Can any one tell how to measure the ampere hour of battery when i know the voltage and current of the battery...
The ampere hour of a battery is a known/constant that should be on the battery somewhere. No need to measure it.
If you know how much current is being drawn from the battery over a certain time you can work out the ampere hours left on the battery.
Say if the battery is a 5 Amp/hr bat and you draw 2 amps for 1 hr then you have 3 amp/hrs left.
Note ampere hour rating is the power that you can get out of a battery before it falls below a certain voltage level. So for the above battery you can draw 5 amps for 1 hr before it falls below the recommended voltage. So if it was a 12V battery that would be 12 X 5 = 60 watts for 1 hr
Hope this answers your question.
well... not quite so easy as that.
a lead acid battery has a sulfication chemical reaction on the surface of the lead plates.
this starts the moment you add the electrolyte of sulphuric acid.
the amp hour rating of a car battery is more like how many amp hours it will test at 12 months after being started.
Like LED's, it starts our full of vigor and decays so that at some point in the future, there is less available.
your car may need 50 cranking amps, so you buy a 350 AH battery and each year loose 50 ah to the chemical reaction.
one way to test is to get a 24 hour clock of 12v and connect it to the battery and then connect a load.
check the clock each day.
do that once a year to get the decay rate for your battery.
Arent amp hr and cold cranking amps completely different. You buy a battery for the size of your car taking into account both cca and a/hr ratings required. It relates to the size of each plate and to how many plates there are in the battery? CC bats have more plates that are thinner giving more surface area for a larger chemical reaction to take place and deliver more current whilst deep cycle bats have thicker plates and less of them allowing them to store charge more efficiently.
Also I think you mean a full charge not just starting the car. I am not sure but i would not think that the amp/hr rating of a battery would be given for 12 months off the charge as there are so many factors that may effect this. I would more think it was after being on float fully charged that you would get the full amp/hr rating?
Lots of things effect the ampere hr rating if you want to get technical. Temperature and even current draw.
The amp hour capacity of a battery changes depending on the load and temperature. A battery rated at 100 amp hours has to be specified at what current (and what cutoff voltage). Pulling 100 amps for 1 hour is not the same as pulling 1 amp for 100 hours - the numbers are the same, but the battery will not perform the same at a 1 amp rate as it does at a 100 amp rate.
chethanbo:
Can any one tell how to measure the ampere hour of battery when i know the voltage and current of the battery...
"Measure" isn't possible, but I feel that you meant "estimate" the battery state-of-charge from a voltage and current measurement. That is possible, but the estimate isn't going to be perfect. There is good information about how state-of-charge is estimated from voltage/current here (even though I disagree with them using the word "measure") -> BU-903: How to Measure State-of-charge - Battery University.
I also wrote a description of how to do it in this thread -> Lead-acid battery capacity monitoring - #9 by BigBobby - Project Guidance - Arduino Forum
Do you have a datasheet for your battery? Something that shows the charge/discharge characteristics like this one? -> https://industrial.panasonic.com/cdbs/www-data/pdf2/ACA4000/ACA4000CE417.pdf
I agree with Reply #5
In addition, no lead acid battery can repeatedly produce the Amp-hrs on the sticker - maybe not even once without damaging the battery. If you are lucky it will provide 50% of the sticker capacity. I have no idea how the manufacturers get away with the numbers on their stickers.
...R