In the period from 2020 to 2022, known as the "no parts available" era, there was a recommendation to use a 1756-OBV8S instead of the PointIO safety modules typically utilized. While I successfully connected the 1756-OBV8S to a servo drive safe-off through direct wiring, I encountered difficulties when attempting to activate a 24V Coil Allen-Bradley 700S emergency stop relay. The Card Output consistently faulted whenever an attempt was made to activate the relay. The issue was set aside as the relay was intended for future use, but now the need arises to replace multiple hardwired 120V relays with Safety PLC controlled 24V relays. As I delved into the AB knowledgebase, it became evident that others have faced similar challenges. One technote suggested incorporating diodes to avoid faults when connecting in Bipolar mode, although this was not applicable in my case. The card was configured for sourcing, with the output wires connected to the relay coil+ and the relay coil- wired to 24V common. Another technote implied the necessity of employing a SELV/PELV listed 24V power supply. Surprisingly, my search for a SELC power supply on the AB platform yielded no results. Additionally, a technote raised concerns about the reliability of the modules, citing incidents of False Overload Faults with OBV8S/OBV8SK in Sourcing mode. In response to this issue, a firmware update (V2.011) and Add-On Profile (V2.01) were released for 5069-OBV8S / 5069-OBV8SK modules, while a resolution for 1756-OBV8S / 1756-OBV8SK V1.011 is expected in a future firmware update. In light of these challenges, my queries to the group are as follows: 1. Has anyone successfully utilized a 1756-OBV8S card? Any insights to share? 2. Is a SELV power supply indispensable for its operation? 3. I recently acquired 700-HN123 8-pin safety relays to assist in activating the larger 700S relays, in case of a potential load issue. Has anyone else encountered this scenario? Given the delayed delivery of the 1756-OBV8s, it may have been more prudent to opt for PointIO initially.
One common issue when using a non-safe interposing relay is the loss of safety integrity. To ensure safety, I opt for the AB 700-HPS2Z24, a "Pin" style safety relay, to serve as an interposing relay. This relay is securely mounted in a 700-HN123 base for added protection.
I recently purchased 700-HPSXZ24 safety relays to use with my 700-HN123 bases. However, I am facing an issue with the compatibility of the 1756-OBV8S card with the 700S-DCP1020DZ24 relay. It seems that the card is not able to activate the relay as needed. This situation is quite frustrating as I may need to resort to using a 24Vdc safety relay instead.
Have you found a solution to this issue? Upon reviewing past designs, I encountered no issues with integrating safety contactors into this module.
When you refer to "reviewed previous designs," what exactly do you mean? A colleague recently spoke with Rockwell and found them receptive to the issue of integrating a 700S-DCP1020DZ24 relay. Without hesitation, Rockwell suggested their latest model, the 700S-EF620QJC, which features a coil with low current. This new relay could be a potential solution to the problem at hand.
In my prior designs, I utilized the low current coil version which has been a longstanding option. Upon verifying that the relay's holding current was within the module's supply capacity, I made the decision to use this particular version. I presumed that the necessary checks were also carried out for the circuit in question, facing challenges. In instances where a relay's hold current exceeds the module's capability, the most effective solution would be to opt for an interposing relay if a low current option is not accessible.
I've been working with 1756-OBV8S for a while now. In my experience, while it can be slightly trickier to set up than PointIO, it does get the job done optimally once configured correctly. Regarding SELV power supply, I've had success utilizing a regular 24V supply, though it's always safer to abide by AB's recommendations as different systems may behave differently. In response to your last query, I had a similar situation with 700-HN123 safety relays and ended up using them to buffer the load issue. Worked like a charm! In hindsight, PointIO might be convenient, but sometimes it's about working with what you have. Stick with it and you should get it sorted out.
I've had some experience with the 1756-OBV8S card, and I can tell you it's quite a versatile safety module. But they do require a bit of finesse - the SELV power supply certainly isn't indispensable, but I've found it does help with preventing false overload faults. You might be surprised about this, but I've actually powered it successfully with a commonly available 24V DC supply. I do believe the recent firmware update has resolved a lot of the issues. I haven't used the 700-HN123 8-pin safety relays myself, but if you're experiencing load issues, it might be a good workaround. And yes, in hindsight, using the readily available PointIO would have saved you some headaches. All the best with your project!
I’ve had a similar experience with the 1756-OBV8S cards. From what I've discovered, the issue often lies not so much with the need for a SELV power supply, but rather with the load characteristics of the relay being driven. The 1756-OBV8S may not be able to provide the necessary current to actuate some relays due to their inrush requirements. Your idea of using the 700-HN123 safety relays as intermediaries could be a potential solution, as they might provide the necessary buffering to prevent the 1756-OBV8S from faulting out. Lastly, with regard to the False Overload Faults, version 2.011 did improve the situation, but keep an eye on the load values to make sure you're not flirting with the card's upper limits.
It sounds like you've really done your homework on this! I can relate to the frustrations with the 1756-OBV8S—finding the right power supply and dealing with those fault issues can be a real nightmare. To your questions, yes, I have successfully used the 1756-OBV8S but only after ensuring the correct configuration and power supply setup. While a SELV power supply seems to be highly recommended, I've seen varying experiences, so it might be worth experimenting if you have a reliable one. As for using those 700-HN123 relays to activate the larger 700S relays, I think that could be a good workaround to manage the load better—definitely let us know how that goes! It's a shame about the delays; sometimes going with a proven solution like PointIO saves a lot of headaches.
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Answer: 1. Q: Has anyone successfully utilized a 1756-OBV8S card? Any insights to share? The user successfully connected the 1756-OBV8S to a servo drive safe-off through direct wiring but faced difficulties when attempting to activate a 24V Coil Allen-Bradley 700S emergency stop relay.
Answer: While a technote implied the necessity of employing a SELV/PELV listed 24V power supply, the user's search for a SELC power supply on the AB platform yielded no results.
Answer: The user acquired 700-HN123 8-pin safety relays to aid in activating larger 700S relays, potentially to address load issues.
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