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123 terms
A measure of electric charge (battery capacity). A 100Ah battery can theoretically deliver 10A for 10 hours. Always multiply by voltage to get Wh: 100Ah × 12V = 1,200Wh.
Electric current that periodically reverses direction. Mains power (grid) is AC — 230–240V at 50Hz in AU/EU/NZ, 120V at 60Hz in North America. Inverters convert DC to AC.
Absorbent Glass Mat — a sealed lead-acid battery where the electrolyte is absorbed in fibreglass mat. Maintenance-free, spill-proof, and no venting required. 400–800 cycles at 50% DoD. Heavier and less efficient than LiFePO4.
Stage 2 of multi-stage charging. The controller holds a constant voltage (absorption voltage) while current tapers as the battery fills. For LiFePO4: 14.2–14.6V (12V system). Duration is shorter for lithium than lead-acid.
The maximum continuous current a cable can carry without exceeding its temperature rating. Depends on cable cross-section, insulation rating, ambient temperature, and installation method. Cables in conduit or bundles must be derated.
A high-current bolt-down fuse rated for lead-acid (AGM) battery protection. Interrupt rating: ~6,000A. Semi-slow blow. Adequate for AGM fault currents but NOT for LiFePO4 — lithium fault currents can cause ANL elements to arc and weld closed.
The US/CA wire sizing standard. Unlike metric mm², AWG uses an inverse scale — a larger AWG number means a thinner wire. AWG 14 ≈ 2.5mm², AWG 12 ≈ 4mm², AWG 10 ≈ 6mm², AWG 8 ≈ 10mm², AWG 6 ≈ 16mm², AWG 4 ≈ 25mm², AWG 2 ≈ 35mm², AWG 1/0 ≈ 50mm². Used in USA and Canada; AU/EU/UK use mm².
The generator driven by the vehicle engine that charges the starter battery and powers electrical accessories. Output voltage varies — conventional alternators: ~14.4V. Smart alternators (Euro 5/6): 11.5–15V variable.
Australian/New Zealand standard for solar PV installations. Covers string fusing, cable types, DC isolators, labelling, and minimum clearances. Mandatory solar DC isolators, double-pole isolation, and PV1-F cable for string wiring.
Australian/New Zealand standard for electrical installations in caravans, motorhomes, and transportable structures. Covers DC system requirements, RCD protection on AC circuits, earthing, and cable types. Required for insurance compliance in AU/NZ.
American Boat and Yacht Council standard for AC and DC electrical systems on boats. Mandates tinned copper cable, specific wire sizing, overcurrent protection within 72 inches of the battery, two-wire systems (no chassis return), and RCD protection on AC circuits.
A protection device required by NEC 690.11 for PV output circuits operating above 80V DC. Detects the signature of arcing faults (which can ignite insulation) and disconnects the circuit. Required for all new US solar installations in most jurisdictions. Not required in AU/EU/UK.
Electronics that monitor and protect individual cells in a lithium battery pack. Functions: over-voltage cutoff (HVC), under-voltage cutoff (LVC), over-current protection, short circuit protection, temperature protection, and cell balancing.
Related Terms
A solar panel that generates power from both the front and rear surfaces. The rear captures reflected light (albedo) from the ground or roof surface. Bifacial gain is typically 5–30% depending on mounting and ground reflectivity.
Stage 1 of multi-stage charging. The controller delivers maximum available current until the battery reaches the absorption voltage (typically 14.4–14.6V for 12V LiFePO4). Most of the charging capacity is recovered in this stage.
Small coloured plastic fuses for branch circuits (5A–40A). Colour-coded by amperage (red=10A, blue=15A, yellow=20A, etc.). Used for lights, fans, USB chargers, and other low-current accessories. Interrupt rating: ~1,000A.
A solid copper or tin-plated copper bar with multiple bolt holes, used to distribute power to multiple circuits from a single connection point. Must be rated for the total combined current of all cables attached. Separate positive and negative busbars required.
A small pin-type crimp terminal for fine-strand wire ends, inserted into screw terminals on MPPT controllers, inverters, and chargers. Prevents strand splaying and ensures consistent contact in screw terminals.
