---- START NEW MESSAGE --- Received: from cherry.ease.lsoft.com [209.119.0.109] by dpmail10.doteasy.com with ESMTP (SMTPD32-8.05) id AFBC20CE020E; Fri, 30 Jan 2004 09:09:16 -0800 Received: from PEAR.EASE.LSOFT.COM (209.119.0.19) by cherry.ease.lsoft.com (LSMTP for Digital Unix v1.1b) with SMTP id <12.00CC4FEB@cherry.ease.lsoft.com>; Fri, 30 Jan 2004 12:06:34 -0500 Received: from MITVMA.MIT.EDU by MITVMA.MIT.EDU (LISTSERV-TCP/IP release 1.8e) with spool id 1528 for PICLIST@MITVMA.MIT.EDU; Fri, 30 Jan 2004 12:06:28 -0500 Received: from MITVMA (NJE origin SMTP@MITVMA) by MITVMA.MIT.EDU (LMail V1.2d/1.8d) with BSMTP id 3569; Fri, 30 Jan 2004 12:04:29 -0500 Received: from balin.rl.ac.uk [130.246.135.155] by mitvma.mit.edu (IBM VM SMTP Level 430) via TCP with ESMTP ; Fri, 30 Jan 2004 12:04:29 EST X-Comment: mitvma.mit.edu: Mail was sent by balin.rl.ac.uk X-RAL-MFrom: X-RAL-Connect: Received: from sstdwkiwi (sstdwkiwi.ag.rl.ac.uk [130.246.189.231]) by balin.rl.ac.uk (8.12.8/8.12.8) with SMTP id i0UH4XVL014758 for ; Fri, 30 Jan 2004 17:04:33 GMT References: <20040129215352.735cee92.sunkist@iastate.edu> <4019D786.2030107@audiovisualdevices.com.au> <20040129221837.5e45b6c4.sunkist@iastate.edu> MIME-Version: 1.0 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1106 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-CCLRC-SPAM-report: 0 : X-Scanned-By: MIMEDefang 2.39 Message-ID: <017901c3e753$20b8a720$e7bdf682@space.rl.ac.uk> Date: Fri, 30 Jan 2004 17:04:31 -0000 Reply-To: pic microcontroller discussion list Sender: pic microcontroller discussion list From: "Alan B. Pearce" Subject: Re: [EE]: High current PCB To: PICLIST@MITVMA.MIT.EDU Precedence: list X-RCPT-TO: Status: U X-UIDL: 371856529 >> Probably not what you want to hear but... >> Why can't he just use a really heavy duty switch? >> David... > >He would like to use the high-power MOSFETs so that he doesn't have to deal with >arcing destroying the contacts of the switch. When the 2 batteries are >connected in parallel, there will likely be a big current flow. > >Also, many of the automotive battery cutoff switches are only rated for a a >couple hundred amps. OK lets run a couple of bits first. two batteries in vehicle. Often done by ham radio people, emergency vehicle fleets, and others (such as camper vans) where there is a possible long term high current load, but they still want to start the vehicle with an emergency battery. So the system is normally set up so both batteries charge, but are isolated through diodes. OK having got to a point where both batteries will always get charged once the vehicle is running, without switching anything over, why not just have two starter solenoids? Have a change over switch to select which one will power the starter, but set up so that you cannot (easily) have both operate together. This way only one battery gets connected to the starter at once. If necessary the other can get switched in. If things are really bad then maybe have an emergency state that allows both to operate together, but require some gymnastics on the part of the driver to enable this state so it cannot be done as a normal provision. case of the KISS principle. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body .