Off-grid power system troubleshooting

A whole-system power failure — where none of your loads are running and you can't immediately tell why — is a different problem from a single component that has stopped working. Individual components each have their own failure-mode documentation: inverters, batteries, generators, and solar basics all cover component-level symptoms in detail. This page synthesizes those atom-level diagnostics into a cross-component decision tree for the harder scenario: you have no power (or wrong power), you don't know which component failed, and you need to work through it systematically.

This page is a routing surface. When it identifies the likely culprit, it hands you off to the relevant atom page for the deep fix.

Action block

Do this first: Measure battery voltage at the battery terminals with a multimeter (2 min) — this single measurement narrows the fault class before you touch anything else Time required: Active: 15–45 min for a full systematic walkthrough; most faults isolate in the first 10 min Cost range: Inexpensive for the primary diagnostic tool (an auto-ranging multimeter handles 90% of this); a clamp meter for AC/DC current is an affordable addition Skill level: Beginner for symptom identification and display reading; intermediate for multimeter measurements at live DC bus; advanced for panel-level IV measurement and live AC diagnostics Tools and supplies: Tools: digital multimeter (DMM), clamp meter (for AC/DC current without breaking the circuit), infrared (IR) thermometer or thermal imaging adapter. Supplies: flashlight, pen and paper for logging readings. Safety warnings: See Stop immediately for these conditions below — burn smell, smoke, water ingress, or arc marks require de-energizing before any further diagnosis

Educational use only

This page is for educational purposes only. Hands-on skills should be learned and practiced under qualified supervision before relying on them in emergencies. Use this information at your own risk.

Quick-reference symptom table

Use this table to identify the most likely fault class and jump to the relevant decision-tree section.

Symptom	Most likely component	Jump to
No AC output — inverter display dark	Battery voltage too low, BMS lockout, or inverter fault	AC output missing
No AC output — inverter display active / fault code showing	Inverter fault or overload protection triggered	AC output missing
AC output present but loads drop out under load	Inverter undersized for surge; battery voltage sag	AC output missing
Battery not charging — charge controller dark	Source input (solar or generator AC) not reaching controller	DC charging missing
Battery not charging — controller shows absorption/float	Battery is actually full; not a fault	DC charging missing
Battery discharging too fast	Parasitic drain; load increase; battery capacity degradation	DC charging missing
Solar not producing on clear day	Shading, soiling, MC4 (multi-contact 4mm PV connector) fault, or controller tapering (full battery)	Solar not producing
Generator starts but loads won't run	Transfer switch issue; generator not connected to load bus	Generator fault
System fails at night or in cold weather	LiFePO4 battery management system (BMS) cold-charge cutoff; parasitic drain draining battery overnight	Intermittent and nighttime failures

Before you start:

Use this when: You have a system-level fault — no power or unexpected loss — and you don't know which component failed.
Do not use this when: You already know which component failed; go directly to its atom page (inverters, batteries, generators, solar basics).
Stop and escalate if: You detect burning smell, visible smoke, water on or near electrical components, scorch marks at any terminal or panel, or you hear repeated loud snapping sounds from a circuit breaker or busbar. De-energize the system at the main DC disconnect and main AC disconnect before continuing. Call a licensed electrician. See Stop immediately admonition below.

Choosing a method

The right diagnostic path depends on whether you have any AC output, any DC charging, or complete failure.

Situation	Entry point
Inverter completely dark, no output	Start at AC output missing — battery or BMS is the most likely cause
Inverter has display/fault code, no output	Start at AC output missing — read the fault code first
Inverter works but battery drains unusually fast	Start at DC charging missing
Battery charges fine but solar input is zero on a clear day	Start at Solar not producing
Generator runs but doesn't power loads or charge battery	Start at Generator fault
System fails reproducibly at night or in cold weather	Start at Intermittent and nighttime failures

Steps

AC output missing

Before you start, record the ambient temperature — cold affects diagnosis differently than warm.

