OL code on Giandel 12v 3000W inverter with nothing plugged in.

Had this exact issue with a cheaper inverter a while back — not Giandel specifically but same sort of unit. The OL (overload) fault with nothing connected is almost always one of a few things:

1. Internal fault on startup
Some inverters will throw OL if there's a problem with the internal circuitry — a failed capacitor or MOSFET can cause it to read a phantom load.

2. Low battery voltage
What's your battery voltage sitting at when it triggers? If the 12v bank is sagging below ~10.5v under the inverter's own startup draw, some units misread that as an overload condition rather than a low voltage fault. Worth checking with a multimeter directly at the terminals.

3. Dodgy connection
Loose or undersized cable between battery and inverter can cause a voltage drop that confuses the unit. What cable gauge are you running? For a 3000W inverter you really want 70mm² minimum, ideally with the shortest run possible.

I'd try:

• Fully charge the battery first
• Check all connections are tight and correct gauge
• Do a factory reset if the unit has one (hold the power button sequence — check the manual)

If it's still doing it after all that, the unit itself may be faulty. Giandel's warranty support can be a bit hit and miss depending on where you bought it from.

What battery setup are you running — lead acid or lithium? And is this a new unit or has it worked previously? That'll narrow it down quite a bit. Others on here may have had direct Giandel experience too, be curious what they say.

@Max1970 welcome to the forum mate, glad you're getting stuck in! 🎉

Worth also checking the inverter's soft-start capacitors internally if you're comfortable opening it up — a failed cap can cause it to read a phantom load on startup. Seen this on a couple of units aboard my boat over the years.

Also — is your battery voltage solid under load? A sagging 12v system (say dropping below 11v at startup) can confuse cheaper inverters into throwing OL rather than a proper low-voltage fault. Bit daft but there it is.

What's your battery setup? If it's lead-acid and a bit tired, that'd be my first suspect before pulling anything apart.

Good point from @Max1970 on the internal fault angle.

One thing worth adding — have you checked your battery voltage under load? A 12v system can look fine on a multimeter at rest, then sag badly the moment the inverter's own circuitry draws current. If the inverter sees voltage drop below its low-voltage cutoff during startup, some units will throw OL rather than LVD — confusing labelling, but I've seen it.

What battery are you running? If it's AGM or lead-acid, internal resistance matters a lot here. My narrowboat setup had similar ghost faults before I moved to lithium.

Also — what cable gauge and how long are your DC runs? Undersized or lengthy cables will cause exactly this kind of voltage sag at the inverter terminals even with healthy batteries.

Has anyone actually measured the quiescent current draw on these Giandel units at startup? I'm wondering if the internal capacitors are charging so fast they're briefly spiking above the OL threshold before anything's even connected.

On my setup I've noticed some cheaper inverters can trigger OL during their own initialisation cycle if the battery voltage is slightly low — the unit struggles to charge its own internals cleanly.

What's the battery voltage sitting at when you power it on? If it's dipping below ~11.8V even momentarily under the inverter's own startup load, that could be your culprit before you even start suspecting the inverter itself is faulty.

@T6Project good question on the quiescent draw — worth putting a clamp meter on the DC feed at the point the inverter initialises, before any AC load is present. On my Fiat Ducato build I caught a similar ghost-overload by datalogging through a Victron SmartShunt; the inverter's internal toroidal transformer was saturating momentarily on startup due to residual magnetisation, which the protection circuitry read as an overload condition.

The fix was simply powering down fully, waiting 60 seconds for the transformer core to demagnetise, then restarting. Resolved it completely.

If that doesn't help, check whether your DC cable cross-section is appropriate. Undersized cable creates a voltage drop spike on inrush that can confuse the protection logic into triggering OL even with no AC load. For a 3000W unit you really want 25mm² minimum on short runs.

@DucatoSolar raises a good point about the clamp meter, but I'd go one step further — when my Victron Phoenix threw phantom faults during initial commissioning, it turned out the DC cable run was undersized for the inverter's inrush demand, even with zero AC load. The inverter's internal capacitors charging at startup can look like an overload event to the protection circuit.

Worth checking:

• Cable gauge vs. recommended spec for that inverter
• Fuse/breaker rating between battery and inverter
• Connection integrity at both ends — even a slightly loose lug creates resistance that compounds the problem

The Giandel units aren't known for their forgiving protection thresholds. If the voltage drops even briefly during that capacitor charge cycle, some units will flag OL rather than UV. Classic budget inverter behaviour, sadly.