A main disconnect switch on the positive cable between the battery and system. Allows safe maintenance, vehicle storage, and emergency shutdown. Must be rated for DC voltage — AC switches can arc and weld under DC load. Size to 1.25× maximum system current.
An instrument that tracks battery state of charge using a shunt to measure current in and out. Essential for LiFePO4 (flat voltage curve makes voltage-only SoC useless). Examples: Victron BMV-712, Victron SmartShunt.
Bureau of Indian Standards certification — mandatory for solar panels (IS 16221), charge controllers (IS 16169), and inverters (IS 16046) used in MNRE-subsidised installations in India. Products without BIS certification are not eligible for government subsidies.
The open-circuit voltage of a solar panel at minimum expected temperature. Calculated as: Cold Voc = Voc_STC × (1 + |Temp_Coeff| × (25 − T_min)). Must not exceed MPPT maximum input voltage.
The rate at which a battery is charged or discharged relative to its capacity. 1C = full charge/discharge in 1 hour. 0.2C = 5 hours. LiFePO4 is typically rated 1C continuous discharge; AGM 0.2C. Exceeding the C-rate reduces capacity and damages batteries.
The number of charge/discharge cycles a battery can complete before capacity degrades to 80% of original. LiFePO4: 3,000–6,000 cycles. AGM: 400–800 cycles. Flooded lead-acid: 200–500 cycles.
The process of equalising voltage across all cells in a battery pack. Passive balancing dissipates excess energy as heat from higher cells. Active balancing transfers energy between cells. Ensures all cells charge and discharge evenly.
The ratio of charge output to charge input over one cycle. LiFePO4: ~99%. AGM: ~85%. Means for every 100Ah drawn from an AGM battery, you must put back ~118Ah. Affects solar array sizing calculations.
Battery capacity degradation over time, independent of cycling. Accelerated by heat and storing at high SoC. LiFePO4 stored at 100% SoC ages faster than at 50–80% SoC. Typical LiFePO4 calendar life: 10–15 years.
The sequence of voltage and current settings a charger uses for each battery chemistry. MUST match the battery type. LiFePO4 profiles: different absorption voltage and no equalization vs lead-acid. Setting the wrong profile damages batteries.
The reduction of a cable's ampacity based on installation conditions. Cables in conduit: multiply by 0.75. Bundled cables: multiply by 0.70–0.80. High ambient temperature: multiply by 0.71–0.87. Always derate before selecting cable size.
A fast-blow, current-limiting fuse mandatory for LiFePO4 battery terminals. Interrupt rating: ~20,000A. Clears in microseconds — fast enough for lithium fault currents. Littelfuse KLKD series is the most common. Requires a Class T fuse holder.
A ring terminal crimped onto large cable ends (10–120mm²) for bolted connections to busbars, batteries, and components. Must be crimped with a hydraulic or ratchet tool — soldering is not appropriate for high-current connections.
A protective tube (corrugated plastic or rigid PVC) that encloses cables to protect from UV, abrasion, heat, and rodents. Required for any exposed cable runs. Cables in conduit must be derated for ampacity.
Victron Energy's system monitoring and control hub. Connects to all Victron devices via VE.Bus, VE.Can, and VE.Direct. Provides a unified system view, logs to the VRM portal, and supports a touchscreen display (GX Touch 50/70).
India's statutory body under the Ministry of Power that sets technical standards for electrical installations. The CEA (Measures Relating to Safety and Electric Supply) Regulations 2010 govern electrical safety for all installations including solar PV systems.
Electric current that flows in one direction only. Batteries, solar panels, and most off-grid components produce and use DC. System voltages are typically 12V or 24V DC for most mobile and small off-grid builds.
The percentage of battery capacity that has been used. 80% DoD = 20% charge remaining. LiFePO4 can safely use 80–95% DoD. AGM should be limited to 50% DoD to preserve cycle life.
A battery-to-battery charger that takes power from the vehicle start battery/alternator and converts it to the correct multi-stage charge profile for the leisure battery. Works with smart alternators, provides galvanic isolation, and limits current draw.
