Solar & Off-Grid Power · DIY Electrical
DIY 12V Solar Setup Guide — Build a 2000W Off-Grid Power System with Inverter, Charge Controller & Fuse Block
System Output12V · 2000W inverter
Estimated Cost$800 – $2,000
Build Time6 – 8 hours
Skill Level★★★☆☆ Intermediate
Overview
This guide follows a classroom-then-lab structure. The classroom section explains the reasoning behind each component choice and the key formula that governs all your wiring and fuse decisions. The lab section walks through the physical assembly in the order that makes the build easiest — starting with the thickest, least flexible cables and working toward the smaller gauge connections.
The finished system outputs approximately 2000 watts of AC power — comparable to a standard North American home wall socket — and can power phones, laptops, refrigerators, and light power tools. It suits RVs, vans, boats, and off-grid sheds.
Solar Panels
4 × 100W monocrystalline, connected in series
MPPT Charge Controller
40A · regulates panel energy into the battery bank
LiFePO4 Batteries
2 × 12V 100Ah, connected in parallel (200Ah total)
2000W Inverter
Pure sine wave · converts 12V DC to 120V AC
Positive & Negative Bus Bars
Central distribution hubs for all positive and negative connections
12V DC Fuse Block
125A rated · powers 12-volt DC devices directly
The Classroom — Planning & Calculations
The core formula: W ÷ V = A
W ÷ V = A
Watts ÷ Volts = Amps
2000W ÷ 12V = 166.67A base draw
Factor in 85% inverter efficiency: 2000 ÷ 12 ÷ 0.85 = 196A
2000W ÷ 12V = 166.67A base draw
Factor in 85% inverter efficiency: 2000 ÷ 12 ÷ 0.85 = 196A
This single formula determines the wire gauge, fuse rating, and switch capacity you need for every major connection in the system. The 196A figure tells you that the cable between the battery and the inverter must be able to carry at least 196 amps continuously. Everything else — charge controller wiring, fuse block wiring — gets the same treatment using its own rated current.
For context: a typical North American home circuit runs 120V at 15A, giving a maximum of 1800W per wall socket. A 2000W system closely matches that output, which is why this is one of the most practical entry-level off-grid configurations.
Wire gauge sizing
Use a wire amperage chart to select the correct gauge for each cable run. Always round up to the next gauge if your amperage falls between two values — undersized wire overheats and can start a fire.
| Connection | Current Draw | Wire Gauge | Colour |
|---|---|---|---|
| Battery → Inverter | 196A (at full load) | 2/0 AWG | Red (+) / Black (−) |
| Charge controller → Bus bars | 40A max | 8 AWG | Red (+) / Black (−) |
| Bus bar → 12V Fuse block | Up to 100A | 4 AWG min | Red (+) / Black (−) |
| Grounding cables | Safety ground | 6 AWG | Green |
| Solar panel output (4× series) | ~5.2A Isc | 10 AWG | Red (+) / Black (−) |
Fuse placement rules
Fuses protect wiring, not devices. Place every fuse as close as possible to the power source — at the battery terminal, at the charge controller output, at the solar panel positive cable. Size each fuse to match the maximum rated current of the wire it protects, not the device it feeds.
| Location | Fuse Rating | Type |
|---|---|---|
| Battery positive terminal | 200A | ANL fuse + holder |
| Charge controller positive output | 40A | Inline blade fuse |
| Solar panel positive cable | 10A | Inline MC4 fuse |
| 12V Fuse block input | Size to wire | ANL or blade fuse |
Cable lugs — sizing matters
Cable lugs connect wires to terminal posts. Each lug must match two dimensions: the wire gauge it crimps onto, and the inner diameter of the stud or bolt it connects to. Different components — bus bars, inverters, fuse holders — have different stud sizes. Check the product specification for each component before ordering lugs. Keep both ends of every cable oriented the same way (lugs facing the same direction) so the finished cable aligns with the terminals it connects.
