For several years, I have been focused on designing winder systems utilizing AC induction motors and PowerFlex 755 drives equipped with braking resistors rated at 110% of their power capacity. This setup stems from what I perceive as an overly robust layout. However, I'm beginning to question the necessity of such large braking resistors, as I have observed that on every unit I've constructed, the resistors typically remain close to ambient temperature. To enhance the efficiency of these systems, I am exploring effective methods for measuring the actual usage of the braking resistors. Given their operational characteristics, I am uncertain of the best approach for this measurement. I understand that the DC bus is pulsed to the braking resistor, which leads me to consider measuring the voltage across those lines. Nevertheless, I am concerned about whether I can capture and log data quickly enough over a significant period. If you have any suggestions or ideas regarding how to accurately assess braking resistor performance within winder systems, I would greatly appreciate your input. Thank you!
Is your system equipped with a controlled emergency stop (e-stop)? If that’s the case, it's crucial to ensure that it can stop the entire load swiftly in the event of an e-stop scenario before you proceed to decrease the braking power.
You've already found the answer to your question—simply take the temperature measurement.
Approximately a year ago, I reached out to AB's Tech Connect regarding monitoring database usage, and here’s what they shared with me: "To determine whether the brake is currently engaged or released, you can refer to Parameter 935, bit 20. For tracking power consumption, utilize Test Point 676 to calculate the dynamic brake resistor’s power (which is derived from volts multiplied by amps over a specified interrupt period). By entering the value 676 into Parameter 970 [test point selection 1], the resulting calculated power will be recorded in Parameters 971 and 972.” This approach proved effective for my needs. Additionally, once you have extracted data at the parameter level, there are multiple ways to log this information. I have successfully implemented the aforementioned method using third-party trending software as well as leveraging AB's native trending tools. Furthermore, I connected it to one of the analog outputs on an I/O option board and set up a voltmeter to visually monitor the performance while I tested the equipment. By using these techniques, you can optimize your data collection and analysis, making it easier to track your system’s performance effectively.
Consider implementing a line regeneration drive to completely eliminate the need for resistors. This innovative solution ensures you achieve 100% regenerative braking efficiency at all times, allowing excess energy to be utilized by other equipment. E-stop mechanisms operate differently; they require the drive to enter a safe mode or disconnect the motor leads. In either case, the motor will gradually coast to a stop. It is acceptable to have a brief time delay when activating the E-stop function, allowing for rapid deceleration using the drive. Once the motor has come to a halt, the drive can be switched to safe mode, a process that typically takes just a few seconds. Many safety relays are equipped with built-in timers designed specifically for this purpose.
It sounds like you're on the right track questioning the robustness of your braking resistor setup! To measure the actual usage effectively, consider using a combination of a high-speed data logger with a voltage and current sensor across the braking resistor—it can help you capture transient events without missing any quick spikes or fluctuations. Additionally, utilizing software that can analyze the data in real-time might give you better insights into how often the resistors are engaged and under what conditions. Lastly, don't forget to check if your drive system has built-in monitoring capabilities; it could provide valuable metrics without requiring additional hardware. Good luck with your project!
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