Sample build: 38 ft cruising sailboat — 12 V house bank, solar arch, alternator

The brief

38 ft cruising sailboat

A liveaboard cutter cruising the US East Coast and the Bahamas.

A cruising couple at anchor most nights: 12 V fridge and freezer draw, cabin lights and fans, water pressure pump, Starlink, an evening of TV, phones and laptops. They motor about an hour a day and want three days of autonomy for cloudy spells.

Van / boatUS · AWG · 120 VMaritime / coastal climate3 days backupAlternator · 1 h/day · 30 A DC-DC

Appliances: LED lighting · 12V fridge / freezer · Phone & laptop charging · TV / entertainment · Roof fan / vent · Water pump · Starlink / internet

That is all the designer needs. Everything below was produced from those inputs in a few seconds — and any of it changes the moment the inputs do.

The system

Battery

Victron Lithium NG 12.8V 200Ah — 10.24 kWh at 12 V (8,192 Wh usable). Sized for 3 days with no sun at 2,170 Wh/day.

Solar

800 W across 4 panels, producing about 2,302 Wh on a typical maritime / coastal day through a SmartSolar 150/70.

Inverter

MultiPlus 12/2000 120V — chosen to start the largest surge in the appliance list and run the whole AC load at once.

Charging while moving

30 A DC-DC charger from the alternator — about 1 h/day of engine time, on top of solar. The battery is never shrunk to rely on it.

Safety & standards — what the design flagged

Victron Lithium is a managed (non-drop-in) battery: ABYC E-13 requires a BMS, and Victron Lithium needs a system BMS (e.g. VE.Bus BMS NG) plus an independent main disconnect so charge and load are cut on a fault.

A BMS can disconnect the battery suddenly: protect the alternator/DC-DC path against the resulting load-dump (ABYC E-13 13.6.10.1) and use a lithium-aware charge profile.

LiFePO4 cannot charge below +5 C (Victron) - keep the bank in a heated/insulated space or use a battery with low-temperature charge cut-off (design low -5 C). Usable capacity also falls to ~73% at that temperature.

Parallel bank 853 Ah (>500 Ah): ABYC E-11 11.10.1.4.1 requires a battery AIC-safety fuse (e.g. Class T) between EACH battery and the main fuse, in addition to the main OCP.

These are the checks a parts list alone cannot make: fault current versus fuse interrupting rating, BMS behaviour, cold-charge limits, string voltage in the cold. Each one cites the clause it comes from.

Full parts list Build Pass

Every line is a real, current model with the spec that made it the pick. Prices are market estimates for planning.

