Step-by-Step Selection Process
Three-phase asynchronous(induction) motors are common in industrial systems. How the motor starts affects the equipment’s life, the stability of the power grid, and overall efficiency. Low voltage Soft Starters are widely used today for motor starting. They help motors start smoothly, reduce inrush current, and protect the motor.
Choosing the right soft starter is important. It should meet technical needs, be cost-effective, and easy to maintain.
This guide explains the basics. It includes key parameters, how to select a model, product comparisons, and common mistakes. It will help you make a clear and smart choice.
1. Overview of Low-Voltage Soft Starter Selection
1.1 Basic Electrical Parameters
Before selecting a soft starter, consider the following key electrical parameters:
• Voltage Rating:
◦ Typically 3-phase 380V, 400V, or 415V; some models support 220V or 480V. Choose based on your power supply.
• Control Power & Main Power:
◦ Main Power: Supplies power to the motor.
◦ Control Power: Powers the soft starter’s control circuit (usually 110V/220V AC or DC).
◦ Some models require separate control power. Check wiring requirements in advance.
• Frequency Range:
Most soft starters support both 50Hz and 60Hz.
1.2 Key Selection Factors
Follow this selection order:
⭐Core Factors (Must Consider):
1. Motor Rated Power & Current
◦ The soft starter’s rated current should be equal to or higher than the motor’s rated current.
◦ Consider the load type (e.g., heavy-duty crushers vs. light-duty fans).
| Simple rule: ◦ For normal start, Select the softstarter according to the rated motor power. ◦ For heavy duty start, select one size larger soft starter compared to the rated motor power. |
2. Starting Frequency
◦ For frequent starts per day, choose models with better heat dissipation or built-in bypass.
3. Application Environment
◦ Consider harsh environments: frequent starts/stops, long runtime, dust, or humidity.
4. Protection Features
◦ Do you need under-voltage, overload, phase loss, overheating, or start timeout protection?
⭐Secondary Factors (for better usability):
• Multi-language display interface;
• Modbus communication support.
• Flexible mounting (DIN rail/wall-mounted).
• Remote control or PLC integration capability.
2. Comparison of our 4 Low-Voltage Soft Starters
Here is a side-by-side comparison of four typical models of our soft starters.
| Model | Main Voltage | Power Range | Control Power | Built-in Bypass | Display① | COM interface and protocol② | Key Features |
| CMC-LX | AC380V ±15% | 7.5–710 kW | AC110V -10% to 220V+15% | ❌ | 7-segment LED display | RS485 (Add on)，Modbus-RTU | Cover essential requirements, Cost-effective |
| CMC-HX | 380V AC/660V/1140V ±15% | 7.5–995 kW | AC110V to AC220V±15% | ❌ | LCD display | RS485 (Standard), Modbus RTU; Ethernet (Add-on), Modbus TCP | Balanced performance, Wide voltage |
| CMC-MX | 380V AC ±15% | 7.5–280 kW | AC110V to AC220V±15% | ✅ | 7-segment LED display | RS485 (Standard), MODBUS-RTU | Built-in bypass, simple wiring, better cooling |
| XST260 | AC220/380/480V ±10% | 7.5–400 kW | AC110V to AC220V±15% | ✅ | LCD/LED display (optional) | RS485 (Standard), MODBUS-RTU; Profibus-DP (Add-on) | Smart, Multi-voltage, ideal for standardized projects |
| ① LED and LCD Display： 7-Segment LED Display: ◦ Mostly limited to numbers and some letters (eg. STOP, Er01, etc ). ◦ Very bright and visible in low light or dark environments. LCD display: ◦ Can display both text and graphics. ◦ Less bright; depends on ambient light or backlight. |
| ② Modbus RTU and Modbus TCP： Modbus RTU: • Slower than TCP, strong compatibility, suitable for cost-sensitive and harsh environments. • Transmission via RS-485/RS-232 (serial port) for short distance industrial sites (e.g. PLC, sensors) Modbus TCP: • Faster with lower latency, suitable for long-distance and multi-device communication. • Transmission via Ethernet (TCP/IP) for remote monitoring or high-speed network environments. |
3. Common Selection Mistakes (Q&A)
Q1: Can a soft starter fully replace a star-delta starter?
A: Technically yes, but soft starters cost more. They’re ideal for mid- to high-end equipment needing protection and reduced inrush. Recommended for fans and pumps.
Q2: Is matching motor power enough for selection?
A: No. You also need to consider rated current, load type, and start frequency. Heavy-duty loads require extra margin.
Q3: Can a soft starter adjust motor speed?
A: No. Soft starters control only the start and stop process. Use a Vfd (Variable Frequency Drive) for speed control.
Q4: Is there a big difference between models with and without built-in bypass?
A:
• Built-in Bypass: Lower heat loss, energy-saving, fewer external connections, and easier to install.
• Non-bypass: Requires an external contactor, increasing complexity and installation cost.
Q5: Do all soft starters support communication?
A: No. Not all models come with communication interfaces. If your project needs PLC or remote control, choose models that support Modbus or Profibus protocols.
4. Summary & Recommendations
When selecting a soft starter:
• Avoid choosing based solely on “universal” or “lowest price.”
• Prioritize motor specs, operating conditions, protection features, and system integration.
For large-scale or multi-project selections:
• Consult manufacturers or a technical engineer
• Configure startup modes based on actual conditions
• Reserve extra capacity to ensure system reliability
| ✅ Next Step Recommendation: 📎 Visit our product page for detailed specifications: • CMC-LX Soft Starter • CMC-HX Soft Starter • CMC-MX Soft Starter • XST260 Smart Soft Starter 📬 Contact our professional sales consultant for personalized selection advice and technical documentation—simply send your requirements to our email: sales@bgacs.com. |