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How do you imagine what an ampere hour is?

stabilizator 31425 8
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  • How do you imagine what an ampere hour is?
    The receivers draw a certain current from the battery or accumulator. How long they can operate depends on the capacity of the cells that make up the battery. If the receiver draws a current of 1A, it will take a 1Ah charge within an hour. A 10Ah battery could theoretically power a receiver requiring 1A for 10 hours. In theory, for a receiver requiring a current of 2A, the working time on a 10Ah battery will be shortened to 5 hours (in practice, the higher the discharge current, the smaller the actual battery capacity). Resistive loads (e.g. a light bulb) will consume lower current as the battery voltage drops. Receivers equipped with a DC / DC converter can receive constant power with changes in voltage, i.e. when the supply voltage drops, they will consume more current.


    We left out the voltage of the battery and only focused on the ampere-hours for its capacity. Both the 12V 10Ah battery and the 6V 10Ah battery can power a receiver using 1A current for 10 hours, but in the case of 12V the receiver will use 12W and in the case of 6V it will be a 6W receiver. Therefore, the capacity of the batteries is often specified in Wh, i.e. a 10Wh battery can supply a receiver with 1W power for 10 hours. The aforementioned batteries have a capacity per Wh, respectively: battery 12V 10Ah -> 120Wh, while 6V 10Ah -> 60Wh. You will also find watt hours, or rather kWh, in electricity meters in the home power supply system.

    Information about the basic parameters such as voltage, current, power, more information can be found here: Voltage, current, power - what are these values and how are they related by Ohm's law?

    Cool? Ranking DIY
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    stabilizator
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    stabilizator wrote 132 posts with rating 282. Been with us since 2020 year.
  • #2
    sanfran
    Network and Internet specialist  
    Ampere-hour as a unit was (and is) used for families of fixed voltage batteries, e.g. on-board batteries in passenger cars, which was closely related to the current capacity of the device - including the ability to start an internal combustion engine. In the case of such batteries - acid batteries - I have not encountered the capacity in Wh.

    It got more interesting when powering portable electronic devices. For example, some DELL laptop models (and probably other companies as well) accept both 11.1V (standard) and 14.4V (extended) batteries. They both had the same (mile) ampere-hours, but the capacity differed.

    It got even more interesting when portable USB power adapters called PowerBank appeared.
    You already need a fortune teller to find out whether the 5000 mAh inscription applies to the cell itself, most often with a voltage of 3.7V, or efficiency from a 5V socket.

    In any event, traction battery batteries in electric vehicles are only given in kWh. Because the standard lead battery needed to power low voltage circuits is still referred to as Ah.
  • #3
    stabilizator
    Editor  
    Thank you for developing the topic well and maintaining the description that will facilitate easy understanding of the issue for people who are just starting their adventure with electronics. :spoko:
  • #4
    Tomek515
    Level 23  
    Recently, I was wondering what it is like when I have a 12V 7Ah battery. I could get 1A from it for 7 hours. But whether this capacity is given to the safe level of battery discharge, i.e. in the case of a gel battery, probably 10.7V, or is it its overall capacity, and in fact I can take less for a safe voltage.
  • #5
    sanfran
    Network and Internet specialist  
    From what I can remember from the old days, the value was 10 hours for standard lead-acid batteries. So in the above case 700mA for 10 hours until full discharge - that is, voltage drop to a certain level. When more current was drawn, the capacity dropped drastically, and it was directly proportional to the degree of battery consumption. In the 1980s, the average toddler user knew this all too well when trying to start his vehicle in winter.
  • #6
    electro
    Level 18  
    Tomek515 wrote:
    Recently, I was wondering what it is like when I have a 12V 7Ah battery. I could get 1A from it for 7 hours. But whether this capacity is given to the safe level of battery discharge, i.e. in the case of a gel battery, probably 10.7V, or is it its overall capacity, and in fact I can take less for a safe voltage.


    For acid batteries, the so-called Peukert's law which determines the dependence of the available capacity on the current consumed from the cell. In short, the more current we draw, the smaller the effective capacity. Here is one of the many descriptions, complete with graphs Link
  • #7
    stabilizator
    Editor  
    In small UPSs, the batteries have difficult operating conditions, the discharge currents are high, as you write, then the available capacity and back-up time are reduced. In larger UPS units, the batteries work in series connected units, the operating currents are lower and the working conditions are better.
  • #8
    kowal011
    Level 21  
    For small AGM batteries, or the popular "gel" batteries from UPS, capacity is given as 20 hours.
  • #9
    gold-game
    Level 21  
    It is worth mentioning that the use of battery 'protectors' is becoming more and more popular. It is about preventing excessive discharge of the battery in a domestic installation, e.g. in a motorhome. The main point here is that a lead-acid battery is very destructive when deeply discharged. Such battery protect keeps the cell in good condition for a long time.
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