Custom Robot Servo

24V Servo Drive

Estimate DC supply current, compare 24V and 48V, and prepare the motor data for a servo drive RFQ.

24V servo drive current estimator

Compare DC supply current at 24V and 48V; check motor phase current separately.

1–10,000 W at a moving operating point.

1–100%; drive + motor. 100% is ideal only.

1–10× estimated demand; not a torque factor.

No estimate yet. All fields are required; defaults are an illustrative example. Method and limits

Published and reviewed by Custom Robot Servo on . This guide supports preliminary selection; exact drive specifications, availability and quotation require an RFQ review.

Selection guide · DC supply budgeting

What the estimate can help you decide

  1. Use the result for preliminary DC supply budgeting. Drive phase-current selection is a separate check. maxon: input current versus motor current.
  2. Choose voltage from the motor operating points and the full supply envelope. This page establishes no universal 400W cutoff. maxon: required controller supply voltage.
  3. Compare current ratings on the same basis. For example, Elmo lists 30 A sinusoidal amplitude and 21 A RMS for its Gold Twitter 30/60 variant; these are different conventions, not DC input-current estimates. Elmo: Gold Twitter electrical specifications.
  4. Provide a path for regenerated energy. If available storage cannot absorb it, review a compatible energy-dissipation solution. Beckhoff: regenerative energy and braking resistors.
  5. A 24V label does not establish SELV, medical compliance or robot motion safety. Review separation and the complete application. Schneider Electric: SELV circuit requirements; maxon: meaning and limits of STO.

Calculation method and limits

At a moving operating point: Pinput = Pmechanical ÷ efficiency; IDC = Pinput ÷ VDC. The scenario current is IDC × the user-entered demand factor. Efficiency is total drive-and-motor efficiency written as a fraction (85% = 0.85). This is a steady-state energy balance, with no additional reserve, auxiliary load, battery sag or transient model. The factor is an assumption, not a motor overload rating. maxon: input current versus motor current.

24V supply → 235.3 W input / 9.80 A

Drive + motor → 85% assumed efficiency

Shaft → 200 W output + 35.3 W combined losses

Worked example, not a measured product result. Motor phase current is unknown until torque, winding and controller data are supplied.
What is known and what must still be measured or specified
Input / outputStatus and boundary
Mechanical power and efficiencyUser assumptions at one moving operating point; defaults are examples. Tool input ranges are arithmetic limits, not a product capability envelope.
24V and 48V DC bus currentCalculated at fixed nominal voltage. Lower loaded voltage increases demand for equal power; recalculate at the measured minimum.
Motor phase RMS / peak currentUnknown. Obtain torque-current data, current convention and duty cycle; never copy the DC estimate into a drive phase-current specification.
Standstill, acceleration and brakingNot modeled. Use torque/thermal data at standstill and time-based motion and energy analysis for transients.
Peak duration, wiring and coolingUnknown. Require component ratings and installation-specific validation. No universal cable gauge, peak duration or temperature limit is supplied.

24V versus 48V: compare the complete system

Analytical comparison at equal output power, assumed efficiency and cable resistance; not a hardware recommendation
Decision factorKeep 24VEvaluate 48V
DC bus currentBaseline I0.5 × I; phase current must be checked separately
DC cable lossBaseline I²R0.25 × I²R for unchanged resistance; other losses are not predicted
Motor speed / torqueConfirm points at minimum bus voltageCheck voltage headroom and all motor/drive limits
Integration costMay retain an existing supply and charger if compatibleReview supply, charger, auxiliaries, harness and validation cost
Regeneration / safetyDocument absorption and protective designReassess voltage limits and protection across every connected component

The ratios follow the stated power model. Architecture selection still needs the motor curve and voltage checks described by maxon: required controller supply voltage.

Three reproducible sizing scenarios

Illustrative moving operating points at 85% efficiency; values rounded to 2 decimals, no design reserve
Assumption24V → 48V bus currentNext decision
80 W lab axis, 2× demand3.92 → 1.96 A; scenario 7.84 → 3.92 ACheck the existing supply and actual phase-current ratings before retaining 24V.
200 W mobile axis, 3× demand9.80 → 4.90 A; scenario 29.41 → 14.71 ACheck BMS discharge duration, loaded voltage and regenerative charge acceptance.
600 W moving axis, 2× demand29.41 → 14.71 A; scenario 58.82 → 29.41 ACompare harness, cooling and architecture cost; the current estimate alone does not approve either option.

Reproduce each row using the estimator. Example: 200 ÷ (24 × 0.85) = 9.80 A; 9.80 × 3 ≈ 29.41 A using unrounded intermediate values.

