X-Authentication-Warning: delorie.com: mail set sender to geda-user-bounces using -f X-Recipient: geda-user AT delorie DOT com X-Original-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=earthlink.net; s=dk12062016; t=1579116315; bh=t3xvlM0lKP7xHVlrfyUWhJIUWO1YtyPG3Tut DNiehgU=; h=Received:From:Subject:To:References:Organization: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To:Content-Type: Content-Language:Content-Transfer-Encoding:X-ELNK-Trace: X-Originating-IP; b=Zqvn4sbBwsCoVk5FxxKlRHYxpShI0RsmBRkuiZR3NIl2IT WLnJxavkUeSGwL8gHcUyfao0BIRiIC+Rp7Gsxp2/HOOrQLws2Db0qL7JODz8I2wGWwi Us7gObyjCmt4bUO8fHNcHk1pK4Dl1/mIgcgp2Z0g5CksdCjbXhVJNMYwjCHWaJXTNVm eZRg5TUsJT3zH/cTPATQzVra7Y2MeVMZxdgZdNdXUYJDKowuH8abrkx1Zq+8I92cyd7 L86QAahvcAlOF+qXEzDgZSB7BtLQjlqA6qk8XJUQntm0oXVIeumlbZIozJ2gVJYKDw8 LNI6rqz/NWJNMue4gDC8z44zuDBQ== DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=dk12062016; d=earthlink.net; b=qs4/4Gpbey/CMoHg/2xEfTtcwJP11uPBSY3Tsf4fsvMIAR2bPKk40ZjfqxLq93JHPsaZ9+G5whiYkMYCEA73a8zbjvLK2+wdAvf89GvnuavlTx9EmewuerxSogAaaLZMhxKFvawmmo2g35OrZDPz23ilZwbUBSACvp/SATxtu3WVNyPVDKkS43+KkbltnUteFH2pl1/n4Kvf+GycRbn7OMlOIh64JVJv7irNi9yk7htWcm2+pbQipxwQmnLt2SGWkEzV6I6Qa55f4QggxD8+fblin9VZmqpOAbTqn5WmyuWq0JQicDBPtCBjbECgncvwDwQAabH41rAq72NpnigJdw==; h=Received:From:Subject:To:References:Organization:Message-ID:Date:User-Agent:MIME-Version:In-Reply-To:Content-Type:Content-Language:Content-Transfer-Encoding:X-ELNK-Trace:X-Originating-IP; From: "David W. Schultz (david DOT schultz AT earthlink DOT net) [via geda-user AT delorie DOT com]" Subject: Re: [geda-user] Maximum current for thermals? To: geda-user AT delorie DOT com References: <5244f7b5-c5d7-33ec-cd8a-c16d0595d7bb AT linetec DOT nl> Organization: State of Total Disorganization Message-ID: <68ca3760-0748-1934-816e-4f67f8570ff3@earthlink.net> Date: Wed, 15 Jan 2020 13:24:39 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <5244f7b5-c5d7-33ec-cd8a-c16d0595d7bb@linetec.nl> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-ELNK-Trace: a4aefb9622f3b04c5fcedd19d8a1076574bf435c0eb9d478262a2c92633e336ee24d7a27a337d36719b153157e48feae350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 108.194.108.75 Reply-To: geda-user AT delorie DOT com Errors-To: nobody AT delorie DOT com X-Mailing-List: geda-user AT delorie DOT com X-Unsubscribes-To: listserv AT delorie DOT com Precedence: bulk On 1/15/20 9:47 AM, Richard Rasker (rasker AT linetec DOT nl) [via geda-user AT delorie DOT com] wrote: > Still, I wonder what the approximate current capacity of these thermals > is? I know from experience that a few amps is no problem at all, but I'm > pretty certain that they'll fail upwards of 25A or so. If possible, I > prefer thermals for easier soldering, so a more accurate estimate of the > limits would be appreciated. > Tis a complicated question. This might help: https://www.amazon.com/PCB-Trace-Via-Currents-Temperatures/dp/1530389437 Too rich given my level of curiosity. A paper by that books author that I found discusses fusing current. t = 0.0346 * (A/I)^2 where A is area in square mils. Looking at a TO-220 thermal I see a flared trace but the center is about 20 mils so that is the starting point. Assuming 1 second then I is about 5A. Since I have both top and bottom pours that gives 8 connections and a limit of about 40A. But that equation ignores all heat loss. With a short trace connected to a large area of copper and the device lead this is a lot. So fusing current should be way more than 40A. -- https://web.archive.org/web/20190214181851/http://home.earthlink.net/~david.schultz/ (Web pages available only at the Wayback Machine because Earthlink terminated that service.)