Return-Path: Received: from tomcat.al.noaa.gov ([140.172.240.2] verified) by logan.com (CommuniGate Pro SMTP 4.3c2) with ESMTP id 754357 for flyrotary@lancaironline.net; Tue, 22 Feb 2005 12:23:08 -0500 Received-SPF: none receiver=logan.com; client-ip=140.172.240.2; envelope-from=bdube@al.noaa.gov Received: from PILEUS.al.noaa.gov (pileus.al.noaa.gov [140.172.241.195]) by tomcat.al.noaa.gov (8.12.0/8.12.0) with ESMTP id j1MHMMsX014469 for ; Tue, 22 Feb 2005 10:22:22 -0700 (MST) Message-Id: <5.2.1.1.0.20050222102130.056011d8@mailsrvr.al.noaa.gov> X-Sender: bdube@mailsrvr.al.noaa.gov X-Mailer: QUALCOMM Windows Eudora Version 5.2.1 Date: Tue, 22 Feb 2005 10:22:06 -0700 To: "Rotary motors in aircraft" From: Bill Dube Subject: Battery load testing (was: Amps required to run engine & amp- hours available) In-Reply-To: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed I have found that the cheapest way to load test (capacity test) a battery is with a home-made water-cooled dummy load, a voltmeter, a stop watch, and something to measure current. You can make a very effective dummy load from a short length of 1/4" stainless steel tubing, two short lengths of 1/4" copper tubing, two compression Tees, and a mop bucket. Measure the resistance of a section of the stainless tube to see how much you will need. Depending on the wall thickness, you will need between 3 inches to a foot of thin-wall to draw 25 amps from a 12 volt battery. Cut about twice the length that you need. Volts Amps = -------------------- Resistance Volts Resistance = ----------------- Amps For 25 amps, you need about 1/2 ohm. Drill through the Tees so that the stainless tubing can slide through. Slice the ferrules so that they will release and not swage. Slide the stainless tubing through both Tees and snug them up a bit more than finger tight. Connect copper tubing to each of the Tees. Drill a couple of holes in a scrap piece of wood and pass the copper tubes though those holes. Hang the stainless tubing in the center of the bucket by the copper tubes. Fill the bucket with water. With the battery fully charged, connect a voltmeter to the battery terminals. (If you are using a regular ammeter, hook it in series with the battery. If you are using a clamp-on ammeter, clamp it around ONE of the leads of the jumper cables.) Using a set of jumper cables, briefly connect the battery to the copper tubes. Read the current. Disconnect one of the jumper cables at the copper tube. Loosen and slide the Tees on the stainless tube to set the current. Once you have the current set to your desired value, start the stopwatch, connect the jumper cables, and watch the voltmeter. Note the volts and amps periodically. When the voltmeter reaches 10.5 volts, stop the test and note the time on the stopwatch. Put the battery on charge right away. Take the average of the amperage and divide it by the time and you will have the amp-hr capacity. Bill Dube http://www.killacycle.com/Lights.htm