Part	What it does	Qty	Est.	Where to buy
Power electronics
MultiPlus 12/2000 120VContinuous output: 1400 W · Surge (peak): 3500 W · Battery voltage: 12 V	Turns battery power into household AC	1	$760	Find this part ›
SmartSolar 150/70Max charge current: 67 A · Solar array: 4s1p · String Voc (cold): 109.4 V	Charges the battery from solar	1	$490	Find this part ›
DC-DC 30A chargerOutput: 30 A · From driving: ~306 Wh/day @ 1 h · Alternator needed: ≥ 67 A	Charges the battery from the alternator while you drive	1	$500	Find this part ›
SmartShunt 1000AFunction: Precision battery monitor · Reads: State of charge, current, voltage	Monitors battery charge level	1	$500	Find this part ›
Lynx Distributor M10Function: DC busbar / distribution · Bars: Positive + negative	Central hub linking all DC parts	1	$185	Find this part ›
VE.Bus BMS NGRole: System BMS for Victron Lithium · Requires: VE.Bus-compatible inverter/charger	System battery management — Victron Lithium is not drop-in; the BMS cuts charge and load on a fault (ABYC E-13)	1	$500	Find this part ›
Energy storage
Victron Lithium NG 12.8V 200AhBank configuration: 1s4p x 200Ah 12.8V (4 packs) · Usable capacity: 10.24 kWh · Modules: 4	Stores your energy for later use	4	$4,600	Find this part ›
Solar array
200W solar panelPer panel: 200 W · Quantity: 4 · Array total: 800 W	Generates electricity from sunlight	4	$680	Find this part ›
Cabling & protection
Battery → inverter cableCable size: 2/0 AWG · Total length: 4 m · Conductors: 2	Main power cable to the inverter	4 m	$80	Find this part ›
Battery → inverter fuseRating: 300 A · Class / style: Class T · Interrupting capacity (AIC): 20,000 A	Protects the cable — 300 A · Class T	1	$20	Find this part ›
Battery → inverter fuse holderFits fuse: 300 A · Type: Class T holder	Holds the 300 A Class T fuse	1	$20	Find this part ›
Battery → inverter lugsFor cable: 2/0 AWG · Quantity: 4 · Material: Tinned copper	Crimp terminals for the cable ends	4	$80	Find this part ›
MPPT → battery cableCable size: 2 AWG · Total length: 6 m · Conductors: 2	Charge cable from the controller	6 m	$120	Find this part ›
MPPT → battery fuseRating: 100 A · Class / style: Class T · Interrupting capacity (AIC): 20,000 A	Protects the cable — 100 A · Class T	1	$20	Find this part ›
MPPT → battery fuse holderFits fuse: 100 A · Type: Class T holder	Holds the 100 A Class T fuse	1	$20	Find this part ›
MPPT → battery lugsFor cable: 2 AWG · Quantity: 4 · Material: Tinned copper	Crimp terminals for the cable ends	4	$80	Find this part ›
Solar → MPPT cableCable size: 10 AWG · Total length: 14 m · Conductors: 2	Cable from the panels to the controller	14 m	$280	Find this part ›
Solar → MPPT fuseRating: 20 A · Class / style: inline PV fuse (gPV, MC4) · Interrupting capacity (AIC): 1,500 A	Protects the cable — 20 A · inline PV fuse (gPV, MC4)	1	$20	Find this part ›
Solar → MPPT fuse holderFits fuse: 20 A · Type: inline PV fuse (gPV, MC4) holder	Holds the 20 A inline PV fuse (gPV, MC4) fuse	1	$20	Find this part ›
Solar → MPPT lugsFor cable: 10 AWG · Quantity: 4 · Material: Tinned copper	Crimp terminals for the cable ends	4	$80	Find this part ›
Alternator → battery cableCable size: 8 AWG · Total length: 4 m · Conductors: 2	DC-DC charger output cable to the battery	4 m	$80	Find this part ›
Alternator → battery fuseRating: 40 A · Class / style: Class T · Interrupting capacity (AIC): —	Protects the cable — 40 A · Class T	1	$20	Find this part ›
Alternator → battery fuse holderFits fuse: 40 A · Type: Class T holder	Holds the 40 A Class T fuse	1	$20	Find this part ›
Alternator → battery lugsFor cable: 8 AWG · Quantity: 4 · Material: Tinned copper	Crimp terminals for the cable ends	4	$80	Find this part ›
Grounding / bonding conductorCable size: 4 AWG · Sized to: main OCPD 300 A · Basis: ABYC A-31 Table 1 / E-11.17.2	Single-point bond from the DC negative bus to ground	1 run	$20	Find this part ›
Per-battery AIC-safety fuseRating: 250 A · Class / style: Class T · Interrupting capacity (AIC): 20,000 A	One fuse between each battery and the main fuse — 250 A · Class T	4	$80	Find this part ›
Balance of system
Battery main switchFunction: Main battery isolator · Rating: ≥ 300 A continuous	Shuts off all battery power	1	$65	Find this part ›
MC4 connector pairsUse: PV string connections · Type: Standard MC4	Connect the solar panels	2 pr	$16	Find this part ›
Adhesive-lined heat shrinkType: Adhesive-lined · Use: Seal all terminations	Insulates and seals connections	1 kit	$16	Find this part ›

Estimated total (29 items)$9,452

Wiring & protection

Each run is sized to carry its fuse and stay under a 3 % voltage drop; the main fuse is chosen for the bank's real fault current.

Run	Cable	Load	Protection	V-drop	Note
Battery → inverter	2/0 AWG	125 A	300 A Class T	1.5 %	Prospective bank short-circuit ~42,650 A exceeds 20 kA; ABYC 11.10.1.3.2.3 accepts a 20 kA @125 VDC Class T, with per-battery fusing so each battery stays within one fuse’s rating.
MPPT → battery	2	67 A	100 A Class T	2.4 %	Prospective bank short-circuit ~42,650 A exceeds 20 kA; ABYC 11.10.1.3.2.3 accepts a 20 kA @125 VDC Class T, with per-battery fusing so each battery stays within one fuse’s rating.
Solar array → MPPT	10	10 A	20 A inline PV fuse (gPV, MC4)	0.9 %	sized to the practical minimum gauge for an exposed PV run (ruggedness), not just the calculated current
dcToBattery	8	30 A	40 A	2.9 %
dcDistribution	14	7 A	10 A	2 %

The build pack Build Pass

The part that actually wires it. Labels (GB1, F1, W+ …) match the diagram above.

