Deye SUN-8K-SG04LP3 Error F18: AC Over Current Fault
Fault F18 occurs when instantaneous AC output current exceeds the hardware peak current threshold, indicating a downstream short circuit, heavy inrush current, or internal inverter bridge failure.
Hardware Diagnostic Matrix
Spec Ref #4bb43abfRequired Diagnostic Tools & Instrumentation
Multimeter Probing Targets & Circuit Tolerances
Bench Calibrated ±5%| Test Point / Circuit | Target Nominal Spec | Expected State | Fault Condition |
|---|---|---|---|
| Main Logic DC Bus | 3.3V / 5.0V DC (±0.1V) | Stable DC Potential | <2.9V (Brownout / Sag) |
| Thermistor / NTC Sensor | 10kΩ - 100kΩ @ 25°C | Smooth Thermal Curve | 0Ω (Short) or ∞ (Open) |
| Safety Ground / PE Continuity | < 0.5Ω Resistance | Solid Earth Bond | > 1.0Ω (Floating Chassis) |
Common Symptoms & Fault Manifestations
- Fault F18 pops up on screen with emergency audible tone
- UPS / Backup load port instantly de-energizes
- Usually triggers simultaneously with starting heavy electric motors or welders
Root Causes & System Failure Modes
Short circuit in household AC wiring or failed electrical appliance
Inrush current of large inductive motor (e.g. submersible pump, air compressor) exceeding peak surge rating
Severe phase unbalance on three-phase models exceeding single-phase capability
Internal AC current sensor (CT) malfunction or damaged IGBT module
High-Voltage & Mechanical Safety Isolation
Prior to opening access panels, disconnecting terminals, or probing wiring, perform complete lock-out / tag-out (LOTO). Disconnect all AC mains, DC string isolators, and lithium battery banks. Allow internal smoothing capacitors at least 3 to 5 minutes to dissipate stored residual energy below safe threshold (<30VDC).
Step-by-Step Diagnostic & Resolution Procedure
Isolate the AC Backup Loads
Trip the output breaker supplying the backup circuits to isolate the inverter from the premise wiring.
Inspect Downstream Circuits for Short Circuits
Test circuit continuity and insulation resistance between Phase-to-Neutral and Phase-to-Ground on the disconnected load lines. Eliminate any shorted appliances.
Boot Inverter Without Load
Power cycle the Deye unit with the AC load breaker turned OFF. If F18 appears immediately without any load connected, the internal AC current sensor or power module has failed.
Sequential Load Re-engagement
If the inverter starts normally without load, switch on individual branch circuit breakers one by one to pinpoint the specific high-draw or shorted load.
Hardware Reset & Fault Clear Sequence
Controller ProcedurePrevention & Routine Maintenance Guidelines
- Install dedicated soft-starters or VFDs on motors exceeding 2.5kW
- Balance single-phase loads evenly across L1, L2, and L3 phases
- Ensure backup circuits do not exceed continuous 8000W / 12000W surge threshold
Frequently Asked Diagnostic Questions
What does error code F18 indicate on Deye SUN-8K-SG04LP3?
Fault F18 occurs when instantaneous AC output current exceeds the hardware peak current threshold, indicating a downstream short circuit, heavy inrush current, or internal inverter bridge failure. In engineering telemetry, it indicates ac over current fault requiring circuit verification.
What are the primary triggers causing error F18?
Diagnostic bench telemetry isolates the following common root causes: Short circuit in household AC wiring or failed electrical appliance; Inrush current of large inductive motor (e.g. submersible pump, air compressor) exceeding peak surge rating; Severe phase unbalance on three-phase models exceeding single-phase capability; Internal AC current sensor (CT) malfunction or damaged IGBT module.
How do I reset and clear Deye error F18?
Clear the error via the LCD touchscreen fault log, or power cycle the inverter completely after disconnecting the shorted load. If the error status repeats immediately after clearing, discontinue clearing and test circuit continuity.
Can I safely resolve error F18 without specialized shop tooling?
This fault is graded as Intermediate difficulty with High severity. Standard diagnostics require an insulated digital multimeter and appropriate hand tools. Always observe high-voltage isolation procedures.