What it means
A06921 is the braking chopper's asymmetry alarm: the drive has detected that the three resistors of the braking chopper are not symmetrical. Oscillations of the DC link voltage, which fluctuating loads of the connected drives can produce, trigger the same detection even when the resistors themselves are in order. Depending on the drive configuration, the same condition can also be issued with no reaction (N).
Why it appears
- The three resistors of the braking chopper are not symmetrical with one another.
- DC link voltage oscillations caused by fluctuating loads of the connected drives.
What to check
- Check the feeder cables to the braking resistors.
- If required, increase the value in p1364 with which the braking chopper detects the resistor asymmetry.
Parameters the manual names
- p1364 (Braking chopper resistor asymmetry) is the value the remedy acts on: if the feeder cables to the braking resistors are in order and the alarm still appears, increase p1364.
- p1360 (Braking chopper braking resistor cold), p1362 (Braking chopper activation threshold) and r1363 (CO: Braking chopper output voltage) are further braking chopper parameters that the manual lists under this message.
Acknowledging and restarting
No acknowledgement is required: the drive does not intervene, and the alarm signal drops out again by itself once the braking chopper no longer detects the asymmetry. Checking the feeder cables or increasing p1364 therefore ends the message without any reset step at the operator panel.
What differs between the drive families
Straight from the manuals' own fields — A06921 is not described identically everywhere.
| Drive family | Reaction | Acknowledge | Message class | Component | Manual |
|---|---|---|---|---|---|
| G130, G150 | NONE | NONE | Braking Module faulted (14) | Motor | SINAMICS G130, G150 List Manual · p. 1533 |
| S120, S150 | NONE | NONE | Braking Module faulted (14) | Motor | SINAMICS S120, S150 List Manual · p. 2776 |
| G120 | NONE | NONE | Braking Module faulted (14) | — | SINAMICS G120 · p. 869 |
The drives this code lives on
A06921 is described for G120, G130, G150, S120, S150. These are the converters of those families in our catalogue — price on request.
Questions technicians ask
What does alarm A06921 mean on a SINAMICS drive?
The braking chopper has detected that its three resistors are not symmetrical. DC link voltage oscillations caused by fluctuating loads of the connected drives can trigger the same detection.
How do I clear alarm A06921?
Check the feeder cables to the braking resistors first. If required, increase the value in p1364 with which the drive detects the asymmetry.
Does A06921 stop the drive or require an acknowledgement?
No. The drive takes no protective action and no acknowledgement is needed; the alarm clears itself once the asymmetry is no longer detected.
Why does A06921 keep coming back although the resistors are intact?
Fluctuating loads of the connected drives can make the DC link voltage oscillate, and the monitoring then reads an asymmetry. In that case the remedy is to increase the detection value in p1364.
Codes next to this one
Source
Written from Siemens' own List Manuals and operating instructions; every number, designation and parameter on this page is checked against them before publication.
All SINAMICS codes: fault and alarm codes · the A06xxx group · SINAMICS manuals · Siemens manuals