Connection schedule

From	To	Conductor	Cable	Protection	Note
1 · Battery bank (+)	6 · Load busbar	positive (+, red)	2/0 AWG mfr spec	300 A Class T fuse (4, at the battery +)	through the main switch 5
1 · Battery bank (−)	3 · Negative busbar	negative (− return)	2/0 AWG mfr spec	battery monitor 2 in line	2 is the only thing on battery − before 3
200 W rigid (+)	Next panel in the string (−)	PV series link (MC4)		no fuse inside a series string	join 4 200 W rigid panels end to end to make one string
8 · Solar array (combined output)	9 · Solar isolator	PV (solar)	10 AWG	20 A inline PV fuse	keep 9 open until the end
9 · Solar isolator	10 · Solar charge controller	PV (solar)	10 AWG	check + / − polarity first	reversed PV polarity can destroy 10
10 · Solar charge controller	7 · Charge busbar	positive (+, red)	2 AWG	100 A Class T fuse
11 · Alternator	12 · Starter battery	positive (+, red)		per the vehicle / charger manual	engine-side wiring
12 · Starter battery	13 · DC-DC charger	positive (+, red)		per the charger manual
13 · DC-DC charger	7 · Charge busbar	positive (+, red)	8 AWG	40 A fuse
7 · Charge busbar	6 · Load busbar	positive (+, red)		size for the combined charge current
6 · Load busbar	14 · Inverter (+)	positive (+, red)	2/0 AWG mfr spec	protected by the main fuse (4)
14 · Inverter (−)	3 · Negative busbar	negative (− return)	2/0 AWG mfr spec
14 · Inverter (AC out)	16 · AC panel (GFCI)	AC	by a qualified electrician	15 A main + RCD/GFCI	AC mains
6 · Load busbar	15 · DC fuse panel	positive (+, red)	14 AWG	10 A fuse
15 · DC fuse panel	LED lighting	positive (+, red)	18 AWG	5 A fuse	return to 3
15 · DC fuse panel	12V fridge / freezer	positive (+, red)	18 AWG	5 A fuse	return to 3
15 · DC fuse panel	Roof fan / vent	positive (+, red)	18 AWG	5 A fuse	return to 3
16 · AC panel (GFCI)	Phone & laptop charging	AC	18 AWG	5 A breaker
16 · AC panel (GFCI)	TV / entertainment	AC	18 AWG	5 A breaker
16 · AC panel (GFCI)	Water pump	AC	18 AWG	5 A breaker
16 · AC panel (GFCI)	Starlink / internet	AC	18 AWG	5 A breaker
3 · Negative busbar	18 · Single-point ground	ground / bond	4 AWG	one bonding point only	depends on platform + local code

Build it, step by step

Before you start

Switch off and disconnect every power source. Leave the main fuse out and all breakers open while you wire. Lay out the parts loosely first and confirm your cable runs reach.Work on a dead system — a connected battery can push thousands of amps into an accidental short.

Wire the battery negative through the monitor

Connect the battery bank negative (1, −) to the battery monitor / shunt (2), then connect the monitor to the negative busbar (3) using 2/0 AWG mfr spec cable.Nothing else may connect to the battery negative before the monitor — it must carry 100% of the current to read correctly. Every other negative in the system returns to the negative busbar (3).

Wire the battery positive and main protection

Connect the battery bank positive (1, +) to the main fuse (4), then to the main battery switch (5, rated ≥ 300 A), then to the positive busbar (6) using 2/0 AWG mfr spec cable. The main fuse is your 300 A Class T fuse. Fit the fuse itself last, at the check stage.Keep the main fuse within 178 mm (7 in) of the battery + terminal so the cable to it is always protected (ABYC E-11).

Wire the solar charge source

Build the array first: join 4 200 W rigid panels end to end in series to make one string. Before you connect to the controller, check the array’s + and − leads with a multimeter — reversed polarity can destroy the controller instantly. Connect the array through the solar isolator (9) to the solar charge controller (10) using 10 AWG cable, then connect the controller’s battery output to the positive busbar (6) using 2 AWG cable, protected by its 100 A Class T fuse.In a series string the panel voltages add up, and they rise further in the cold — your design already sized the string so its coldest-day voltage stays under the controller’s limit, so keep to that layout. Use matching panels in a string; a weaker or shaded panel drags down the whole string. Keep the panels covered, or 9 open, until the very end — sunlight makes the array live whether you’re ready or not.

Wire the alternator charge source

Connect the alternator (11) to the starter battery (12), then to the DC-DC charger (13, 30 A), then to the positive busbar (6), protected by its 40 A fuse. Wire the charger’s ignition / engine-run trigger so it only charges while the engine runs.Protect the DC-DC path against a sudden battery-management cut-off (load-dump) and use a lithium-aware charge profile (ABYC E-13).

