Received: from PCH.mit.edu (18.7.21.50) by mail.efplus.com (192.168.0.8) with Microsoft SMTP Server (TLS) id 8.3.485.1; Wed, 4 Aug 2021 16:59:10 -0700 Received: from PCH.MIT.EDU (localhost.localdomain [127.0.0.1]) by PCH.mit.edu (8.14.7/8.12.8) with ESMTP id 174NnGmo019520; Wed, 4 Aug 2021 19:50:10 -0400 Received: from outgoing-exchange-7.mit.edu (OUTGOING-EXCHANGE-7.MIT.EDU [18.9.28.58]) by PCH.mit.edu (8.14.7/8.12.8) with ESMTP id 174NnF56019517 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL) for ; Wed, 4 Aug 2021 19:49:15 -0400 Received: from w92exedge4.exchange.mit.edu (W92EXEDGE4.EXCHANGE.MIT.EDU [18.7.73.16]) by outgoing-exchange-7.mit.edu (8.14.7/8.12.4) with ESMTP id 174NnEm1003061 for ; Wed, 4 Aug 2021 19:49:15 -0400 Received: from w92exhyb6.exchange.mit.edu (18.7.71.111) by w92exedge4.exchange.mit.edu (18.7.73.16) with Microsoft SMTP Server (TLS) id 15.0.1497.23; Wed, 4 Aug 2021 19:48:29 -0400 Received: from oc11exhyb1.exchange.mit.edu (18.9.1.60) by w92exhyb6.exchange.mit.edu (18.7.71.111) with Microsoft SMTP Server (TLS) id 15.0.1497.23; Wed, 4 Aug 2021 19:49:14 -0400 Received: from NAM02-DM3-obe.outbound.protection.outlook.com (104.47.56.46) by oc11exhyb1.exchange.mit.edu (18.9.1.60) with Microsoft SMTP Server (TLS) id 15.0.1497.23 via Frontend Transport; Wed, 4 Aug 2021 19:49:14 -0400 Received: from DM5PR2201CA0022.namprd22.prod.outlook.com (2603:10b6:4:14::32) by BN6PR01MB2596.prod.exchangelabs.com (2603:10b6:404:cd::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4394.15; Wed, 4 Aug 2021 23:49:12 +0000 Received: from DM6NAM11FT020.eop-nam11.prod.protection.outlook.com (2603:10b6:4:14:cafe::7f) by DM5PR2201CA0022.outlook.office365.com (2603:10b6:4:14::32) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4394.15 via Frontend Transport; Wed, 4 Aug 2021 23:49:11 +0000 Received: from mai.hallikainen.org (74.208.193.200) by DM6NAM11FT020.mail.protection.outlook.com (10.13.172.224) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4394.16 via Frontend Transport; Wed, 4 Aug 2021 23:49:11 +0000 Received: from mai.hallikainen.org (localhost [127.0.0.1]) by mai.hallikainen.org (8.14.4/8.14.4) with ESMTP id 174NnBlI028351 for ; Wed, 4 Aug 2021 16:49:11 -0700 Received: (from apache@localhost) by mai.hallikainen.org (8.14.4/8.14.4/Submit) id 174NnBVB028345; Wed, 4 Aug 2021 16:49:11 -0700 Received: from 70.177.184.232 (SquirrelMail authenticated user harold) by mai.hallikainen.org with HTTP; Wed, 4 Aug 2021 16:49:11 -0700 From: Harold Hallikainen To: "piclist@mit.edu" Sender: "piclist-bounces@mit.edu" Date: Wed, 4 Aug 2021 16:49:11 -0700 Subject: Re: [EE] Latching relay ratings Thread-Topic: [EE] Latching relay ratings Thread-Index: AdeJjLhdUHWdZ4LiSV6v5pCMwRnalw== Message-ID: <4d39603407c2fb7757af7b81775a1b75.squirrel@mai.hallikainen.org> References: List-Help: List-Subscribe: , List-Unsubscribe: , In-Reply-To: Reply-To: Microcontroller discussion list - Public. Accept-Language: en-US X-MS-Exchange-Organization-AuthAs: Anonymous X-MS-Exchange-Organization-AuthSource: TS500.efplus4.local X-MS-Has-Attach: X-Auto-Response-Suppress: All X-MS-Exchange-Organization-SenderIdResult: Pass X-MS-Exchange-Organization-PRD: mit.edu X-MS-TNEF-Correlator: received-spf: Pass (protection.outlook.com: domain of mai.hallikainen.org designates 74.208.193.200 as permitted sender) receiver=protection.outlook.com; client-ip=74.208.193.200; helo=mai.hallikainen.org; dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mitprod.onmicrosoft.com; s=selector2-mitprod-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=1F/IxAYR1LlzrN6VspS7HjhK8qTEO14Nch+Ejqb5nG0=; b=U5izVF4al48b8/26fNAa/Q5rd/K4DaKUF/3BlTORqe6LrwTwqpS37yzG8qh7dRjHDTKwEQRHXiXf0IyOaSbgqlQuZoCArkJyGdUJGVr2yTqZT0YUvTdIreheGVSlFX7eEF+N0oocLR8wSGg0dXU7sVUHRE5r6PygVB7h60N5ac4= authentication-results: spf=pass (sender IP is 74.208.193.200) smtp.mailfrom=mai.hallikainen.org; mit.edu; dkim=none (message not signed) header.d=none;mit.edu; dmarc=permerror action=none header.from=mai.hallikainen.org; user-agent: SquirrelMail/1.4.22-5.el6 errors-to: piclist-bounces@mit.edu list-id: "Microcontroller discussion list - Public." list-post: x-beenthere: piclist@mit.edu x-mailman-version: 2.1.6 x-authentication-warning: mai.hallikainen.org: apache set sender to harold@mai.hallikainen.org using -f x-topics: [EE] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 > I'm helping a friend out with his camper's auxiliary 12 volt power, and > I'd like to set up an automatic low battery disconnect. His solar > controller has a low battery voltage dry contact output but it's rated fo= r > only 0.5A. I know I could just connect a 40 Amp automotive relay to that, > but then there'd be a constant 120 milliamp drain until the battery > disconnected. So I am thinking of using a high current latching relay and > some logic. But all the affordable latching relays, such as this 120 Amp > Omron G9TB-K1ATW-E DC12 are rated for AC only. I'm assuming it's because > high DC current could cause the relay to unlatch due to electromagnetism, > and running 12VDC at 30 Amps through the 277VAC 120A contacts isn't reall= y > going to be a problem. Or am I wrong? > > Bob Most (all?) fuses, switches, and relays have much lower voltage ratings for DC than for AC. With AC, zero crossing suppresses the arc that is formed as the contacts open. With DC, the arc continues until the contact are farther than the arc can be sustained. It's interesting that the datasheet does not seem to even consider switching DC. Harold --=20 FCC Rules Updated Daily at http://www.hallikainen.com Not sent from an iPhone. --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .