Why is there no power at anchor and other problems...

"Blackout at anchor" is one of the most common service reports I deal with every season in Sardinia and more broadly in the Mediterranean Sea. Unlike mechanical failures, power issues rarely have one obvious cause — they are usually the result of several minor shortcomings in the DC or AC installation, which accumulate under conditions of high temperature, intense usage, and long hours at anchor without connection to shore.

The following Q&A collects eight questions that I most often hear from owners, skippers, and fleet managers. I answer them based on solid electrical diagnostics of the yacht and ABYC (American Boat & Yacht Council) standards — a benchmark recognized in the industry for safe electrical installations on yachts, regardless of the flag. I deliberately omit the mechanics of main engines — I focus solely on power systems: battery banks, chargers, inverters, DC/AC installations, and monitoring systems.

1. Why does my inverter cut off power when I start the coffee maker or desalination unit, even though the batteries are charged?

This is one of the most common misconceptions on board: the "100% charged" indication on the battery monitor refers to the amount of stored energy (amp-hours), not the bank's ability to deliver high current in a short time. A coffee maker or desalination unit are high inrush current loads (surge current) — devices can initially draw 2-3 times the rated current, and the high-pressure pump of the desalination unit starts under full hydraulic load.

When such a surge current passes through the DC installation powering the inverter, every component — wire, fuse, main switch, terminal on the battery pole — contributes its resistance. According to Ohm's law (U=IR), at currents of 100-150 A (typical for a load of 1.5-2 kW on the AC side, converted to 12 V DC), even a small transient resistance results in a real, momentary voltage drop at the inverter terminals. If this drop goes below the low voltage disconnect threshold programmed in the inverter, the device cuts off the power for protection — even though the battery bank, measured at rest, still shows full charge.

The most common causes related to the installation are:

- DC wire with too small a cross-section for the given length and current (chosen "by eye", instead of from ampacity tables),

- too long a cable run between the bank and the inverter and degraded connections — loose terminal screws,

- corrosion on the terminals, lack of dielectric grease on the contacts.

ABYC standard E-11 defines the maximum allowable voltage drop in a circuit as a percentage of the nominal voltage:

Diagnostics involve measuring the voltage under load — not at rest — directly at the battery bank terminals and at the inverter input, at the moment the device generating the surge starts. A difference greater than allowable clearly indicates an issue with the installation, not with the batteries. The solution is to recalculate the wire cross-section according to ABYC ampacity tables (considering the length of the run in both directions and ambient temperature), shortening and organizing the wiring, and a complete inspection and tightening of all connections with the appropriate torque. Regular inspections of the installation are also necessary, where salt can gradually degrade connections.

2. I bought new onboard batteries (AGM) and after one season in the Mediterranean, they are ready for disposal. What went wrong?

A yacht battery (AGM) that does not hold a charge after just one season in the Mediterranean is usually the result of two simultaneous causes: temperature and chronic undercharging.

The engine compartment in full sun can reach 45-55°C in summer, and directly near the battery set installed close to the engine or generator can be even hotter. Lead-acid chemistry is particularly sensitive to temperature: the generally accepted industry rule states that every 8-10°C above the reference 25°C shortens the battery life by about half. A battery that would last 5-6 seasons in a temperate climate can degrade in just one season in a hot engine compartment in southern Europe.

The second mechanism is PSOC (Partial State of Charge) — chronic undercharging. A yacht at anchor rarely returns to a full 100% charge: the generator or engine runs briefly, the shore charger may be poorly configured (profile for gel or wet batteries instead of AGM, too low absorption voltage, too short absorption phase time), and the bank spends most of the time in the 50-80% SOC range. In this state, hard lead sulfate (sulfation) builds up on the lead plates, which does not dissolve back during the next charging and permanently reduces capacity and ability to accept current.

Diagnostics: checking the actual temperature at the battery installation site, reading logs from the Victron charger/monitor (voltage and duration of the absorption phase in successive cycles), and — if possible — measuring the internal resistance of the cells. A systemic solution, alongside correctly selecting batteries for the yacht at the purchasing stage, includes: relocating the bank outside the engine compartment or providing additional ventilation, adjusting the charger settings for a specific type of AGM according to the manufacturer's catalog (absorption voltage, temperature compensation, full cycle time), and — if the usage specifics (long stays at anchor) do not allow for completing the cycle to 100% — considering switching to a chemistry less sensitive to PSOC, i.e., LiFePO4 (see question 3).

3. After switching to a lithium bank (LiFePO4), can I do without a generator?

This is one of the most widespread myths I encounter when modernizing to lithium batteries for yachts. Lithium indeed changes the rules of the game: it allows for practically 100% capacity utilization (compared to the safe 50% DoD for lead), accepts much higher charging current, and does not suffer from PSOC. However, it is a matter of capacity and efficiency of energy storage — not generation. The generator does not disappear from the installation; its role simply changes.

