NXS-SXD Five-Key Water Heater

NXS-SXD-P1.3 Five-Key Instant Electric Water Heater PCBA with Wide-Voltage Input

The NXS-SXD-P1.3 is a customizable instant electric water heater PCBA designed for appliances requiring wide-voltage operation, a five-key touch interface, preset temperature selection and multiple firmware power levels.

The complete solution combines the NXS-SXD-P1.3 power board with the NXS-13560-5KEY-XH3-B2/B3-C1.3 display board. Based on a 16-pin BYD control IC, it integrates temperature adjustment, water-flow activation, automatic temperature learning, parameter memory, display feedback and multiple safety-diagnostic functions.

SunSam can customize the hardware, firmware, display artwork, key layout, temperature range and protection logic according to the customer’s heating system, enclosure design and target market.

Key Specifications

Power Board Model: NXS-SXD-P1.3

Display Board Model: NXS-13560-5KEY-XH3-B2/B3-C1.3

Control IC: BYD 16-Pin Control IC

Standard Power Supply: Switch-Mode Power Supply

Standard Input Voltage: 65–280 VAC

Optional Transformer Input: 180–280 VAC

Control Interface: Five-Key Touch Control

Preset Temperatures: 38°C and 42°C

Standard Temperature Range: 30–55°C

Extended Temperature Option: Up to 75°C, Subject to Firmware and Safety Validation

Power-Level Settings: P12, P15, P18, P21 and P24

Touch Panel Compatibility: 4 mm Glass Panel or 2 mm Plastic Panel

Temperature Sensor: 50K NTC

Flow Activation Threshold: 1.8 L/min

Heating Shutoff Threshold: 1.5 L/min

Water-Flow Switch: Three-Wire Flow Switch

Leakage Detection Range: 15–30 mA

Buzzer Frequency: 2.5 kHz

Operating Temperature: -15°C to 65°C

Operating Humidity: 10–95% RH

Wide-Voltage Power Supply

The standard configuration uses a switch-mode power supply with a 65–280 VAC input range. During internal sample validation, the controller operated continuously at 280 VAC for eight hours without abnormality.

An optional transformer-based configuration supports an input range of 180–280 VAC. The transformer configuration operated continuously at 265 VAC for eight hours without abnormality.

These two power-supply solutions allow the control platform to be adapted to different regional voltages, product structures and cost requirements.

Five-Key Touch-Control Interface

The user interface includes five touch keys:

- 38°C Preset

- Temperature Down

- Power

- Temperature Up

- 42°C Preset

The 38°C and 42°C keys provide direct access to commonly used temperature settings. The Temperature Up and Temperature Down keys support individual adjustment and continuous adjustment when pressed for more than one second.

Every valid key operation produces one audible beep, providing clear feedback to the user.

The touch-control design can operate through a 4 mm glass panel or a 2 mm plastic panel. It supports individual light-touch activation without requiring sliding gestures.

Configurable Temperature Range

The standard program supports a temperature setting range of 30–55°C. The test report also records a request to extend the upper limit to 75°C.

A 30–75°C configuration can be developed, but the over-temperature protection threshold, heating components, sensors, water path and complete-appliance safety design must be adjusted and validated together.

The current sample report specifies over-temperature protection at 63°C. Therefore, the 75°C upper setting should only be enabled after the protection logic has been reconfigured and verified.

P12–P24 Power-Level Settings

The firmware includes five configurable power levels:

- P12

- P15

- P18

- P21

- P24

Pressing and holding the Temperature Up and Temperature Down keys together for approximately three seconds while the controller is off opens the power-level setting interface.

P12–P24 are firmware level codes. The sample report does not formally define their corresponding wattage values. They should not be presented as confirmed 12 kW, 15 kW, 18 kW, 21 kW and 24 kW ratings until the firmware mapping and complete power circuit have been verified.

The actual appliance power depends on the heating element, relay or semiconductor power stage, wiring, terminals, PCB copper design, thermal management and complete electrical system.

Display and Operating Feedback

When power is connected, the buzzer sounds once and all display segments illuminate for approximately one second. This provides a basic visual and audible self-check.

While the controller is off, the display can show the configured power level. After the Power key is pressed, the display shows the outlet water temperature.

The display language, printed film, symbols, icons and operating information can be customized for different appliance designs and destination markets.

Water-Flow Activation

The reference heating activation threshold is 1.8 L/min. Heating stops when the flow drops to approximately 1.5 L/min.

The sample uses a three-wire water-flow switch. The controller coordinates the detected flow condition with the heating output to avoid normal heating operation when water flow is insufficient.

Flow thresholds can be adjusted after engineering evaluation according to the water path, flow sensor, heating power and intended application.

Automatic Temperature Learning and Memory

The controller supports inlet and outlet water-temperature monitoring through 50K NTC temperature sensors.

Its firmware includes automatic temperature learning and calibration. The control parameters can adapt to water flow, inlet temperature, outlet temperature, heating power and the thermal characteristics of the complete appliance.

