Searching to replace DIN relays - Page 1
Forum section: electronics / beginners

author: Yddet
author_rank: Newbie
timestamp: June 10, 2020, 01:36:49 pm
content: Hello,I want to replace physical relays mounted on DIN rails and would like the same functions for through holes components. I have trouble finding IC's doing the same simple job. I found some components close to what I need but not quite.On the PCB there is are 24V and 5V suppliesFirst relays are four FINDER 40.52https://docs.rs-online.com/41ea/0900766b816bcbd5.pdffour 24V powered relays with 2 NO contacts each for 5V signals ;<50mAI have found the CD4066B which is a CMOS Quad Bilateral Switch but I can't supply it with 24V. However I could connect VDD to the 5V to switch a 5V signal. Is it correct ?While writing this message I realise I was completely focused on finding an IC. But I could continue to use the FINDER 40.52 without the DIN socket mount and solder on the PCB... Probably not the cheapest solution as each relay is >5€ and I need four of them.Second relay is the PHOENIX CONTACT PSR-SCP- 24UC/URM/5X1/2X2 - 2963747https://www.phoenixcontact.com/online/portal/gb?uri=pxc-oc-itemdetail:pid=2963747&library=gben&tab=124V powered relay with 5 NO contacts for 24V signals, <50mAIs there a chip able to switch 5 contacts with one or more control input ? The CD4066B could work but it does not work with voltages higher than 20 volts.I could probably use 5 NPN transistors but there must be a solution in one package that I don't find.I've searched on Digikey and Mouser. But I suppose my key words and filters aren't the best.Thank you for any recommandation, comment, explanationYddet

author: Ian.M
author_rank: Super Contributor
timestamp: June 10, 2020, 01:59:17 pm
content: No, there is no general IC replacement for multipole electromagnetic relays. CMOS analog switches are limited to switching voltages between their supply rails, and even the best ones have much higher on resistance, and significantly higher leakage when off. PhotoMOS optoisolaters come the closest, as their output side is bidirectional (with respect to load current) and fully isolated, but typically are SPST. For AC applications a TRIAC output optocoupler may be suitable, driving the gate of a power TRIAC, but again they are SPST, so for five independent signals, you'd need 5x the whole circuit.For some types of optocoupler, you can get multiple optocouplers in the same package (typically x2 or x4), but you'll need to check the specific datasheet *VERY* carefully for channel to channel isolation, as the isolation between channels on either the input or output side may well be *FAR* less than the 'headline' rated input to output isolation voltage.

author: wraper
author_rank: Unknown
timestamp: June 10, 2020, 02:12:18 pm
content: You cannot simply do a drop-in replacement of a relay with something else. If you want to get rid of relays, you need to redesign a circuit so it does the same job differently. The closest to general replacement would be SSR (solid state relay) but again, they are not a drop-in replacement. You need to consider if they are appropriate for particular use.

author: wraper
author_rank: Unknown
timestamp: June 10, 2020, 02:24:35 pm
content: QuoteIf switched signals are what you state, you don't need such powerful relay. Subminiature relays are much more appropriate. Say you could use two of these instead:https://www.tme.eu/en/details/az952-1c-24dse/miniature-electromagnetic-relays/zettler/Also you don't need to use particular Finder relay. Say you could get similar Omron relays for around EUR 1.5-1.8 at low quantities. Or for half of that if from less reputable brand.

author: Yddet
author_rank: Newbie
timestamp: June 10, 2020, 03:42:31 pm
content: Thank you both for the comments.I will head towards subminiature relays. We have OMRON G5V-2 in stock, I think it is the equivalent of the ZETTLER relay Wraper suggested with a DPDT configuration .https://omronfs.omron.com/en_US/ecb/products/pdf/en-g5v_2.pdfI will use a flylback diode in parallel of each relay.At the end of the datasheet of the G5V-2 :QuoteDoes that mean the NO contacts could stay permanently closed after some time ?What does a fail-safe circuit consist of ?

author: WattsThat
author_rank: Frequent Contributor
timestamp: June 10, 2020, 05:07:08 pm
content: No, it is saying the opposite. A film building up on unused contacts becomes an insulator which leads to the “unstable contacts”. This is very common in cases where very low current loads are being switched because there is no arcing when the contacts make which tends to burn through any oxides or crap that is deposited on the contacts. If you are switching logic level signals with mechanical relays, the contacts should be specifically rated for the very low currents. Welded contacts are a result of over-current and high switching rates.A fail safe circuit is one that one that is tolerant of a failed relay, that is nothing bad happens should the relay fail. Every case is unique and specific to how the relay is used and it’s purpose.It would be very helpful if you could tell us what is being switched and if both the n/o and n/c contacts are being used in the circuit. As it stands, you’re forcing people to make assumptions about what you’re doing to provide answers. The quality of the answers you get is proportional to the quality of the question and so far, we are working with very limited information about your application.

author: Yddet
author_rank: Newbie
timestamp: June 11, 2020, 09:06:31 am
content: Thank you for the technical explanation, it makes sense.I attach the schematic for the DIN relaysOnly the n/o contacts are used. SIMS_SHDNWC_FLSW, EM_THSW, PSW_CTRL and SIMS_SHDN are n/o contacts located on several other PCBs or safety switches (flow / thermoswitch)The four relays FINDER (K4 to K7) switch the 5v for four digital inputs of an acquisition board. The contacts in series connected to EMPS_EN are then connected to the enable pins of a power supply. Unfortunately neither the datasheet nor the user manual specifies the signal used (if any).The PHOENIX CONTACT relay switches the 24V supply of G5V1 subminiature relays on other electronic boards.Is there a better section of the forum to ask for a review of the schematic I will design ?