LEAD ACID BATTERY
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From: RHRRC on 2 Apr 2006 11:13 budgie wrote: > On 1 Apr 2006 04:10:42 -0800, "RHRRC" <h.lewis(a)connect-2.co.uk> wrote: > > > > >budgie wrote: > >> On 31 Mar 2006 13:26:58 -0800, "RHRRC" <h.lewis(a)connect-2.co.uk> wrote: > >> > >> (snip good stuff > >> > >> >'C' is merely a short-hand way to refer to the capacity of a battery at > >> >its declared (20hr) discharge rate. > >> > >> Sorry, couldn't let that one go through to the keeper. > >> > >> 'C' refers to the capacity of the battery at the rate that (superficially) is > >> the one-hour rate. > >> > >> i.e. the 13Ah battery's 'C' is 13A. > >> > ><snipped> > > > >Sorry to say you are in error. > > > >The nominal 'C-rate' of a 13Ah battery is 13amps. > > > >As previously stated 'C' is a capacity - not a current - that is why C > >is used rather than A or I! > > > FFS what extreme pedantry. "C" vs "C-rate" indeed. Just ahve a quick look at > the usage of 'C' in describing charge rates. You'll be scratching to find many > references to 'C-rate'. > > And your line: " 'C' is merely a short-hand way to refer to the capacity of a > battery at its declared (20hr) discharge rate." was so wonderfully precise? > You obviously do not understand that, for example the origional posters 13Ah Pb-acid battery, when discharged at 13amps will not last for 1 hour. When discharged at any rate other than C/20 it will not provide 13Ah! Since a batteries available capacity is a function of its discharge rate some form of standardisation is required to be able to readily quantify different batteries. IEC, EN, JA, etc,etc, have standardised a methodolgy which, for rechargeable lead acid batteries, is the quantity 'C' defined as the available Ah obtained when the battery is discharged at a rate that causes the battery to reach the given (end) terminal voltage in 20 hrs This seems to work for most which is perhaps why its is a worldwide standard and is adopted by *every* significant battery manufacturer. For interest the rate for NiCd is C/5. If you have another methodology that you think is advantageousnby all means advocate its use please do not use the symbol 'C' as this is already used by the battery fraternity. How do you intend to measure battery capacity? > Review your other line: "The nominal 'C-rate' of a 13Ah battery is 13amps." > > Try reading the two in conjunction.
From: budgie on 2 Apr 2006 21:20 On 2 Apr 2006 08:13:20 -0700, "RHRRC" <h.lewis(a)connect-2.co.uk> wrote: > >budgie wrote: > >> On 1 Apr 2006 04:10:42 -0800, "RHRRC" <h.lewis(a)connect-2.co.uk> wrote: >> >> > >> >budgie wrote: >> >> On 31 Mar 2006 13:26:58 -0800, "RHRRC" <h.lewis(a)connect-2.co.uk> wrote: >> >> >> >> (snip good stuff >> >> >> >> >'C' is merely a short-hand way to refer to the capacity of a battery at >> >> >its declared (20hr) discharge rate. >> >> >> >> Sorry, couldn't let that one go through to the keeper. >> >> >> >> 'C' refers to the capacity of the battery at the rate that (superficially) is >> >> the one-hour rate. >> >> >> >> i.e. the 13Ah battery's 'C' is 13A. >> >> >> ><snipped> >> > >> >Sorry to say you are in error. >> > >> >The nominal 'C-rate' of a 13Ah battery is 13amps. >> > >> >As previously stated 'C' is a capacity - not a current - that is why C >> >is used rather than A or I! >> >> >> FFS what extreme pedantry. "C" vs "C-rate" indeed. Just ahve a quick look at >> the usage of 'C' in describing charge rates. You'll be scratching to find many >> references to 'C-rate'. >> >> And your line: " 'C' is merely a short-hand way to refer to the capacity of a >> battery at its declared (20hr) discharge rate." was so wonderfully precise? >> > >You obviously do not understand that, for example the origional posters >13Ah Pb-acid battery, when discharged at 13amps will not last for 1 >hour. I most certainly do. >When discharged at any rate other than C/20 it will not provide 13Ah! Indeed. it