series | 2kW Single-Axis Servo Drive | T3D-H (380V Heavy Duty Series) - 5.5kW High Performance Servo Motor Drive |
| Rated Power | 2000W | 5500W |
| Matched Motor | 130ST / 150ST frame, 6–15 N·m | 180AST-AM35015, 35 N·m rated |
| Typical Rated Current | 50A / 75A (optional) | 20.6A on 380V supply |
| Input Voltage | Three-phase 220V AC | Three-phase 380V AC |
| Control Modes | Position, speed, JOG, torque | Position / speed / torque (switchable) |
| Encoder Feedback | 2500-line incremental or 17/23-bit absolute | High-resolution absolute encoder |
| Built-in Protection | Over-voltage, over-current, overheating, under-voltage (IPM 4-fold + soft-start) | Overcurrent, overvoltage, undervoltage, overload, overheat alarm |
| Best-Fit Load Profile | Mid-duty, fast cycles, moderate inertia | Heavy-duty, high-inertia, continuous high torque |
Energy Consumption at the AC Input
A 2kW drive and a 5.5kW drive do not consume 2kW and 5.5kW at the wall - real energy draw depends on the load profile, the cycle time and how much of the time the motor is regenerating versus motoring. The chart below compares typical operating-point energy draw for three common duty patterns, assuming both drives are paired with their matched motor and a standard efficiency servo system.
Indicative AC input draw (per axis, full-cycle average, including regen losses):
2kW · light cycle~0.9 kW
2kW · heavy cycle~1.7 kW
5.5kW · light cycle~1.1 kW
5.5kW · heavy cycle~4.4 kW
Three things stand out. First, a heavy-duty 5.5kW unit run on a light cycle is no longer an efficient machine - it draws a similar amount of wall power as a 2kW drive on a heavy cycle, while delivering less torque density. Second, a 2kW drive run on a heavy cycle starts to lose efficiency because the bus capacitors spend more time absorbing regenerated energy than the drive has margin to push it back. Third, the right sizing point is the one where the 2kW drive sits at roughly 60–75% of its continuous rating on the heavy cycle - that is where its efficiency curve is flattest and where a step up to the heavy-duty 5.5kW unit is not yet justified.
Energy cost compounds faster than most machine builders expect. A 2kW drive that spends an extra 0.5 kW of draw per axis because it is mis-sized for a heavy cycle, multiplied by three shifts and four axes, adds up to tens of thousands of kWh per year. Conversely, a heavy-duty 5.5kW unit installed on a light cycle is a stranded asset that ties up cabinet space, cooling budget and capital for no throughput gain.
Thermal Behavior and Component Lifecycle
Servo drive lifetime is dominated by three thermal-sensitive components: the bus capacitors, the IGBT/IPM power module and the cooling fan. The 2kW single-axis drive uses a Smart IPM module that integrates over-voltage, over-current, overheat and under-voltage protection in one package - a design that runs cool under its rated 2kW load but starts to derate if the cycle forces it to 130% of rated current for more than a few seconds at a time. The heavy-duty 5.5kW unit, running on a 380V three-phase supply with a matched 180AST motor, has more thermal headroom by design: the larger heatsink, the heavier bus capacitors and the higher over-current ceiling all push the operating junction temperature further below its limit.
The practical effect is a longer mean-time-between-failure. Under a continuous heavy-load profile, a properly sized 2kW drive will run 5–7 years before the bus capacitors or the IPM approach end-of-life. A properly sized heavy-duty 5.5kW unit, with more thermal margin and a 380V supply that puts less current stress on the input rectifier, will typically run 7–10 years. The cost-of-ownership trade-off therefore depends not on the sticker price of the drive, but on the operating load factor and the expected service life of the machine.
| Lifecycle Indicator | 2kW Single-Axis Servo Drive | Heavy-duty 5.5kW Unit |
|---|---|---|
| Typical Continuous Load Factor (recommended) | 40–75% of rated | 30–80% of rated |
| Overload Margin (short term) | ~2× rated current for a few seconds | 2–3× rated current, depending on cycle |
| Cooling Approach | Forced-air fan, integrated heatsink | Larger heatsink + forced-air, 380V design |
| Expected Service Life @ rated load | 5–7 years | 7–10 years |
| Best Lifetime Strategy | Stay under 80% continuous; avoid chronic peak | Use the thermal headroom; de-rate for cooler running |
Comparative Table: 2kW VS 5.5kW
| Evaluation Dimension | 2kW Single Axis Servo Drive | Heavy-duty 5.5kW Unit |
|---|---|---|
| Power Class | Mid-power | Heavy-duty |
| Rated Output | 2000W | 5500W |
| Matched Motor Torque | 6–15 N·m (130ST / 150ST frame) | 35 N·m (180AST-AM35015) |
| Input Supply | Three-phase 220V AC | Three-phase 380V AC |
| Typical Energy Draw (heavy cycle) | ~1.7 kW | ~4.4 kW |
| Typical Energy Draw (light cycle) | ~0.9 kW | ~1.1 kW (under-utilized) |
| Speed Regulation / Stability | Good under mid-duty | Excellent, with extra thermal headroom |
| Encoder | 2500-line incremental or 17/23-bit absolute | High-resolution absolute encoder |
| Cabinet Footprint | Compact | Larger, requires more clearance |
| Cost-of-Ownership Sweet Spot | Mid-duty, fast cycles, low-inertia loads | Heavy-duty, high-inertia, continuous-load machines |
| Best-Fit Application | CNC routers, small packaging, labeling, light assembly | CNC machining centers, palletizers, heavy gantries, slitters |
Application Fit: Which Rating Goes on Which Machine
The 2kW single axis servo drive tends to win on machines that are fast, light and cycle-hungry. Think a horizontal flow wrapper's film-feed axis, a desktop CNC engraver, a small-format labeling head, a pick-and-place conveyor or a textile winder. These are applications where the cycle time is short, the inertia is low and the load factor sits between 30% and 70% of rated torque. In this band, a 2kW drive delivers excellent dynamic response at a competitive cost and an acceptable thermal load.
