How is battery capacity calculated

Let's say it's Battery capacity calculator: advanced mode If you open the advanced mode of this battery capacity calculator, you will be able to compute three other parameters of a battery. It is simply the time t needed to fully charge or discharge the battery when using the discharge current, measured in minutes. Battery capacity. Advanced mode. People also viewed…. Pay Gap US This pay gap calculator shows the difference between the median wages of US full-time working men and women.

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TV Size Calculator. However, the actual energy storage capabilities of the battery can vary significantly from the "nominal" rated capacity, as the battery capacity depends strongly on the age and past history of the battery, the charging or discharging regimes of the battery and the temperature. The energy stored in a battery, called the battery capacity, is measured in either watt-hours Wh , kilowatt-hours kWh , or ampere-hours Ahr.

The most common measure of battery capacity is Ah, defined as the number of hours for which a battery can provide a current equal to the discharge rate at the nominal voltage of the battery. The unit of Ah is commonly used when working with battery systems as the battery voltage will vary throughout the charging or discharging cycle.

The Wh capacity can be approximated from the Ahr capacity by multiplying the AH capacity by the nominal or, if known, time average battery voltage. A more accurate approach takes into account the variation of voltage by integrating the AH capacity x V t over the time of the charging cycle. However, because of the large impact from charging rates or temperatures, for practical or accurate analysis, additional information about the variation of battery capacity is provided by battery manufacturers.

If the battery is being discharged very quickly i. Some batteries, such as Carbon-Zinc, Alkaline, or Lead Acid become less efficient when you discharge quickly. Step 1. Back of the envelope. If the current drawn is x amps, the time is T hours then the capacity C in amp-hours is.

For example, if your pump is drawing mA and you want it to run for 24 hours. Step 2. Cycle life considerations. Step 3 : Rate of discharge considerations. Some battery chemistries give much fewer amp hours if you discharge them fast. This is called the Peukart effect. This is a big effect in alkaline, carbon zinc, zinc-air and lead acid batteries.

For example if you draw at 1C on a lead acid battery you will only get half of the capacity that you would have if you had drawn at 0. For lead acid batteries the rated capacity i. If you are discharging at a slow rate you will get the rated number of amp-hours out of them.

However, at high discharge rates the capacity falls steeply. A rule of thumb is that for a 1 hour discharge rate i. Charts that detail this effect for different discharge rate can be used for greater accuracy. For example, if your portable guitar amplifier is drawing a steady 20 amps and you want it to last 1 hour you would start out with Step Then proceed to Step 2. Then take the high rate into account.

Thus you would need a 50 amp hour sealed lead acid battery to run the amplifier for 1 hour at 20 amps average draw. Step 4. The obvious thing to do is the thing to do. Figure out an average power drawn. Consider a repetitive cycle where each cycle is 1 hour.