Scope of this technical record
Control Techniques Unidrive SP / Unidrive M diagnostic records for OI.AC overcurrent, Over Volts, PS.24V, O.ht thermal and encoder-feedback instability cases.
These records are for qualified drive-service and motion-control personnel. Closed-loop axes, hoists and winders can move unexpectedly during command, feedback or braking tests; secure the machine before diagnosis.
Why Unidrive is different from a generic VFD
Unidrive SP and Unidrive M are often installed in higher-performance machine-control applications where a short trip label does not identify the failed component. Encoder feedback, option modules, braking energy and machine mechanics can all create symptoms that look like a drive fault. That creates a content gap for pages that combine trip-code lookup with machine-level evidence.
A database page that simply lists OI.AC or Over Volts is weak. The useful page asks whether the machine is closed loop, whether the brake released, whether the encoder cable is noisy, whether PS.24V follows an external load, and whether overvoltage appears only during regeneration.
Trip-to-boundary map
The service cluster routes each search into a boundary: motor/output and vector loop for OI.AC, DC bus and braking path for Over Volts, external control loads and option modules for PS.24V, cooling/thermal feedback for O.ht, and feedback/noise path for instability.
Unidrive first-pass routing
| Trip / symptom | First boundary | Wrong first move |
|---|---|---|
| OI.AC | Motor/output/load/feedback | Replacing power stack before checking feedback and brake |
| Over Volts | DC bus, brake path, regenerative load | Resetting without changing ramp/brake evidence |
| PS.24V | External 24 V loads and option modules | Blaming internal supply before isolating loads |
| O.ht / O.ht1 | Fan, heatsink, ambient, sensor | Bypassing thermal protection |
| Feedback instability | Encoder cable, shield, option module, tuning | Replacing output module first |
Commercial signal
Unidrive searches can become high-value leads because many applications are hoists, winders, packaging machines and retrofits where downtime and safety matter. A support-ready page should request option-module photos, encoder type, motor/brake evidence and machine context, not only the trip code.
Field record checklist
- Exact Unidrive model and firmware context where available
- Trip label and occurrence timing
- Open-loop or closed-loop mode
- Encoder/feedback option and cable evidence
- External 24 V loads and option modules
- Braking resistor, load inertia and thermal evidence
Technical basis and reference documents
This is an independent editorial technical reference. Original manufacturer documentation remains controlling for installation, repair and commissioning decisions.
Database layer for Control Techniques / Nidec trip routing.
Model records
Fault records
Unidrive SP or Unidrive M trips on OI.AC during enable, acceleration, load change or unstable closed-loop operation.
Unidrive trips on Over Volts during deceleration, hoist lowering, winder stop or high line condition.
Unidrive reports PS.24V, loses option/module supply, or drops control logic when external loads are connected.
Unidrive reports O.ht or O.ht1 after load operation, high ambient temperature or poor cabinet cooling.
Closed-loop Unidrive application is unstable, trips under load, hunts, overspeeds or reports feedback-related symptoms.
Circuit and diagnostic records
Routes OI.AC and unstable closed-loop behaviour through motor cable, output bridge, current feedback, brake release, encoder feedback, shielding and tuning context.
Routes Over Volts evidence through line voltage, DC bus, load regeneration, deceleration ramp, brake resistor, brake chopper and feedback-induced instability.
Routes PS.24V, thermal feedback and encoder instability through external 24 V loads, option modules, feedback wiring, sensor supply, heatsink feedback and control-board evidence.
Unidrive SP/M reports OI.AC or trips during enable, acceleration, load change or closed-loop instability.
Unidrive reports Over Volts during deceleration, lowering, stop, winder unwind or unstable closed-loop operation.
Unidrive reports PS.24V, thermal feedback symptoms, O.ht/O.ht1 or feedback instability with option modules and external control wiring.