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Source-backed boundaries
Safety, FOC sensing limits, and I2t limits are separated from supplier-specific claims.
Check whether a 100A class PMSM servo drive is a real fit for your current envelope, cooling condition, and FOC loop requirements before locking the robot actuator design.
Published September 24, 2026; evidence and assumptions reviewed September 24, 2026. The calculator is a screening tool; final release still requires supplier derating data and thermal validation.
Screen continuous current, peak current, pulse duration, and cooling condition before deciding whether a 100A PMSM servo drive is the right procurement target for your FOC system.
Use phase RMS current; range for this screen is 0.1A to 300A.
Must be equal to or higher than continuous current.
Pulses above 60s should be modeled as continuous thermal load.
Cooling changes whether the result is fit or boundary review.
Enter Arms continuous phase current
Enter Arms peak current and pulse duration
Safety, FOC sensing limits, and I2t limits are separated from supplier-specific claims.
Calculator examples cover compact robotics, mobile automation, and direct-drive high-torque axes.
The RFQ list forces continuous, pulse, cooling, motor-control, and FOC loop evidence into one review.
For the same phase resistance, moving from 50A to 100A creates 4x conduction loss (I²R). A 100A peak pulse (10,000 A²) generates heat 4x faster than a 50A nominal load (2,500 A²), rapidly filling the drive's I²t thermal bucket.
FOC requires high-resolution phase current sensing. A ±100A range on a standard 12-bit ADC yields ~0.05A/bit resolution. Controlling a 2A holding torque with only 40 discrete steps creates severe quantization noise and torque ripple.
A compact drive advertised as 100A may mean 100A peak, not 100A continuous. Ask for continuous current, peak duration, repetition rate, and cooling condition together to calculate the true RMS limit.
The calculator intentionally screens conservatively. It does not assume that a short pulse above 100A is acceptable, because pulse ratings are supplier-specific and depend on I2t limits, cooling, and repetition rate.
| Input | Why it matters | Screening rule |
|---|---|---|
| Continuous current | Sets average heat load in FETs, copper, connectors, and enclosure surfaces. | If it exceeds the cooling-adjusted ceiling, treat the result as a boundary case. |
| Peak current | Checks whether torque bursts fit the advertised 100A envelope before I2t protection trips. | Any value above 100A is outside this page envelope unless a supplier gives a pulse exception. |
| Peak duration | Separates a fast torque impulse from a thermal event that behaves like continuous load. | Longer pulses require a vendor I2t curve, ambient temperature, and repetition rate. |
| Cooling condition | The same PCB can be safe on a chassis plate and unsafe inside a sealed joint. | Sealed, conduction, and active cooling use different conservative thresholds. |
The page separates general engineering rules from vendor-specific ratings. Public sources support the safety and technology framing; supplier datasheets must still confirm the exact 100A current envelope for a purchase decision.
Review cycle: refreshed every six months, or sooner when supplier ratings, safety standards, or GaN motor-drive guidance change.
