Locked-Rotor, No-Load, T-N Curve: The Six Motor Tests That Decide Whether Your Appliance Ships On Time

Certification delays are rarely caused by a bad motor. They are caused by a test report that answers the wrong question. Six measurements settle most small-motor approvals — if the bench can produce them under 8,000 r/min.

1. The 8,000 r/min problem

Small motors keep getting faster. Appliance, power-tool and pump duty points that used to sit near 3,000 r/min now run at 8,000 r/min and above, with torque in the fractional range of 0.5–1.7 N·m. On a bench sized for larger machines, that is a measurement problem: the transducer's lower limit sits right where the useful data lives. A IEC60334 dynamometer test bench pairs an 8,000 r/min ceiling with a 0.5–1.7 N·m torque window, PLC control and an aluminium alloy control cabinet, on AC 220 V 50 Hz supply.

2. The six tests that unblock a file

1. Cold and hot DC resistance. Establishes the winding baseline that every later temperature calculation depends on.
2. No-load test. Produces the no-load characteristic curve and separates iron loss from mechanical loss.
3. Locked-rotor test. Yields starting torque and current — the numbers protection coordination is built on.
4. Load test. Generates the load characteristic curve and the corrected motor parameters.
5. Temperature rise. Resistance method, with winding and core temperatures monitored throughout.
6. T-N curve. Plotted live, including maximum and minimum torque and the speed at which a centrifugal switch drops out on single-phase units.

3. What the data looks like when it is done properly

4. Where labs lose weeks

Two avoidable failures dominate. First, tests run at a single voltage, which makes the results non-comparable when the destination market differs. Second, no-load and locked-rotor data taken on the same day as the load test without stabilisation — leaving temperature drift inside the efficiency numbers. Fixing the sequence is free; re-running a certification file is not.

5. Related configurations

Where the duty point sits slightly differently, the motor performance testing system covers the same 8,000 r/min class with the same 0.5–1.7 N·m window and PLC control, while the low-speed high-torque dynamometer bench variant targets lower-speed, higher-torque duty with the same accuracy philosophy. All three are built by Guangzhou Hejin Automation Control Technology Co., Ltd., a Guangzhou manufacturer since 2003 with 50–60% of output exported, and shipped with a documented acceptance run plus a one-year warranty.

FAQ

Does the bench cover single-phase and three-phase motors? Yes — the T-N routine includes the centrifugal switch drop-out test specific to single-phase induction motors.

Can the T-N curve be exported? Test data is logged automatically and exportable for the certification file.

What supply does it need? AC 220 V 50 Hz for the standard configuration.

Specifications and delivery: IEC60334 Dynamometer Test Bench, 8,000 rpm  |  Motor Performance Testing System, 8,000 rpm  |  Dynamometer Test Bench, 800 rpm / 0.5–1.7 N·m