Nomenclature question - Page 1
Forum section: electronics / general

author: paulca
author_rank: Super Contributor
timestamp: April 02, 2025, 01:38:18 pm
content: AmpHour.If you were referring to a battery in terms of "AmpHour", you are defining a fixed current for a fixed time as a way to suggest the battery capacity.I have got slated badly in other forums for referring to this as a "Current source based measurement."The argument for this is that it mentions no voltage. If you fix the current draw/charge in amps and the time in hours, then the only variable left for most batteries I know is the voltage.If you are characterising something and "voltage" is the variable and "current" is fixed... is this not be definition a "Current source analysis"?

author: Langdon
author_rank: Frequent Contributor
timestamp: April 02, 2025, 01:46:05 pm
content: Voltage has nothing to do with it.2x 7Ah batteries = 1x 7Ah batteryBut double voltage.Voltage across a lead-acid battery, for example, is not really reliable.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 02, 2025, 01:50:07 pm
content: Quote from: paulca on April 02, 2025, 01:38:18 pmNo, not fixed current, no fixed time. It's just an integral. 1A for 1h results in 1Ah, but so does 0.5A for 0.9h and then 5.5A for 0.1h.Ah is just alternative non-SI unit for charge. SI unit is Coulombs, also known as ampere-seconds.QuoteSure, it ignores voltage. It is somewhat analogous of counting number of liters of water. Then voltage would be somewhat analogous to from what height these liters are poured from. Multiple these two together, and you have potential energy.

author: Langdon
author_rank: Frequent Contributor
timestamp: April 02, 2025, 02:06:42 pm
content: Exactly.1 litre, poured off a roof, will hit the ground with far mre energ than if it were poured from a foot above ground.But the pitcher holds no more than 1 litre, regardless of the height of pouring.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 02, 2025, 02:16:55 pm
content: And "capacity" is not any sort of SI definition but a more practical hand-wavy one: after being fully charged per instructions, how much <x> can battery deliver before it stops working desirably, or use has to be stopped to prevent permanent damage.And that <x> can be energy capacity, or charge capacity; Wh or Ah, respectively.Voltage is often the indicator of "when to have to stop (dis)charging". There can be more sophisticated rules, and exact details depend on battery chemistry.Note that charge, as in coulombs, is different from the verb "to charge".

author: bw2341
author_rank: Regular Contributor
timestamp: April 02, 2025, 02:44:32 pm
content: The amp hour rating alone is insufficient for indicating the energy capacity of the battery. You need both the amp hour rating in Ah and the battery voltage in V. Ah times V is Wh (watt-hours) which is 3600 J (joules).The confusion happens because the battery voltage is assumed to be common knowledge from the context. For instance, when comparing smartphones, it is assumed that there is a single lithium polymer battery of about 4 volts. So the battery capacity of smartphones is often given in Ah even though it should be given in Wh to be strictly correct.