The heavy-duty 5.5kW unit wins on machines that are heavy, continuous and inertia-sensitive. Think a vertical machining center's spindle-feed axis, a large-format slitter's rewind axis, a palletizer's main lift, an injection-molding-machine mold-closing axis or a heavy-feed automated welding cell. In these applications, the load factor is high, the cycle is long, and the inertia ratio (load inertia / motor inertia) is often above 5×. The extra torque headroom and the larger thermal mass of the heavy-duty 5.5kW unit are not luxuries - they are what keep the drive from tripping on every cycle.
There is also a middle band where the choice is genuinely close. A medium-format CNC router with a heavy table, a robotic pick-and-place arm with a long reach, or a labeling machine with a large rotary table can be served by either rating, depending on how aggressively the machine builder wants to push the cycle. The right answer in that band is to size by load-inertia ratio, not by nameplate power, and then sanity-check with Tonghang's engineering team before committing to a build.
Practical Sizing Rules for Mid-power and Heavy-duty Axes
Compute the continuous load torque (friction + gravity + process load) and add 20–30% margin. If that figure lands in the 6–15 N·m band, the 2kW single-axis drive is the right home; if it lands in the 20–40 N·m band, the heavy-duty 5.5kW unit is.
Compute the peak acceleration torque (J × α + friction) and check that it is within the drive's short-term overload. If the peak is more than 2.5× the continuous rating, oversize to the 5.5kW.
Check the inertia ratio (load inertia / motor inertia). Below 5×, the 2kW drive is comfortable; above 10×, the heavy-duty 5.5kW unit's tuning range is the safer choice.
Confirm the AC supply. The 2kW drive takes three-phase 220V; the 5.5kW takes three-phase 380V. If the cabinet only has 220V available, the 5.5kW will need a step-up transformer - which adds cost and energy loss that the comparison should account for.
Project the duty cycle. A machine that runs one shift in light cycles is almost always a 2kW job. A machine that runs three shifts in heavy cycles is almost always a 5.5kW job - even if the nameplate torque looks closer to the 2kW rating, the thermal lifecycle argument pushes the choice up.
Price the lifecycle, not the sticker. A heavy-duty 5.5kW unit that lasts 8 years at a 30% premium beats a 2kW drive that needs capacitor replacement at year 5 every time.
Tonghang sells both drives on the same platform, with the same tuning tool and the same support contract, so the cost of being wrong on a single axis is the cost of swapping a drive - not the cost of re-learning an ecosystem. That makes the sizing exercise worth doing properly on the first pass.
FAQ
When the load is heavy, the duty cycle is continuous, or the load inertia is more than 10× the motor's own rotor inertia. The 5kW+ rating buys you thermal headroom and a higher short-term overload, both of which extend drive life on a demanding machine.
Does a heavy-duty 5.5kW unit consume 5.5kW at the wall?
No. Real wall-power draw depends on the operating load factor. On a light cycle the 5.5kW drive may draw about 1.1 kW - close to a 2kW drive on a heavy cycle, but delivering less torque density, which is exactly why you do not over-size.
Can a 2kW single axis servo drive run a heavy CNC router?
A small CNC router is a comfortable 2kW job. A medium or heavy CNC router with a large table or a heavy spindle should be sized to the heavy-duty 5.5kW unit, because the load inertia and the peak acceleration torque are the deciding factors - not just the continuous rating.
What supply does the heavy-duty 5.5kW unit need?
The T3D-H 5.5kW drive takes a three-phase 380V AC supply. If the cabinet only has 220V available, a step-up transformer is required; for a greenfield build, plan the 380V distribution from the start.
How long does a heavy-duty 5.5kW unit typically last?
With proper sizing and a continuous load factor between 30% and 80%, the heavy-duty 5.5kW unit typically delivers 7–10 years of service before bus capacitors or the power module reach end-of-life. Mis-sizing - either way - is the most common reason a servo drive fails earlier.
Request a Sized Configuration
Share your machine's continuous load torque, peak acceleration, load inertia, supply voltage and duty cycle, and Tonghang's engineering team will return a sized recommendation - 2kW, 5.5kW or a mixed configuration - with a thermal-lifecycle estimate and a sample test plan. Sample testing, dimension drawings, wiring diagrams and remote commissioning support are all available.
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