A voltage signal from the alternator excitation circuit that indicates the engine is running. Used by DC-DC chargers and VSRs to start charging when the engine is on. Also called the ignition signal or charge light wire.
A periodic overcharge applied to flooded lead-acid batteries (typically 15.5–16V for 12V) to prevent cell stratification and remove sulfation. NEVER apply to lithium batteries — will permanently damage cells.
The number of AC cycles per second, measured in Hertz. Australia, NZ, and Europe use 50Hz. North America uses 60Hz. Running a 60Hz appliance on 50Hz can cause motors to run slower.
The original rechargeable battery — liquid electrolyte, removable cell caps for watering. Cheapest option but requires regular maintenance (watering, equalization), produces hydrogen gas, and has the lowest cycle life of any option.
A thin-film or semi-flexible solar panel that can be adhered to curved surfaces. Lower efficiency (10–15%) and shorter lifespan than rigid panels. Only appropriate when rigid panels physically won't fit.
Stage 3 — maintenance charging. The charger holds a lower voltage to keep the battery at 100% without overcharging. For LiFePO4: often disabled or set to 13.5V. For AGM: 13.6–13.8V. For flooded: 13.5–13.8V.
A lead-acid battery with silica gel electrolyte — no liquid spillage, tolerates vibration well, suited to deep discharge. Slower charging than AGM, sensitive to overcharging. Used in marine and caravan applications.
A rubber ring inserted into a hole in a metal panel through which a cable passes. Prevents the cable insulation from chafing on the metal edge. Any cable passing through a metal surface must have a grommet.
Complete electrical isolation between two circuits. Used in DC-DC chargers to prevent DC current from flowing between start and leisure battery systems. Prevents galvanic corrosion in marine applications and protects both batteries.
US equivalent of RCD. Required on all AC inverter output circuits under NEC. Disconnects in ~25ms when current leakage to ground is detected. Available as outlets, breakers, or standalone units.
The BMS protection that disconnects charging when any cell reaches maximum voltage. For LiFePO4: typically 3.65V/cell (14.6V for 4S 12V pack). Prevents overcharging and potential thermal runaway.
A hydraulic tool that applies precise, consistent compression to cable lugs. Required for reliable crimps on cable 10mm² and above. A ratchet crimper is not adequate for large lugs — use a hydraulic tool for professional results.
Power dissipated as heat in a cable. P_loss = I² × R. Doubling the current quadruples the heat generated — which is why undersized cables overheat so rapidly under high loads.
The opposition to current flow within a battery cell. Lower internal resistance means less voltage sag under load and less heat. LiFePO4 has very low internal resistance (~0.1–0.5mΩ/cell). Increases as batteries age.
The power of solar radiation hitting a surface, measured in W/m². Peak irradiance is 1,000W/m² (STC). Average daily irradiance integrated over time gives insolation (Wh/m²), which equals peak sun hours.
The panel current at rated wattage under STC. Paired with Vmp to give Pmax (W = Vmp × Imp). Used to size cables and verify MPPT output current.
The maximum current a solar panel produces when terminals are shorted. Used to size string fuses: fuse rating = 1.56 × Isc. Slightly higher than Imp under STC.
A device that converts DC battery power to AC mains power. Pure sine wave inverters produce clean AC identical to the grid. Modified sine wave inverters produce a stepped approximation that can damage sensitive electronics.
A combined unit containing a pure sine wave inverter, multi-stage battery charger, and AC transfer switch. When shore power or generator power is available, it charges the battery and passes AC to loads simultaneously. The standard for full-time van/cabin builds.
The momentary high current drawn by motors, capacitors, and transformers when first switched on. Can be 3–10× the steady-state current. Causes voltage sag in weak battery systems and can trip BMS over-current protection.
The power consumed by an inverter with no load connected. Also called no-load draw. Can range from 8W to 50W+ depending on inverter size and quality. A 30W idle draw wastes 720Wh per day — significant for small systems.
International standard for PV array design. Covers string fusing requirements for parallel arrays, cable sizing, earthing, and protection against reverse current. Widely adopted in Europe and Australia alongside local standards.
