Yaskawa Σ-7 (Sigma-7) SERVOPACK alarm A.400: Overvoltage
Alarm A.400 on a Yaskawa Σ-7 SERVOPACK is Overvoltage: the main circuit DC voltage is too high. It is detected in the main circuit power supply section and can be reset once the cause is removed.
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When it happens
- During deceleration of a high-inertia load (regenerated energy)
- During acceleration or deceleration when the AC supply is already high
- At any time with an unstable supply or a lightning surge
Likely causes and checks
1Supply voltage above the specified range, or unstable/surge
- Points to it
- Trips even with no motion; other equipment on the same supply sees surges.
- Check
- Measure the power supply voltage; set it within range and fit a surge absorber where needed.
2External regenerative resistance too high for the operating conditions
- Points to it
- Trips on deceleration; resistor value larger than needed.
- Check
- Check the operating conditions against the regenerative resistance and select a suitable value.
3Moment of inertia ratio or mass ratio above the allowable value
- Points to it
- Trips on fast stops of a heavy load.
- Check
- Check that the moment of inertia ratio is within the allowable range; increase the deceleration time or reduce the load.
4Regenerative resistor disconnected while the supply voltage was high
- Points to it
- Resistor open-circuit when measured.
- Check
- Measure the regenerative resistor; replace the external resistor, or the SERVOPACK if the built-in one has failed.
5SERVOPACK failure
- Points to it
- Alarm persists after cycling control power with the main circuit OFF.
- Check
- Yaskawa’s listed action is to replace the SERVOPACK.
Telling it apart
- If A.400 trips only during deceleration, the problem is regenerated energy (decel time, inertia, resistor); if it trips at standstill, look at the supply.
- A.320 (Regenerative Overload) means the regenerative resistor is overworked over time; A.400 is the DC voltage itself going too high.
Relevant parameters
| Parameter | Name | Why it matters |
|---|---|---|
| Pn600 | Regenerative Resistor Capacity | Must match the external regenerative resistor fitted. |
Evidence to collect
- Alarm history and the motion at the trip
- Measured supply voltage
- Regenerative resistor value and Pn600 setting
- Load inertia and deceleration time
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