Draw the diagram first
Before buying a single component, sketch the full system on paper using red for positive, black for negative, and green for ground. Mark each wire run with its gauge (W), each fuse with its rating (F), and each switch (S). Confirming terminal post sizes from product listings lets you order the right cable lug inner diameters the first time.
Tools & Materials
Items marked ✦ are used across multiple connection stages. The 2/0 AWG cable requires different cutting and crimping tools than smaller gauges — do not assume the same stripper and crimper will handle both.
✦ 2/0 AWG welding cable (red + black)
✦ 8 AWG wire (red + black)
4 AWG wire (fuse block run)
6 AWG green wire (grounding)
2000W pure sine wave inverter
40A MPPT charge controller
12V 100Ah LiFePO4 batteries × 2
100W monocrystalline solar panels × 4
Positive + negative bus bars (colour-coded)
200A ANL fuse + holder
40A inline blade fuse
10A inline MC4 fuse
275A battery disconnect switch
DC circuit breaker (solar disconnect)
12V DC fuse block (125A rated)
Battery shunt + monitor
✦ Cable lugs (various gauges + stud sizes)
✦ Heat shrink tubing (red + black)
Parallel battery interconnect cables
Mounting plywood + screws + cable clips
Bolt cutter (2/0 AWG)
Wire stripper + ratchet crimper (small gauges)
Lug crimping hammer tool (2/0 AWG)
Heat gun · multimeter · measuring tape
Safety & Warnings
Read before starting any wiring work
- Never connect batteries before all other wiring is in place. A charged lithium battery connected to an incomplete circuit can cause immediate, uncontrollable arcing.
- Always turn the battery disconnect switch OFF before making or changing any connection in the system.
- Undersized wiring is a fire hazard. If you are unsure of the amperage your setup will draw, always round up to the next wire gauge — never down.
- Place the 200A fuse as close to the battery positive terminal as physically possible. This is the last line of defence if a short circuit occurs anywhere in the system.
- Keep positive and negative cables clearly colour-coded throughout the build. Use red tape or red heat shrink on any black cable used as a positive run.
- When connecting batteries in parallel, verify both batteries show equal voltage first. Mismatched voltages cause high current to flow between cells, which can damage or destroy the batteries.
- Lithium iron phosphate batteries are significantly safer than other lithium chemistries, but they are not fireproof. Install in a ventilated space away from flammable materials.
The Lab — Step-by-Step Assembly
Start here because 2/0 AWG cable is thick, stiff, and does not bend easily once crimped. Mounting all components after wiring rather than before prevents the problem of lugs being even a quarter-inch out of alignment with terminal studs.
Positive run: Inverter → fuse → bus bar → switch → battery
- 1Place cable lugs on the inverter positive terminal and the fuse holder stud. Hold the cable against them to measure the exact length needed — do not estimate.
- 2Cut the 2/0 AWG cable with a bolt cutter. Strip approximately 20mm of insulation from each end using careful scoring cuts — avoid nicking the copper strands inside.
- 3Crimp cable lugs onto both ends using the hammer crimping tool, keeping both lugs at the same orientation. Apply red heat shrink over the lug-to-cable joint. If using black cable for the positive run, wrap the full length in red electrical tape.
- 4Connect: inverter positive stud → 200A fuse holder → positive bus bar → 275A disconnect switch. Leave the switch end of the cable free — it connects to the battery positive terminal only after all other wiring is complete.
Negative run: Inverter → bus bar → shunt → battery
- 1Repeat the cable measuring, cutting, and crimping process for the negative run using black cable.
- 2Connect: inverter negative terminal → negative bus bar → shunt → battery negative terminal. The shunt sits between the negative bus bar and the battery; the battery monitor connects to the shunt via its signal cable.
Pro tip
Mount all components to the plywood board only after all cable lengths are confirmed and cut. Stiff 2/0 AWG cable that is even slightly too short cannot be stretched — and remounting a bus bar or fuse holder wastes significant time.