Bureau of Indian Standards (BIS) specification for solar photovoltaic modules used in India. Covers performance, safety, and durability requirements. MNRE requires BIS certification (IS 16221) for all solar panels used in government-subsidised off-grid and grid-connected systems.
Bureau of Indian Standards code for design loads for buildings and structures. Part 3 covers wind loads — relevant for solar panel mounting structures in India, particularly for rooftop and ground-mounted systems that must withstand cyclone-prone coastal regions.
1,000 watts. Used for larger power ratings such as inverters and generators. A 3kW inverter delivers 3,000 watts of AC power.
1,000 watt-hours. The standard unit for energy billing and large battery capacities. A 10kWh battery stores 10,000Wh of usable energy.
Lithium Iron Phosphate — the safest and most durable lithium battery chemistry for off-grid use. Rated 3,000–6,000 cycles, 80–95% usable DoD, no thermal runaway risk. Requires a BMS and specific charge voltages.
The BMS protection that disconnects the load when any cell drops below minimum voltage. For LiFePO4: typically 2.5V/cell. Prevents deep discharge damage that permanently reduces capacity.
A solar panel made from a single silicon crystal. Highest efficiency (20–23% at cell level), best low-light performance, and smallest size for a given wattage. The dominant technology for off-grid applications.
Industry-standard weatherproof connectors for solar panel wiring. Rated IP67, 1000V DC, 30A. Must be crimped with a matched MC4 crimping tool. The 'MC4' designation refers to the 4mm contact pin. Never use mismatched brand connectors.
A charge controller algorithm that continuously adjusts its input impedance to extract the maximum possible power from the solar array. Typically 93–98% efficient. Handles array voltages higher than battery voltage — allowing longer cable runs and higher-voltage panel strings.
The MPPT output current must accommodate: (Array Watts ÷ Battery Voltage) × 1.25. The MPPT input voltage must exceed Cold Voc of the array. Round up to the next standard controller size (20A, 30A, 40A, 50A, 60A, 80A, 100A).
A stepped waveform that approximates a sine wave. Cheaper, but can damage motors, cause transformers to buzz, reduce battery charger efficiency, and fail to operate some electronics. Not recommended for serious off-grid systems.
A mid-range slow-blow fuse (30A–200A) suitable for MPPT controller battery cables, DC-DC charger feeds, and sub-distribution runs. Interrupt rating: ~2,000A. Available in a convenient bolt-down format.
India's central government ministry responsible for renewable energy policy, including off-grid solar. Sets guidelines for system design, component certification, and subsidy programs. MNRE-approved components are required for government-subsidised installations.
A more realistic panel rating condition: 800W/m², 20°C ambient, 1m/s wind. Typical NOCT is 45–50°C. At NOCT, panels produce ~85–90% of their STC rating.
National Electrical Code Article 690 (USA) — covers all solar PV systems. Mandates string fusing for parallel arrays, DC disconnects, arc fault protection (AFCI) for systems over 80V, and specific labelling requirements.
The unit of electrical resistance. Higher resistance means less current flows for the same voltage. Cable resistance causes voltage drop and heat generation.
The fundamental relationship: V = I × R (Voltage = Current × Resistance). Rearranged: I = V ÷ R and R = V ÷ I. The foundation of all DC circuit analysis.
The voltage produced by a solar panel or battery with no load connected. Always higher than working voltage. Increases as temperature drops — critical for MPPT controller sizing.
The ratio of real power (watts) to apparent power (volt-amps) in an AC circuit. Purely resistive loads have a PF of 1.0. Motors and electronics typically have a PF of 0.7–0.95. Inverters rated in VA must be derated by the PF.
The phenomenon where lead-acid batteries deliver less capacity when discharged at higher rates. A 100Ah AGM at 1C may only deliver 60–70Ah. LiFePO4 is minimally affected. Peukert's exponent (n) quantifies this — typically 1.05–1.15 for AGM.
Connecting battery positives together and negatives together. Doubles capacity (Ah) while maintaining the same voltage. All batteries must be the same chemistry, capacity, and age. Use equalised cable lengths to ensure even sharing.