Sources, dates and evidence limits

Sources checked on . Manufacturer examples explain selection principles; they do not certify or establish ratings for a Custom Robot Servo product. Published performance, lead time and price for your proposed configuration remain to be confirmed. Tables below are RFQ and validation requirements, not test results.

Primary references used in this guide
ReferenceDate / scope
maxon: input current versus motor currentUpdated 29 Aug 2024. PWM power conversion; not a product rating.
maxon: required controller supply voltageUpdated 4 Apr 2023. Operating-point voltage, sag and charging considerations.
Elmo: Gold Twitter electrical specificationsLive product table, checked 21 Sep 2026. Exact variant and current convention matter.
Beckhoff: regenerative energy and braking resistorsChecked 21 Sep 2026. General energy-path explanation; its resistor products are not selected for this 24V design.
Schneider Electric: SELV circuit requirementsModified 20 Aug 2024. Protective separation and fault conditions; not a certificate.
maxon: meaning and limits of STOUpdated 29 Aug 2024. Torque removal does not define stopping or holding behavior.

Source discrepancy: Elmo’s live Gold Twitter highlights list a 6V lower bound for the 60V family, while the 30/60 electrical table lists 8V. Resolve supply limits against the exact variant’s current hardware manual before selection; neither value is adopted as a general 24V-drive limit.

Selection Priorities

  • Estimate nominal DC supply demand before checking motor phase-current ratings separately.
  • Check the full supply voltage envelope, including sag, full charge and regeneration.
  • Confirm cooling, feedback, communication and protection on the exact drive variant.

Application Fit — Subject to Validation

  • AGV / AMR axes with verified battery, braking and torque-speed limits
  • Robot joints with a separately validated motion-safety design
  • Lab automation with defined duty cycle and enclosure cooling
  • Medical equipment only after device-specific electrical and safety assessment

Engineering Focus Areas

DC bus current versus motor phase RMS and peak currentSupply voltage envelope and regenerative energy pathEncoder compatibility and CANopen / EtherCAT integration

Specification Status and Required Evidence

MetricValue / Evidence StatusEngineering Impact
DC input currentCalculated: 9.80 A at 200 W / 24V / 85%An operating-point supply estimate; it does not specify motor phase current or include design margin.
Continuous / peak phase currentUnknown until motor and drive are specifiedMatch RMS versus amplitude conventions, duty cycle, peak duration and thermal derating to the exact datasheet.
Permitted DC voltage envelopeModel- and configuration-specificA nominal 24V label does not establish undervoltage, charging or regenerative overvoltage limits.
Safety / compliance evidenceNot established by this pageRequest the exact product documentation and assess the complete application. Supply voltage alone cannot establish compliance.

Selection Logic

SituationRecommended PathEvidence to Confirm
Choosing between 24V and 48VCompare bus-current demand, voltage headroom, cooling and total integration cost. Keep 24V if the complete system meets the defined operating envelope.Torque-speed curves at minimum supply voltage, phase-current limits, supply/BMS ratings, harness losses and thermal test records.
Shutdown during deceleration or downhill travelDiagnose from synchronized drive/BMS logs and DC bus measurements. Verify the regenerative energy path before choosing a mitigation.Fault codes, measured voltage, charge acceptance and energy per braking event; approved clamp thresholds and energy ratings if needed.
Insufficient top speedCheck winding constants, loaded supply voltage and controller output-voltage limits; compare winding, gearing and supply alternatives.Motor curve, Ke, winding resistance, required torque/RPM, drive voltage drop and mechanical speed limits.

RFQ Checklist

  1. Motor part number, torque-speed curve, Kt / Ke, phase-current convention and required operating points
  2. Supply minimum under load, nominal and maximum charge voltage; BMS charge/discharge limits
  3. Peak event duration, repetition rate, simultaneous axes and auxiliary loads
  4. Cooling path, enclosure, ambient range, cable length and connector ratings
  5. Regenerative energy estimate, absorption path and overvoltage protection coordination
  6. Encoder and protocol details, drawings, prototype quantity and acceptance criteria

Risk Controls

  • Undersized drive or wiring: Separate bus and phase-current calculations. Size each cable and connector for its actual current, installation, ambient, voltage drop and protection requirements.
  • Regenerative overvoltage: Check measured bus voltage and BMS fault logs. Confirm absorption capability; size an approved capacitor, regenerative supply or chopper/resistor solution for the energy and duty cycle.
  • Architecture change cost: Compare the complete 24V and 48V bill of materials, including supply, charger, harness, auxiliary converters and requalification. Lower bus current alone does not establish a lower-cost system.
  • Motor or application mismatch: Check the required torque-speed points at minimum bus voltage. If they do not fit, review winding, gearing or architecture before ordering prototypes.

