SANYOU Relay NO & NC Current Specifications - Page 1
Forum section: electronics / beginners

author: 2X
author_rank: Frequent Contributor
timestamp: February 25, 2024, 02:18:57 pm
content: Hello, I have the relay (SRU-S112L) on the attached image and I can't understand what means the Ampere values on the red box. It means that at 240VAC or 24VDC between common and NO contact can pass 10A current and between common and NC contact can pass 5A current? But why in NO contact can pass bigger current? I haven't seen something like this before.I have seen something like this in orange box where declares that at 120VAC can pass 15Amax (on both VC & NO contacts), at 240VAC can pass 10Amax and at 24VDC can pass 10Amax.Relay Datasheet:https://www.mpja.com/download/sru-s-112l.pdf

author: Zero999
author_rank: Super Contributor
timestamp: February 25, 2024, 02:50:46 pm
content: I haven't seen a relay like that, with different ratings for the normally closed vs open contacts. No mention of it is made on the datasheet. The marking is probably wrong. It's rated to 15A at 120VAC, or 10A at 24VDC or 240VAC.It's very common for parts to have a lower DC current rating, because a DC arc is more difficult to break, as the current doesn't pass through zero 100 to 120 times per second.

author: keymaster
author_rank: Regular Contributor
timestamp: February 25, 2024, 05:28:21 pm
content: the reason is contact pressure . In one state ,the contact pressure depends from the force of the springe and the other state , is depending from the much higher force of the electromagnet. me guess.

author: wraper
author_rank: Unknown
timestamp: February 25, 2024, 05:44:45 pm
content: Quote from: keymaster on February 25, 2024, 05:28:21 pmI would not count on that. Contacts can be of a significantly different size.

author: 2X
author_rank: Frequent Contributor
timestamp: July 18, 2025, 07:43:54 pm
content: Google AI 1st:https://www.google.com/search?q=relay+NO+contact+higher+current+than+NC&sca_esv=369e25cd873469d4&sxsrf=AE3TifOV5qKULePhuFa8KOrIhF2lF2W5Dw%3A1752868184031&ei=WKV6aM7ZAbON7NYPmqG6gQM&ved=0ahUKEwjO5cnrlseOAxWzBtsEHZqQLjAQ4dUDCBA&uact=5&oq=relay+NO+contact+higher+current+than+NC&gs_lp=Egxnd3Mtd2l6LXNlcnAiJ3JlbGF5IE5PIGNvbnRhY3QgaGlnaGVyIGN1cnJlbnQgdGhhbiBOQzIIEAAYgAQYogQyCBAAGIAEGKIEMgUQABjvBUj1D1C-C1i-C3ACeAGQAQCYAf4BoAH-AaoBAzItMbgBA8gBAPgBAZgCA6AChALCAgoQABiwAxjWBBhHmAMAiAYBkAYIkgcFMi4wLjGgB5oCsgcDMi0xuAeAAsIHAzAuM8gHBQ&sclient=gws-wiz-serpGoogle AI 2nd:https://www.google.com/search?q=relay+normally+open+higher+carrent+thank+normally+colse&sca_esv=369e25cd873469d4&sxsrf=AE3TifPj7D3XsUbuAGhgkF2yCV-9ABY0pQ%3A1752867458143&ei=gqJ6aIi-CJmFxc8PuofQ4Q8&ved=0ahUKEwiIh7mRlMeOAxWZQvEDHboDNPwQ4dUDCBA&uact=5&oq=relay+normally+open+higher+carrent+thank+normally+colse&gs_lp=Egxnd3Mtd2l6LXNlcnAiN3JlbGF5IG5vcm1hbGx5IG9wZW4gaGlnaGVyIGNhcnJlbnQgdGhhbmsgbm9ybWFsbHkgY29sc2UyChAjGLACGLADGCcyChAjGLACGLADGCdI0QdQugZYugZwAngAkAEBmAGZAaABmQGqAQMwLjG4AQPIAQD4AQGYAgKgAgSYAwDiAwUSATEgQIgGAZAGApIHATKgB9QJsgcAuAcAwgcDMC4yyAcD&sclient=gws-wiz-serpSo maybe the reason for higher current on the NO contact is the bigger gap between the COM and NO that the gap between NC and COM.I can't find any clear answer.. half opinions are the contact pressure and half the gap between contacts.If any have a documented answer please tell me.

