If you are researching how to construct an inverter by winding your own toroidal transformers and soldering MOSFET H-bridges, stop right there. For any AC load over 200W, building the power electronics from raw components is a severe fire hazard and economically unviable compared to mass-produced high-frequency modules. Instead, professional makers and off-grid installers construct an inverter power system—integrating a commercially certified pure sine wave inverter/charger with a correctly sized DC battery bank.
This guide provides the exact math, hardware selection, and wiring procedures to build a robust 2000W 24V LiFePO4 inverter system capable of running a refrigerator, microwave, and lighting circuit simultaneously.
The Source-to-Load Block Diagram
A reliable inverter system is not just a battery and an inverter; it is a managed power pipeline. Understanding the source-to-load block architecture prevents catastrophic failures and ensures your protective devices actually function when a fault occurs.
- Energy Sources: Solar array (via MPPT charge controller) and/or Utility Grid/Generator (via AC input).
- DC Bus (Storage): The battery bank acts as the system's shock absorber, buffering the difference between generation and load.
- DC Protection: A DC disconnect switch and a Class T fuse located within 7 inches of the battery positive terminal.
- Inverter/Charger: Converts DC bus voltage to 120V/240V AC for loads, and rectifies AC to DC to charge the batteries when grid/generator power is present.
- AC Subpanel/Load: The final destination, protected by standard AC branch circuit breakers.
Battery Bank Sizing: Series vs. Parallel and Discharge Limits
The foundation of your system is the battery bank. How you wire your cells dictates your voltage, current, and ultimately, the thickness of the copper you need to buy.
Series vs. Parallel Consequences
Wiring batteries in series adds voltage while keeping Amp-hours (Ah) identical. Wiring in parallel adds Ah while keeping voltage identical. Total energy (Watt-hours) remains the same in both configurations, but the operational characteristics change drastically.
| Configuration | Voltage | Capacity (Ah) | Total Energy | Current at 2000W Load |
|---|---|---|---|---|
| 2x 12V 100Ah (Parallel) | 12V | 200Ah | 2400Wh | ~190 Amps |
| 2x 12V 100Ah (Series) | 24V | 100Ah | 2400Wh | ~95 Amps |
As the table shows, a 24V series configuration halves the DC current draw compared to 12V. Because resistive heat loss is calculated as $I^2R$, halving the current reduces cable heat generation by 75%, allowing you to use smaller, cheaper wire and reducing voltage drop.
Discharge Limits: C-Rate, DoD, and Peukert's Law
You cannot simply pull the rated Ah from a battery. You must account for Depth of Discharge (DoD) and discharge rates.
- Depth of Discharge (DoD): Lead-acid batteries should only be discharged to 50% DoD to preserve cycle life. Lithium Iron Phosphate (LiFePO4) can safely be discharged to 80%-90% DoD. A 100Ah LiFePO4 battery yields ~85 usable Ah, whereas a 100Ah lead-acid yields only 50 usable Ah.
- C-Rate: This defines the maximum safe continuous discharge current relative to capacity. Most LiFePO4 cells are rated for 0.5C to 1C continuous. A 100Ah battery at 0.5C can safely deliver 50A continuously. Exceeding this triggers the Battery Management System (BMS) to disconnect the load.
- Peukert's Law: This formula ($t = H(C/IH)^k$) describes how capacity shrinks as discharge current increases. For lead-acid, the Peukert exponent ($k$) is typically 1.2 to 1.3, meaning high loads severely reduce available runtime. For LiFePO4, $k$ is approximately 1.05, making the discharge curve nearly linear and highly predictable even under heavy surge loads.
Inverter and Charger Sizing Math
Sizing the inverter requires calculating both continuous and surge loads, then factoring in inverter efficiency to determine the true DC current draw.
Target AC Load Profile:
- Refrigerator: 150W continuous, 800W surge (compressor startup)
- Microwave: 1000W continuous, 1100W surge
- Lighting & Router: 100W continuous
- Total: 1250W continuous, 2000W peak surge.
Inverter Sizing: Select an inverter rated for at least 2000W continuous to handle the combined loads without thermal throttling, with a surge rating of at least 4000W to handle motor startups.
