Source: https://guthlabs.ai/docs/instruments/dc-motor-starting-current-back-emf-estimator/
instrument / verified-clean
# DC Motor Starting Current & Back-EMF Estimator
The current ledger marks this instrument verified clean within the source-bound verification corpus.
Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**
## Inspectable records
[01**Overview**Purpose and lifecycle]()[02**Mechanism**Method and assumptions]()[03**Implementation**Binding and validation]()[04**Qualification**Evidence and errata]()
## Ledger state
The current ledger marks this instrument verified clean within the source-bound verification corpus.
**Area**: Electrical & Electronics Engineering — Circuits, Power Systems, Electronics Lab
**Tranche**: tranche-4
**Evidence ID**: t4-102
**Ledger rows**: 1
No ledger note is attached.
## Review findings
The simplified separately-excited DC motor label is honest only if the instrument clearly states that it uses a steady-state model with supplied speed and combined SI-compatible motor constant K_e=kΦ. Define the warning rule, the speed unit, the motor-constant definition, the locked-rotor condition, and the allowed sign/range constraints before release.
### Formula and scope findings
- Ia=(V−Eb)/Ra is the standard steady-state armature-current relation for a separately excited DC motor, provided Ra is the total armature circuit resistance and Ra>0.
- The back-EMF relation is standard as Eb=K_e·ω, or Eb=k·Φ·ω when k·Φ is not already combined. The specification writes Eb=kΦN without defining whether N is angular speed in rad/s or rotational speed in rpm; using rpm requires a 2π/60 conversion or an rpm-specific motor constant.
- The listed inputs provide a motor constant but do not explicitly provide flux Φ. The formula is complete only if motor constant means the combined constant kΦ, equivalently K_e.
- The claimed locked-rotor current requires the explicit condition speed=0, giving Eb=0 and I_start=V/Ra; this condition is implied but not stated as a separate formula.
- The claimed armature current under load is only estimated from a supplied speed. No load torque, mechanical losses, or speed-dynamics relation is included, so the instrument does not calculate speed or current from load.
- The starting-current warning has no defined threshold, trigger condition, or output semantics, so it cannot be verified.
### Unit assumptions
- V is terminal armature voltage in volts.
- Ra is total armature-circuit resistance in ohms and must be strictly greater than zero.
- The motor constant used in these vectors is K_e=kΦ in volts per radian per second, numerically V·s/rad.
- Speed is angular speed ω in rad/s unless explicitly converted from rpm.
- Eb is in volts and Ia is in amperes.
- For rpm input, ω=rpm·2π/60 must be used before applying Eb=K_e·ω.
## Boundary hardening
**BREAK_CLAIMED** · SELF_FLAGGED
The specification provides no stated validation for Ra=0, which makes Ia undefined. It also leaves the speed and motor-constant units unspecified, allowing materially different back-EMF and current results.
## Errata and corrections
No applied erratum is attached to this unique-name record.
## Inspectable example
4 review vectors are recorded. One source-bound sample is shown below.
````
{
"inputs": {
"V_V": 240,
"Ra_ohm": 1.2,
"motor_constant_Vs_per_rad": 0.8,
"speed_rad_per_s": 0
},
"expected_outputs": {
"Eb_V": 0,
"Ia_A": 200,
"starting_current_warning": null
},
"working": "Eb=K_e·ω=0.8·0=0 V. Ia=(V−Eb)/Ra=(240−0)/1.2=240/1.2=200 A. Speed is zero, so this is the locked-rotor case; the warning result is null because the specification defines no warning policy."
}
````
## Related workflows
[Motor & Drivetrain BenchDC start]()
## Sources and evidence
These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.
- `VERIFIED_LEDGER.json · VERIFIED_CLEAN`
- `evidence-tranche4/tranche4-results.json`
- `BOUNDARY_HAZARD_CATALOG.json`