VFD Overvoltage Fault (Err05, Err06, Err07): Cause & Fix | SHZK

A DC-bus overvoltage fault on the SHZK 300N shows as Err05 (acceleration), Err06 (deceleration) or Err07 (constant speed). It is especially common on fans, centrifuges, conveyors and any high-inertia or overhauling load. Unlike overcurrent, the cause is almost always the motor feeding energy back into the drive — and the fix is usually about where that energy goes.

Where the extra voltage comes from

When a motor turns faster than the frequency the drive commands — for example a fan that keeps spinning during a fast stop, or a downhill conveyor — the motor acts as a generator. That energy flows back through the IGBTs and charges the DC-bus capacitors. As the bus rises past the protection threshold (about 810 V on a 400 V-class drive), the drive trips to protect the capacitors and modules. An overvoltage trip is therefore a sign of regenerated energy with nowhere to go.

First — check the actual bus voltage

Before changing timing, confirm the problem is really regeneration and not a high supply:

1. Measure the incoming line-to-line voltage. Err05/06/07 is also triggered if the input voltage itself is too high — for example a transformer tap set wrongly or regen from another drive on the same bus.
2. In run or stop state, watch the DC-bus readout (it is one of the monitored values, U-02). A healthy 400 V bus is roughly 540–560 V at idle and rises only slightly during normal operation.
3. If the bus climbs toward 800 V whenever the load slows, regeneration is confirmed.

Three places the energy can go

1. Back into the load slowly — lengthen deceleration so regen stays below the limit.
2. Into a braking resistor — converted to heat via the P+/PB terminals.
3. Back to the mains — a regenerative (active-front-end) drive for continuous regen.

Fix by when it trips

Sizing and wiring a braking resistor

The resistor connects to the P+ and PB terminals (on small drives the brake chopper is built in; larger drives need an external braking unit). Sizing depends on inertia, stop time and duty — the manual lists recommended values by power rating. Key points our engineers always check:

• Resistance must not be lower than the minimum for your power rating, or the chopper current is excessive.
• The resistor gets hot — mount it away from wiring and plastic parts, and rate it for the actual duty cycle (occasional stops vs. repeated cycle work).
• For a continuously overhauling load — such as a downhill conveyor — a resistor cannot dissipate energy non-stop; use a regenerative drive instead.

One more cause: shared DC bus and other drives

If several drives run on the same supply and one regenerates, it can raise the bus for the others and cause a “mysterious” Err07 with no change on that machine. When overvoltage appears on multiple drives at once, check for a regenerating crane, elevator or centrifuge on the same panel and consider a common-bus arrangement that feeds the energy to the motoring drives.

From our test bench

When we demonstrate a fast stop on a high-inertia fan motor without a brake resistor, the drive trips Err06 every time — that is expected physics, not a fault. Lengthen the decel time first because it costs nothing; only when the application genuinely demands a quick stop do we add a resistor. Matching the resistor to the real inertia and duty cycle is what makes the fix permanent.