There is a big difference between ampere and ampere-hours. And the OP probably doesn´t have a clue what he actually wants to know.There really are too many variables to get a definitive Ah figure.
As has been indicated elsewhere in the thread, you need to be clear on the difference between amp-hours and amps. They are two fundamentally different things. The first is a measurement of total charge and, indirectly, energy delivered to a load over time while the second is a measure of the instantaneous rate at which charge is being delivered to load at a moment in time.My question is thiswhen I buy a battery, lets says a 12V battery, the ampere-hour is 7.5 ampere. How did they measure 7.5 ampere-hour? Can you explain, please? I am trying to build a home-made battery. I know how to measure the voltage but I do not know how to measure the AMP-Hour. Please explain. Thanks.
You can't accurately determine the amp-hour capacity of the battery with this data. The current draw will vary as the voltage on the battery drops. You need to construct a constant-current load. I suppose if you had many many datapoints you could get a decent estimate this way, but it's not practical. Also, under different loads the amp-hour capacity of a battery varies, because more or less power is dissipated as heat within the battery itself.Okay guys, thanks for sharing the info. But I am not still getting the concept right. Lets say I have 12V, 7.5 amp-hour battery. I am measuring the amp-hour. I add a 10 ohm resistor between the positive and negative terminal and started measuring the voltage. Here is the table:
Voltage Duration
12 V 1st hour
11 V 2nd hour
10 V 3rd hour
..
1 V 12th hour
0 V 13th hour
From this chart, how do I measure the amp-hour? Can you please explain step by step? Thanks
No, you don't need a constant current load, though that does make things easier.You can't accurately determine the amp-hour capacity of the battery with this data. The current draw will vary as the voltage on the battery drops. You need to construct a constant-current load. I suppose if you had many many datapoints you could get a decent estimate this way, but it's not practical. Also, under different loads the amp-hour capacity of a battery varies, because more or less power is dissipated as heat within the battery itself.
Batteries are typically specified over 10 hours. A 150 Ampere hour battery is supposed to support 15 Amperes for 10 hours. At 30 Amperes it may only support 4 hours or even less. Read about the chemistry of each cell for more insight. Being a chemical reaction this current has a temperature specified as well. Thats why you see electric line plugs on the front of cars in Montana. The cold saps the battery and thickens the oil and starting can be a trick.My question is thiswhen I buy a battery, lets says a 12V battery, the ampere-hour is 7.5 ampere. How did they measure 7.5 ampere-hour? Can you explain, please? I am trying to build a home-made battery. I know how to measure the voltage but I do not know how to measure the AMP-Hour. Please explain. Thanks.