The charge controller has three sets of connections: solar panels in (PV+ / PV−), battery bank out (BAT+ / BAT−), and optionally a load output. Use 8 AWG wire for all connections between the charge controller and the bus bars.
Solar panels to charge controller
- 1Connect the four solar panels in series using MC4 connectors (positive of one panel to negative of the next). The series string has one positive cable and one negative cable exiting to the charge controller.
- 2Insert a 10A inline MC4 fuse on the positive cable from the panels. This protects the wiring in the event of a short on the panel side.
- 3Run the positive and negative cables through a DC-rated circuit breaker acting as the solar disconnect switch, then into the PV+ and PV− ports on the charge controller.
Charge controller to bus bars
- 1Measure the distance from the charge controller BAT+ port to the positive bus bar. Cut 8 AWG red cable to length, strip the ends, crimp a cable lug on the bus bar end only (the charge controller end plugs directly into the port).
- 2Install a 40A inline fuse on the positive cable as close to the charge controller as possible. Connect the cable: charge controller BAT+ → 40A fuse → positive bus bar.
- 3Repeat for the negative: charge controller BAT− → negative bus bar using 8 AWG black cable (no fuse on the negative run).
Pro tip
Many MPPT charge controllers include a Bluetooth module option. Adding it allows you to monitor panel input wattage, battery voltage, and charge state from a phone app — particularly useful once the system is installed in a vehicle or shed where the controller is hard to reach.
The 12V fuse block provides individual fused outputs for DC-powered devices — fans, LED lighting, USB charge ports, water pumps. Each output slot accepts a standard blade fuse sized to its individual load. The block input connects to the bus bars.
- 1Determine your planned maximum DC load. If running a single low-power device (under 5A), 4 AWG input cable is sufficient. If running multiple high-draw devices approaching the full 125A block rating, use 1 AWG cable and install a correctly rated ANL fuse on the positive input.
- 2Run 4 AWG (or larger) cable from the positive bus bar to the fuse block positive input. Run a matching negative cable from the negative bus bar to the fuse block negative input.
- 3Insert blade fuses into each occupied slot on the block sized to match the individual device load — not the block's total input rating.
Batteries are always the last component connected, and only after all wiring from the inverter, charge controller, and fuse block is already in place. With the battery disconnect switch confirmed in the OFF position, the system is safe to wire.
- 1Test both batteries with a voltmeter. Both must read the same voltage before parallel connection. If they differ, charge each to full capacity individually before connecting.
- 2Connect the parallel interconnect cables: battery 1 positive to battery 2 positive, battery 1 negative to battery 2 negative. Connect a CAT5 cable between them if the manufacturer supports battery-to-battery communication.
- 3Activate each battery per the manufacturer's process (some LiFePO4 batteries ship in storage mode and require a brief activation button press).
- 4Connect the 200A fuse to the positive terminal of battery 1 (or whichever battery the positive system cable runs to). Connect the system positive cable to the fuse. Connect the negative system cable (via the shunt) to battery 2 negative terminal.
- 5Connect the battery monitor signal cable from the shunt to the battery positive terminal as specified in the monitor instructions.
Grounding protects against electrical faults reaching the chassis or enclosure of your installation. Both the inverter and the charge controller have dedicated grounding terminals that must be connected.
Grounding
- 1Run a 6 AWG green cable from the inverter grounding terminal to your grounding point — vehicle chassis, a grounding rod driven into the ground, or the negative bus bar (which then connects to the grounding device).
- 2Repeat for the charge controller grounding terminal, connecting to the same grounding point.
Testing
- 1Perform a visual check of every connection: correct polarity, no exposed copper, heat shrink applied, all cable lugs fully seated on their studs.
- 2Turn the battery disconnect switch ON. The inverter should power on. The charge controller display should light up. The battery monitor should show battery voltage.
- 3If solar panels are connected in daylight, the charge controller should show panel input wattage within moments.
- 4Run a load test: plug a known-wattage device into the inverter and run it for 10–15 minutes. After the test, carefully touch each cable lug with the back of your hand. Lugs should feel barely warm or cool. Any lug that feels hot indicates an undersized wire or a loose connection at that point.
