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Source-backed boundaries
Safety, GaN switching, current sensing, and I2t limits are separated from supplier-specific claims.
Check whether a 100A class BLDC servo drive is a real fit for your current envelope, cooling condition, and procurement risk before locking the robot actuator design.
Published July 19, 2026; evidence and assumptions reviewed July 19, 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 BLDC servo drive is the right procurement target.
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 current
Enter Arms peak current and pulse duration
Safety, GaN switching, current sensing, 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 regeneration evidence into one review.
For the same phase resistance, moving from 50A to 100A creates 4x conduction loss by I^2R. Cooling method matters as much as the advertised current number.
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.
GaN can help with switching loss and power density, but it does not remove connector, capacitor, copper, sensor, or regeneration limits.
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 July 19, 2026 |
| Texas Instruments GaN technology and motor-drive guidance | Wide-bandgap GaN devices can reduce switching loss and support high-frequency compact power stages. | GaN benefits depend on layout, gate drive, cooling, and EMI validation; do not copy a frequency target blindly. | TI source reviewed July 19, 2026 |
| Texas Instruments motor-drive current sensing resources | Current measurement range, sensor selection, and ADC resolution affect low-current torque control quality. | ADC resolution calculations are implementation-specific; this page uses them as a screening risk, not a finished sensor design. | TI source reviewed July 19, 2026 |
| Synapticon drive documentation for I2t protection | I2t protection is a practical way drives limit accumulated thermal stress from current over time. | I2t parameters are set by each drive vendor and firmware configuration; request the actual curve before procurement. | Vendor documentation reviewed July 19, 2026 |
If your result is a boundary case, package the duty cycle, cooling path, ambient temperature, and motor data before asking for a written supplier rating.
Send assumptionsOversizing to 100A can be correct for torque bursts, but it also changes the power path, sensing range, regeneration strategy, and mechanical package.
| Parameter | 40A to 60A class | 100A class | Decision impact |
|---|---|---|---|
| Power path | Lower copper and connector burden | High-current PCB, busbar, or bonded thermal path | A 100A design may need heavier copper, busbars, or parallel FET paths; verify manufacturable trace width and temperature rise. |
| Connector and cabling | Easier routing inside compact joints | Larger contacts and lower-resistance harnessing | Oversizing can make the joint harder to package even when the motor torque looks attractive on paper. |
| DC bus energy | Lower braking energy and ripple stress | Higher bus capacitance and braking path review | Regeneration can trip the DC bus before current capability becomes the limiting factor. |
| Current sensing | Better low-current resolution | Wider range with possible resolution tradeoff | A wide measurement range can reduce low-current holding smoothness if sensing and filtering are not designed for it. |
| Procurement cost | Lower BOM and simpler qualification | Higher drive, thermal, cable, and test cost | Use the smaller class when 100A is only a vague safety margin, not a measured duty-cycle requirement. |
| Tool result | Typical condition | Required action |
|---|---|---|
| Candidate fit | Continuous current is moderate and peak is below 100A for a short pulse. | Proceed to supplier quotation with explicit current and cooling clauses. |
| Boundary case | Peak is near 100A, duration is several seconds, or cooling is sealed. | Request thermal simulation, I2t curve, duty cycle review, and mounting details. |
| Outside envelope | Continuous current or peak current exceeds 100A. | Move to a larger drive class or reduce the torque requirement. |
| Likely oversized | Continuous current is low and peak current stays below about 60A. | Compare 40A to 60A classes first to improve size, cost, and sensor resolution. |
The highest-impact mistakes are usually not the headline current rating. They are thermal assumptions, regeneration handling, 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 | A 100A range is used for a joint that holds position near 1A to 3A | Ask for ADC range, sensor type, 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 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 current-loop bandwidth are supported? | Confirms the drive can control the BLDC/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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