How to Use 4S Battery 18650 Lithium ion: Examples, Pinouts, and Specs

The 4S battery configuration consists of four 18650 lithium-ion cells connected in series. This arrangement increases the voltage output while maintaining the same capacity as a single cell. Each 18650 cell typically has a nominal voltage of 3.7V, so a 4S configuration provides a nominal voltage of 14.8V (3.7V × 4). This makes it ideal for applications requiring higher voltage, such as electric vehicles, power tools, drones, and portable electronics.

• Electric vehicles and e-bikes
• Drones and RC vehicles
• Portable power banks
• Solar energy storage systems
• High-power LED lighting systems

Below are the key technical details for a typical 4S 18650 lithium-ion battery pack:

A 4S battery pack typically includes a Battery Management System (BMS) for safety and monitoring. The BMS has the following pin configuration:

1. Connect the Battery Pack: Ensure the 4S battery pack is properly connected to the circuit. Use the B+ and B- terminals for the main power output.
2. Use a BMS: Always include a Battery Management System (BMS) to protect the battery from overcharging, over-discharging, and short circuits.
3. Charging the Battery:
   • Use a dedicated lithium-ion battery charger with a 16.8V output.
   • Connect the charger to the P+ and P- terminals of the BMS.
4. Load Connection: Connect your load (e.g., motor, LED, or other devices) to the P+ and P- terminals of the BMS.

• Avoid Overcharging: Never exceed 16.8V when charging the battery pack.
• Avoid Over-Discharging: Do not let the voltage drop below 12.0V to prevent damage to the cells.
• Use Proper Wiring: Ensure all connections are secure and use wires rated for the current draw of your application.
• Monitor Temperature: Avoid exposing the battery pack to extreme temperatures (above 60°C or below -20°C).
• Balance Charging: Use a charger with a balancing feature to ensure all cells are charged evenly.

To power an Arduino UNO with a 4S battery pack, use a DC-DC step-down converter to reduce the voltage to 5V or 7-12V (the recommended input voltage range for the Arduino UNO). Below is an example circuit and code:

1. Connect the 4S battery pack to the input of the DC-DC converter.
2. Set the output of the DC-DC converter to 7-12V.
3. Connect the output of the DC-DC converter to the Arduino UNO's VIN and GND pins.

// Example code to read a sensor and control an LED using Arduino UNO
// powered by a 4S battery pack with a DC-DC converter

const int sensorPin = A0;  // Analog pin connected to the sensor
const int ledPin = 13;     // Digital pin connected to the LED

void setup() {
  pinMode(ledPin, OUTPUT);  // Set LED pin as output
  Serial.begin(9600);       // Initialize serial communication
}

void loop() {
  int sensorValue = analogRead(sensorPin);  // Read sensor value
  Serial.println(sensorValue);             // Print sensor value to Serial Monitor

  if (sensorValue > 500) {                 // If sensor value exceeds threshold
    digitalWrite(ledPin, HIGH);            // Turn on the LED
  } else {
    digitalWrite(ledPin, LOW);             // Turn off the LED
  }

  delay(100);  // Wait for 100 milliseconds
}

1. Battery Pack Not Charging:

   • Cause: Charger not compatible or BMS malfunction.
   • Solution: Use a charger with a 16.8V output and check the BMS connections.

2. Uneven Cell Voltages:

   • Cause: Cells are not balanced.
   • Solution: Use a balancing charger or replace the BMS with one that supports cell balancing.

3. Battery Overheating:

   • Cause: Excessive current draw or poor ventilation.
   • Solution: Reduce the load or improve airflow around the battery pack.

4. Low Runtime:

   • Cause: Degraded cells or insufficient capacity.
   • Solution: Test individual cells and replace any that are underperforming.

• Q: Can I use a 4S battery pack without a BMS?

  • A: It is not recommended. A BMS is essential for safety and to prevent overcharging or over-discharging.

• Q: How do I calculate the total capacity of a 4S battery pack?

  • A: The total capacity is the same as the capacity of a single cell. For example, if each cell is 3000mAh, the total capacity is 3000mAh.

• Q: Can I connect multiple 4S packs in parallel?

  • A: Yes, you can connect multiple 4S packs in parallel to increase the total capacity, but ensure all packs are balanced and have the same voltage before connecting.

• Q: What is the lifespan of a 4S battery pack?

  • A: The lifespan depends on usage and charging habits but typically ranges from 300 to 500 charge cycles.