author: indeterminate
author_rank: Regular Contributor
timestamp: July 19, 2025, 06:46:59 am
content: Its a bit of the case of all the above and the manufacture being very optimistic with there specifications.The relay has an operating time of 15 msec and a release time of 5 msecso to break the contacts on the NC set takes 15 msecand to break the contacts on the NO set takes 5 msecThe extra 10 msec of opening time for the NC contacts is going to radically shorten the life of the contacts due to arcingafter all its only rated at 4a for an inductive load.I think you would find your big brand name relay manufactures would only rate the relay at ~2ATheirs no way i would mount this in a PCB and pass 15A through a 1mm dia pin and expect it to have a long life

author: Gyro
author_rank: Super Contributor
timestamp: July 19, 2025, 09:13:03 am
content: Quote from: 2X on July 18, 2025, 07:43:54 pmHow on earth can the NO and NC contact gaps be different? You have two fixed contacts at, well, fixed locations, and a moving contact of constant thickness moving between them. Where does the difference in gaps come from and disappear to?The difference is down to different contact pressures and close / release time.

author: 2X
author_rank: Frequent Contributor
timestamp: July 19, 2025, 11:29:43 am
content: Quote from: indeterminate on July 19, 2025, 06:46:59 amI about theoperating timeI understand that because the electomagnet is a coil it needs some time for the current to reach tne maximum value and create a strong magnetic field in order to pull the armature from NC to NO contact.About therelease timeis smaller because when the current from the relay it stops instantaneously it creates a "quick" overvoltage spike and deenergized more quickly (VL = L (di/dt)) and for this reason the release time is smaller than the operating time.My query is that if we put parallel with the relay a diode (like on the below image) in order to avoid this overvoltage spike the release time gets bigger and it is not the same on the datasheet? Maybe now with the freewheel diode the release time is bigger than the operating time?Image Source:https://www.eleccircuit.com/drive-relay-by-digital-circuit/

author: Zero999
author_rank: Super Contributor
timestamp: July 19, 2025, 11:50:28 am
content: Quote from: 2X on July 19, 2025, 11:29:43 amA freewheeling diode will increase the release time of the relay contacts, because it will take longer for the current in the coil to fall below the release current.Relays have hysteresis. The voltage required to activate the relay is always higher than the release voltage. It's not surprising it takes longer to release than activate, with the freewheel diode.

author: tooki
author_rank: Super Contributor
timestamp: July 19, 2025, 12:00:49 pm
content: Quote from: Gyro on July 19, 2025, 09:13:03 amWell, on many relays the “fixed” contactsaren’tphysically fixed, but are on flexible leaf springs. I could see how this could result in the NO spring being deflected by the moving contact when energized, for example. (Not that I disagree with your assessment that the difference actually comes down to the different close/release times.)

author: tooki
author_rank: Super Contributor
timestamp: July 19, 2025, 12:06:29 pm
content: Quote from: 2X on July 18, 2025, 07:43:54 pmPlease don’t do this.Aside from the fact that AI answers are of low quality and thus IMHO functionally useless, when you post a link to a Google search, it’s not sharing that specific “state” of the results, it just performs the search anew. So whatever resultsyousaw, they aren’t necessarily the same resultsIwill see, because of various factors Google takes into consideration.So if you absolutely require someone to see particular search results, you must copy the actual results (the AI text result itself, if you absolutely must torture us; or the links to particular web pages). But I would love to see people completely stop ever posting “well here’s what Google AI/ChatGPT says…” as I consider that to be nothing but pollution.

author: tooki
author_rank: Super Contributor
timestamp: July 19, 2025, 12:19:01 pm
content: Quote from: 2X on February 25, 2024, 02:18:57 pmTake a look at this very different datasheet fromSanyou Canada:https://www.sanyourelay.ca/public/products/pdf/SRU.pdf.The NO/NC ratings on your relay correspond to the UL/CSA ratings, see screenshot.

author: MrAl
author_rank: Super Contributor
timestamp: July 19, 2025, 01:11:26 pm
content: Quote from: 2X on February 25, 2024, 02:18:57 pmHi,Before anything else, it is always wise to consider the rating of a relay as a rating that is twice what it really should be. If it's rated for 10 amps, then go with 5 amps max for example.You don't know how many times I've seen a relay stuck and the cost to repair can be high if you have to call a repair technician. That's because relays are misunderstood when it comes to the contact ratings. If you go with 1/2 the rated current, the relay will last a long time.One reason for the difference in contact rating could be that when the contacts close they can close very fast, but when they open, it depends on the external circuit impedance. With a low impedance to discharge the coil, it will take longer to open the contacts, but it's not just a single time value it's a time span. The contacts start to open but they open slowly, which means the gap opens more slowly than when the contacts close and they close more rapidly.