Hello everyone, We have encountered some issues with our PF 525 Inverters (25B-D024N114) 460V 11KW that are driving two 4KW motors (fans) with a Full Load Current (FLC) of 6.15A at 400V. Each motor has its own overload unit connected after the inverter output. One parameter that has been misconfigured is P39 Torque Mode, which should be set at 0 (V/HZ) instead of the current setting of 1 (SVC). Additionally, there are some puzzling parameter settings: - Motor NP OL Current P33 = 17A (default 24A) - Motor NP FLA P34 = 16A (default 18.5A) - Current Limit 1 A484 = 25.5A (default 36A) - Current Limit 2 A485 = 18.7A (default 26.4A) According to Rockwell literature and discussions on forums, it seems that P33 and P34 should remain at their default settings. The relationship between A484 and A485 in relation to P33 is unclear, especially considering that A485 does not exist in a PF520 inverter. Unfortunately, information on A484 and A485 is scarce on the Rockwell website, with only the PF520 manual providing minimal details. Any insights or explanations on these settings would be greatly appreciated. Thank you, Ian
An overload current in a drive operates similarly to a standard starter's overload. When the current exceeds the overload current, the drive will build up thermal capacity according to the trip curve before tripping at over 100% thermal capacity. On the other hand, a current limit restricts the output current to prevent exceeding a set limit. Setting the limit too low, combined with load characteristics, can cause the drive to struggle to ramp up and accelerate further, potentially leading to issues. By implementing a current limit 2 option, users can switch between different current limits using digital inputs, such as option 26 "Current Lmt2", controlled by a toggle switch or PLC digital output. By default, the active current limit is current limit 1. This setup helps prevent overload faults by keeping the current below or at the set limit.
In a forum post, ian.smith7 raised concerns about the parameter settings for PF 525 Inverters driving two 4KW motors. The motors have overload units after the inverter output, with a FLC of 6.15A at 400V. The issue lies in parameter settings such as P33 and P34, which should not be left at default values. Specifically, P33 should reflect the Motors Nameplate FLA, while P34 should be calculated as the Motors Nameplate FLA multiplied by the Service Factor (typically 1.15). Moreover, questions were raised about the purpose and function of A484 and A485 in relation to P33, as well as the absence of A485 in PF520 models. Despite efforts to find information on these settings on the Rockwell website, ian.smith7 has not been successful. Any insights or guidance on optimizing these parameters would be greatly appreciated. Thank you for your help. - Ian.
Hello Imscar, thank you for your informative response. Rob, I appreciate your insight as well. I'm curious, why is it necessary to set P33 & P34 to match the motor nameplate value? In a scenario where two motors are connected through external overload trip units, should the values be multiplied by x1 or x2? If the answer is x1, what is the reason for this? Thank you, Ian.
Ian Smith7 inquired about why P33 & P34 should be set to the motor nameplate value. Specifically, he asked if when two motors are connected through external overload trips units, should the value be x1 or x2. The answer is, if the motors have reliable separate overloads external to the VFD, you can set the motor OL current to a high number greater than the sum of the two motors' nameplate FLAs. This ensures the appropriate protection for the motors.
lmscar12 mentioned that if the motors are equipped with reliable separate overloads outside of the Variable Frequency Drive (VFD), the motor overload current can be set to a higher number than the combined Full Load Amps (FLAs) of the two motors. This is why P33 & P34 are left at default settings, allowing A484 & A485 to safeguard the VSD from overcurrent.
Hey Ian, I'm no expert, but I've had a bit of experience dealing with similar issues. I would agree that it's generally a good idea to leave P33 and P34 on their default settings. As far as the current limits (A484 and A485), they typically act as a fail-safe to prevent overloading above the setpoint. It's worth noting that these limiters don't really play a direct role in power regulation - they're more about safety. For A485 not existing in a PF520, it could very well be a specific feature for the PF525 model. I hope this helps, and I suggest reaching out to Rockwell support for a more detailed understanding. Cheers, [Your Name]
Hi Ian, It seems you've indeed come across a configuration dilemma with your inverters. While I'm not aware of the reason behind A484 and A485 parameters being set at these values, I'd take a wild guess it might be associated with some motor protection scheme or customized control logic provided by the system integrator. However, you're right about P33 and P34. As both relate to motor protection, their default values are set according to the motor datasheets, so that under most circumstances, they should remain at those settings. As for the P39 Torque Mode, yes, it needs to be reset to 0 (V/Hz) for motor fans application. SVC is for sensorless vector control, and it's usually used when precise speed control or high torque at low speed is required, which is not quite the typical case for fan motors. For A484 and A485, since the PF525 manual is inadequate, it might be fruitful if you could reach out directly to Rockwell's tech support. They often have deeper product knowledge and could clarify these specific settings. Best, [Your Name]
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Answer: - The recommended Torque Mode setting for the Power Flex 525 Inverters should be 0 (V/HZ) instead of 1 (SVC).
Answer: - According to Rockwell literature and forum discussions, it is recommended to keep P33 and P34 at their default settings.
Answer: - The Current Limit 1 (A484) and Current Limit 2 (A485) settings determine the current limits for the inverters. A484 is set at 25.5A (default 36A) and A485 at 18.7A (default 26.4A).
Answer: - The relationship between A484, A485, and P33 may be unclear due to limited information available on these settings from the Rockwell website. Additionally, it is noted that A485 does not exist in a PF520 inverter.
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