Battery Reserve Capacity Calculator

A labels on a battery may have a number like 140 RC. The RC represent the reserve capacity of the battery. The reserve capacity is different than amp hour because reserve capacity measures how long the battery will provide a 25 amp load before it reaches the low voltage that its connected device require to operate.

If the devices from which you are drawing power require a slow amount of energy, then the reserve capacity rating of the battery is not a direct indication of how long the device will run. Batteries has a reserve capacity that indicates the length of time that they can provide high-current discharges, but the devices in most homes requires batteries to provide low-current discharges. For these reasons, it is not wise for a person to attempt to utilize all of the capacity of a battery.

Planning a Home Battery Backup

Deep cycling lead acid batteries to completely drained (zero amp hours) will damage the battery. If the battery is damaged in this way, it will no longer function correctly. A person must take into account the depth of the battery that can be utilized without damaging the battery.

For instance, a person may utilize a deep cycle marine battery in only fifty percent of its total capacity to ensure that the battery lasts for a more longer period of time while in use. By utilizing only the portion of the capacity of the battery, a person is making a trade-off between the amount of energy that can be drawn from the battery today as opposed to in the future due to the need to replace the battery. In order to determine the total energy that a battery can provide, one can calculate the reserve capacity of the battery to provide watt-hours.

Watt hours is a measurement of the total amount of energy that a battery can provide. Once a person calculates the total energy that is required of the battery to power the devices, a person can determine how to connect the batteries in order to provide that energy to the devices. Batteries can be connected in either a series or in a parallel connection to the devices.

If the batteries are connected in a series connection, the voltage will increase to match the requirement of the inverter. By connecting batteries in series, the amp hours will not increase. In order to increase the amp hours of the batteries, batteries must be connected in a parallel connection.

Connecting batteries in parallel will increase the volume of energy that can be provided. By connecting batteries in series, the voltage will increase but the energy will not increase. In addition to considering how to connect the batteries to the devices that will utilize the energy from those batteries, there are additional considerations for each device.

For instance, different devices will have different requirement for both average and surge loads of energy. Devices such as a CPAP machine may require batteries to provide a relatively low average load of energy to the device, which will determine for how long the battery will last when the device is in operation. However, devices such as a sump pump may have high surge loads of energy with their devices.

A surge load is the amount of energy that is required from a device at the beginning of its operation. Such high surge loads of energy can lead to an inverter being tripped if the size of the inverter does not accommodate the surge load of the device that is being operated. Therefore, in addition to ensuring that the battery has enough energy to supply the devices with the energy that they require, it is also necessary to ensure that the inverter has enough capacity to handle the surge load of those devices.

In addition to accounting for the energy that is required by the devices, it is also necessary to account for the energy that is lost during the conversion from the battery to the devices. In order for devices to be powered, an inverter will convert the energy from the battery to the devices. Batteries have a relatively low voltage compared to the voltage that is required to power the devices.

In order to increase the voltage from the battery to the devices, an inverter is used. During this process energy is lost as heat from the inverter. The loss of energy during this process is approximately ten percent of the total energy of the battery.

Thus, the batteries will provide less energy then is calculated for the devices. Batteries will also lose energy through normal operation as they age and as the temperatures of the batteries decreases. To account for this energy loss in the calculations of energy requirements of the devices, a buffer of energy will need to be added to the total energy requirements for the devices.

A fifteen percent energy buffer ensures that devices will continue to run even as the batteries lose their capacity. Another consideration in the creation of a battery backup system is the chemistry of the batteries. For instance, one type of battery is a flooded battery.

Flooded batteries are not ideal for deep cycling, meaning they should not be deeply drained of their energy. In contrast, a second type of battery is a LiFePO4 battery. These batteries can be deeply drained without damaging the battery.

Because the LiFePO4 battery can be deeply drained, it can provide more usable energy than a flooded battery of the same capacity. The downside to using a LiFePO4 battery is that it has a higher initial cost to purchase the batteries. However, because usable energy from a battery is depth of energy that can be drawn from the batteries without damaging them, the depth of usable energy of the LiFePO4 battery is much greater than that of the flooded battery.

In order to create a backup system for a home or other structure, considerations must be made regarding energy loss due to conversion, battery chemistry, and the loads of the devices that will be powered by the system. Each person will have to decide which devices they deem as essential and which will not be necessary for operation during a power outage in order to ensure that they have an adequate amount of energy for those essential devices. By accounting for energy loss due to conversion and considering the chemical composition of the batteries, it will be possible to know how long the battery will run for in relation to the devices.

By knowing how long the batteries will run for in relation to the devices that will be using that energy, it will be possible to effectively plan for the power outage and know when the batteries will run out of energy.