>> >Vasile Surducan wrote: >> > >> >> You are trying to brake a good rule of measurements: do not >> >> influence the measured value with your measurement system. >> >> When the battery is going to die, your system will be >> >> valuable like the battery itself. >> > >> >-----Original Message----- >> >From: Gerhard [mailto:piclist-bounces@mit.edu] >> >Sent: 09 August 2005 13:42 >> >To: Microcontroller discussion list - Public. >> >Subject: Re: [EE[ Re: Measurement of cell voltages within a battery >> > >> >Not necessarily... with ~24 V nominal battery voltage, it's >> >quite possible to report a critical condition of the battery >> >to a higher-order supervisor system (that's not dependent on >> >the battery) way before the battery is too weak to supply the >> >battery supervision circuit. >> > >> >So while one could say that /after/ the battery died, the >> >circuit that's powered by the battery is not worth much >> >anymore, it still is worth something (and can be worth /a >> >lot/) when the battery is still /going to die/ -- that is, >> >before it actually died. And probably even help prevent that >> >the battery in fact is going to die... >> > >> > >On 8/9/05, Michael Rigby-Jones wrote: >> >> Exactly, this is essentialy the point of any battery monitoring >> system, i.e. to let the user/other systems know how much capacity is >> remaining, not to tell them the battery is dead. >-----Original Message----- >From: Vasile Surducan [mailto:piclist-bounces@mit.edu] >Sent: 09 August 2005 20:13 >To: Microcontroller discussion list - Public. >Subject: Re: [EE[ Re: Measurement of cell voltages within a battery > >Absolutely, but this will not be possible when the measuring >system is eating the battery. As long there is no charging >system and the battery is almost gone, the measuring system >must be supplied from it's own power supply. > Vasile , Have you ever taken a laptop battery apart? It's simply not possible to power the monitoring system from it's own supply in many cases (including my own little project), hence the need to use micropower techniques to reduce parasitic current draw to a minimum. If the battery were constructed from tiny button cells I would agree that this approach is not feasible, but the cells have a capacity of several Ah, so a average continuous draw of maybe 20uA would take a couple years or so to discharge. I am also including a removable link to power down the circuit for long term storage, the only current draw will then be leakage current through the various MOSFETs that connect to the cell tappings. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. ======================================================================= -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist