Electric Hoist Common Fault Troubleshooting Guide

Electric Hoist Common Fault Troubleshooting Guide covers seven major fault categories: insufficient lifting power (voltage/braking/phase loss), slow hoisting speed (brake clearance/voltage/load), brake failure to hold (taper brake ring/spring/friction surface), oil leakage (seal ring/oil seal/oil level), abnormal noise (gear/bearing/wire rope/motor), rope guide replacement steps, and limit switch malfunction (contact/over-travel limit/stroke switch). Each fault is organized using a four-step diagnostic approach: "Fault Symptom → Possible Cause → Diagnostic Method → Solution."

Weak lifting is usually caused by low supply voltage or single-phasing of the motor. Follow this sequence to isolate the problem:

① Check the voltage: Use a multimeter set to AC 500V and measure the three-phase voltage at motor terminals U1/V1/W1 — normal range is 380V ±10% (342–418V). If it reads below 340V, the issue is on the supply side (overlong cable runs with undersized conductors, or an undersized transformer).

② Check for single-phasing: If the three-phase voltage is normal but one phase reads near 0V, the motor is single-phasing. Inspect the fuse FU, the main contacts of contactor KM1, and the terminal block. A single-phased motor hums and either fails to rotate or turns very slowly — winding burnout can occur within minutes.

③ Check the brake: If all three phases are normal, verify that the brake rectifier module outputs DC 99V. A partially engaged cone brake adds load to the motor.

④ Check the load: If the hoist runs fine unloaded but struggles under load, the cause is either overload or extra resistance from multi-layer winding of the wire rope.

The most common cause is an undersized brake clearance (the cone brake is partially engaged); low voltage is the second most likely culprit.

① Brake clearance: Factory specification is 1.5–2mm. After extended service, brake ring wear increases axial float, so the brake does not fully release during motor operation — the motor must drive the load while also overcoming brake friction.

② Adjustment method: Remove the motor end cover and turn the brake adjusting nut (clockwise to reduce clearance, counterclockwise to increase it). The standard clearance is 1.5–2mm. After adjustment, perform a No-Load Test Run; with power removed, load drop must not exceed 80mm (per ISO 4301 Crane Design Standard).

③ When to replace: Replace the brake ring if wear exceeds 50% of its original thickness (standard thickness is approx. 5mm; scrapping is required once worn to 2.5mm or less).

④ Voltage factor: When voltage drops below 360V, motor output torque falls by 15–20%. Address the power supply issue first rather than adjusting the hoist.

Load slipping (brake failing to hold) has three primary causes:

① Worn cone brake ring (most common) — Raise the empty hook to 1m, then cut power. If load drop exceeds 80mm, adjust or replace. The brake ring is about 5mm thick when new; scrap it once worn to 2.5mm or less.

② Brake spring fatigue — On CD1-type hoists, the spring free length is about 60mm, compressed to 50mm in service. Replace the spring if its force has attenuated by more than 15%.

③ Oil contamination on friction surfaces — Gearbox oil leaking onto the brake friction faces drastically reduces the friction coefficient. Clean the surfaces with alcohol or acetone and repair the leak source.

About 90% of leaks originate in the gearbox. Diagnose by leak location:

① Output shaft (drum side) leak — The skeleton oil seal (SG40×62×12 or SG45×70×12) is worn. If the output shaft has developed a groove, replace the shaft as well, or build up the worn area by welding and machine it back to spec.

② Input shaft (motor side) leak — Misalignment between the motor and gearbox causes uneven oil seal wear. Realign the shafts (coaxiality deviation ≤0.2mm) and replace the input shaft oil seal.

③ Gearbox mating surface leak — The sealant has aged or the tightening bolts have loosened. Clean the surface, apply Loctite 587 or K-5903 gasket sealant, and tighten diagonally to 20N·m.

④ Overfilling — Oil above the upper level mark vents through the breather during operation. Fill to the middle of the sight glass with N220# medium-duty industrial gear oil. Ignoring a leak leads to gear wear and brake slippage.

First identify where the noise is coming from, then address the specific cause:

① Metallic "clanking" from the drum side — The wire rope is spooling incorrectly or jumping off the drum; the rope guide is damaged or has reached its limit. Stop immediately, rotate the drum by hand to respool the rope, and inspect the rope guide.

② Low-frequency "thumping" from the gearbox — worn gears or damaged bearings. Drain the oil and inspect the gear teeth for pitting or spalling; disassemble and check the tapered bearing clearance.

③ Motor "humming" but not rotating — single-phasing. Cut power immediately and inspect fuse FU and the main contacts of contactors KM1/KM2.