The selected temperature and power-level settings are stored automatically. When power is restored, the controller defaults to the off state while retaining the previously configured parameters.

Sample Temperature-Control Performance

Temperature-control testing was performed with an inlet water temperature of 26°C and flow rates of 1.5 L/min and 3.0 L/min.

After completing the initial learning calibration, the controller achieved temperature stabilization within 20 seconds under the recorded test conditions.

At a flow rate of 1.5 L/min:

- 30°C setting: measured at 29–31°C

- 36°C setting: measured at 35–38°C

- 40°C setting: measured at 39–41°C

- 45°C setting: measured at 44–47°C

- 48°C setting: measured at 47–50°C

At a flow rate of 3.0 L/min:

- 30°C setting: measured at 29–31°C

- 36°C setting: measured at 35–37°C

- 40°C setting: measured at 39–41°C

- 45°C setting: measured at 44–46°C

- 48°C setting: measured at 47–49°C

The recorded temperature-control tests cover settings up to 48°C. Performance above this temperature must be validated separately if the extended 75°C program is required.

Actual temperature accuracy and response time depend on inlet water temperature, flow rate, heating power, sensor position and complete water-path design.

Safety Protection and Fault Diagnostics

E1 Over-Temperature Protection

The current program stops heating and activates an alarm when the detected water temperature reaches 63°C or above. Heating resumes after the temperature falls to 50°C.

For applications requiring a temperature setting above 63°C, the protection threshold and complete-appliance safety design must be reconfigured and validated.

E3 Leakage-Current Protection

If a leakage-current fault is detected, the controller disables heating and activates an alarm. Operation can resume after the fault is repaired and the appliance is restarted.

The sample report specifies a leakage-detection range of 15–30 mA. The measured sample value was 24 mA using a three-wire leakage-detection coil.

The final threshold must be matched to the selected leakage coil and complete-appliance safety requirements.

E2 Outlet Temperature Sensor Fault

If the outlet temperature sensor is open or short-circuited, the controller disables heating and activates an alarm. Heating resumes automatically after the fault is corrected.

E0 Inlet Temperature Sensor Fault

An open or short circuit in the inlet temperature sensor activates an alarm. The sample firmware indicates that heating can continue, while temperature-control relearning is required after a cold restart.

This behavior can be modified according to the customer’s safety requirements.

Zero-Crossing Control

The firmware supports zero-crossing detection and burst-fire heating control. The final fault definition and recovery method depend on the selected power-control circuit.

Communication Diagnostics

The firmware reserves E9 for communication-fault diagnostics. The heating response, alarm behavior and recovery logic can be defined in the final customer program.

Environmental and Reliability Validation

The specified operating temperature range is -15°C to 65°C, while the operating humidity range is 10–95% RH.

The sample completed the following internal tests:

- Eight hours of operation at 280 VAC with the switch-mode power supply

- Eight hours of operation at 265 VAC with the transformer configuration

- Eight hours of operation at 65°C and 90% RH

- Whole-unit dielectric withstand testing at 1800 V and 5 mA for one minute

- Thirty fluorescent-lamp switching cycles at intervals of 0.5–3 seconds

- Normal-temperature water-change testing

- Circulating-water temperature-control testing

No abnormal operation was recorded during these sample tests.

These results represent internal sample validation and should not be interpreted as independent EMC, electrical-safety or complete-appliance certification.

Typical Applications

The NXS-SXD-P1.3 control solution can be used in:

- Residential instant electric water heaters

- Commercial point-of-use water heaters

- Kitchen and washbasin hot-water appliances

- Hotel and apartment water-heating equipment

- Glass-panel touch-control water heaters

- Water heaters requiring preset temperature keys

- Products requiring configurable firmware power levels

- Custom high-temperature water-heating equipment after safety validation

OEM/ODM PCBA Development and Manufacturing

Foshan Shunde SunSam Electronic Co., Ltd. has 15 years of experience in custom PCBA development and manufacturing. Water heater control boards are one of our core product categories.

Our one-stop OEM and ODM services include:

- Product-function evaluation

- Hardware and firmware development

- Circuit and PCB design support

- Component sourcing

- Prototype production

- SMT assembly

- Wave soldering

- Firmware programming

- ICT and FCT testing

- Functional verification

- Material and production traceability

- Volume manufacturing

The input voltage, temperature range, preset temperatures, power levels, key layout, display content, flow thresholds, sensor parameters, protection functions and fault codes can be customized after engineering evaluation.

Start Your Custom Water Heater PCBA Project

Customers can provide an existing sample, BOM, Gerber files, schematic, enclosure drawing or functional specification for evaluation.

For an accurate technical proposal and quotation, please provide:

- Target-market voltage requirements

- Heating-element rated voltage and power

- Power-control method

- Required temperature range

- Water-flow sensor specifications

- Temperature-sensor specifications

- Display and key-layout requirements

- Enclosure dimensions

- Required testing standards

- Estimated order quantity

- Project schedule