"High" current @56VDC relay. - Page 1
Forum section: electronics / projects

author: forrestc
author_rank: Unknown
timestamp: July 02, 2019, 06:13:51 am
content: I have a design which currently uses a TX2-3V relay. Has been a solid performer, but I do occasionally get feedback from customers that they'd like a bit more switching capacity at 48V/56V. The TX2-3V switches around 1A at this voltage.I've dug through all of the distributors I normally used and the only PCB mount relay I've found that is better in a meaningful way at this voltage is a G5LE, however it is mechanically too tall - I only have around 0.65" at the absolute maximum.For this application, a relay contact is the correct solution, a solid state relay has some shortcomings (including the complexity of doing a normally closed contact).I'm hoping someone on here has come across a reasonably small relay which will switch around 2A or more (is better) at 56VDC. And by reasonable sized, I mean something PCB mount and not over 0.65" tall. Of course inexpensive is a plus since we consume around 1000 of these a year.And yes, I realize I'm asking for a unicorn....

author: Zero999
author_rank: Super Contributor
timestamp: July 02, 2019, 08:43:06 am
content: According to the data sheet, it's DPDT and rated to 2A, as 30V. If you're not using both of the contacts, simply connect them in series and it should be fine at 2A, up to 60V. It's breaking the arc, which is challenging for DC and two contacts in series, will do a better job than one.https://www.mouser.co.uk/datasheet/2/315/mech_eng_tx-1075670.pdf

author: Someone
author_rank: Super Contributor
timestamp: July 03, 2019, 01:32:27 am
content: Quote from: Zero999 on July 02, 2019, 08:43:06 amIts not always that simple, relays with manufacturer ratings for series operation such as the Schrack RT2 for instance. Its possible to go the other way too and use a lower current relay with both contacts in parallel. Really needs testing on the specific load application.

author: forrestc
author_rank: Unknown
timestamp: July 03, 2019, 07:23:39 am
content: Quote from: Someone on July 03, 2019, 01:32:27 amPlus, in this application I need to expose both the normally open and normally closed contacts. Which is challenging. I've wondered about doing some odd wiring where you take the common of one pole and wire it to both "throws" of the second pole. That way the 'common' of the first pole is interrupted briefly by the switching of the second pole between the two poles, hopefully gaining you series wiring.I've actually looked at the schrack RT2, but wasn't sure about the series wiring with needing both NO and NC contacts. I tonight noticed they have a latching version available which may actually negate the need for both contacts, but it's pretty pricey.The Schrack RT2 is one of the few relays I've found which actually states the series wiring rating. At the voltage we're talking about, it's 2A for a single, but 8A for both in series. I wish that more relays were rated this way as I might find one that would work for this. Unfortunately, I'm not particularly willing to pass on a rating which I haven't had verified by a vendor, and we're small enough that asking a vendor to specify something else in their datasheet isn't likely to be result in any useful outcome.

author: Someone
author_rank: Super Contributor
timestamp: July 03, 2019, 07:31:08 am
content: Quote from: forrestc on July 03, 2019, 07:23:39 amAnother possibility to look at is a hybrid relay + SSR or roll your own on the board. Or some other similarly sturdy active arc suppression.

author: Zero999
author_rank: Super Contributor
timestamp: July 03, 2019, 08:54:10 am
content: Quote from: Someone on July 03, 2019, 01:32:27 amParallel operation to increase the current rating is generally discouraged.Series operation is generally acceptable, even if it isn't explicitly stated in the data sheet, see the document linked below:https://www.finder-relais.net/en/Finder-general-technical-information-en.pdfQuoteQuoteQuote from: forrestc on July 03, 2019, 07:23:39 amThat sounds sensible and will work, as long as it's break before make, which it will be, unless stated otherwise on the data sheet.QuoteUnfortunately it's not possible for the manufacturer to specify everything and often isn't necessary either, especially for things which are generally accepted to work, such as connecting two contacts in series to achieve higher current breaking capacities. If your anxious about it, use a relay made by finder, who explicitly state the DC current rating can be increased, by connecting contacts in series.This can be de-risked even further by conducting some experiments on the bench.EDIT:Some more information from ABBhttps://library.e.abb.com/public/2ec461ba2df91433c12578570041d719/UG03-0203E_en_Auxiliary_relays_Self-reset_and_latching.pdfAnother article:https://pdfs.semanticscholar.org/0ba8/59cc5c27befe658e693fa8cd948347fee325.pdf