The key is the energy balance, not the battery technology itself. Marine air conditioning (even a single unit of 9,000–12,000 BTU) can draw an average of 500–900 W of continuous load during its operating cycle, and a membrane desalinator additionally consumes several hundred watts each time it starts. With typical daily production from photovoltaic panels on the yacht ranging from 1–3 kWh (see question 5) and limited engine running time (which means limited charging from the alternator), daily demand easily exceeds what renewable sources and the alternator can return to the bank — regardless of whether the bank is lead or lithium.

The generator (power generator) thus remains essential as a source of quick, high-current recharging in a short time and as direct power for large, continuous loads (24-hour air conditioning, desalination working for hours). However, a well-designed Victron Energy system (Quattro or MultiPlus with the Auto Generator Start assistant in Cerbo GX) can radically improve the economics of this collaboration: the generator starts automatically only when the bank's SOC drops below a set threshold, operates under high load — instead of idling with a single small load — and turns off as soon as the bank returns to the programmed level, instead of running for hours "just in case," as is often the case with manual control. The effect: fewer hours of generator operation and lower fuel consumption, but the generator is still part of the installation.

4. When I connect the yacht to shore power in a marina (Sardinia/Greece/Croatia), it immediately trips the breaker at the dock. Why?

A power failure on the yacht immediately after connecting to shore power usually has one of four causes, and it is worth checking them in order from the simplest.

First, reversed polarity — in many Mediterranean marinas, especially older infrastructures, the phase/neutral assignment on the post is not always standardized. A yacht without an indicator or polarity relay at the AC input, connected "backwards," can trigger the ground fault protection at the dock if the onboard installation relies on correct polarity relative to ground.

Second, leakage currents — every device with an EMI filter (chargers, inverters, navigation electronics, LED lighting with power supplies) introduces a small but non-zero leakage current to the protective conductor. Individually, they are negligible, but collectively on a yacht with extensive electronics, they can approach the tripping threshold of the ground fault breaker at the post (typically 30 mA), especially in a humid marine environment.

Third, the absence of a galvanic isolator (ABYC A-3) on the protective conductor — apart from the risk of galvanic corrosion of the hull, which is the main reason for its installation, its absence or damage can also facilitate the transfer of stray currents from neighboring installations at the common dock, burdening the protection in a non-obvious way.

Fourth, the inrush current of powerful combi chargers (e.g., the charging section in Victron Quattro) — when starting simultaneously with a large AC load on board, the instantaneous current draw can exceed the rating of the circuit breaker at the post (typically 16 A single-phase in many Mediterranean marinas), especially if the charger does not have an input current limit configured to match the shore power.

Diagnostics: measuring leakage current with a differential clamp meter on the protective conductor with loads off, and then sequentially switching on the loads; checking polarity with a tester before each connection; inspecting the condition and continuity of the galvanic isolator; and verifying the input current limit setting in the charger against the actual circuit breaker at the post.

5. My solar panels in July in Sardinia charge weaker than in May in Poland. Are they damaged?

This is a physical phenomenon, not a malfunction — and a very common report in the summer season. Photovoltaic cells have a negative temperature coefficient of power: typically from -0.3% to -0.45% of the rated power for each degree Celsius above the reference temperature (25°C under STC conditions). A panel mounted flat on the deck or hard roof, in full sun in Sardinia, without airflow underneath, can heat up to 65–70°C. With a coefficient of -0.4%/°C and a difference of 40–45°C from reference conditions, the actual power drop reaches 16–18% compared to the rated value on the data sheet — and this is under clear skies, in theoretically "ideal" sunlight conditions.

In May in Poland, the angle of sunlight and total insolation (irradiance) are lower, but the cell temperature is closer to the optimal 25°C — so despite weaker sunlight, the panel operates closer to its rated efficiency. This explains the seemingly paradoxical effect: less sun, but higher effective performance.

The role of the controller is significant here. An MPPT (Maximum Power Point Tracking) controller, such as from the Victron SmartSolar series, continuously tracks the maximum power point of the I-V curve of the panel, which shifts with temperature, and keeps operation as close to that point as possible — unlike a simpler PWM controller, which does not compensate for this change and loses an additional few to several percent. A good quality MPPT will not "fix" the physics of silicon, but it minimizes additional losses on the electronics side.

Practical conclusions for installing solar panels on a yacht: lack of airflow under the panel is the most common installation mistake to correct — even a few centimeters of ventilation gap lowers the cell temperature and effectively improves performance; when designing installations for units mainly operated in hot climates, it is advisable to select the rated power with a margin relative to actual demand, taking thermal losses into account; and the power drop in summer in southern Europe, with a properly functioning MPPT, is not in itself a reason to complain about the panels.

6. The Victron control panel (Cerbo GX / Color Control) shows 100% battery, but after an hour the current disappears. What’s going on?