Validation and QC Flow

CheckpointMethodPass Evidence
Thermal duty validationUse the agreed operating profile, cooling arrangement and worst-case ambient. Log temperatures until the relevant thermal behavior is established.Recorded temperatures and currents remain within the exact component limits and agreed derating envelope; no universal 85°C or 60-minute pass rule.
Regenerative energy validationOn a secured test setup, begin with low-energy trajectories and increase within a reviewed test plan while monitoring bus voltage and the absorption path.Bus transients, component temperatures and absorbed energy remain within documented limits, including the defined full-charge condition.
Peak demand validationApply the required motion profile within documented motor, drive and supply limits; record phase current separately from DC input current.Measured peak magnitude, duration and repetition rate meet the agreed duty envelope without violating voltage or thermal limits.

Download RFQ and Validation Templates

Use these templates before sending a 24V Servo Drive inquiry so torque-speed data, drawings, thermal assumptions, and sample acceptance evidence arrive in one package.

CSV

Servo RFQ Baseline Checklist

A field-by-field checklist for torque-speed-duty targets, drawings, protocol, sample quantity, acceptance tests, and open decisions.

Use before the first supplier email so engineering, sourcing, and procurement are aligned on required inputs.

CSV

CSV

Servo Validation Plan Template

A starting validation matrix for torque, current, heat rise, backlash, encoder zero, communication, burn-in, and outgoing inspection.

Use when samples are being scoped and the buyer needs pass/fail evidence before pilot approval.

CSV

CSV

Thermal Derating Worksheet

A compact worksheet for comparing ambient, housing, winding, duty cycle, current limit, and sealed-joint thermal margin.

Use when peak torque looks acceptable but continuous-duty heat rise is still the main project risk.

CSV

Buyer FAQ

Calculator and current

Does the calculator give the drive phase-current rating?

No. It estimates DC supply current from mechanical power and assumed total efficiency. Match drive phase RMS and peak ratings using the motor torque-current data and duty cycle; see the method and current-conversion source above.

What efficiency should I enter?

Use total drive-plus-motor efficiency at the operating point. The 85% default is an illustration, not measured product performance. Add drivetrain losses if your power target is measured after gearing. A 100% input gives an ideal lower bound only.

Does the demand factor predict acceleration current?

No. It scales an assumed DC demand scenario. Peak torque, phase current and permitted duration require a motion profile and the motor/drive ratings. The default 3× does not claim a three-second overload capability.

Can I use zero watts for a holding joint?

The power-based estimate excludes standstill and rejects zero. A holding motor can draw current and heat up with no shaft power. Use holding torque, Kt, winding resistance and a thermal assessment instead.

Architecture and motor fit

Is 400W the limit for a 24V servo drive?

There is no universal cutoff established here. The required current, voltage headroom, thermal limits and available hardware determine feasibility. Compare architectures against your constraints rather than a single power threshold.

Can a nominal 24V battery connect directly?

Only after matching the drive to minimum loaded voltage, maximum charge voltage, transients and BMS charge/discharge behavior. Chemistry or nominal pack voltage alone is not a compatibility check.

Will changing to 48V halve motor phase current?

Not necessarily. The comparison halves modeled DC supply current at equal power and efficiency. Motor phase current remains tied to torque, winding and control. Confirm the drive, motor and auxiliary devices can use the new supply.

What if the required top speed is not reached?

Review winding constants and the torque-speed curve at the minimum loaded bus voltage, allowing for controller voltage drop. Consider a suitable winding, different gearing or supply architecture; confirm mechanical speed limits as well.

Protection and purchasing

Does 24V establish SELV or collaborative-robot safety?

No. SELV also depends on protective separation and fault conditions. Motion hazards and any required safety functions need their own assessment. This page provides no robot-safety or medical-device certification; see the safety sources above.

How should braking-related shutdown be investigated?

Record drive and BMS faults with bus voltage, charge state and motion data. Determine whether recovered energy exceeds the available absorption capacity before choosing a compatible braking solution. Do not assume every shutdown is a BMS overvoltage trip.

Does STO provide controlled braking?

STO prevents torque generation but does not define a controlled stop or hold a gravity-loaded axis. Use the drive safety manual and application risk assessment to design stopping and holding functions; see the maxon STO reference above.

What should I send for a useful quote?

Send the checklist below the comparison sections: motor data, voltage envelope, peak duration, duty cycle, cooling, regenerative energy path, protocol, drawings and quantity. Mark unknown items explicitly so the supplier can identify missing evidence.

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