Mitsubishi FR-E800 Fault E6 — What It Means
Fault E6 on the Mitsubishi FR-E800 inverter indicates a brake transistor fault — the internal braking transistor (used to dissipate regenerative energy during deceleration) has failed or is operating outside normal parameters. The FR-E800 monitors the braking transistor duty cycle and temperature; if the transistor shorts or the braking resistor circuit is open, E6 trips to prevent a DC bus overvoltage condition.
Common Causes
- Failed braking transistor — The internal brake IGBT can fail short-circuit, triggering E6 immediately on power-up.
- Braking resistor open or disconnected — If an external braking resistor is specified and becomes open-circuit or disconnected, the transistor has no path to dissipate energy and the fault trips.
- Braking resistor overheating/overload — Excessive regenerative energy from a large inertia load overheats the braking resistor. Most resistors have a thermal switch that opens on overheat.
- Deceleration time too short — An aggressive decel ramp on a high-inertia load puts more energy into the braking circuit than it can handle.
Step-by-Step Fix {#fix}
- Check for a shorted braking transistor — With power off, measure resistance between the P/+ terminal and PR terminal. Near-zero resistance in both directions indicates a shorted transistor.
- Inspect the braking resistor — Measure resistance across the braking resistor terminals (if external resistor installed). Open circuit = burned-out resistor. Check thermal fuse/switch on the resistor.
- Extend deceleration time — Increase Pr.8 (Deceleration Time) to reduce regenerative current per unit time. This is the first parameter fix to try before replacing hardware.
- Check wiring to braking resistor — Verify the resistor is connected between P/+ and PR terminals with correct wire gauge. Loose connections cause intermittent E6.
- Reset and test — After repair, cycle power and run a ramp-down cycle. Confirm E6 does not return.
Parts Often Needed
| Part | Notes |
|---|---|
| Braking resistor | Amazon | Match to FR-E800 frame size and duty cycle requirement |
| FR-E800 inverter unit | Amazon | If internal brake transistor has failed |
When to Call a Pro
Internal braking transistor replacement requires drive disassembly and component-level repair. Mitsubishi authorized service handles transistor-level repairs for FR-E800 units.