1. Introducción
The COTEC SD3500-148 GFCI Pure Sine Wave Inverter is designed to convert 48VDC battery power into 120VAC pure sine wave electricity, suitable for sensitive electronics and various applications. This inverter features a dual GFCI outlet, an integrated AC circuit breaker, and an automatic transfer switch (ATS) for reliable power supply. It supports parallel connectivity for power expansion and offers advanced communication options for monitoring and control.
2. Información de seguridad
Read all instructions and warnings before installing or operating this inverter. Failure to follow these instructions may result in electric shock, fire, serious injury, or death. Keep this manual for future reference.
- Peligro eléctrico: Esta unidad produce un alto volumentage. No abra el inversor casing. Deje todo servicio a personal cualificado.
- Seguridad de la batería: Work in a well-ventilated area. Batteries can produce explosive gases. Do not smoke or allow sparks or flames near batteries. Wear eye protection and protective clothing.
- Alambrado: Ensure all wiring is correctly sized and properly terminated. Use 4/0 AWG wire for DC connections not longer than 5 feet for optimal performance, especially at full capacity. Incorrect wiring can cause overheating and fire.
- Toma de tierra: Proper grounding is essential. Ensure the inverter is correctly grounded according to local electrical codes. Be cautious with bonded grounds; some inverters may not operate correctly with them.
- Entorno de instalación: Instale el inversor en un área seca, fresca y bien ventilada, lejos de la luz solar directa, fuentes de calor y materiales inflamables.
- Protección contra sobrecarga: No exceda la potencia de salida nominal del inversor. La sobrecarga puede dañar la unidad y los aparatos conectados.
3. Características
The SD3500-148 GFCI inverter incorporates several advanced features for enhanced performance and reliability:
- Salida de onda sinusoidal pura: Provides clean, stable power suitable for all types of loads, including sensitive electronics.
- Dual GFCI 120VAC Outlets: Equipped with two Ground Fault Circuit Interrupter outlets for safety.
- Automatic Transfer Switch (ATS): Seamlessly switches between inverter power and utility/generator AC input.
- Built-in AC Circuit Breaker: Provides protection for the AC output.
- Parallel Redundancy Design: Allows for power expansion by connecting multiple inverters of the same model.
- Puerto de comunicación RS-232: Enables monitoring and control via a computer or optional remote.
- Input & Output Isolation: Ensures safety and reduces interference.
- Modos de ahorro de energía: Selectable modes to optimize energy consumption.
- Protecciones integrales: Includes reverse polarity (fuse), under/over voltage, short circuit, overload, over temperature, and over voltage protección.
- Configuración del interruptor DIP: Allows customization of various settings.
4. Configuración
4.1 Instalación física
Mount the inverter in a secure, well-ventilated location. Ensure adequate clearance around the unit for airflow, especially around the cooling fans. The inverter can be mounted horizontally or vertically.

Figure 1: Rear panel of the SD3500-148 GFCI inverter, illustrating the DC input terminals, AC input/output connections, GFCI outlets, and communication ports.

Figura 2: Lado view of the SD3500-148 GFCI inverter, highlighting the dual cooling fans for thermal management.
4.2 Conexiones eléctricas
All electrical connections should be performed by a qualified electrician. Ensure all power sources are disconnected before making any connections.
- Entrada de CC (batería): Connect the 48VDC battery bank to the DC input terminals on the inverter's rear panel. Observe correct polarity (positive to positive, negative to negative). Use appropriate gauge wiring (e.g., 4/0 AWG for runs under 5 feet) and ensure connections are tight.
- Salida de CA (carga): Connect your AC loads to the dual GFCI outlets or hardwire to the AC output terminals.
- Entrada de CA (servicio público/generador): If using the Automatic Transfer Switch (ATS) function, connect your utility or generator AC power to the AC input terminals.
- Toma de tierra: Conecte el terminal de tierra del chasis del inversor a una tierra confiable.
4.3 Configuración del interruptor DIP
The inverter features DIP switches for customizing various operational parameters, such as output voltage, power saving mode, and communication settings. Refer to the detailed specifications table for specific DIP switch functions and recommended settings for your application.

Figure 3: Excerpt from the SD3500 series specifications, detailing features and various model specifications, including notes on DIP switch configurations.
5. Operación
5.1 Encendido / Apagado
After all connections are secure and verified, switch the inverter's main power switch to the 'ON' position. The inverter will perform a self-test, and the LED indicators will illuminate to show its status. To power off, switch the main power switch to 'OFF'.
5.2 Indicadores LED
The inverter is equipped with LED indicators to display its operational status and any fault conditions. Refer to the LED Status table for detailed explanations.

