Editable DC examples
Compare two 12 V dual battery wiring diagrams for a vehicle starter battery and a fixed auxiliary bank. Choose an Orion XS 12/12-50A or REDARC BCDC1240D DC-DC charger, then follow the charging path and fused load branches. The drawings show a shared negative connection; isolator-only systems, detachable batteries and towing connections need their own layout.
Starter and auxiliary roles
A dual-battery system gives engine starting and auxiliary loads separate battery banks. In these examples, a DC-DC charger takes power from the starter side to charge the auxiliary bank; the lights and other DC load connect to the auxiliary fuse block.
The auxiliary battery supplies the lights and DC load. Keeping vehicle charging off helps preserve the starter battery for starting. That depends on the charger’s input controls and settings: these drawings do not establish engine detection or include ignition and remote-control wiring.
The vehicle supply feeds the DC-DC charger, which supplies the auxiliary side using the selected battery charge profile. Loads share that supply, so battery charging depends on load demand, available vehicle power and the battery’s limits. Engine running alone does not guarantee full charging output.
Orion XS example. The diagram’s IN− and OUT− represent one physical GND terminal. Configure charger mode, engine shutdown detection and input limits for the vehicle; disabling detection can allow charging from the starter battery while parked. Read Victron’s operating guidance.
REDARC example. The vehicle input, auxiliary output and shared black return are shown. The blue input-mode wire, orange charge-profile wire and solar input are omitted. Their configuration depends on the alternator and battery; follow the BCDC1240D model notes and manual. Neither example includes a solar charging path.
6 components · 10 conductors · 12 V house system
Live Crimp simulation. Try equipment states and battery charge, or choose Wiring to inspect the circuit. Connections and cable sizes are listed below.
View full screenRed = positive · dark = return. Crossings are not junctions. Read the assumptions before adapting a circuit.
Protection is unfinished. Check the exact fuses, battery-end placement and charger settings before building.
Current engine findings use design allowances and an assumed battery fault current, not measurements. Exact fuse products, holders and battery-end placement still require verification. Review each finding against the actual installation.
Each length is one way. In these complete drawn circuits, each drop value is the calculated loss in that individual conductor. The complete circuit includes its feed, branch and negative return; a single row is not the total circuit loss. Shared legs can have different conservative design-current bounds. “Pinned” marks an explicit example choice to review after edits. AWG is approximate; retain the stated conductor area when selecting actual wire.
| Circuit / endpoints | One-way length | Conductor | Design current | Fuse | Drop / allowance |
|---|---|---|---|---|---|
| C1 · 200 Ah house bank + ↔ Blue Sea 5025 ST Blade Fuse Block IN + | One-way length1 m3.3 ft | Conductor4 mm²AWG 11 · 45 A table | Design current10 A | Fuse15 A | Drop / allowance0.36% / 3% |
| C2 · 200 Ah house bank − ↔ Blue Sea 5025 ST Blade Fuse Block IN − | One-way length1 m3.3 ft | Conductor4 mm²AWG 11 · 45 A table | Design current10 A | Drop / allowance0.36% / 3% | |
| C3 · Blue Sea 5025 ST Blade Fuse Block 1 + ↔ Cabin lights + | One-way length3 m9.8 ft | Conductor1.5 mm²AWG 16 · 25 A table | Design current2 A | Fuse3 A | Drop / allowance0.58% / 10% |
| C4 · Blue Sea 5025 ST Blade Fuse Block 1 − ↔ Cabin lights − | One-way length3 m9.8 ft | Conductor1.5 mm²AWG 16 · 25 A table | Design current2 A | Drop / allowance0.58% / 10% | |
| C5 · Blue Sea 5025 ST Blade Fuse Block 2 + ↔ Auxiliary DC load + | One-way length2 m6.6 ft | Conductor2.5 mm²AWG 13 · 35 A table | Design current8 A | Fuse10 A | Drop / allowance0.93% / 3% |
| C6 · Blue Sea 5025 ST Blade Fuse Block 2 − ↔ Auxiliary DC load − | One-way length2 m6.6 ft | Conductor2.5 mm²AWG 13 · 35 A table | Design current8 A | Drop / allowance0.93% / 3% | |
