D250SE (1044 / 40-315)
See the CTEK D250SE 20A connection points and wiring example. Open the diagram in Crimp to add your equipment and plan the cables between them.
Open this example as a new project. Use your own parts and cable lengths to make the plan yours.
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.
2 m one way
12 V system
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.
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.
The example connects starter and house batteries through the D250SE, with solar disconnected. Both battery-positive paths use the manual's 30 A protection. The 2 m output uses 10 mm²; the 3.048 m input also uses 10 mm², above the table's 6 mm² minimum for runs up to 5 m. Verify battery chemistry, control wiring and protection location before installation. Manufacturer installation manual
Wiring diagram
Open this example in Crimp to use your own parts and cable lengths. Review the assumptions and installation notes as you adapt the circuit.
The example connects starter and house batteries through the D250SE, with solar disconnected. Both battery-positive paths use the manual's 30 A protection. The 2 m output uses 10 mm²; the 3.048 m input also uses 10 mm², above the table's 6 mm² minimum for runs up to 5 m. Verify battery chemistry, control wiring and protection location before installation. Manufacturer installation manual
Edit this wiring exampleInstallation notes
Guidance for this model, with sources linked beside the relevant advice.
Verified against the manufacturer's documentation (rev. D250SE / SMARTPASS 120S UK English manual; models 1044 / 1058), checked 2026-10-01. Manufacturer documentation →
The CTEK D250SE charges a 12 V house battery from alternator power, solar, or both, with 20 A maximum output. Its 25 A input limit differs from that output rating. The starter battery must be lead-acid; the service bank can use a supported lead-acid or LFP profile.
Connect alternator/start-battery positive to ALT +, panel positive to SOLAR +, service positive to SERVICE +, and returns to the common earth connection. The manual’s cable table specifies 30 A battery-side fuses and length-dependent conductors. The output table reaches 2 m using 10 mm²; route longer installations from a fresh conductor/drop assessment rather than extrapolating silently. Main M8 connections tighten to 8 Nm.
The red smart-alternator lead needs the manual’s ignition connection when that mode is required. The black battery-select lead selects Normal, AGM or lithium behavior; follow the wiring combinations for the actual battery. Attach the supplied temperature sensor near the service battery’s positive post. These control/sensor wires are not represented as power terminals on the symbol.
The solar array’s cold open-circuit voltage must stay below 23 V; panel watts alone cannot establish compatibility. Charging derates with temperature. Mount in ventilated surroundings and check source LEDs when output is absent. The unit lacks reverse-polarity protection and is not spark-free. A SMARTPASS adds a separate power path; it does not increase this converter’s own 20 A rating.
Build it out
Add D250SE (1044 / 40-315) to your diagram, then connect your batteries, chargers and loads. Crimp calculates cable sizes and checks the connections as you draw.
Every cable you draw there is sized against ABYC E-11, from the same tables as the reference on this page.
Technical reference
Check the model, ratings and connection points against your own unit before choosing installation hardware.
Check stud sizes, fuse type, run length and how warm the space gets against the gear you actually have before you order.
Catalog connection points, current direction and planning limits. Check the manufacturer's pinout and connector ratings before installation.
ALT +
in-pos
positive · input
SOLAR +
pv-pos
positive · input
SERVICE +
out-pos
positive · output
EARTH −
gnd
negative · bidi
Method & provenance
Manufacturer specifications describe the equipment. Crimp calculates cable results from the circuit and assumptions you enter.
From the maker
Manufacturer, model, ratings and which terminal does what come from the catalog. A newer revision, or the nameplate on the unit in your hand, can say something different — when it does, the nameplate wins.
ABYC E-11
Sized against ABYC E-11. Boats built to UK or EU rules answer to ISO 13297 — check these figures against it before you build. The run length and the current above are what drive the result. Crimp doesn't know how warm your space gets; draw the cable inside an engine-bay zone on the canvas and it sizes for the heat.
Next step
Open this example as a new project. Add your equipment and cable lengths, then review the sizing and checks for your setup.