Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/17/84; site hao.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!hao!hull From: hull@hao.UUCP (Howard Hull) Newsgroups: net.consumers,net.physics Subject: Re: Applicability of rechargeable batteries Message-ID: <1250@hao.UUCP> Date: Sun, 11-Nov-84 12:32:53 EST Article-I.D.: hao.1250 Posted: Sun Nov 11 12:32:53 1984 Date-Received: Mon, 12-Nov-84 07:17:23 EST References: <1789@garfield.UUCP> <488@aluxe.UUCP> <392@ihu1h.UUCP> <4603@fortune.UUCP> <371@crystal.UUCP> Organization: High Altitude Obs./NCAR, Boulder CO Lines: 31 Many battery-operated devices contain *switching regulators* which make up for low supply-side voltage by drawing more current. This is in accordance with the formula: Power at the Load = Source Voltage X Source Current Since, for any given instance of a fixed load power, the source voltage will slowly decrease as the battery discharges, the source current will gradually rise. At some point, the source current will increase rapidly and then become so great as to exceed the maximum current specification of the regulator parts and the regulator will burn out. Some manufacturers protect such regulators by means of a fuse; however, replacing the fuse every time the battery gets too low is inconvenient for most consumers. Using a low-value resistor in place of the fuse is another technique, but that makes the regulator inefficient - and efficiency is the primary reason for using a switching regulator in the first place. Instead, most manufacturers prefer to rely on the discharge characteristics of the carbon-zinc battery. For such batteries, the resistance is low during most of the battery life, but increases under heavy current draw - and does so to a much greater extent at the end of battery life. With Nicad batteries, resistance is uniformly lower during most of the battery life. As has been pointed out, the voltage is uniformly lower as well. This causes a uniformly higher current draw than would be experienced for a zinc- carbon battery under the same load conditions. Then, near the end of a nicad battery's life, the voltage sluggishly rolls off while the resistance becomes only moderately higher. The switching regulator is thus subjected to a rather longer period of greater input current stress, during which time it is more vulnerable to even brief load surges. Howard Hull, HAO. > {ihnp4!stcvax | decvax!stcvax | seismo} !hao!hull