Editable DC examples

12 V dual battery wiring diagrams with DC-DC charging

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.

mm² / metresAWG / feet

Orion XS B2B charging

6 components · 10 conductors · 12 V house system

Open this example in Crimp →

Live Crimp simulation. Try equipment states and battery charge, or choose Wiring to inspect the circuit. Cable IDs match the table below.

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Red = positive · dark = return. Crossings are not junctions. Read the assumptions before adapting a circuit.

Protection is unfinished. The shown fuse ratings do not select an exact protective device or locate it at the battery. Battery-end placement and unspecified-fuse warnings remain in Crimp. All charging and load currents below are design allowances, not measured operating currents.

Current engine findings

The fuse interrupt check uses the engine’s chemistry-based fault-current assumption. This is not measured fault current. Resolve the bank and protection design before installation.

Check the exact fuse, holder and battery evidence →

warning: Check fuse distance: 200 Ah house bank (C1, C9)
warning: Check fuse distance: AGM starter bank (C7)
warning: Check fuse suitability: 200 Ah house bank (C1, C3, C5, C9)
warning: Check fuse suitability: AGM starter bank (C7)

Cable table — every displayed connection

Each length is one way. Drop is the engine’s run estimate including return, not a measured end-to-end system result; shared legs can have different conservative design-current bounds. “Pinned” marks a manufacturer-based example choice to review after edits. AWG is approximate; retain the stated conductor area when selecting actual wire.

Orion XS B2B charging cable schedule in metric with AWG
Circuit / endpoints	One-way length	Conductor	Design current	Fuse	Drop / allowance
C1 · 200 Ah house bank + ↔ 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 − ↔ Fuse block IN −	One-way length1 m3.3 ft	Conductor4 mm²AWG 11 · 45 A table	Design current10 A		Drop / allowance0.36% / 3%
C3 · 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 · 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 · 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 · 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 table and exact example assumptions

Components in Orion XS B2B charging
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. Voltage drop includes a 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.
Fuse blockPlanning placeholder	12 V Generic blade-fuse block showing two fused positive branches and a shared negative bus. The 100 A feed and 30 A branch terminal limits are planning placeholders, not verified product ratings. Select an actual block and compatible ATC fuses; input feed protection is separate.
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.

REDARC BCDC1240D 4WD setup

6 components · 10 conductors · 12 V house system

Open this example in Crimp →

Live Crimp simulation. Try equipment states and battery charge, or choose Wiring to inspect the circuit. Cable IDs match the table below.

View full screen

Red = positive · dark = return. Crossings are not junctions. Read the assumptions before adapting a circuit.

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 engine’s generic input estimate does not verify REDARC’s voltage conversion or vehicle headroom.

Current engine findings

The fuse interrupt check uses the engine’s chemistry-based fault-current assumption. This is not measured fault current. Resolve the bank and protection design before installation.

Check the exact fuse, holder and battery evidence →

warning: Check fuse distance: 200 Ah house bank (C1, C9)
warning: Check fuse distance: AGM starter bank (C7)
warning: Check fuse suitability: 200 Ah house bank (C1, C3, C5, C9)
warning: Check fuse suitability: AGM starter bank (C7)

Cable table — every displayed connection

REDARC BCDC1240D 4WD setup cable schedule in metric with AWG
Circuit / endpoints	One-way length	Conductor	Design current	Fuse	Drop / allowance
C1 · 200 Ah house bank + ↔ 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 − ↔ Fuse block IN −	One-way length1 m3.3 ft	Conductor4 mm²AWG 11 · 45 A table	Design current10 A		Drop / allowance0.36% / 3%
C3 · 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 · 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 · 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 · 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 table and exact example assumptions

Components in REDARC BCDC1240D 4WD setup
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. Voltage drop includes a 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.
Fuse blockPlanning placeholder	12 V Generic blade-fuse block showing two fused positive branches and a shared negative bus. The 100 A feed and 30 A branch terminal limits are planning placeholders, not verified product ratings. Select an actual block and compatible ATC fuses; input feed protection is separate.
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

What these drawings assume

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.

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. Voltage drop includes a 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.

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

Exact models and manuals

Checked 11 September 2026. Component notes identify the source-backed ratings and the choices made for this example.

Victron EnergyOrion XS 12/12-50A installation and cable/fuse tableRev. 11 — 06/2026, §3.3 and charger-mode connections; checked 11 September 2026. Single physical GND and external battery protection.Victron EnergyOrion XS 12/12-50A exact-model technical dataThe 50 A model’s input and output setting limits. These do not establish available vehicle power.REDARCBCDC Classic Dual Input manualINST173-3 EN, BCDC1240D column, pp. 6 and 12–18. 60 A input/output fuses, minimum cable area and short auxiliary run; checked 11 September 2026.REDARCBCDC common-ground and detachable-battery wiringVehicle current sensing may require a chassis return. The separate detachable-battery illustration explains why a towing installation needs another layout.

Keep goingWire size calculatorEnter one-way length, current and installation conditions to compare ampacity and voltage drop.Keep goingDC-DC charger size calculatorCheck vehicle headroom and battery acceptance before choosing a charging current.Keep going12 V boat wiring diagramsA boat engine, starter and house banks, bilge pump and navigation lights, plus the full onboard demo.Keep goingCampervan & RV 12 V wiring diagramsSimple campervan solar and DC loads, or add a starter-to-leisure-battery B2B charger.Keep goingLiFePO₄ fuse size calculatorCheck exact fuse/holder, voltage, whole-bank fault current and placement evidence.Keep goingLead-acid to LiFePO₄ conversion guideReview charging, protection and monitoring when changing battery chemistry.Keep goingSizing methodologyRead the engine’s ABYC assumptions and limits before adapting an example.

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