CHARGING AND DISCHARGING TIME

CHARGING AND DISCHARGING TIME

Time in Hours

At any particular instant the actual current delivered by any cell depends on the load. The Time in hours(H) theoretically would be

Time(H) = Capacity (Ah)/Current(A).

If current is measured in amps and Capacity of a cell/battery in amp-hour, then time is measured in hours for charging and discharging.

For instance,

A 20Ah battery pack delivering 0.5A will last for 40hours

A 20Ah battery pack delivering 1A will last for 20hours

A 20Ah battery pack delivering 2A will last for 10hours

A 20Ah battery pack delivering 20A will last for 1hour

CHARGING TIME AND DISCHARGING TIME

The charging and discharging rate are usually specified by the current.

Example, charged at 10A and discharged at 20A

Charging Time

Charging time is the proportion of charge added to the battery per unit time.

In general scenario charging Time is found by,

Charging Time = Battery Capacity / Applied Current

For instance,

Consider 80Ah battery pack, if the applied current is 20Ah, then the

Charging Time = 80 / 20 = 4 hours.

Discharging Time

Discharging Time= (Battery Capacity x Battery Volt)/Device Watt.

For instance,

Consider a 3.7V 20Ah battery, device watt=20watt

Discharging Time = 20Ah*3.7V/20 = 3.7 hours

Li-ion/ / LiPo batteries with power efficiency of 90%

Then,

Discharging Time = (Battery Capacity x Battery Volt x 0.9)/Device Watt

For instance,

Discharging Time = 20Ah*3.7V*0.9/20 = 3.33 hours

C RATING

C RATING

C rate of the battery is the rate at which the capacity of the battery is charged or discharged to the load. C rating is important in applications which draw high amounts of current.

Maximum Current Draw = Capacity (Ah) x C-Rate

Example, a 3S 2.5Ah 5C LiPo battery pack will draw a maximum safe current of

2500mAh x 5C = 12.5A

Discharging a battery too quickly is not good considering the health of the battery. Due to which internal resistance (IR) will increase than discharging within the battery’s limit.

The battery capacity is generally rated at 1C, which means that the fully charged battery rated at 2Ah must provide 2A for 1 hour. The same battery if rated at 0.5C should provide 1A for 2 hours. Same battery rated at 2C should provide 4A for 30 minutes.

C/10 = C10 = which means C amount of discharge current flowing for 10 hours

C/5 = C5

C/0.5 = C0.5 = 2C

20C = The discharge current the battery is capable of discharging is 20 times C

The higher quality batteries are capable of handling higher charge rates with minimum or no degradation but the lower quality batteries have higher possibility of getting overheat at higher charge rates. It’s always suggested to charge at 1C or follow the recommendations from battery manufacturer regarding high performance and long battery life.

Lets go through some of the mathematical calculations

  • Average Battery Current

IB=C/N

IB = Average battery current

C= Capacity in Ah

N= No of hours of discharge

Example:

For 10Ah of battery and 10hours of discharge

IB=30Ah/10h = 3A

It means that 30Ah of battery is capable of supplying 3Ah of average current to the load up-to 10hours. Though due to losses 30Ah battery can supply 3A average current for less than 10 hours.

  • Continuous Discharge

2500mah battery with 5C rating

Continuous Discharge Amperage = (mAh/1000) x C Rate)

= (2500 /1000) x5=12.5A

  • Run Time for Safe Continuous Discharge

2500mah battery with 5C rating

Run Time = (60min/C-Rate) = (60min/5) = 12min

Therefore, Discharge 25A for 12min

C rating of a battery is very important factor as the energy stored in a battery is dependent on the speed of charging and discharging current.

BATTERY TERMINOLOGIES

Voltage – The potential difference is measured in terms of voltage. The SI unit is a volt and is defined as the measurement of electromotive force, or the difference in potential, which will cause a current of one ampere to flow through a resistance of one ohm.

 How to measure the value of voltage in a cell?

1] Set the multimeter knob to DC voltage measuring mode.

2] Connect the probes into the multimeter.

3] Connect the positive and negative end of the cell to the appropriate probe ends of the multimeter.

4] The voltage value of the cell will be displayed.

Ampere: The flow of electric current is measured in terms of Amperes and its SI unit is Amp.One Amp is defined as the amount of current generated by one volt of electromotive force acting through one ohm of resistance.

Ampere-Hour: The electrical energy stored in the battery pack is measured in terms of Ampere-hour or Ah. The value of current multiplied by time in terms of hours equates ampere-hours. One ampere hour is equal to a current of one ampere flowing for one hour. Also, 1 ampere-hour is equal to 1,000 mAh.