Check the inverter display or LED indicators. If the display is completely dark, the inverter has no power or is in hard shutdown. If there are LED codes or a display fault message, photograph it and look it up in your inverter manual. Common codes: over-voltage shutdown, under-voltage shutdown (low battery), overload, and over-temperature. For Victron, Magnum, and Outback inverter-specific fault code lookups, see inverters.
Measure battery voltage at the battery terminals. Use your multimeter on DC voltage. Place probes directly on the battery posts or the terminal bus, not at the inverter's DC input lugs. This distinction matters: voltage drop across undersized or corroded DC cable between the battery and inverter can read as a battery problem at the inverter but shows normal at the terminal.
Lithium iron phosphate (LiFePO4): resting voltage 13.2–13.4 V (12V nominal system) indicates 50–60% state of charge. Below 12.0 V resting, the battery management system (BMS) has likely tripped. Above 14.6 V, the battery may be in high-voltage protection.
AGM lead-acid: 12.6–12.7 V = ~100%; 12.0 V = ~50%; 11.8 V = ~25%. Below 11.8 V resting, the battery is deeply discharged and the inverter's under-voltage lockout has engaged.
Flooded lead-acid: same voltage range as AGM; confirm with a hydrometer (specific gravity 1.265 = full; 1.120 = 0%).
If voltage is normal (above 12.0 V on a 12V system), check the DC fuse or breaker between the battery and inverter. A blown fuse produces zero voltage at the inverter input while showing normal voltage at the battery. Test the fuse continuity with your multimeter on resistance mode — a good fuse reads near 0 ohms; a blown fuse reads open (OL).
If the fuse is good and battery voltage is normal, check for BMS lockout. LiFePO4 batteries with a BMS will disconnect if the battery management system has triggered a protection event: low cell voltage, high cell voltage, over-temperature, or under-temperature (below 32°F (0°C) for charging; below −4°F (−20°C) for discharging). Some BMS units require a manual reset; others reset automatically when the fault condition clears. Check your BMS indicator LEDs or connect a Bluetooth app (many LiFePO4 batteries from Renogy, Battle Born, and similar brands include Bluetooth BMS monitoring).
If battery voltage is low (deep discharge), allow the battery to recover before troubleshooting. Apply charging from an available source: solar, generator-AC charger, or shore power. If the battery won't accept a charge, the BMS may have entered low-voltage lockout — some BMS units require a specific recovery charge procedure (typically a 0.1C trickle charge for 30 minutes to bring cells above the lockout threshold). See batteries for BMS recovery procedures.
Under-load voltage sag test. If the inverter shows normal voltage at rest but shuts down when loads come on, measure battery voltage again with a 500W or larger load running. Sag below 11.5 V (12V system) under that load indicates: (a) the battery is near-depleted even if its resting voltage looked acceptable, or (b) the DC cable between battery and inverter is undersized, producing excessive voltage drop under current. Check cable gauge against National Electrical Code (NEC) 690.8(B) / NEC Table 310.16 for the expected current.

Field note

The first measurement is always battery voltage at the battery terminals, not at the inverter input. Voltage drop across undersized or corroded DC wiring fools you into chasing inverter faults that don't exist. A 12V system drawing 100A through 10 feet (3 m) one-way of 4 AWG cable — 20 ft (6 m) round-trip — drops roughly 0.6 V end-to-end (4 AWG ≈ 0.000308 Ω/ft × 20 ft × 100 A). That's enough to push a marginal battery past the inverter's under-voltage trip threshold even though the battery is fine. Add corroded terminals and the drop doubles.

DC charging missing

"DC charging missing" means the battery isn't accepting charge from its source — solar, a generator-side AC charger, or shore power. The symptoms are: battery state of charge declining despite available source, or charge controller showing no input.

Check the charge controller display. Most Maximum Power Point Tracking (MPPT) and Pulse Width Modulation (PWM) controllers (Victron SmartSolar, Renogy Wanderer, Outback FlexMax, Morningstar TriStar) show the current operating stage: Bulk, Absorption, Float, or Equalize. If the display shows Float or Absorption, the battery is full — this is not a fault. If the display is dark or shows a fault LED, proceed.
Confirm source input is reaching the controller.
For solar: measure DC voltage at the controller's PV input terminals. If it reads 0V or near-0V during daylight, the issue is upstream of the controller — see Solar not producing.
For a generator-side AC charger: confirm the generator is running and the AC charger is receiving voltage. Measure AC voltage at the charger's input; 120V/240V expected. A running generator that shows no AC output has an internal fault — see Generator fault.
Confirm the BMS is in charge-accept state. If the BMS has tripped its charge-protection, it opens the charge circuit internally. Check BMS app or LED. On most lithium batteries, the charge-enable output is independent of the discharge output — the battery may still power loads (inverter works) while refusing to accept charge (BMS charge-protection active). Common triggers: high-voltage protection (battery already full — again, not a fault), under-temperature protection (below 32°F / 0°C), or a cell imbalance fault.
Check charge settings on the controller. A controller configured for lead-acid chemistry with a 14.4 V absorption setpoint will charge a LiFePO4 bank incorrectly (LiFePO4 absorption = 14.2–14.6 V, float = 13.5–13.6 V). Mismatched chemistry settings produce under-charging and, in some cases, premature BMS trip on float. Verify the controller's battery type profile matches your chemistry.
Verify wiring continuity from controller to battery. Measure resistance across the DC positive cable from controller to battery positive terminal — any reading above 0.1 ohm in a short run indicates a corroded terminal, loose lug, or failed connection. Retorque all lugs to the battery manufacturer's published spec — do not guess. Typical LiFePO4 battery terminal torque is 9–11 ft-lb (108–132 in-lb / 12–15 N·m) per Battle Born, Renogy, and similar production datasheets; busbar-to-lug connections on 2/0 and larger cable are typically 95–120 in-lb (11–14 N·m). Under-torqued lugs produce resistive heat and are a leading cause of terminal-fire damage. Use a calibrated torque wrench, not feel.

