For this example problem, the battery has a reserve of 45 minutes of capacity. As mentioned above, this is a unit of time the battery can run at 25 amps without dropping below 10.5 volts. The following example problem illustrates the steps and required information needed to calculate amp hours from reserve capacity.įirst, determine the reserve capacity. How to calculate amp hours from battery reserve capacity? The battery reserve capacity is a measure of the total amount of time a battery can run at 25 amps of current without the voltage dropping below a set value of 10.5 volts. To calculate amp hours from battery reserve capacity, multiply the capacity in minutes by. BR is the battery reserve capacity (minutes).For example, most car batteries have a DOD of 20%, so only 20% of capacity can be withdrawn. Manufacturers usually specify the depth of discharge (DOD) of a battery, which determines the fraction of power that can be withdrawn from it. Why should you care about this? In many types of batteries, the battery cannot be fully discharged without causing serious, and often irreparable, damage to the battery. The calculator below does this.īut note that it shows the discharge time for a different depth of discharge. This link provides more information on the subject.įinally, knowing the Peukert capacity and Peukert exponent you can calculate the discharge time for a given discharge current. R – the hour rating (ie 20 for 20 hours, or 10 for 10 hours etc) you can calculate the Peukert capacity using the following formulaĬ – the specified capacity of the battery (at the specified hour rating) In other words, a 100-Ah battery could discharge 5 amps per hour for 20 hours for a total of 5×20100 amp-hours However, shorter discharge times which is typical in the RV world actually lessen the amount of useable energy You might only get 80 or 90 amp-hours out of that same battery. Knowing the hour rate of your battery, its specified capacity and Peukert's exponent. The same battery discharged at 0.5C provides 500mA for two hours. The Amp hour rating can be useful to know when. For example, a battery rated at 1000mAh provides 1000mA for one hour if discharged at 1C rate. This calculator converts a battery or battery packs Watt hours (Wh) rating into its Amp Hours rating. A discharge of 1C draws a current equal to the rated capacity. If not specified, manufacturers commonly rate batteries at the 20-hour discharge rate or 0.05C.Ġ.05C is the so-called C-rate, used to measure charge and discharge current. This is known as the "hour" rate, for example 100Ahrs at 10 hours. Battery manufacturers rate capacity of their batteries at very low rates of discharge, as they last longer and get higher readings that way. Our watt hour calculator allows you to use electric charge in milliamp or amp hours and voltage in volts to calculate the energy in watt-hours or joules. Batteries are rarely specified with Peukert capacity. Peukert's capacity is the capacity of the battery measured at 1 amp discharge rate. Peukert's exponent can be calculated from these graphs or tables, or by running two discharge tests at two different discharge rates. But sometimes they have tables giving different run times at different discharge rates, or a graph of discharge rates against run times. Many batteries do not have Peukert's exponent available in specification. Peukert's exponent changes as the battery ages. Peukert's exponent is determined empirically, by running the battery at different discharge currents. Peukert's exponent shows how well the battery holds up under high rates of discharge – most range from 1.1 to 1.3, and the closer to 1, the better. The formula for calculating it is known as Peukert's equation, and the important number, unique to each battery type, that is put into the equation in order to perform the calculation is known as Peukert's exponent. Thus the effect is now known as Peukert's effect. This effect had been known for many years but it was Peukert who first devised a formula that showed numerically how discharging at higher rates actually removes more power from the battery than a simple calculation would show it to do. However, battery capacity decreases as the rate of discharge increases. for a given capacity C and a discharge current I, the time will be You may think that calculating how long a battery will last at a given rate of discharge is as simple as amp-hours: e.g. I'm not an electrician, so please pardon me for any mistakes.īattery capacity is a measure (typically in Amp-hr) of the charge stored by a battery. With Calculator Between Hours, monitoring work schedules and tracking labor hours is as easy as a few taps on your screen. Everything below was created after spending several hours searching and reading the internet.
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