Date: Sat, 29 Sep 2001 09:30:52 -0500 From: David VanHorn <[EMAIL PROTECTED]> Subject: Re: Homebrew battery packs
At 11:06 PM 9/28/01 -0700, Raymond wrote: >Date: Sat, 29 Sep 2001 13:59:37 +0800 >From: Raymond <[EMAIL PROTECTED]> >Subject: Re: Homebrew battery packs > >Hi Pres, > > >I had a 50 and never got more than 40-50 mins on the standard battery, but > >the extended gave almost 3 hours! Twice the milliamp-hour rating yet more > >than 2x the life has to do with the RATE compared to the capacity of > >withdrawal. >Umm ... OK I'm confused ... what exactly do you mean by the 'rate'? One >wouldn't have thought the Libretto would draw enough current for the >internal resistance difference of the 2 packs to have any impact ... Of >course, I guess that means the claimed '1.5-2h on standard pack, 3-4h on >extended pack' claim by Toshiba is a pile of ____ .... The rate of withdrawal. If you take energy out of a 1AH battery, at a rate of 1A, then you'll get somewhat less than 1H. You only get the nameplate AH rating if you take the energy out over 10-20H. Confusing, isn't it? :) >I'm hoping to make use of a 12 volt 3.5AH NiMH battery pack I've got lying >around (it was a pack purchased for a laptop that died a month afterwards, >its been sitting gathering dust ever since). You would be better off, to make a 15.6V pack, by adding three more cells. That way, you won't have to do the funky booster. Charge could come from an 18-24V wall-wart with appropriate current limiting resistor. >Since the extended pack is 2.4AH, I'm hoping to get a few hours runtime on >this 3.5AH pack ... if I can figure out how to charge it without blowing >it up! I'm not too concerned if the external (12 volt) battery pack won't >charge the internal (10.8 volt) battery pack (although it'd be nice if it >did) ... of course, if it DOES charge each battery individually then why >would it need 15 volts? (I was of the understanding that older laptops >needed 13-15 volts because they needed to have an input greater than the >packs they were charging which would have been all in series and charged >all together). The L does contain battery charging circuitry, but nobody I know has a schematic, so I wouldn't try to make use of it. It's designed to work with Li-Ion cells, and that's a totally different game. >I take it therefore using a constant voltage to charge NiMH packs such as >plugging it into the Libretto's 15 volt regulated supply with 4x1N4004 >diodes to drop the voltage (in the hope that once the battery pack reaches >the charge voltage it'll stop charging due to a lack of voltage gradient) >would be a dangerous way of doing things? 4.1 or 4.2V per cell, regulated within 1%. Current limited, temperature limited, time limited. Too low, less than full charge. Too high, run away. -- Dave's Engineering Page: http://www.dvanhorn.org Got a need to read Bar codes? http://www.barcodechip.com Bi-directional read of UPC-A, UPC-E, EAN-8, EAN-13, JAN, and Bookland, with two or five digit supplemental codes, in an 8 pin chip, with NO external parts. ************************************************************** http://libretto.basiclink.com - Libretto mailing list http://libretto.basiclink.com/archive - Archives http://www.picante.com/~gtaylor/portable/faq.html - FAQ -------TO UNSUBSCRIBE------- Reply to any of the list messages. The reply mail should be addressed to: [EMAIL PROTECTED] - Then replace any text on the message's subject line: cmd:unsubscribe --------TO UNSUBSCRIBE DIGEST------ Do above but with this on subject line: cmd:unsubscribe digest **************************************************************