The number of hours per day a location receives full-strength sunlight (1,000W/m²). Not daylight hours — a location with 12h of daylight may have only 4–5 PSH. Critical for solar array sizing. Varies significantly by season and location.
The rated wattage of a solar panel under STC. Pmax = Vmp × Imp. The headline number on a panel's label. Real-world peak output is typically 75–85% of Pmax.
An enhancement to monocrystalline cells that adds a passivation layer to the rear, improving efficiency by reducing electron recombination. Most modern mono panels are PERC. Achieves 21–22% efficiency.
A solar panel made from multiple silicon crystal fragments. Lower efficiency (15–17%) and larger size than monocrystalline for the same wattage. Cheaper, but the price advantage has largely disappeared. Recognisable by its blue speckled appearance.
Connecting two or more solar strings positive-to-positive and negative-to-negative. Adds current (A) while voltage stays the same. Requires string fuses (MC4 inline) when 2+ strings are parallel.
A simpler charge controller type that forces the panel to operate at battery voltage. Loses the potential power difference between panel Vmp and battery voltage — typically 20–30% less efficient than MPPT. Only suitable for very small systems where panel Vmp closely matches battery voltage.
An inverter output waveform identical in shape to grid AC. Required for all sensitive electronics, induction motors, variable-speed tools, and medical equipment. The correct choice for all off-grid applications.
Double-insulated, UV-resistant solar panel cable rated 1000V DC. Mandatory for all outdoor PV string wiring. Not interchangeable with standard DC cable — the double insulation and UV resistance are essential for roof-mounted applications.
Electrical current drawn from a battery when a vehicle is parked with engine off. Normal vehicle parasitic drain: 20–50mA. Off-grid systems can add significant drain from inverter standby, monitoring equipment, and wiring faults.
Opposition to current flow in a circuit. Measured in ohms (Ω). All cables have resistance — thinner or longer cables have more resistance, causing more voltage drop and heat.
A safety device that disconnects AC power within 30ms if current leaks to earth (ground fault). Mandatory for all AC circuits from an inverter in AU/NZ under AS/NZS 3001.2. US equivalent: GFCI (Ground Fault Circuit Interrupter).
How full a battery is, expressed as a percentage. 100% = fully charged, 0% = completely discharged. LiFePO4 has a flat voltage curve making SoC hard to measure from voltage alone — use a shunt-based monitor.
The formation of lead sulfate crystals on the plates of a lead-acid battery, typically from chronic undercharging or sitting in a partially discharged state. Reduces capacity and increases internal resistance. Partially reversible with desulfation charging.
The rate at which a battery loses charge when not in use. LiFePO4: ~2%/month. AGM: ~3%/month. Flooded: ~5%/month. Important for storage — batteries left discharged for extended periods can be permanently damaged.
Connecting the negative of one battery to the positive of the next. Doubles voltage while maintaining the same Ah. Used to build 24V banks from 12V batteries. Batteries must be identically matched.
A combination configuration: batteries are first connected in series pairs to achieve the target voltage, then those pairs are connected in parallel to increase capacity. Example: 4× 12V batteries in 2S2P = 24V with doubled Ah.
The laboratory conditions under which solar panels are rated: 1,000W/m² irradiance, 25°C cell temperature, AM 1.5 spectrum. Real-world output is typically 70–85% of STC due to heat, dust, and wiring losses.
Fusing each solar string's positive cable when two or more strings are wired in parallel. Required by NEC 690 and IEC 62548. Fuse rating = 1.56 × panel Isc. Prevents reverse current from parallel strings damaging a faulted string.
Connecting solar panels end-to-end (positive to negative). Adds voltage while current stays the same. Higher voltage = smaller cables for same power. Must verify cold Voc doesn't exceed MPPT maximum input voltage.
A device that regulates charging of a battery from solar panels. Prevents overcharging and applies the correct multi-stage charge profile. Two main types: MPPT (efficient, handles higher voltages) and PWM (simpler, less efficient).
The peak power an inverter can deliver momentarily (typically 2–3 seconds) for motor startup. Motor loads surge to 3–6× running wattage at startup. The surge rating must exceed the highest single-load startup surge.