Pro tip
Use cable management clips to secure runs against the plywood board after testing is complete. Stiff 2/0 AWG cable rarely needs many clips, but smaller gauge cables benefit from being pinned every 20–30 cm to prevent movement vibration from loosening connections over time — especially important in RV and van installations.
Building Your Wiring Diagram
Draw the system diagram before purchasing any parts. A clear diagram helps you identify the correct cable lengths, lug sizes, and fuse ratings at every junction — and it gives you a reference to return to during the build when connections can seem confusing.
How to approach it
- 1Place the inverter at the centre of your diagram — it is the largest component and the most demanding in terms of cable size. Build outward from there.
- 2Use red lines for all positive runs, black for negative, and green for grounding. Where lines must cross, draw a small half-dome arc over the crossing line to show they do not connect at that point.
- 3Label every wire segment with its gauge (e.g. "2/0 AWG"), every fuse with its rating (e.g. "200A"), and every switch with "SW". Note these in a legend at the side of the diagram.
- 4Cross-reference each component's product listing for the stud sizes on its terminals — this determines cable lug inner diameter for every connection point before you place a single order.
Tip
Search online for "12V solar wiring diagram RV" or "off-grid solar one-line diagram" to find professionally drawn reference examples. These show standard conventions for how components are represented and how fuse and switch symbols are typically drawn — useful even if your setup differs from the diagram you find.
Frequently Asked Questions
What is the W ÷ V = A formula and why does it matter for solar wiring?
W ÷ V = A means Watts divided by Volts equals Amps. For a 12V system with a 2000W inverter: 2000 ÷ 12 = 166.67A. Accounting for 85% inverter efficiency raises this to approximately 196A. This figure directly determines the minimum wire gauge, fuse rating, and switch capacity for every major connection. Getting it wrong risks overheated cables or a fire — there is no workaround.
What wire gauge connects a 2000W inverter to a 12V battery?
For a cable run under 3 metres (10 ft), 2/0 AWG welding cable is the correct choice — it is rated for approximately 200A and comfortably covers the 196A maximum draw. For longer runs, step up to 3/0 AWG. Always use a wire gauge amperage chart specific to your cable type and run length, and round up to the next gauge if you fall between chart values.
Where exactly should fuses be placed in a DIY solar system?
Place a fuse as close as possible to each power source — not at the destination. In this 12V system: a 200A ANL fuse on the positive cable at the battery terminal, a 40A inline fuse on the positive output cable at the charge controller, and a 10A inline MC4 fuse on the positive cable from the solar panels. The fuse protects the wire between itself and the next device in the circuit.
Should I connect my batteries in series or in parallel?
For a 12V system, connect batteries in parallel. Parallel connection (positive-to-positive, negative-to-negative) keeps voltage at 12V and doubles amp-hour capacity — two 100Ah batteries become 200Ah. Series connection would double voltage to 24V, creating a different system entirely. Before connecting in parallel, verify both batteries show identical voltage readings to prevent damaging equalisation currents.
Do I need a bus bar, or can I wire directly to a common bolt?
Technically you can join all positive wires at a single stud bolt and all negative wires at another. In practice, bus bars are strongly preferable: they provide individual secure terminals for each cable, keep positive and negative circuits visually and physically separated, simplify troubleshooting by making every connection individually accessible, and make it easy to add devices to the system later without dismantling existing wiring.
Is a battery shunt and monitor necessary?
A shunt and monitor are optional but highly useful. The shunt measures current flowing in and out of the battery bank in real time; the monitor displays state of charge, voltage, current draw, and estimated runtime. Without one you are guessing battery state from voltage alone, which is imprecise with lithium batteries (their voltage curve is very flat). Many MPPT charge controllers also provide basic battery monitoring via a Bluetooth app, which may suffice for simpler setups.
Building a similar system, or have a question about sizing? Share your setup details or ask below.