Calculating Battery Amp Hours

Frequently we get asked how to compute or calculate how amp hours the client needs to run a gadget or various gadgets. Ampere-hours, or amp-hours, are regularly used to describe the energy capacity of batteries, in spite of the fact that they can be utilized to calculate the required load for any electrical scenario. To calculate amp-hours from watts, you have to use equivalent terms: either the number of watt-hours or how long something works at a specific number of watts. Couple this with voltage, and you can simple ascertain amp-hours. This may seem a bit trick but with the necessary guidelines and proper calculation, determining this is not such a tedious task.

Step 1

Multiply the number of watts by the number of hours to calculate watt-hours. For instance, in the event that you know your laptop computer uses 30 watts of power and you need a battery to power it for four hours, you need 120 watt-hours of stored energy.

More information on how to properly calculate amps per hour can be found here.

Step 2

Divide this figure by the energy productivity of the battery to adjust for the lost energy. The battery’s proficiency is listed in its particulars. In the example, if the battery has an 85 percent proficiency, you divide 120 by 0.85 to derive a required 141 watt-hours. In the event that you wish to ascertain just theoretical values, you can skip this step.

Step 3

Partition this figure by the voltage to calculate amp-hours. Voltage is additionally listed in the battery’s particulars. In this example, if the battery is evaluated at 19 volts, divide 141 watt-hours by 19 volts. This tells you your new battery needs at least 7.42 amp-hours to run your computer for four hours.

Some battery chemistry gives much fewer amp hours if you discharge them fast. This is known as the Peukart effect. This is a major effect in alkaline, carbon zinc, zinc-air and lead-acid batteries. For instance, if you draw at 1C on a lead-acid battery you will just get half of the capacity that you would have gotten if you had drawn at 0.05C. It is a small effect in NiCad, Lithium Ion, Lithium Polymer, and NiMH batteries.

For lead-acid batteries, the rated capacity (for example the number of AH stamped on the side of the battery) is ordinarily given for a 20-hour discharge rate. If you are discharging at a moderate rate, you will get the evaluated number of amp-hours out of them. Notwithstanding, at high discharge rates the capacity falls steeply. A standard guideline is that for a 1-hour discharge rate (for example drawing 10 amps from a 10 amp hour battery or 1C) you will just get half of the rated capacity (or 5 amp-hours from a 10 amp-hour battery). Diagrams that detail this effect for various discharge rates can be utilized for more prominent precision. If you followed the above steps properly, then you can now accurately calculate battery amps per hour.