DC Current Draw Calculation:
Inverters are not 100% efficient. High-frequency pure sine wave inverters typically operate at 88% to 92% efficiency under heavy load. We will use a conservative 88% (0.88) efficiency factor.
$$I_{dc} = \frac{P_{ac}}{V_{dc} \times \text{Efficiency}}$$
$$I_{dc} = \frac{2000W}{24V \times 0.88} = 94.7 \text{ Amps}$$
Your battery bank, BMS, and cabling must be rated to handle at least 95A continuously. Because our 2x 100Ah LiFePO4 bank in series has a 0.5C rating (50A per battery), we need to ensure our continuous draw stays under 50A, or we must parallel two series strings (4 batteries total) to achieve a 100A continuous limit. For this build, we will assume typical loads average 1000W (47A draw), reserving the 2000W for brief surges.
Charger Sizing: The integrated AC charger should replenish the bank at 10% to 20% of the total Ah capacity. For a 200Ah total bank (two parallel strings of 24V 100Ah), a 40A to 50A internal charger is optimal, ensuring a full recharge in 4-5 hours from a generator.
Decision Tree: Picking Your Exact Inverter and Battery Hardware
Use this decision matrix to select your system voltage and exact hardware based on your maximum continuous AC load.
| Max Continuous AC Load | Recommended DC Voltage | Recommended Inverter/Charger | Battery Bank Configuration |
|---|---|---|---|
| < 1000W | 12V | Victron MultiPlus 12/1200 | 1x or 2x 12V 100Ah LiFePO4 (Parallel) |
| 1000W - 3000W | 24V | Victron MultiPlus-II 24/2000 | 2x 12V 100Ah LiFePO4 (Series) |
| 3000W - 5000W | 48V | Victron MultiPlus-II 48/5000 | 4x 12V 100Ah LiFePO4 (Series) |
The Concrete Pick for a 2000W System:
For the vast majority of off-grid cabins, van builds, and backup systems requiring 2000W, the definitive choice is the Victron Energy MultiPlus-II 24/2000 (Part # PMP242200000, typically ~$1,150). Pair this with two Ampere Time 12V 100Ah LiFePO4 batteries wired in series (~$220 each). This combination provides a 24V DC bus, a built-in 50A AC charger, and seamless UPS-style transfer switching during grid outages.
Wiring, Fusing, and Commissioning Steps
With your hardware selected, proper execution separates a reliable power wall from a melted terminal lug. According to NEC Article 706 guidelines for stationary storage systems, overcurrent protection and conductor ampacity must be meticulously calculated.
- Wire Sizing: A 95A maximum draw requires wire rated for at least 120A to account for ambient heat and conduit derating. Use 1/0 AWG fine-strand copper welding cable or THHN. Fine strand is mandatory for mobile applications (vans/RVs) to resist vibration fatigue.
- Overcurrent Protection: Install a 150A Class T fuse on the positive battery cable. Class T fuses have a high interrupting capacity (20,000A at 125VDC), which is critical for stopping lithium battery short circuits. Do not use ANL fuses for main battery protection; their interrupt rating is too low for large lithium banks.
- Lug Crimping: Strip the 1/0 AWG wire and crimp 3/8-inch closed-end copper lugs using a hydraulic crimping tool. A hand-crimped lug on 1/0 wire will loosen under thermal cycling and cause a high-resistance fire.
- Torque Specifications: Connect the battery cables to the Victron MultiPlus DC terminals. Torque the M8 nuts to exactly 10 Nm (7.4 ft-lbs) using a calibrated torque wrench. Under-torquing causes arcing; over-torquing strips the inverter's internal busbar.
- BMS Commissioning: Before connecting the inverter, use a multimeter to verify the series battery bank reads between 26.4V and 27.2V. Connect a Bluetooth dongle to the BMS to verify cell voltage delta is less than 0.05V across all cells.
- AC Wiring: Wire the AC-in and AC-out ports using 10 AWG THHN copper. Ensure the neutral and ground are bonded only at the main service entrance or inside the inverter if configured as a standalone off-grid system, never at both.
By following this exact architecture and respecting the DC current math, you transition from experimenting with dangerous DIY power electronics to deploying a commercial-grade, code-compliant inverter system that will reliably deliver power for over a decade.