| C7 · AGM starter bank + ↔ Orion XS 12/12-50A IN + | One-way length3 m10 ft | Conductor16 mm²AWG 6 · 120 A tablePinned choice | Design current50 A | Fuse60 A | Drop / allowance1.39% / 3% |
| C8 · AGM starter bank − ↔ Orion XS 12/12-50A IN − | One-way length3 m10 ft | Conductor16 mm²AWG 6 · 120 A tablePinned choice | Design current50 A | Drop / allowance1.39% / 3% | |
| C9 · Orion XS 12/12-50A OUT + ↔ 200 Ah house bank + | One-way length1 m3.3 ft | Conductor16 mm²AWG 6 · 120 A tablePinned choice | Design current50 A | Fuse60 A | Drop / allowance0.46% / 3% |
| C10 · Orion XS 12/12-50A OUT − ↔ 200 Ah house bank − | One-way length1 m3.3 ft | Conductor16 mm²AWG 6 · 120 A tablePinned choice | Design current50 A | Drop / allowance0.46% / 3% |
| Component | Ratings, role and assumptions |
|---|---|
| 200 Ah house bankPlanning placeholder | 12 V · 200 Ah 12 V, 200 Ah planning placeholder. Select an actual bank, compatible BMS, charge/discharge limits and battery-end protection. Ah does not select the fuse. Planning example, not installation approval. Batteries, the PV array and unnamed loads are placeholders. Battery acceptance, BMS controls, low-temperature charging, short-circuit current and runtime have not been verified. Fuse ratings are preliminary cable protection or stated manufacturer choices. Exact fuse/holder, DC voltage, interrupt rating and battery-end placement still need verification. Cable fuses have no physical placement here; the editor retains its battery-protection warnings. Lengths are physical one-way conductor runs. With a complete return path, each drawn conductor reports its own voltage drop; add the relevant feed, branch and return drops for the circuit. Incomplete paths may use an assumed return. Shared paths use the engine’s conservative current bounds, not a prediction of simultaneous power flow. The calculation does not verify unequal shared-return lengths as one complete circuit. AWG labels are approximate table counterparts to metric conductors, not identical cross-sectional areas. Sizing uses Crimp’s ABYC-based tables for 105°C copper outside engine spaces, with no additional heat or bundling derating in these examples. Explicit 3% circuit targets and 10% cabin-light allowances are planning choices; terminals on placeholders carry generic planning limits, not verified connector ratings. US RV, UK campervan and Australian 4WD wording does not establish UK or AS/NZS installation compliance. |
| Blue Sea 5025 ST Blade Fuse Block5025 | Blue Sea 5025: 6 ATO/ATC branches, 100 A maximum block total, 30 A maximum per branch, 32 V DC. Only two branches used. Input feed protection is separate; fuses are sold separately. Source: Blue Sea 5025 product page and instructions, checked 2026-10-21. https://www.bluesea.com/products/5025/ |
| Cabin lightsPlanning placeholder | 12 V · 2 A load allowance 2 A continuous planning allowance. No measured duty cycle or energy budget. |
| Auxiliary DC loadPlanning placeholder | 12 V · 8 A load allowance 8 A continuous placeholder; replace with the actual appliance and its startup requirements. |
| AGM starter bankPlanning placeholder | 12 V · 80 Ah 12 V AGM source placeholder. Engine cranking and alternator are outside this drawing. No vehicle input headroom, idle output or factory wiring has been verified. Dedicated logical return: use the vehicle’s designated ground point where required by battery current sensing. |
| Orion XS 12/12-50AOrion XS 12/12-50A | 50 A rated / planning output Non-isolated Orion XS 12/12-50A, rev 11 (06/2026). Logical IN− and OUT− represent its single physical GND terminal. Input/output limits are each up to 50 A; full output is not guaranteed at low input voltage. 60 A battery fuses and 16 mm² conductors are pinned choices. Remote/BMS control, charge profile, engine detection and alternator headroom require review. |
6 components · 10 conductors · 12 V house system
Live Crimp simulation. Try equipment states and battery charge, or choose Wiring to inspect the circuit. Connections and cable sizes are listed below.
