Choosing the right inverter braking resistor is essential to ensure effective braking and prevent equipment damage. The process begins with calculating the braking power and drawing an accurate braking curve. Based on this curve, you should determine the braking cycle and the required braking power. Then, select the appropriate braking resistor considering the reference voltage, resistance, and other relevant conditions.
The selected braking resistor must not be lower than the value specified in the selection manual. If it is, the inverter may be directly damaged. Always check the resistor’s rating before installation. In some cases, the braking power might be uncertain or safety could be a concern, so choosing a resistor with a higher braking capacity is advisable.
Siemens’ MM4 series braking resistors are designed for a 5% braking cycle. This means the resistor can handle 100% of the braking power for 12 seconds, followed by a cooling period of 228 seconds. It's important to note that when using these resistors, parameter P1237 should be set to the correct braking cycle, and P1240 should be set to 0 to disable the DC voltage controller.
Calculating the braking cycle can sometimes be confusing. A 5% braking cycle doesn’t mean continuous operation; it refers to the average over time. For example, if the inverter brakes for 5 seconds per minute at 50% power, the equivalent braking cycle would be around 8%. In such cases, it's generally recommended to choose a slightly larger resistor than the calculated value and adjust the braking cycle accordingly in P1237.
Here’s an example for better understanding: Suppose a 7.5 kW inverter requires 5 braking actions per minute, each lasting 2 seconds, with a braking power of 50%. Over 240 seconds (4 minutes), this equates to 40 seconds of braking time. At 50% power, this converts to 20 seconds of full power braking. Therefore, the braking cycle is approximately 20/240 = 8%. The corresponding braking power would be 625W, so a 750W resistor is chosen, and the braking cycle is set to 10% in P1237.
A simple formula to estimate the required braking resistor power is: (Braking time × number of cycles × braking power) / 60. For instance: (2 × 5 × 50%) / 60 = 7.5W. Always round up to the next available standard resistor power rating for safety and reliability.
MPPT Solar Charge Controller,MPPT Charge Controller,MPPT Solar Charger,MPPT Solar Regulator
Easun Power Technology Corp Limited , https://www.easun-power.com