Watt – The total power of the battery pack is measured in terms of watts. Watts is the SI unit for electric power. The wattage of a battery is obtained by multiplying amperes by volts.

Watt-Hour: A Watt Hour is a unit of measurement for power over a period of time. One watt-hour equals one Watt of average power flow over an hour cycle. One Watt of power will be two Watt-Hours for two hours.

Cell – It is an electrochemical device, consisting of positive and negative plates and separated by electrolyte, which is capable of storing electrical energy. It is the basic “building block” of a battery.

Capacity – The capacity of a battery is an indicator or the measurement of the amount of energy that it can deliver in one discharge. Battery capacity is normally mentioned as amp-hours (Ah or mAh) or in terms of watt-hours.

Direct Current (DC) – The unidirectional flow of electric charge. It is the type of electrical current that a battery can supply. One terminal is always positive and the other is always negative.

Cycle – A cycle refers to one sequence of charging and discharging of the battery of its full capacity.

Charge – process of converting electrical energy, given in the form of a current, into chemical  energy and storing it within the cell or battery.

Discharge – The conversion of the chemical energy stored in the battery into electric energy.

Battery-Charge Rate – The rate at which the battery is recharged is known as the battery charge rate and is expressed in amperes (A) or milli amps (mA).

Cycle Life – The total number of charge/discharges cycles a rechargeable cell can sustain before its capacity is significantly reduced is the cycle life of a cell. End of cycle life is commonly considered when the cell or battery only delivers 80 percent of the rated capacity. A battery cycle is greatly influenced by cycle type depth (deep or shallow) and recharging process. Improper cutoff of the charging period will significantly reduce a battery’s cycle life.

Depth of Discharge – The amount of energy that has been harnessed or utilized from a battery (or battery pack). It is usually expressed as a percentage of the total capacity of the battery. For example, 80% DOD means eighty percent of the energy was discharged,  so the battery now only retains 20 percent of its maximum charge.

Energy Density: The volumetric energy storage density of a battery, expressed in Watt-hours per litre (Wh/l).

Power Density: The volumetric power density of a battery, expressed in Watts per litre (W/l).

State of Charge [SOC]: The amount of charge remaining in a cell as a percentage of the charge contained by the cell when it is fully charged. Since, one cannot accurately determine the SOC of a cell without fully discharging it first, the calculation for SOC is usually performed by subtracting the charge removed from the cell so far from the charge contained when it was last charged to 100% SOC.

State of Health [SOH]: It is an indicator of the amount of charge that the cells can hold as they age when compared to its initial stage. In case of Electric Vehicle, the capacity of the cells in the battery pack is the important parameter in determining the range which can be achieved in one charge.

Hence State of Health of an Electric Vehicle battery pack, that is SOHe, which is the amount of charge the cells in the battery pack can hold as they age is  calculated as,

Over a succeeding number of cycles of cells, the capacity of a lithium-ion cell will drop owing to a number of factors including loss of lithium inventory and failing of the electrodes inside the cell. Hence when an aged cell is charged and discharged to its maximum and minimum voltage values respectively, the charge obtained will be lower than charge obtained when the cell was new.

Source: https://www.dukosi.com/blog/what-are-state-of-charge-and-state-of-health/

BATTERY MARKET TREND

The battery is a device that stores energy. It provides power to all the electronic units in the system. Charge storing is relatively uncomplicated but the limitations affect their operation. With growing battery technology, the declaration of new battery type often makes people wonder whether it offers high energy density, high charge, and discharge cycles? Every battery technology has its own pros and cons. It depends on the applications, that is where it is used. Sometimes size and density matter and sometimes the size and safety. The encounter of smaller technology and development of the same gives’way for new possibilities in battery technology.

A battery by definition is a collection of cells. So the cell is a little can of chemicals. And the challenge is taking a very high-energy cell, and a large number of them, and combining them safely into a large battery.”

ELON MUSK

A battery pack has one or more cells and each cell has positive electrode, negative electrode and an electrode between the two electrodes. The properties such as amount of energy stored, power, discharge and charge cycles etc are impacted by the different materials and chemicals used in cells.