View full screenRed = positive · dark = return. Crossings are not junctions. Read the assumptions before adapting a circuit.
Protection is unfinished. Check the exact fuses, battery-end placement and charger settings before building.
Current engine findings use design allowances and an assumed battery fault current, not measurements. Exact fuse products, holders and battery-end placement still require verification. Review each finding against the actual installation.
Both battery returns join at the modeled BATT− connection, representing the common black ground lead; PV− is unused. This is a logical connection, not a physical harness pinout. The generic current estimate does not verify REDARC’s conversion efficiency or vehicle headroom.
Each length is one way. In these complete drawn circuits, each drop value is the calculated loss in that individual conductor. The complete circuit includes its feed, branch and negative return; a single row is not the total circuit loss. Shared legs can have different conservative design-current bounds. “Pinned” marks an explicit example choice to review after edits. AWG is approximate; retain the stated conductor area when selecting actual wire.
| Circuit / endpoints | One-way length | Conductor | Design current | Fuse | Drop / allowance |
|---|---|---|---|---|---|
| C1 · 200 Ah house bank + ↔ Blue Sea 5025 ST Blade Fuse Block IN + | One-way length1 m3.3 ft | Conductor4 mm²AWG 11 · 45 A table | Design current10 A | Fuse15 A | Drop / allowance0.36% / 3% |
| C2 · 200 Ah house bank − ↔ Blue Sea 5025 ST Blade Fuse Block IN − | One-way length1 m3.3 ft | Conductor4 mm²AWG 11 · 45 A table | Design current10 A | Drop / allowance0.36% / 3% | |
| C3 · Blue Sea 5025 ST Blade Fuse Block 1 + ↔ Cabin lights + | One-way length3 m9.8 ft | Conductor1.5 mm²AWG 16 · 25 A table | Design current2 A | Fuse3 A | Drop / allowance0.58% / 10% |
| C4 · Blue Sea 5025 ST Blade Fuse Block 1 − ↔ Cabin lights − | One-way length3 m9.8 ft | Conductor1.5 mm²AWG 16 · 25 A table | Design current2 A | Drop / allowance0.58% / 10% | |
| C5 · Blue Sea 5025 ST Blade Fuse Block 2 + ↔ Auxiliary DC load + | One-way length2 m6.6 ft | Conductor2.5 mm²AWG 13 · 35 A table | Design current8 A | Fuse10 A | Drop / allowance0.93% / 3% |
| C6 · Blue Sea 5025 ST Blade Fuse Block 2 − ↔ Auxiliary DC load − | One-way length2 m6.6 ft | Conductor2.5 mm²AWG 13 · 35 A table | Design current8 A | Drop / allowance0.93% / 3% | |
| C7 · AGM starter bank + ↔ BCDC1240D Classic40 ALT + | One-way length3 m10 ft | Conductor16 mm²AWG 6 · 120 A tablePinned choice | Design current44.4 A | Fuse60 A | Drop / allowance1.23% / 3% |
| C8 · AGM starter bank − ↔ BCDC1240D Classic40 BATT − | One-way length3 m10 ft | Conductor16 mm²AWG 6 · 120 A tablePinned choice | Design current44.4 A | Drop / allowance1.23% / 3% | |
| C9 · BCDC1240D Classic40 BATT + ↔ 200 Ah house bank + | One-way length80 cm2.6 ft | Conductor16 mm²AWG 6 · 120 A tablePinned choice | Design current40 A | Fuse60 A | Drop / allowance0.29% / 3% |
| C10 · BCDC1240D Classic40 BATT − ↔ 200 Ah house bank − | One-way length80 cm2.6 ft | Conductor16 mm²AWG 6 · 120 A tablePinned choice | Design current40 A | Drop / allowance0.29% / 3% |
| Component | Ratings, role and assumptions |
|---|---|
