Charger
Morningstar SunSaver Duo SSD-25 wiring diagram
12 V PWM solar controller with a shared 25 A budget for two lead-acid banks. Outputs have independent sealed/flooded selection and configurable charging priority.
- Compatible systems
- 12 V
- Rated output
- 25 A
- PV open-circuit limit
- 30 V
Wiring diagram
How the SSD-25 is wired.
Open this example in Crimp to use your own parts and cable lengths. Review the assumptions and installation notes as you adapt the circuit.
Single-bank example uses the shared 25 A rating. Manual specifies 30 A battery fuse per connected bank; 5 mm² at 25 A permits 4.3 m one-way, rounded up to 6 mm² here. Another battery needs its own fuse and shares the same 25 A total. PWM lead-acid only, cold PV Voc <=30 V. Manufacturer installation manual
Edit this wiring exampleCable sizing for this example
Use the diagram as a starting point for your installation. Replace the example equipment and cable lengths with your own, and check the connections against your exact model's instructions.
3.3 ft one way
12 V system
- Wire
- 10 AWG · 6 mm²
- Example fuse
- 30 A
- Design current
- 25 A
- Voltage drop
- 1.2%
Sized against ABYC E-11. The design current is the unit's rated output. The length is one way; voltage drop includes an equal-length return.
Run-length and manufacturer assumptions
The editable example uses 3.048 m (10 ft) runs unless a shorter run is stated. Metric overviews round these to 3 m. Adapt the parts and lengths to your installation before choosing cable and protection.
Single-bank example uses the shared 25 A rating. Manual specifies 30 A battery fuse per connected bank; 5 mm² at 25 A permits 4.3 m one-way, rounded up to 6 mm² here. Another battery needs its own fuse and shares the same 25 A total. PWM lead-acid only, cold PV Voc <=30 V. Manufacturer installation manual
Supporting parts
- 6.6 ft total of 10 AWG (6 mm²) marine cable
- Terminations for 10 AWG cable, matched to the equipment's screw terminals, leads or studs
- 30 A fuse and holder on the positive run
- Heat-shrink, strain relief and terminal boots sized to the cable
Check stud sizes, fuse type, run length and how warm the space gets against the gear you actually have before you order.
Installation notes
Before you install.
Open a question for model-specific guidance and sources.
Verified against the manufacturer's documentation (rev. MS-001164 v2.1, 2016), checked 2026-10-01. Manufacturer documentation →
Two banks share one solar budget
SSD-25 is a PWM, 12 V, lead-acid controller. Its two outputs share 25 A total; two attached banks do not create a 50 A charger. Select sealed or flooded charging separately for each bank. The priority switch allocates 90/10 or 50/50 while both need charging, and unused capacity can pass to the other bank. These profiles do not establish LiFePO4 compatibility. See configuration, PDF p. 8.
Identify the six power terminals
Connect the PV pair and the two battery pairs to their marked positive and negative screws. The negative terminals are electrically common. The optional remote temperature sensor and meter use dedicated connections; they carry no battery charging current. Keep cold-weather PV open-circuit voltage below the published 30 V maximum, which rules out many higher-voltage residential modules.
Fuses, cable and mounting
Fit a 30 A fuse in each battery-positive lead. The installation drawing places battery fuses within 305 mm; a stricter applicable installation rule takes precedence. At 25 A the cable table allows 5 mm² conductors over 4.3 m one way; rounding up to 6 mm² for a short run is a practical metric choice. Terminals accept up to 10 mm² and are tightened to 4 Nm. Leave 75 mm above and below for cooling and avoid a sealed flooded-battery compartment. See wiring sequence, PDF p. 12 and terminal specifications, PDF p. 27.
Verify priority in service
Set the DIP switches before charging, connect and verify both bank polarities, then introduce solar. Check that each bank sees its selected charging voltage. Observe the allocation while both banks need charge and again when one is full; instantaneous current can move between outputs. A wiring example with one bank uses the whole shared limit but does not illustrate the second bank's required fuse. The detailed cable-distance table is on wire sizing, PDF p. 28.
Technical reference
Specifications and terminal map.
Check the model, ratings and connection points against your own unit before choosing installation hardware.
Catalog specification
12 V PWM solar controller with a shared 25 A budget for two lead-acid banks. Outputs have independent sealed/flooded selection and configurable charging priority.
- Compatible systems
- 12 V
- Rated output
- 25 A
- PV open-circuit limit
- 30 V
Terminal map
Catalog connection points, current direction and planning limits. Check the manufacturer's pinout and connector ratings before installation.
PV +
positive · input
PV −
negative · input
BANK 1 +
positive · output
BANK 1 −
negative · output
BANK 2 +
positive · output
BANK 2 −
negative · output
REMOTE TEMP
signal · bidi
REMOTE METER
signal · bidi
A dash means a current rating is not specified here.
Sources and sizing method
Equipment specifications. Model details, ratings and terminal roles come from the catalog. Check your unit’s label and current manufacturer documentation for its exact revision.
Example sizing. Sized against ABYC E-11 — the US reference, and what Transport Canada accepts as an alternative to TP 1332 for pleasure craft under 24 m. Results use the example current and run length shown above. Set your actual equipment, lengths and installation conditions in Crimp before choosing hardware.
Read how the sizing worksNext step
Plan your installation with SSD-25.
Open this example as a new project, or add this component to your existing diagram. Use your equipment and cable lengths to review the sizing.
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