Figure 4: LED Status table for the SD3500 series, indicating different operational states and fault conditions via green, orange, and red LED signals.
5.3 Modo de ahorro de energía
The inverter offers selectable power saving modes to reduce idle power consumption. These modes can be configured via DIP switches or the optional remote control (CR-10). In power saving mode, the inverter will periodically check for load and enter a low-power state if no significant load is detected.
5.4 Automatic Transfer Switch (ATS)
The built-in ATS allows the inverter to automatically switch between battery power and an external AC source (utility or generator). This ensures an uninterrupted power supply to connected loads. The transfer time is typically very fast, often less than 4ms, depending on the mode (STS, ATS).

Figure 5: Transfer Time Table for the SD3500 series, detailing switching speeds for different transfer switch modes (ATS, STS).
5.5 Funcionamiento en paralelo
The SD3500 series supports parallel redundancy design, allowing multiple inverters of the same model to be connected to increase total power capacity or provide redundancy. This feature is ideal for applications requiring higher wattage or enhanced reliability. Consult the advanced manual for detailed instructions on parallel setup.
6. Mantenimiento
El mantenimiento regular garantiza la longevidad y el rendimiento óptimo de su inversor.
- Limpieza: Keep the inverter's exterior clean and free from dust and debris. Ensure ventilation openings and cooling fans are unobstructed. Use a dry cloth for cleaning.
- Inspección del ventilador: Periodically check the cooling fans for proper operation and cleanliness. If fans become noisy or stop working, they may need replacement by a qualified technician.
- Comprobaciones de conexión: Annually inspect all electrical connections (DC input, AC input/output, ground) for tightness and corrosion. Tighten any loose connections.
- Mantenimiento de la batería: Follow the battery manufacturer's maintenance guidelines for your battery bank. Ensure batteries are properly charged and maintained.
7. Solución de problemas
If the inverter is not operating as expected, refer to the LED Status table (Figure 4) for diagnostic information. Common issues and their potential solutions are listed below:
- Sin potencia de salida:
- Compruebe el volumen de entrada de CCtage; ensure it is within the specified range (40.0-64.0VDC for 48V models).
- Verify DC input connections for correct polarity and tightness.
- Check the inverter's main power switch is 'ON'.
- Inspect the AC output circuit breaker on the inverter.
- Look for fault indications on the LED status panel (e.g., OVP, UVP, OLP, OTP).
- Overload Protection (OLP):
- The inverter has detected an excessive load. Reduce the connected load.
- Disconnect all loads, power cycle the inverter, and reconnect loads one by one.
- Protección contra sobretemperatura (OTP):
- The inverter is overheating. Ensure adequate ventilation and clear any obstructions from the cooling fans.
- Reduzca la carga en el inversor.
- Deje que la unidad se enfríe antes de reiniciarla.
- Bajo VoltagProtección electrónica (UVP):
- El volumen de la bateríatage is too low. Recharge or replace the battery bank.
- Check DC wiring for excessive voltage gota.
- RS-232 Communication Issues:
- Ensure DIP Switch 8 is in the 'OFF' (0) position for RS-232 communication.
- The power switch must be set to 'ON', not 'REMOTE', for RS-232. 'REMOTE' is for the optional LCD remote module only.
- Verify the RS-232 cable pinout is correct as described in the manual.
8. Especificaciones
Key technical specifications for the COTEC SD3500-148 GFCI Pure Sine Wave Inverter:
- Modelo: SD3500-148 GFCI
- Output Power (Continuous): 3500 vatios
- Potencia máxima de salida: 4200 Watts (0.2 sec)
- Vol de entradatage: 48 VDC (Operating Range: 40.0-64.0 VDC)
- Vol de salidatage: 120 V CA
- Frecuencia de salida: 50 / 60 Hz selectable
- Forma de onda de salida: De onda sinusoidal pura
- Efficiency (Max): 90%
- Distorsión armónica total (THD): <3% @ linear load
- Consumo de energía sin carga: <1.4A (DC)
- Disyuntor de CA: 35A
- Transfer Switch Time (ATS): <10ms (Normal), <4ms (STS)
- Temperatura de funcionamiento: -20°C to 40°C (de-rating above 40°C)
- Dimensiones (Ancho x Alto x Profundidad): 283 x 125 x 496 mm (11.14 x 5.04 x 19.53 pulgadas)
- Peso: 24.8 libras (11.25 kg)
- Normas de seguridad: Certified UL 458 (UL only for hardwire)

Figure 6: Comprehensive technical specifications for the SD3500 series, including electrical parameters, protection features, and environmental ratings.

Figure 7: Mechanical drawings of the SD3500 series inverter, showing overall dimensions in millimeters and inches.
9. Garantía y soporte
COTEK products are designed for reliability and performance. For warranty information, please refer to the warranty card included with your product or visit the official COTEC website. For technical support, troubleshooting assistance, or to inquire about replacement parts, please contact COTEC customer service or an authorized service center. When contacting support, please have your product model number (SD3500-148 GFCI) and serial number available.