Hello everyone, I am currently learning how to interpret motor contactor datasheets, and I am facing challenges in determining the DC ratings for different contactors. Most contactors in the market are geared towards 3-phase AC motors, making it difficult to find ones suitable for our application involving a safety circuit for a BLDC motor and motor controller powered by batteries. Specifically, we are working on enhancing our safety circuit, which currently utilizes a standard safety relay with a dual channel e-stop setup. This setup involves redundant pairs of high current DC contactors wired in series to disconnect power to the drive when the safety circuit is activated. The BLDC motor in question is used to move a heavy cart along rails at high speeds with e-stop actuators for quick shutdown. I am seeking advice from the community on the availability of DC-rated force-guided safety contactors that can handle up to 20A of current at 24-28VDC. I am exploring options similar to Schneider TeSys but specifically designed for DC applications. I have noticed that most hermetically sealed high current DC contactors lack NC aux. contacts, which might pose compatibility issues with relays requiring these contacts for EDM functionality. Considering the limitations with current contactors, I am also contemplating if switching to a BLDC controller that supports STO (Safe Torque Off) input would eliminate the need for these high current contactors altogether. Additionally, I am curious if having a safety circuit with STO output to the controller would still necessitate the use of contactors for power input. Any insights or suggestions on these questions would be greatly appreciated. Thank you!
Can DC rated force guided safety contactors like Schneider TeSys be used for applications requiring 20A maximum current at 24-28VDC? Yes, these contactors can be used for DC applications, but it's important to consider the varying ratings for AC vs DC. Most contactors are considered 'safety contactors' and if they have a MTTFd rating, they can be used in safety applications. The term 'force guided' indicates that if one power contact welds, the aux contact will follow suit, causing a fault detection in the safety circuit. Look for the 'force guided' symbol, which is represented by an arrow in a circle. Additionally, if a safety circuit outputs to controller STO, do you still need contactors for the power input? No, contactors are not needed in this scenario.
When it comes to safety circuits and controllers, the need for contactors in the power input depends on the desired safety rating. While some drives with integrated safety features are rated for SIL3/PLe, others are only rated for SIL2/PLd. In cases where a higher safety rating is required, an external contactor may be necessary to upgrade to SIL3/PLe. However, in practice, this additional step is rarely implemented.
mk42 inquired about drives with integrated safety ratings of SIL3/PLe. It has been some time since I last checked, but I am curious to know which drives offer SIL3/PLe capabilities on their own without the need for an additional load contactor. The drives I observed were all rated for SIL2/PLd/CAT3, so finding one that does not require an extra component would be convenient.
Joseph_e2 inquired about which safety-rated controllers support SIL3/PLe on their own, without the need for an additional load contactor. While SIL2/PLd/CAT3 has been the standard for some time, there is a growing trend towards SIL3/PLe. The latest 200 generation drives from Siemens are reported to offer this support, as well as some newer models from Kinetix and ABB. It would be convenient to eliminate the need for extra components in safety-rated systems.
That's actually valuable information to have.
Hi there! Larger DC contactors with NC aux are admittedly hard to come by, and the Schneider TeSys units are great but they might be overkill for your needs. Look into Kilovac/TE Connectivity for the hermetically sealed contactors, albeit lacking the NC aux contacts. One approach to tackle this issue could be integrating a separate NC relay into the safety circuit for the EDM functionality. As for implementing a controller that supports STO, that could simplify your setup and increase reliability. An STO-enabled controller typically contains an input for an e-stop or safety relay, which would cut power to the motor directly, hence potentially eliminating the need for high current contactors for power input. However, the need for a contactor may still exist if there are other devices on the same power line that need to be disconnected during an e-stop event. Always best to examine your specific application to determine your exact needs, of course! Hope this helps, best of luck with your project!
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Answer: - Answer: Many contactors in the market are designed for 3-phase AC motors, making it challenging to find DC-rated contactors suitable for applications like safety circuits with BLDC motors and motor controllers powered by batteries.
Answer: - Answer: The user is looking for DC-rated force-guided safety contactors that can handle up to 20A of current at 24-28VDC, similar to options like Schneider TeSys but specifically designed for DC applications.
Answer: - Answer: The user has noticed that most hermetically sealed high current DC contactors lack NC aux. contacts, which might pose compatibility issues with relays requiring these contacts for EDM functionality.
Answer: - Answer: The user is contemplating whether switching to a BLDC controller that supports STO input would eliminate the need for high current contactors in the safety circuit.
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