Field note

LiFePO4 BMS cold-charge cutoff is the single most common "mystery failure" in cold climates — the system powers loads without complaint but refuses to charge. The battery is protecting itself from permanent lithium plating, not malfunctioning. The solution is thermal management, not component replacement: insulate the battery enclosure, add a self-regulating heating pad on a thermostat, or (for systems with Bluetooth BMS) simply confirm the battery temperature reading in the app. The fix costs a fraction of replacing a battery bank.

Solar not producing

The first instinct when solar panels aren't producing is to climb on the roof. In most cases, the problem is diagnosable from the charge controller display and a multimeter at ground level.

Check the charge controller display for PV input voltage. A Victron SmartSolar or any MPPT controller shows the panel string voltage at its PV input terminal. If this reads 0V or an anomalously low value on a sunny day, the issue is upstream of the controller: panel disconnects, combiner fuses, or cable/connector faults.
Confirm the battery is not already full. On a clear afternoon, if the controller shows Float stage and low or zero PV current, it is tapering correctly — the battery is full and the controller is reducing input to maintain float voltage. This is not a fault.
Check all PV-side disconnects and breakers. NEC 690.13 requires a PV system disconnecting means; most systems also have per-string fusing or breakers in a combiner box. If a combiner box breaker has tripped, no PV voltage reaches the controller. Reset the breaker (once only — if it trips again, there's a fault in that string) and measure PV input voltage at the controller again.
Measure open-circuit voltage (Voc) at the panel or string.
Disconnect the string from the combiner or controller.
Measure DC voltage across the PV positive and negative leads.
Compare to the panel's spec sheet Voc (typically 35–45 V per panel in a 12V system, scaled by the series string count).
A string reading near-zero Voc on a clear day confirms a panel or connector fault in that string.
A string reading 50–80% of expected Voc suggests partial shading, soiling, or a failing cell.
Inspect MC4 connectors for physical damage. MC4 connectors are the most common solar field failure after years of UV and thermal cycling. Signs of a faulty connector: discoloration, cracking, corrosion inside the barrel, or a connector that pulls apart with light tension (indicating an uncrimped pin). A failed MC4 produces either an open circuit (complete fault) or elevated resistance (partial power loss without obvious cause). Use a properly rated MC4 extraction tool — do NOT use a screwdriver, which can damage the connector body and create a fire hazard.
Check for shading and soiling. A single shaded cell on a series string can reduce the entire string's output by 30–60% depending on the inverter/controller's shading tolerance. Soiling (dust, bird droppings, pollen) causes similar proportional losses. Clean panels with water and a soft brush — no abrasives, no high-pressure washers. Re-measure after cleaning.

Field note

When solar isn't producing on a sunny day, check the inverter or charge-controller display before climbing on the roof. In 80% of cases the issue is upstream of the panels — a tripped breaker, a full battery tapering correctly, or an MC4 connector fault — and you can identify and fix it from the ground. Roof climbing introduces fall risk; don't skip the ground-level steps.

Generator starts but loads won't run

If the generator engine runs but loads won't power up, or the generator isn't charging the battery bank through an AC charger, the fault is usually in the connection path rather than the generator itself. Generator-specific no-start diagnostics live on generators and are not duplicated here.