AC power from a campsite electrical hookup, marina berth, or building mains supply. An inverter-charger connects shore power to its AC input, charges the battery, and passes AC to loads simultaneously.
A double-pole DC isolator installed between the solar array and MPPT controller. Allows safe disconnection of solar input for maintenance. Mandatory under AS/NZS 5033 (AU/NZ). Must be rated for array open-circuit voltage and 1.25× short-circuit current.
A precision low-resistance resistor in the negative cable. A battery monitor measures the tiny voltage drop across it (mV) to calculate current flow and track state of charge. Must be the only path for all negative current — any bypass causes inaccurate readings.
A modern alternator with variable output voltage controlled by the engine ECU to improve fuel economy. Output may be as low as 11.5V at times. Makes VSR-based charging unreliable — a DC-DC charger is required.
The component in an inverter-charger that switches between inverter output and shore/generator power. Transfer time is typically 10–20ms — fast enough for most appliances but may cause sensitive electronics to restart.
Thermoplastic Heat and Water-resistant Nylon-coated cable. The US/CA equivalent of V90/TFX flexible DC cable for conduit installations. Rated 90°C wet/dry, 600V. Used for DC wiring runs inside conduit in US off-grid systems. Not suitable for outdoor direct exposure — use USE-2 for that.
Copper cable with tin plating on each strand. Prevents oxidation at terminations in salt-air and high-humidity environments. Required by ABYC E-11 for all marine DC wiring. Significantly extends cable life in boats and coastal installations.
Underground Service Entrance cable rated for outdoor and direct-burial use. The US/CA equivalent of PV1-F solar cable. Rated 600V DC, UV-resistant, suitable for all outdoor PV string wiring per NEC 690. Required for solar panel string wiring in US installations.
The unit of electrical potential difference (voltage). It measures the 'pressure' that pushes electric current through a circuit. Named after Alessandro Volta.
Apparent power in an AC circuit: V × A without considering power factor. Some inverters and UPS units are rated in VA rather than watts. Watts = VA × Power Factor.
The reduction in voltage along a cable due to its resistance. Calculated as V_drop = I × R_cable. Aim for less than 3% on any circuit run. For 12V: max 0.36V; for 24V: max 0.72V.
The rate at which a panel's Voc changes with temperature. Typically −0.28% to −0.40%/°C for silicon panels. Voc rises in cold weather — use this to calculate Cold Voc for MPPT sizing.
The panel voltage at which it produces its rated wattage under STC. This is what an MPPT controller continuously tracks to extract maximum power. Always lower than Voc.
Victron Energy's Bluetooth and USB configuration app for MPPT controllers, battery monitors, inverters, and DC-DC chargers. Available for iOS and Android. Used to configure settings, monitor performance, and read firmware updates.
Flexible DC cable with 90°C rated insulation. The standard for all high-current DC wiring in off-grid systems. Multi-strand construction provides flexibility and vibration resistance. Available 1mm² to 120mm².
Victron Energy's mid-range battery monitor. Shunt-based, displays SoC, voltage, current, power, and time-to-go. Has Bluetooth for VictronConnect app. The gold standard for most off-grid builds. Works with any battery chemistry.
Same accuracy as the BMV-712 but without a physical display — relies on the VictronConnect app via Bluetooth. Ideal when you want system data only on your phone or tablet. Mounts directly in the negative cable.
Victron Remote Monitoring — a free cloud portal at vrm.victronenergy.com that displays real-time and historical data from Victron GX devices. Accessible from any browser or the VRM app. Supports remote firmware updates and alerts.
A relay that connects start and leisure batteries when alternator voltage exceeds ~13.7V. Simple and cheap, but unreliable with smart alternators (variable voltage may never trigger) and unsafe for LiFePO4 (no current limiting). Use a DC-DC charger instead.
The unit of power. W = V × A. Measures the rate of energy transfer or consumption at any given moment. Named after James Watt.
A unit of energy. 1 Wh = 1 watt consumed for 1 hour. Used to measure battery capacity and daily energy consumption. 1,000Wh = 1kWh.
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