What a full-load test catches that a bench power-up misses

The cheapest way to “test” a repaired drive is to power it up, see the display come on, perhaps spin a small motor with no load, and ship it. Many faults pass that test.

Faults that only show under load

• A weak IGBT or a marginal gate drive. It switches correctly at a few amps and fails when the current rises.
• Thermal faults. A dried thermal interface, a slow fan or a failing temperature sensor only shows up after the heatsink has had time to warm.
• DC-bus problems. Capacitors with high ESR can look fine at no load and cause ripple, overvoltage trips or heating at rated current.
• Current feedback errors. A drifting current sensor can go unnoticed until the drive is asked to deliver real torque.

Our routine

Every drive we repair goes through the same steps before dispatch:

1. No-load power-up, checking output voltage, frequency and waveform
2. A test motor matched to the drive’s rating
3. Full load at rated current for at least 30 minutes
4. IGBT and heatsink temperatures checked under load
5. Parameters verified against the customer’s settings
6. A written report with input and output measurements

It takes longer than a bench power-up. It also means the first time your drive meets real current is in our workshop, not on your line.