may be more, or less, depending on whether the rate is less, or more. Kid stuff. >Since a batteries available capacity is a function of its discharge >rate some form of standardisation is required to be able to readily >quantify different batteries. > >IEC, EN, JA, etc,etc, have standardised a methodolgy which, for >rechargeable lead acid batteries, is the quantity 'C' defined as the >available Ah obtained when the battery is discharged at a rate that >causes the battery to reach the given (end) terminal voltage in 20 hrs > >This seems to work for most which is perhaps why its is a worldwide >standard and is adopted by *every* significant battery manufacturer. It actually isn't a worldwide standard. it is widespread practice, but we have worked with a large number of cells where the "default" rating time was 10 hours. >For interest the rate for NiCd is C/5. That isn't a standard either. >If you have another methodology that you think is advantageousnby all >means advocate its use please do not use the symbol 'C' as this is >already used by the battery fraternity. > >How do you intend to measure battery capacity? I was commenting on the pedantry in your post, seemingly objecting to 'C' vs 'C-rate'. I do understand 'C' and its purpose/role TUVM. >> Review your other line: "The nominal 'C-rate' of a 13Ah battery is 13amps." >> >> Try reading the two in conjunction. Apaprently you haven't.
From: Robert Baer on 3 Apr 2006 11:46 budgie wrote: > On Sat, 01 Apr 2006 08:44:01 GMT, Robert Baer <robertbaer(a)earthlink.net> wrote: > > >>budgie wrote: >> >> >>>On Sat, 01 Apr 2006 08:47:10 +0800, budgie <me(a)privacy.net> wrote: >>> >>> >>> >>>>and as the O/P's required current is 700mA the redcution in performance would be >>>>absolutely marginal, giving his target of 12 hours almost spot-on. >>> >>> >>> >>>Aaarrrggghh! My turn to stuff up! Ignore that line, >>> >>>Particularly if the O/P really meant: >>> >>>" I have to design a voltage source ( +/- 18volts, 13A )" > > >> So? Use of three 6V batteries in series gives 18V. > > > You totally missed the point. 13A? or 700mA? 13A i believe was the batttery rating, and 700mA was the maximum proposed load..
From: John Fields on 3 Apr 2006 14:26 On Mon, 03 Apr 2006 15:46:21 GMT, Robert Baer <robertbaer(a)earthlink.net> wrote: >budgie wrote: >> You totally missed the point. 13A? or 700mA? > 13A i believe was the batttery rating, and 700mA was the maximum >proposed load.. --- 13A has nothing to do with it. The _capacity_ of the battery is 13AH (ampere-hours) at a 20hour rate, which means the voltage at the initially fully charged battery's terminals will fall to 5.25V when a constant current of 13AH ------ = 0.65A 20H is drawn from the battery, continuously, for a period of 20 hours. -- John Fields Professional Circuit Designer
From: RHRRC on 3 Apr 2006 14:29
budgie wrote: > On 2 Apr 2006 08:13:20 -0700, "RHRRC" <h.lewis(a)connect-2.co.uk> wrote: > > > > >budgie wrote: <snipped> > >If you have another methodology that you think is advantageousnby all > >means advocate its use please do not use the symbol 'C' as this is > >already used by the battery fraternity. > > > >How do you intend to measure battery capacity? > > I was commenting on the pedantry in your post, seemingly objecting to 'C' vs > 'C-rate'. I do understand 'C' and its purpose/role TUVM. > > > >> Review your other line: "The nominal 'C-rate' of a 13Ah battery is 13amps." > >> > >> Try reading the two in conjunction. > > Apaprently you haven't. I am glad that you understand what 'C' represets. Using some data to hand a discharge of a typical 13Ah sla battery at its nominal C-rate would be a disharge at 13A. However a discharge of a typical 13Ah sla battery at the C rate would be a disharge at 7.8 amps (Yuasa NP series data) Sorry to be so pedantic as to point out the difference between 13 and 7.8 - in your world this is a trivial difference but for the rest it is more than likely significant. |