12V 300W
ATI 12V Water Heater 300W wiring diagram
ATI 12 V / 300 W water-heater family, nominally 25 A while heating. Exact tank and controller must be identified; the verified BS-series manual requires a full tank before energizing and retains thermostat/safety-cutoff control.
- Compatible systems
- 12 V
- Rated power
- 300 W
- Continuous draw
- 25 A
Wiring diagram
How the ATI 300W 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.
Cable 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 m one way
12 V system
- Wire
- 10 mm² · 8 AWG
- Example fuse
- 35 A
- Design current
- 25 A
- Voltage drop
- 2.2%
Sized against ABYC E-11. The design current is the part's continuous draw. 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.
Supporting parts
- 6.1 m total of 10 mm² (8 AWG) marine cable
- Terminations for 10 mm² cable, matched to the equipment's screw terminals, leads or studs
- 35 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.
Reviewed against manufacturer family documentation (rev. 210-0068.04 \u2014 February 2026), checked 2026-10-01. Exact variant details still require confirmation. Manufacturer documentation →
Identify the complete heater
The catalog identifies ATI 12 V/300 W heating but does not give a tank size or full part number. ATI’s BS22032/BS30032/BS45032/BS60032/BS80032 manual verifies 25 A at 12 V for the 300 W versions, covering 22–80 L tanks with engine-coolant heat exchange. This is family-level evidence; it does not identify a loose immersion element or the smaller MB-series heater as the same assembly.
Connect the controlled assembly
`+` and `−` represent the complete heater’s DC supply. Preserve correct polarity and the supplied controller/thermostat circuit. The manual calls for a nearby two-pole isolating switch. Its electrical instructions do not establish one universal upstream fuse value or terminal torque for every installation; select circuit protection against the actual cable, label and installed assembly rather than treating 25 A as the fuse size.
Fill before energizing
The documented controller regulates at 60°C and interrupts heating at 85°C through its safety thermostat. Only energize the element after the tank is full of water; dry operation can destroy it. Follow the cold-water inlet, expansion/relief and engine-coolant plumbing requirements for the exact tank. Do not transfer these thermostat settings to an unidentified replacement element with another controller.
Energy budget and omissions
At nominal voltage, 300 W is a sustained load while the thermostat calls for heat. Daily run time depends on tank size, incoming-water temperature, hot-water use, insulation and any heat supplied by the engine. The catalog 1.5-hour default is not a manufacturer heating-time guarantee. The drawing omits the thermostat, safety cutoff, relief valve, tank and heat exchanger; its single load symbol cannot verify these parts.
Source: manufacturer document — model table printed/PDF p. 5; plumbing pp. 10–11; DC connections p. 12; thermostat and dry-heating warning p. 13.
Technical reference
Specifications and terminal map.
Check the model, ratings and connection points against your own unit before choosing installation hardware.
Catalog specification
ATI 12 V / 300 W water-heater family, nominally 25 A while heating. Exact tank and controller must be identified; the verified BS-series manual requires a full tank before energizing and retains thermostat/safety-cutoff control.
- Compatible systems
- 12 V
- Rated power
- 300 W
- Continuous draw
- 25 A
Terminal map
Catalog connection points, current direction and planning limits. Check the manufacturer's pinout and connector ratings before installation.
+
positive · input
−
negative · input
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. Boats built to UK or EU rules answer to ISO 13297 — check these figures against it before you build. 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 ATI 300W.
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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