Verify the transfer switch or interlock is engaged. A manual transfer switch must be physically switched to generator position. An interlock kit requires the utility-side breaker to be off and the generator-side breaker to be on. Confirm the switch position.
Measure AC voltage at the generator's 120V/240V outlet. Use your multimeter on AC voltage. A running generator should produce 120V ± 5% at the outlet under no load. Below 108V or above 132V indicates a governor or AVR (automatic voltage regulator) fault. Low or absent AC output from a running generator is an internal mechanical-electrical fault requiring service.
Check the generator's outlet breaker. Most portable generators have a circuit breaker on the generator's own outlet panel. Overload during startup (surge from a motor load exceeding the generator's surge rating) trips this breaker. Reset and confirm loads don't exceed the generator's continuous wattage rating.
If the generator powers loads but won't charge the battery through a charger: Confirm the AC charger is plugged into the generator and powered. Some AC-to-DC chargers (particularly inverter-chargers like Victron Multiplus or Magnum MS series) have a minimum AC input voltage threshold — below approximately 105 VAC, they drop the charge function to protect their input circuit. Run the charger under load and measure AC input voltage at the charger's terminals.
Parallel load problem. If other AC loads are running simultaneously with the charger, total AC load may exceed the generator's rating. Shed loads and re-test. A generator running near its continuous limit often trips on surge when the charger's transformer energizes.

Intermittent and nighttime failures

Intermittent faults — system works during the day, fails at night; works when warm, fails when cold — have two dominant causes: LiFePO4 BMS cold-charge cutoff and parasitic drain exceeding overnight recharge.

Log the failure events. Record: time of failure, ambient temperature at time of failure, battery voltage (if readable), which loads were running. Three or more data points with consistent low temperature correlation confirm cold BMS cutoff. Three or more data points with no temperature correlation but consistent overnight timing confirm parasitic drain.
Cold BMS cutoff (LiFePO4 systems). LiFePO4 BMS units cut charge input below 32°F (0°C) to prevent lithium plating. Discharge continues down to approximately −4°F (−20°C) on most quality cells, but charging is blocked below freezing. If your battery won't accept solar or generator charging on a cold morning but powers loads normally, the BMS is doing its job. Solutions: insulate the battery compartment (spray foam, rigid foam board), add a self-regulating heating pad with thermostat controlled to maintain 40°F (4°C) minimum, or relocate the battery bank to a conditioned space. Do not attempt to override or bypass the BMS temperature sensor.
Parasitic drain audit. Everything connected to the DC bus draws current even when "off" — inverter idle draw, charge controller self-consumption, LED indicators, Bluetooth modules, and any small loads left connected overnight. An MPPT charge controller may draw 10–50 mA constantly; an inverter in standby draws 20–200 mA depending on model; a Victron Cerbo GX monitoring unit draws roughly 230 mA at 12 V on its own (2.8 W) and up to ~400 mA at 12 V (4.8 W) with the GX Touch display attached at full backlight per the Cerbo GX datasheet. Measure each device's parasitic draw with a clamp meter in DC mode. Sum the total mA × 24 hours to find overnight Ah loss. If overnight losses consistently exceed solar recharge, either shed parasitic loads (put the inverter on a manual switch) or add panel capacity.
Battery capacity degradation check. An aging lead-acid battery at 5+ years or a LiFePO4 bank approaching its rated cycle count will show acceptable resting voltage but fail under load. Perform a load test: measure battery voltage with a 50% rated load applied for 30 seconds. A healthy 12V 100Ah bank should hold above 12.0 V under a 50A draw. Significantly more sag indicates capacity loss and replacement planning.

Tools and substitutes

Ideal tool	Specs / sizing	Field substitute	Notes and limits
Digital multimeter (DMM)	Auto-ranging, CAT III 600V rated; DC and AC voltage + resistance	Any basic auto-ranging DMM from a hardware store	Accuracy ±1–2% is sufficient for system diagnostics; avoid low-grade uncategorized meters for live AC work
Clamp meter	DC-capable (Hall-effect clamp), 400A range	DMM with a current shunt (breaks the circuit)	Clamp meter is safer for high-current measurement; a shunt requires circuit interruption
IR thermometer	−4°F to 716°F (−20°C to 380°C), ±2°F	Smartphone IR adapter (FLIR ONE or similar)	Thermal imaging adapters reveal hot spots not visible to a spot thermometer; useful for finding resistive faults at terminals
MC4 extraction tool	Brand-matched to connector type	(none — do not substitute)	Using a screwdriver to release MC4 connectors deforms the latch and creates a fire-prone intermittent connection
Hydrometer (flooded lead-acid only)	Specific gravity range 1.10–1.30	None safe	Multimeter voltage gives approximate SoC; hydrometer gives cell-level confirmation

Safety note: Never measure current in series (inline) with a DMM's current port (the A/mA jacks) in a DC bus carrying more than 10A — the meter fuse blows and damage to the meter or wiring is likely. Use a clamp meter for current above 10A. Never bypass a fuse or breaker to "test" a circuit — if a protective device has tripped, it tripped for a reason; diagnose the cause before resetting.