| 200 Ah house bankPlanning placeholder | 12 V · 200 Ah 12 V, 200 Ah planning placeholder. Select an actual bank, compatible BMS, charge/discharge limits and battery-end protection. Ah does not select the fuse. Planning example, not installation approval. Batteries, the PV array and unnamed loads are placeholders. Battery acceptance, BMS controls, low-temperature charging, short-circuit current and runtime have not been verified. Fuse ratings are preliminary cable protection or stated manufacturer choices. Exact fuse/holder, DC voltage, interrupt rating and battery-end placement still need verification. Cable fuses have no physical placement here; the editor retains its battery-protection warnings. Lengths are physical one-way conductor runs. With a complete return path, each drawn conductor reports its own voltage drop; add the relevant feed, branch and return drops for the circuit. Incomplete paths may use an assumed return. Shared paths use the engine’s conservative current bounds, not a prediction of simultaneous power flow. The calculation does not verify unequal shared-return lengths as one complete circuit. AWG labels are approximate table counterparts to metric conductors, not identical cross-sectional areas. Sizing uses Crimp’s ABYC-based tables for 105°C copper outside engine spaces, with no additional heat or bundling derating in these examples. Explicit 3% circuit targets and 10% cabin-light allowances are planning choices; terminals on placeholders carry generic planning limits, not verified connector ratings. US RV, UK campervan and Australian 4WD wording does not establish UK or AS/NZS installation compliance. |
| Blue Sea 5025 ST Blade Fuse Block5025 | Blue Sea 5025: 6 ATO/ATC branches, 100 A maximum block total, 30 A maximum per branch, 32 V DC. Only two branches used. Input feed protection is separate; fuses are sold separately. Source: Blue Sea 5025 product page and instructions, checked 2026-10-21. https://www.bluesea.com/products/5025/ |
| Cabin lightsPlanning placeholder | 12 V · 2 A load allowance 2 A continuous planning allowance. No measured duty cycle or energy budget. |
| Auxiliary DC loadPlanning placeholder | 12 V · 8 A load allowance 8 A continuous placeholder; replace with the actual appliance and its startup requirements. |
| AGM starter bankPlanning placeholder | 12 V · 80 Ah 12 V AGM source placeholder. Engine cranking and alternator are outside this drawing. No vehicle input headroom, idle output or factory wiring has been verified. Dedicated logical return: use the vehicle’s designated ground point where required by battery current sensing. |
| BCDC1240D Classic40BCDC1240D | 40 A rated / planning output BCDC1240D / Classic40 only, INST173-3 EN. Red vehicle input, brown auxiliary output, shared black negative. Solar, blue trigger and orange profile wires are not drawn. 60 A battery fuses and 16 mm² conductors are pinned example choices, with 0.8 m auxiliary run. Generic input estimate does not model conversion efficiency, solar sharing or vehicle headroom. PV-negative is unused; the banks share a common return. |
Before adapting an example
The vehicle examples represent a fixed auxiliary bank with a logical common return. Follow the vehicle manufacturer’s designated ground point, especially around starter-battery current sensors. For a boat, use the distinct starter/house example on the boat page. A removable canopy, camper trailer or caravan needs its own connector, return path, longer-run sizing and protection design; these are not towing layouts or factory vehicle schematics.
Adding monitoring or larger distribution changes the current paths. Read the SmartShunt return-path example and Lynx Distributor example, including their conservative series-current bounds and unresolved protection. The model pages keep those limitations visible.
Manufacturer evidence
Reviewed 21 October 2026. Component notes distinguish manufacturer ratings from the assumptions made for each example.
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