The SOC (State of Charge) indication on the battery monitor — BMV, SmartShunt, or the integrated reading in Cerbo GX — is not a direct measurement. It is the result of integrating the current flowing into and out of the bank over time (so-called coulomb counting), referenced to the programmed capacity. Such a counter naturally drifts: shunt measurement errors, losses not accounted for in a simple model — e.g., the Peukert effect at high discharge currents — and rounding errors accumulate over time.

To correct this, the system must periodically "synchronize" to the actual 100% — this happens automatically when the bank voltage reaches the programmed "Charged Voltage" threshold and the current falls below the "Tail Current" threshold for longer than the "Charged Detection Time". If these three parameters are incorrectly set relative to the actual charging profile on the yacht — e.g., a voltage threshold higher than the actual absorption voltage of the charger, or a tail current threshold too low to ever be reached — synchronization never occurs. The monitor then "drifts in the dark": it may incorrectly indicate a high SOC based on an outdated model for an extended period until the voltage measurement under load brutally reveals the actual, significantly lower state of charge — hence the impression that "current disappears from minute to minute."

"Diagnostics boils down to reviewing the monitor settings: the bank capacity (Ah) in accordance with the actual specifications, synchronization voltage matched to the realistically achieved absorption/float voltage, residual current set to 2–4% of the nominal capacity, and the proper Peukert coefficient for the specific chemistry (different for lead, practically close to 1.0 for LiFePO4). The solution is correct configuration and control of the system during installation or review — not equipment replacement, but correction of parameters to match the actual operating profile of the yacht."

"7. Can I safely charge the LiFePO4 bank from a standard alternator while under engine power?"

"Without additional safeguards — no, and this is one of the most costly oversights I see in service practice when switching to lithium."

"A standard alternator voltage regulator — whether internal or external, but designed for lead — assumes that as charging occurs, the voltage on the battery increases, and the internal resistance of the lead battery naturally limits the current drawn as it approaches full charge. This assumption does not hold for LiFePO4: its internal resistance is low enough that the lithium bank accepts high charging current almost throughout the entire SOC range, until it is close to full charge — the voltage at the terminals remains flat and does not "tell" the alternator to limit the current."

"The result: an alternator designed to operate with high current only briefly — typical use with lead, where the current quickly drops — is forced to operate continuously at a current close to the rated maximum for a long time, meaning hours of engine operation. The effect is overheating of the stator windings, damage to the rectifier diodes, and in extreme cases, complete burning out of the alternator, sometimes during a single longer passage."

"Solutions, in order of increasing effectiveness:"

"The choice depends on the scale of the installation: with a small auxiliary bank, a DC-DC converter is often sufficient; with larger lithium banks as the main power source for the yacht, implementing an external regulator with temperature monitoring is reasonable, and if the demand for charging current is high, reviewing the entire alternator drive system for belt and bearing load capacity is advisable."

"8. Air conditioning on an inverter at night — is it supposed to work?"

"Yes, but a properly designed yacht air conditioning system on an inverter requires a conscious design of three elements: the peak power of the inverter (inverter), limiting the starting current of the compressor, and a sufficiently large bank capacity."

"The air conditioning compressor, like any induction motor, draws a starting current (Locked Rotor Amps) that is 3-5 times higher than the continuous operating current at startup. The inverter must be able to provide this short-term peak power, not just the continuous power — hence selecting an inverter for air conditioning always requires checking its peak power parameter (peak/surge power), not just the nominal power from the nameplate."

""Soft Start" systems — dedicated modules mounted directly at the compressor — solve this problem at the source: they reduce the starting current of the compressor by as much as 60–70%, spreading the startup over time instead of delivering a single sudden spike. The practical effect is the ability to use a smaller, cheaper, and more energy-efficient inverter with the same air conditioning unit and a lower load on the DC system (see question 1)."

"The third element is the bank capacity. For example, a 9,000 BTU unit in a night operating cycle — the compressor does not run 100% of the time, it only cyclically maintains the temperature — consumes an average of about 400–600 W, which over 8 hours of sleep gives 3.2–4.8 kWh of net energy. Adding the inverter conversion efficiency (typically 90–92%), the actual demand from the bank rises to about 3.5–5.3 kWh. For a 12 V lithium bank, this practically means about 300–450 Ah of usable capacity dedicated solely to air conditioning for one night — not counting other loads (refrigerator, lighting, electronics)."

In a classic lead-acid (AGM/gel) battery, this is usually impractical — a safe DoD of around 50% means a battery twice the physical size, and deep, frequent discharge cycles drastically shorten its lifespan (see question 2). This is one of the strongest practical arguments for upgrading to LiFePO4 on yachts operating in warm climates with a 24/7 air conditioning requirement — provided the entire chain is properly sized: the battery, inverter, and charging system.

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