| Source | Supports | Boundary | Date note |
|---|---|---|---|
| IEC 61800-5-1 adjustable speed electrical power drive safety standard | Electrical, thermal, and energy safety must be reviewed for power drive systems, not only motion performance. | Use the standard to frame safety review; it does not publish your vendor-specific current rating. | IEC source reviewed September 24, 2026 |
| Texas Instruments GaN technology and motor-drive guidance | Wide-bandgap GaN devices can reduce switching loss and support high-frequency compact power stages required for low-inductance PMSMs. | GaN benefits depend on layout, gate drive, cooling, and EMI validation; do not copy a frequency target blindly. | TI source reviewed September 24, 2026 |
| Texas Instruments / Industry Current Sensing Principles | In FOC, a ±100A sense range maps to the ADC. For a 12-bit ADC (4096 steps), the resolution is ~0.048A/bit. At low currents, this coarse quantization causes severe control loop noise and torque ripple. | ADC resolution calculations are implementation-specific (e.g. 12-bit vs 16-bit, oversampling); this page uses them as a screening risk, not a finished sensor design. | Industry standard principles reviewed September 24, 2026 |
| Kollmorgen / maxon group I²t protection application notes | I²t is an integrated thermal bucket: I²t_limit = (I_peak² - I_nominal²) × t_peak. A 100A pulse on a 50A nominal drive accumulates heat quickly, forcing the drive to fold back to nominal current once 100% capacity is reached. | I²t foldback curves are vendor-specific and rely on the thermal time constant of the connected motor and drive heat sink. | Vendor application notes reviewed September 24, 2026 |
| Parameter | 100A Target | Smaller Class (40A) | System Impact |
|---|---|---|---|
| Power path & Thermal | High-current PCB, busbar, or bonded thermal path | Lower copper burden and 1/4th the I²R loss | A 100A design requires heavier copper (e.g. 3oz+ or busbars) and parallel FET paths. It squares the I²R loss (4x the heat of 50A), heavily stressing the thermal management of a compact joint. |
| Connector and cabling | Larger contacts and lower-resistance harnessing | Easier routing inside compact joints | Oversizing can make the joint harder to package even when the motor torque looks attractive on paper. |
| DC bus energy | Higher bus capacitance and braking path review | Lower braking energy and ripple stress | Regeneration can trip the DC bus before current capability becomes the limiting factor. |
| FOC Current sensing | Wider range causing low-current quantization tradeoff | Tighter ADC range (e.g. 0.02A/bit) and smoother holding torque | A ±100A sensor on a 12-bit ADC provides only ~0.05A/bit resolution. Attempting to hold a 2A position with just 40 quantization steps introduces severe FOC current-loop noise and torque ripple. |
| Procurement cost | Higher drive, thermal, cable, and test cost | Lower BOM and simpler qualification | Use the smaller class when 100A is only a vague safety margin, not a measured duty-cycle requirement. |
A 100A rating looks safer on paper, but it increases I^2R loss potential and forces wider current-sense ranges. This can degrade the FOC performance at the low currents where a joint spends most of its time holding position.
The highest-impact mistakes are usually not the headline current rating. They are thermal assumptions, regeneration handling, FOC sensing range, and switching/layout validation.
| Risk | Trigger | Mitigation |
|---|---|---|
| Thermal shutdown or unsafe surface temperature | Sustained high current in a sealed or poorly coupled joint | Specify cooling plate, ambient temperature, duty cycle, and firmware thermal protection state in the RFQ. |
| Low-current torque noise in PMSM | A 100A range is used for a joint that holds position near 1A to 3A | Ask for ADC range, sensor type, FOC current-loop bandwidth, and low-current torque ripple test data. |
| Regeneration over-voltage | High deceleration current pushes energy back to the DC bus | Review battery absorption, braking resistor sizing, and over-voltage trip thresholds. |
| EMI or switching instability | High-frequency GaN switching is used without matching layout and filtering | Validate conducted/radiated emissions, layout parasitics, and motor cable length before freezing the PCB. |
| Question | Why it matters |
|---|---|
| What is the continuous phase current rating? | Separates true continuous 100A hardware from compact 100A peak marketing claims. |
| What pulse current is allowed, for how many seconds, and at what repetition rate? | Prevents the common error of treating a one-time pulse rating as a robot duty-cycle rating. |
| What cooling surface, ambient temperature, and enclosure assumptions were used? | Makes the thermal number reproducible in the actual robot joint. |
| What motor inductance, PWM frequency, and FOC loop bandwidth are supported? | Confirms the drive can control the low-inductance PMSM motor cleanly, not just survive the current. |
| How is regenerative energy handled? | High-current braking can fail through DC bus over-voltage even when torque output is adequate. |
| Case | Input assumption | Outcome |
|---|---|---|
| Humanoid knee jump recovery | 35A continuous, 95A peak, 1.5s pulse, chassis conduction | Candidate fit, but quote must include peak repetition rate and I2t curve. |
| AGV steering actuator | 18A continuous, 45A peak, 2s pulse, sealed enclosure | Likely oversized; evaluate 40A to 60A drive classes for lower cost and better sensing. |
| Direct-drive robot shoulder | 72A continuous, 100A peak, 4s pulse, active cooling | Boundary case; proceed only with thermal test plan and supplier derating data. |
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