LEAD ACID BATTERY

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One might think that, but he has voltage constraints that requored a more thorough analysis...

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So? Use of three 6V batteries in series gives 18V.

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I fully appreciate that. The comment was relating to the definition of C and how it can cause major mis-calculation.

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You totally missed the point. 13A? or 700mA?

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!

--- I'll do precisely what I want to, and that includes commenting ("ranting" if you like) on the evils of top-posting and the inability of some Google groupers to post considerately to forums which have customs they seem incapable of accepting or appreciating.

If you find any of my posts annoying or not to your liking, in any way, or you find me irritating, then I suggest you learn how to use your newsreader's filter(s) and simply plonk me.

At least that way you won't feel compelled to gripe about my griping and there'll be that much less noise here.

-- John Fields Professional Circuit Designer

On Fri, 31 Mar 2006 22:40:34 GMT, Robert Baer Gave us:

He DID give an answer, and he DID include a swipe for the idiot being a top poster. So YOU shut the f*ck up.

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?

Review your other line: "The nominal 'C-rate' of a 13Ah battery is 13amps."

Try reading the two in conjunction.

is

You obviously do not understand that, for example the origional posters

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?

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many

I most certainly do.

Indeed. it may be more, or less, depending on whether the rate is less, or more. Kid stuff.

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.

That isn't a standard either.

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.

Apaprently you haven't.

would be

---

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

is drawn from the battery, continuously, for a period of 20 hours.

-- John Fields Professional Circuit Designer

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

would be

Yes, I also assumed 13Ah for the proposed batteries and 700mA for the load. But the O/P's statement "I have to design a voltage source ( +/- 18volts, 13A )" is at odds with that.

Me too.

Please post the source of this 'C-rate' s**te you keep on about.

So much for your "worldwide standard".

Yes, that's true, and the OP seems to have said that his app called for

Cheers! Rich

On Tue, 04 Apr 2006 17:20:49 -0500, John Fields wrote: ...

Noth Hi,

I have to design a voltage source ( +/- 18volts, 13A ) using lead acid batteries. My circuit draw is 700mA and requires plus minus 18 volts to operate efficiently. I need batteries that can atleast run for 10 to 12 hours before the voltage drops to +/- 17 volts. I am thinking of adding three 6 volts, 13AH ( rated for 20AH ) batteries in series to produce

Can anybody advice me that am I doing the right thing that will these six batteries last for 10 to 12 hours maintaining +/- 18 volts @

Thanks Regards John

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I guess when I saw "My circuit draw is 700 mA" I assumed that he means that his circuit draws 700 mA. I also assume that when he said "18 volts,

Hope This Helps! Rich