Solar for a small sailboat
Follow a solar panel through its controller to a house battery, chartplotter and navigation lights.
Follow the circuit
01
Two sides of the controller
The panel connects to PV terminals; the house battery connects to battery terminals. The controller converts the panel output into a suitable charging current.
02
Keep the battery connection short
The charging branch uses a 20 A fuse, within Victron's 20–25 A range for the 75/15. Its short positive and negative runs limit charging voltage loss.
03
Plan for shade
A mast or boom can shade the panel even on a sunny day. Change solar conditions in the editor and compare generation with the loads you actually use.
The source and this example
Victron's MPPT manual shows the panel, controller, battery and DC-load connections, plus battery fuse requirements.
This 175 W example uses a 110 Ah AGM battery and separate fused marine loads. It omits engine charging and uses the battery bus rather than the controller's load output.
- Victron: MPPT installation and basic schematic ↗
Sections 4.2, 4.3 and 4.6.
- Victron: MPPT 75/15 ratings ↗
Before you build
- Check panel cold-weather open-circuit voltage against the controller limit.
- Set the charger profile for the actual battery.
- Keep both PV conductors disconnectable before servicing.
This is a planning example. Cable sizing uses Crimp’s ABYC-based method; the drawing does not certify an installation.
Cable sizes and connections · 12 conductors
Lengths are one way. Sizes and currents come from the same Crimp model as the drawing. Each drop value covers one drawn conductor; the full circuit includes its supply and return. AWG values are approximate counterparts to the metric areas.
| Connection | Length | Wire | Design current | Fuse | Drop |
|---|---|---|---|---|---|
| C1 · Victron 175W Mono + → Solar DP Isolator IN + | 2.5 m | 2.5 mm²AWG 13 | 9 A | — | 0.81% |
| C2 · Victron 175W Mono − → Solar DP Isolator IN − | 2.5 m | 1.5 mm²AWG 16 | 9 A | — | 1.36% |
| C3 · Solar DP Isolator OUT + → Victron MPPT 75/15 PV + | 50 cm | 1.5 mm²AWG 16 | 9 A | — | 0.27% |
| C4 · Solar DP Isolator OUT − → Victron MPPT 75/15 PV − | 50 cm | 1.5 mm²AWG 16 | 9 A | — | 0.27% |
| C5 · Positive Bus Bar 1 + → Victron MPPT 75/15 BATT + | 1 m | 4 mm²AWG 11 | 15 A | 20 A | 0.55% |
| C6 · Victron MPPT 75/15 BATT − → Negative Bus Bar 4 − | 1 m | 2.5 mm²AWG 13 | 15 A | — | 0.88% |
| C7 · House battery + → Positive Bus Bar + | 50 cm | 4 mm²AWG 11 | 15 A | — | 0.27% |
| C8 · Negative Bus Bar − → House battery − | 50 cm | 1.5 mm²AWG 16 | 15 A | — | 0.73% |
| C9 · Positive Bus Bar 2 + → Chartplotter (Garmin GPSMap) + | 2 m | 1.5 mm²AWG 16 | 3.2 A | 7.5 A | 0.62% |
| C10 · Chartplotter (Garmin GPSMap) − → Negative Bus Bar 2 − | 2 m | 1.5 mm²AWG 16 | 3.2 A | — | 0.62% |
| C11 · Positive Bus Bar 3 + → Lanterns (LED) + | 3 m | 1.5 mm²AWG 16 | 0.5 A | 3 A | 0.15% |
| C12 · Lanterns (LED) − → Negative Bus Bar 1 − | 3 m | 1.5 mm²AWG 16 | 0.5 A | — | 0.15% |
A dash means no fuse is assigned to that conductor; upstream protection may apply. Recheck the exact device, holder and placement after edits.
Equipment · 8 components
- Victron 175W Mono
19.4 V · 9.03 A rated / planning output · 175 W · 23.7 V STC Voc
175W rigid mono panel, 12V nominal (Vmp 19.4V, Voc 23.7V) — works with PWM or MPPT controllers. 1485×668×30mm, 11kg, MC4 connectors.
- Solar DP Isolator
Double-pole isolator switch — breaks both the positive and negative solar legs simultaneously for safe panel disconnect.
- Victron MPPT 75/15
15 A rated / planning output
SmartSolar 75/15: 15A MPPT for 12/24V batteries, 220/440W nominal PV power and 75V maximum cold-weather Voc. Bluetooth and a separate 15A LOAD output; battery fuse recommendation 20–25A.
- House battery
12 V · 110 Ah
12 V, 110 Ah AGM Deep Cycle (BAT412101084), rated at C20. Victron prefers charging at 0.2C (22 A); this is a recommendation, not an absolute maximum. Flat terminals have 8 mm through-holes.
- Positive Bus Bar
Positive bus bar — common feed with multiple output studs.
- Chartplotter (Garmin GPSMap)
3.2 A load allowance
GPSMAP 943xsv 9-inch chartplotter with sonar: 1.37A typical and 3.20A maximum at 12V, with 40.2W maximum at 10V. Accepts 10–32V DC and uses a 6A fast-acting fuse. The dedicated power harness is required even when connected to NMEA 2000.
- Lanterns (LED)
0.5 A load allowance · 6 W
Modern LED navigation lights — port, starboard, stern and masthead. Low draw, suitable for night passages.
- Negative Bus Bar
Negative bus bar — common return with multiple output studs.
Crimp checks · 1 finding to review
These are the current engine findings for the saved example. They remain visible when you open it in Crimp.
- warning: Check fuse suitability: House battery
More boat examples
View all five →A bilge pump that stays ready
Keep the automatic bilge circuit powered when you switch off the rest of the boat.
A separate trolling motor battery
Give the trolling motor its own battery and keep the chartplotter on a separate supply.
Charge two batteries at the dock
Use separate charger outputs to replenish two batteries without joining their positive terminals.
Choose either house battery
See how a 1–2–Both switch feeds the same boat circuits from either battery.
Crimp for AI agents · public beta
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