While calculating battery power capacity requirement for a circuit consisting of multiple loads having different power consumption, how should one proceed to avoid any error? How it is done in industries?


For example: a. 12V, 5V at 2A each for 10 Hrs. How a battery should be chosen?


closed as unclear what you're asking by winny, Bort, Harry Svensson, Bimpelrekkie, RoyC Oct 11 '18 at 13:58

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    \$\begingroup\$ Welcome to EE.SE! Find out everything you need to get started by taking a 2-minute tour (electronics.stackexchange.com/tour). \$\endgroup\$ – F.Ahmed Oct 10 '18 at 18:41
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    \$\begingroup\$ Possible duplicate of Battery Run-time/capacity calculation \$\endgroup\$ – winny Oct 10 '18 at 18:51
  • \$\begingroup\$ @winny That never solved the actual query! \$\endgroup\$ – Raj Oct 10 '18 at 18:52
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    \$\begingroup\$ How can we answer "which one to chose" if we don't know what you want to achieve? Consider that I have $100,000. A truck costs $50,000, and a car costs $30,000. Which one to choose? \$\endgroup\$ – Bort Oct 10 '18 at 19:18
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    \$\begingroup\$ @Raj - I've done a rollback to rev 2 of your question, since the changes you made in rev 3 were not helpful (e.g. the tag "capsense" doesn't apply here, and changing the question's title to "Deleted, Deleted, Deleted" is not something that is done here). \$\endgroup\$ – SamGibson Oct 12 '18 at 12:09

Your a. question is unanswerable, if I want to power something that needs 12 V, obviously I'd chose the 12 V battery.

Unless there needs to be a long wire between battery and load, then I'd use 24 V, feed that through a long cable and convert it to 12 V at the load. Using 24 V in the long cable results in less current and lower losses.

What solution is "better" depends on what my priorities are. It is unclear what your priorities are to choose 12 V or 24 V so your question cannot be answered.

Regarding b: There's an online calculator here: https://convert-formula.com/ah-wh

The relation is simple, Ah is the product of Current (in Ampere) and time (in hours) that a battery can store. So a 10 Ah battery can deliver (after a full charge) 10 Ampere for one hour ( 10 A * 1 Hr = 10 Ah) or 1 Ampere during 10 hours ( 1 A * 10 Hr = 10 Ah).

Even though most people think that the amount of Ah tells you everything about the energy in a battery, they could not be more wrong!

Which battery can store more energy?

  • this 10 Ah, 1.2 V NiMh battery?
  • that 10 Ah, 12 V Lead-Acid battery?

Of course the 12 V battery can store more energy because even though the batteries can deliver the same current the Lead Acid battery delivers the current at 12 V, not at a disappointing 1.2 V.

To illustrate the difference we use Whr which is the product of Power (in Watts) and time (in hours). The calculation is the same as Ahr but multiplied by the battery voltage.

So the 10 Ah, 1.2 V NiMh battery is 10 Ah * 1.2 V = 12 Whr

While the 10 Ah, 12 V Lead-Acid battery is 10 Ah * 12 V = 120 Whr, 10 times more!

We can do the reverse also, a 120 Whr battery at 12 V means it is 120 Whr / 12 V = 10 Ah.

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    \$\begingroup\$ @Raj - The questions in your comment are duplicating some of the ones in this earlier question from you. Please don't repeat questions in multiple places! You will get a bad reputation for wasting people's time if you do that, and you might find that your questions get closed and/or downvoted etc. \$\endgroup\$ – SamGibson Oct 10 '18 at 21:22
  • \$\begingroup\$ @SamGibson I apologize for the inconvenience to everyone. \$\endgroup\$ – Raj Oct 11 '18 at 2:57
  • \$\begingroup\$ Between 12V 10Ah and 24V 5Ah, does Ah matters in run time calculation as latter will degrade quickly or watt-hrs matters and both will have same run time? \$\endgroup\$ – Raj Oct 11 '18 at 3:01
  • \$\begingroup\$ @Raj Why will the 24 V, 5 Ah discharge faster? You're thinking of loading the batteries with the same current right? But is that fair? Does 12 V, 1 A (discharge in 10 hours) give the same amount of energy per second as 24 V, 1 A (discharge in 5 hours) ? Note that Power = Voltage * Current. So for the same discharge time, should you load the batteries with the same current or the same power? \$\endgroup\$ – Bimpelrekkie Oct 11 '18 at 6:06
  • \$\begingroup\$ @Bimpelrekkie Thank you. Confusion was to find if I load both the mentioned batteries at same load, then run time must be same and after you cleared, it is same! \$\endgroup\$ – Raj Oct 11 '18 at 6:20

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