Prasad, Jeremy mentioned these two temps as examples, but the question is general. I think in the emails I have seen so far, only Jeremy has mentioned the 0C and 20C; no other specific temps have been mentioned.
Chuck Hursch Larkspur, CA www.geocities.com/nbeaa ----- Original Message ----- From: Prasad <[EMAIL PROTECTED]> To: ev discussion list <[EMAIL PROTECTED]> Sent: Saturday, August 17, 2002 9:36 PM Subject: Re: battery temperature vs charging voltage and amps > Just one question.....what is this cold temperature (?C) and warm > temperature (?C). Is it 0C and 20C as mentioned by Jeremy. > > Prasad > www.geocities.com/aquariangenius > > > > ----- Original Message ----- > From: "Jeremy Maus" <[EMAIL PROTECTED]> > To: <[EMAIL PROTECTED]> > Sent: Saturday, August 17, 2002 6:29 PM > Subject: RE: battery temperature vs charging voltage and amps > > > > Chuck, > > > > There are to ways a battery's characteristics change with temperature, > > voltage and internal resistance. > > > > Pb-acid batteries change their voltage -.01 V per degree C or something > like > > that. A colder battery will have higher voltage than a warmer battery. > > Also, like others have said a warmer battery has less internal resistance. > > > > So if you charge with a constant voltage charger the colder battery will > > have a lower voltage between battery and charger plus it will have a high > > internal resistance. Hence lower current. > > > > If you want the math here goes. > > V(Voltage)=I(current)*R(resistance) --> I = V/R > > Charger is 15V > > Cold battery(0C) is 12V with .016 Ohms > > Warm battery(20C) is 11.8V with .012 Ohms > > > > Current in cold battery > > 15V - 12V = 3V > > I = 3V / .016 Ohms = 187.5 Amps > > > > Current in hot battery > > 15V - 11.8V = 3.2V > > I = 3.2V / .012 Ohms = 266.7 Amps > > > > The effect of the voltage being .2V different is only about 15 Amps. Most > > of the change is the internal resistance. > > > > The warmer battery is more efficient. If charge both batteries at 30 amps > > and the warmer battery only needs 14V where the cold battery needs 15V > than > > the warmer batter is using less power to charge. 14V*30A=420W vs > > 15V*30A=450W. > > > > Regards, > > > > Jeremy Maus > > Belleville, MI > > [EMAIL PROTECTED] > > http://www.emidget.info