④ High-pitched screeching from the motor — motor bearing lacks lubrication or is damaged. Remove the motor and turn it by hand to check whether the bearing feels rough or seized.

⑤ Squeaking or grinding along the rail — friction between the crane wheel and the I-Beam Rail. Check rail straightness (≤1.5mm/m), remove rail corrosion, and lubricate the wheel bearings. Stop the hoist immediately if abnormal noise is detected — never operate a faulty unit.

Six-step replacement procedure:

① Pay out the rope — Lower the hook to its lowest position, leaving only 3 safety wraps on the drum.

② Remove the old rope guide — Take out the two sets of fixing bolts (2× M8 or M10 each). The rope guide is a split two-piece design; mark the mating faces with a marker before disassembly so the new unit aligns correctly with the spiral groove.

③ Clean the drum — Remove wire rope debris and grease from the drum surface, and check the spiral groove for damage.

④ Fit the new guide — The internal spiral rib of the new rope guide must seat into the drum's spiral groove. Tighten the bolts (torque approx. 10 N·m). Rotate the drum by hand to confirm the guide travels smoothly along the groove without binding.

⑤ Re-spool the rope — Raise the hook to its highest position so the wire rope lays neatly in a single layer on the drum.

⑥ Test run — Run a full no-load cycle (raise and lower) and observe rope lay and rope guide movement. A fractured rope guide is usually caused by rope crushing from mis-spooling; inspect the wire rope at the same time — replace it if there are indentations or wire breaks.

This is the most critical safety hazard — stop the hoist immediately and troubleshoot:

① Visual inspection — Check that the trip lever of the power-off limit switch is properly engaged by the hook nut, and that the Travel Switch roller is being actuated by the cam. If stuck, reposition and lubricate.

② Continuity test with a multimeter — With power off, the power-off limit switch terminals should read closed (0 Ω). An open circuit means the internal contacts are burned or the mechanism is jammed. The COM-NC terminals on SQ1/SQ2 should also show continuity; if not, replace the Travel Switch.

③ Clean oxidized contacts — Remove the housing and lightly polish the silver contact surfaces with 600-grit fine sandpaper, or spray and wipe with a contact cleaner.

④ Verify direction matching — After replacing the power-off limit switch, confirm that the motor rotation direction matches the switch actuation direction; otherwise the limit switch will be completely ineffective.

⑤ Check the wiring — Inspect the limit switch leads at the terminal block for looseness or breakage. Never operate the hoist with a faulty limit switch; at minimum, install a temporary external Travel Switch as backup protection.

Q: How often should an electric hoist be serviced?

A: Light duty A1~A3 (≤2 h/day): monthly inspection + minor service every 6 months + major service annually. Medium duty A4~A5 (2–5 h/day): weekly inspection + minor service quarterly + major service every 6 months. Heavy duty A6~A8 (>5 h/day): weekly inspection + minor service monthly + major service quarterly. Daily checks cover the brake, wire rope, pushbutton, and limit switch; monthly checks cover contactor contacts, insulation, and oil level; the annual inspection covers all items plus brake ring, gears, and wire rope replacement assessment.

Q: How can I tell if the electric hoist motor is burned out?

A: First, check for a burnt odor. Second, use a multimeter to measure the DC resistance of the three phases (normal: balanced within ≤2% deviation; an open circuit or near 0 Ω indicates a burn-out). Third, use a 500 V Megohmmeter (Insulation Tester) to measure insulation resistance to ground (normal: ≥1 MΩ; a burned motor reads near 0 MΩ). Main causes: single-phasing accounts for over 60% of failures, followed by overload, frequent starting (>60 starts/h), and brake drag preventing motor rotation. Prevention: install a Phase Loss Protection relay, such as the XJ3 series.

Q: How often should the electric hoist wire rope be replaced?

A: Per GB/T 5972 discard criteria: wire breakage ≥10% within one lay length, diameter reduction ≥7% (fiber core), or whole-strand fracture, kinking, or cage distortion. Inspection intervals: light duty 3–5 years, medium duty 1–2 years, heavy duty 6–12 months. Pay special attention to the drum anchor end, a high-risk zone for fatigue wire breaks — it must be pulled out and inspected during the annual inspection.

Q: What happens when an electric hoist is overloaded?

A: Under 125% overload — increased brake slip and faster motor temperature rise. Above 150% overload — brake failure causing the load to drop, motor burnout within minutes, gear tooth breakage, and wire rope indentation. An overload limiter (trip point ≤110% of rated lifting capacity) is mandatory; once triggered, it must only permit lowering. Never lift a load of unknown weight without an overload limiter.