Failure modes

This diagnostic workflow fails or is insufficient in five scenarios. Recognize them early to avoid wasted time and additional risk.

Intermittent fault that won't reproduce during diagnosis. The system works fine as soon as you start testing. Log events with timestamps, ambient temperature, and load profile for at least three occurrences. A licensed electrician with a data logger can capture the event in real time if the pattern is consistent.
Multiple simultaneous component failures. Rare under normal conditions, but common after a lightning strike or a severe wiring fault (short circuit that propagated through the system). If multiple components appear failed simultaneously, treat the entire system as suspect and call a licensed electrician. Do not attempt to isolate and replace one component at a time — replacing a battery into a system with a failed BMS or shorted wiring will destroy the new battery.

Suspected lithium battery thermal runaway. If you smell a sharp chemical or "burning plastic" odor from a lithium battery, see the battery casing swelling or deforming, or feel heat from the battery case that is not explained by recent discharge, stop all diagnosis immediately. Disconnect what is safely disconnectable, ventilate the space, and call the fire service. Lithium thermal runaway can reignite hours or days after apparent resolution. This is not a diagnostic problem — it is an emergency.

Stop immediately for these conditions

De-energize before continuing diagnosis if you observe any of the following. Shut off the main DC disconnect (battery bank isolator) and the main AC disconnect (transfer switch or main breaker). Then call a licensed electrician or emergency services as appropriate.

Burning smell or smoke from any component, wiring, or enclosure
Scorch marks or discoloration at terminals, busbars, fuse holders, or circuit breakers
Loud repetitive snapping from a breaker or busbar (AC arc-flash precursor)
Water on or near AC wiring — do not diagnose live, kill the main AC breaker first
Swelling or heat from a lithium battery — this is thermal runaway risk; evacuate and call fire service

AC arc-flash hazard. Loud snapping sounds from an AC panel, scorch marks at breakers or busbars, or tripping breakers with no apparent load are signs of an arc fault. Kill the main AC breaker before any further access to the panel. Arc flash at AC distribution voltages can cause severe burns and ignition — this is electrician territory, not DIY troubleshooting.
Wet-environment fault. Water intrusion into an AC panel or battery enclosure (flooding, roof leak, condensation-damaged enclosure) — never diagnose live. Kill the main breaker from outside the affected area first. Water plus AC is immediately lethal; water plus a lithium battery bank creates the conditions for rapid fire. Dry thoroughly and have a licensed electrician inspect before re-energizing.

Diagnostic checklist

Use this before calling for help — it documents what you've already tried and helps an electrician or remote support understand the system state quickly.

With this data recorded, you can hand a clear picture to a licensed electrician, a manufacturer's support line, or a remote technical resource without describing symptoms from memory.

With whole-system faults diagnosed and isolated, the next priorities are hardening your system against recurrence — starting with battery sizing and chemistry selection for a bank that handles your actual load profile, and solar system off-grid design for matching generation to seasonal demand. Medical-device-dependent households and cold-chain medication users should cross-reference the no-power medical device scenario for the parallel human-safety protocol that runs alongside this electrical diagnostic.

Sources and next steps

Last reviewed: 2026-05-24

Source hierarchy:

Victron Energy SmartSolar MPPT Troubleshooting Guide (Tier 1 manufacturer documentation — MPPT fault code reference)
Fluke: Troubleshooting photovoltaic systems (Tier 2 — test-equipment manufacturer field diagnostic guidance)
Phocos: 6 Tips to Troubleshoot When Your Off-Grid Solar System Stops Working (Tier 2 — charge controller manufacturer field guidance)
LiTime: Low Temperature Protection for Lithium Batteries (Tier 2 — LiFePO4 BMS cold-cutoff explanation)

Legal/regional caveats: Permanent installation and repair of battery-based power systems is regulated under NEC Article 706 (Energy Storage Systems) and NEC Article 690 (Solar PV) in most US jurisdictions. Diagnostic measurement at existing terminals is generally within homeowner scope; any modification to wiring, fuses, or panel connections requires a permit and licensed electrician in most states. Confirm with your Authority Having Jurisdiction (AHJ).

Safety stakes: high-criticality topic — recommended to verify thresholds before acting.

Next 3 links:

→ Batteries — chemistry-specific recovery procedures and BMS reset after deep discharge
→ Inverters — fault code lookup by inverter platform and inverter-charger wiring
→ No-power medical device scenario — parallel human-safety protocol for medical-device-dependent households during a power fault