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24 Cards in this Set

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Cell, modules, and packs

Hybrid and electric vehicles have a high voltage batterypack that consists of individual modules and cells organized in series and parallel. A cell isthe smallest, packaged form a battery can take and is generally on the order of one to sixvolts. A module consists of several cells generally connected in either series or parallel. Abattery pack is then assembled by connecting modules together, again either in series orparallel.

Battery Classifications

Not all batteries are created equal, even batteries of the samechemistry. The main trade-off in battery development is between power and energy:batteries can be either high-power or high-energy, but not both. Often manufacturers willclassify batteries using these categories. Other common classifications are High Durability,meaning that the chemistry has been modified to provide higher battery life at the expenseof power and energy.

C- and E- rates

In describing batteries, discharge current is often expressed as a C-ratein order to normalize against battery capacity, which is often very different betweenbatteries. A C-rate is a measure of the rate at which a battery is discharged relative to itsmaximum capacity. A 1C rate means that the discharge current will discharge the entirebattery in 1 hour. For a battery with a capacity of 100 Amp-hrs, this equates to a dischargecurrent of 100 Amps. A 5C rate for this battery would be 500 Amps, and a C/2 rate wouldbe 50 Amps. Similarly, an E-rate describes the discharge power. A 1E rate is the dischargepower to discharge the entire battery in 1 hour

Secondary and Primary Cells

Although it may not sound like it, batteries for hybrid,plug-in, and electric vehicles are all secondary batteries. A primary battery is one that cannot be recharged. A secondary battery is one that is rechargeable.

State of Charge (SOC)(%)

An expression of the present battery capacity as apercentage of maximum capacity. SOC is generally calculated using current integration todetermine the change in battery capacity over time.

Depth of Discharge (DOD) (%)

The percentage of battery capacity that has beendischarged expressed as a percentage of maximum capacity. A discharge to at least 80 %DOD is referred to as a deep discharge.

Terminal Voltage (V)

The voltage between the battery terminals with load applied.Terminal voltage varies with SOC and discharge/charge current.

Open-circuit voltage (V)

The voltage between the battery terminals with no loadapplied. The open-circuit voltage depends on the battery state of charge, increasing withstate of charge.

Internal Resistance

The resistance within the battery, generally different for chargingand discharging, also dependent on the battery state of charge. As internal resistanceincreases, the battery efficiency decreases and thermal stability is reduced as more of thecharging energy is converted into heat.

Nominal Voltage (V)

The reported or reference voltage of the battery, also sometimesthought of as the “normal” voltage of the battery.

Cut-off Voltage

The minimum allowable voltage. It is this voltage that generallydefines the “empty” state of the battery.

Capacity or Nominal Capacity (Ah for a specific C-rate)

The coulometriccapacity, the total Amp-hours available when the battery is discharged at a certaindischarge current (specified as a C-rate) from 100 percent state-of-charge to the cut-offvoltage. Capacity is calculated by multiplying the discharge current (in Amps) by thedischarge time (in hours) and decreases with increasing C-rate.

Energy or Nominal Energy (Wh (for a specific C-rate))

The “energy capacity” ofthe battery, the total Watt-hours available when the battery is discharged at a certaindischarge current (specified as a C-rate) from 100 percent state-of-charge to the cut-offvoltage. Energy is calculated by multiplying the discharge power (in Watts) by thedischarge time (in hours). Like capacity, energy decreases with increasing C-rate.

Cycle Life (number for a specific DOD)

The number of discharge-charge cycles thebattery can experience before it fails to meet specific performance criteria. Cycle life isestimated for specific charge and discharge conditions. The actual operating life of thebattery is affected by the rate and depth of cycles and by other conditions such astemperature and humidity. The higher the DOD, the lower the cycle life

Specific Energy (Wh/kg)

The nominal battery energy per unit mass, sometimesreferred to as the gravimetric energy density. Specific energy is a characteristic of thebattery chemistry and packaging. Along with the energy consumption of the vehicle, itdetermines the battery weight required to achieve a given electric range.

Specific Power (W/kg)

The maximum available power per unit mass. Specific poweris a characteristic of the battery chemistry and packaging. It determines the battery weightrequired to achieve a given performance target.

Energy Density (Wh/L)

The nominal battery energy per unit volume, sometimesreferred to as the volumetric energy density. Specific energy is a characteristic of thebattery chemistry and packaging. Along with the energy consumption of the vehicle, itdetermines the battery size required to achieve a given electric range.

Power Density (W/L)

The maximum available power per unit volume. Specific poweris a characteristic of the battery chemistry and packaging. It determines the battery sizerequired to achieve a given performance target.

Maximum Continuous Discharge Current

The maximum current at which thebattery can be discharged continuously. This limit is usually defined by the batterymanufacturer in order to prevent excessive discharge rates that would damage the battery orreduce its capacity. Along with the maximum continuous power of the motor, this definesthe top sustainable speed and acceleration of the vehicle.

Maximum 30-sec Discharge Pulse Current

The maximum current at which thebattery can be discharged for pulses of up to 30 seconds. This limit is usually defined bythe battery manufacturer in order to prevent excessive discharge rates that would damagethe battery or reduce its capacity. Along with the peak power of the electric motor, thisdefines the acceleration performance (0-60 mph time) of the vehicle.

Charge Voltage

The voltage that the battery is charged to when charged to fullcapacity. Charging schemes generally consist of a constant current charging until thebattery voltage reaching the charge voltage, then constant voltage charging, allowing thecharge current to taper until it is very small.

Float Voltage

The voltage at which the battery is maintained after being charge to 100percent SOC to maintain that capacity by compensating for self-discharge of the battery.

(Recommended) Charge Current

The ideal current at which the battery is initiallycharged (to roughly 70 percent SOC) under constant charging scheme before transitioninginto constant voltage charging.

(Maximum) Internal Resistance

The resistance within the battery, generally differentfor charging and discharging.