Wire the inverter and AC side

Connect the positive busbar (6) to the inverter (14, MultiPlus 12/2000 120V) using 2/0 AWG mfr spec cable, and connect the inverter negative back to the negative busbar (3). Take the inverter’s AC output to the AC panel (GFCI) (16) and on to your sockets.Keep the inverter’s battery cable short — a longer run than your design assumes will drop voltage and trip it. Treat the AC side as mains: have it done or checked by a qualified electrician.

Wire the DC loads

Feed the DC fuse panel (15) from the positive busbar (6), protected by its 10 A fuse. Wire each DC appliance on its own fuse out of 15 and bring its negative back to the negative busbar (3). The per-appliance fuses and cables are in the connection schedule below.Every DC load gets its own fuse sized to its cable — never share one fuse across two loads.

Bond the system to ground

Bond the negative busbar (3) to the vehicle chassis (18) at one single point using 4 AWG cable.Use one bonding point only — a second ground path creates a loop. The correct bond point depends on your platform and local code, so confirm it for your install.

Check before you power up

Work all the way through the pre-energize checklist below before you fit the main fuse or close the main switch.Most install faults are caught here, with the system still dead — not after power is on.

Power up and set the charge profile

Energize in the order given in the checklist, then enter the commissioning settings below into the charger and monitor app. Confirm it is charging, then run a load test.Wrong charge settings can under- or over-charge the bank — set them before the first full charge.

Torque

Connection	Thread	Torque
Battery terminals (1)	M8	124 in-lb (14 N·m)
Busbars (6, 3)	M8	124 in-lb (14 N·m)
Main fuse + switch studs (4, 5)	M8	124 in-lb (14 N·m)
Charge-controller / inverter lugs	M6	53 in-lb (6 N·m)

Commissioning settings

Setting	Value
Charge profile	LiFePO4 (user-defined)
Absorption	14.4 V (14.2–14.6 V)
Float	13.5 V
Absorption time	4 h
Tail current	40 A
Monitor capacity	800 Ah
Inverter cut-off / restart	11.5 V / 13 V

Set the solar charge controller (10) to a User-defined LiFePO4 profile, and set the battery monitor (2) capacity to 800 Ah. These follow standard LiFePO4 charge guidance — confirm the exact voltages against your battery’s datasheet, and keep the inverter cut-off above the battery’s own low-voltage cut to avoid nuisance shutdowns.

Pre-energize checklist

Main fuse (4) still out and every branch fuse/breaker open.
Checked + and − polarity at each terminal with a multimeter before connecting the battery.
Tightened every terminal to its torque figure and marked each one as done.
The battery monitor (2) is the only thing on the battery negative before the busbar (3).
No short between the positive (6) and negative (3) busbars — meter reads open / very high.
One single ground bond to chassis (18) only.
Parallel bank balanced: every battery has equal-length, equal-gauge leads to the busbar (+ and −), torqued the same, and all batteries charged to the same voltage before paralleling.
Solar array covered or its isolator (9) open so the panels are not live while you finish.
Array wired 4s1p, panel + and − verified with a multimeter, and matching panels used in each series string.
DC-DC charger (13) engine-run trigger wired; alternator path protected against a battery cut-off surge.
Air can move around the battery and inverter.
Power-up order: first land the negative (3), then fit the main fuse (4), then close the main switch (5), then enable the charge sources, then switch on the inverter.

Tools you'll need

Multimeter (DC volts + continuity)
Torque wrench / driver covering M6 / M8 terminal studs
Lug crimping tool rated for your main cable (2/0 AWG mfr spec)
Wire strippers and heavy cable cutters
Heat-shrink tubing + heat gun (seal every lug)
Ring lugs / ferrules to match each cable size
Label printer or marker — label every fuse, switch and busbar
MC4 crimp tool + spanner (solar connectors)

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Questions

Is this a real design or a mock-up?

Real. It is generated by the Wattonomy engine from the brief above, at build time, with the same rules and catalog the app uses. Change the brief and every number changes.

Why Victron everywhere?

The default catalog is one ecosystem that connects through a single app, with published datasheets for every spec we size against. The app also offers value-tier and regional alternatives for the battery and solar.

Can I build from this page?

Only if your brief is identical — and it isn't. Your loads, runs and climate change the gauges, fuses and panel count. Design yours; it takes a minute and it's free.

Is this a substitute for an electrician?

No. It is a standards-referenced design and build guide. Have AC mains work reviewed or signed off by a licensed installer in your region.

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