The battery market is divided based on battery type that is the primary battery(not-rechargeable) and secondary battery(rechargeable), and the battery technology [Lead-acid, Ni-Cd, NiMH, Li-ion, LiFePO4, and so on], and alsothe application [EV, HEV, PHEV]

Lead-Acid Batteries: They are evolving since its invention in 1859. Lead-acid batteries are used in Telecommunication, UPS and automobile industries. They have seen a great scale of development with respect to the automobile industry.Low maintenance costs, increase in demand for electric vehicles, and lower replacement cost is some of the drivers of lead-acid battery market. Major constraints for the drop in the market is its dependency on hazardous and restricted lead and the shift in the market towards Lithium-ion batteries. The lead-acid battery market is divided into gel battery, AGM battery, and flooded battery. Though the demand share of flooded batteries is anticipated to decrease,due to cost-effectiveness they are in high demand. There is gradual increase in demand share of AGM batteries.

Ni-Cd: In the section of portable battery applications alkaline rechargeable battery market has been expanded with Ni-Cd. They are more efficient than lead-acid batteries. The NI-Cd has low internal resistance and high current conducting properties, thus can be recharged quickly. Ni-Cd battery market is sinking due to the toxic characteristics in Cadmium which affect the environment and also because of other efficient battery technologies trending in the market.

NiMH: They are the upgraded version of Ni-Cd batteries. NiMH has higher energy density per volume and weight than Ni-Cd but at the cost of reduced cycle life. They are used in digital cameras, digital assistance, automotive batteries, cell phones, and other low-cost devices. Disadvantages are highly expensive and high self-discharge. The competition from other battery technologies such as lithium-ion is limiting the growth of NiMH battery market.

Lithium-ion: One of the reasons for the rapid growth in the development of Li-ion batteries is a huge acceptance of these batteries in cell phones, laptops, and computers. Out of all battery types Li-ion provides the highest density and thus electronic manufacturers prefer these over other battery technologies. The applications are categorized into automotive, medical, aerospace, military,consumer electronics and so on. They are also used in renewable energy areas for energy storage purposes. Other advantages such as long lifespan, low self-discharge, high charge, and discharge cycles have added to the growth of lithium-ion battery market

“Lithium makes a fine battery because it’s a scarily reactive metal. Pure lithium ignites on contact if it touches water – a flake of it would sizzle and fry on the water-rich cells of your skin. “

SAM KEAN

The subclass of the lithium-ion battery market is Lithium-Iron-Phosphate[LiFePO4], Lithium-Nickel-Manganese-Cobalt-Oxide [NMC], Lithium-Manganese-Oxide [LMO], Lithium-Nickel-Cobalt-Aluminium-Oxide [NCA], and Lithium-Cobalt-Oxide [LCO] batteries.

Lithium iron phosphate is used for high power applications. Due to the long cycle life, good thermal stability, upgraded safety, and tolerance features,constant voltage the market demand is increasing in consumer electronics and also in EV sectors.

Due to the high energy density, long life span, and thermal stability, the Lithium-Nickel-Manganese-Cobalt-Oxide [NMC] battery market is predicted to witness the highest growth rate. Researchers are working towards reducing the Cobalt content which would further increase the demand.

Lithium Cobalt Oxide [LCO] is one of the most widely used batteries in applications such as cell-phones, laptops, cameras and so on. Hence has increased the global lithium-ion market share.

One of the developing trends in battery technology is Lithium-Sulphur. Some of the aspects of Lithium Sulphur are sulfur is less expensive compared to Nickel, Aluminium, and Cobalt. They are expected to have high densities compared to other battery technologies.

With the rapid growth in the EV industry, the need for a power revolution is always on topic.

“If you want a product that’s thicker with a bigger battery, it’s also heavier, more costly, takes longer to charge. “

–PHIL SCHILLER

“The depressing thing about battery technology is that it gets better, but it gets better slowly. There are a whole bunch of problems in materials science and chemistry that come in trying to make existing batteries better. “

–NATHAN MYHRVOLD

BATTERY

Battery is a device which is used to store the chemical energy and to convert this chemical energy into electrical energy.  The battery is made up of electrochemical cells, which consists of two electrodes, negative and positive electrode and an electrolyte in the center. When the two electrodes are connected by a wire, electrons will flow from negative electrode to positive electrode. This flow of electrons is called electricity. The cell is considered to be dead when the electrons on the positive and negative electrodes are equal. The electrons are generated by chemical reactions and many different chemical reactions are used in batteries. For instance, the disposable batteries, is a non-rechargeable energy storage device which once dead must be disposed, example Alkaline batteries. Thus, rechargeable batteries are used so regular replacement is not required.

Refer https://futuretronlabs.in/blog/index.php/2019/08/22/basic-components-of-an-ev/ to know more about the battery and other EV parts.

The power stored in battery is used to run the electric motor and other electronic units in an electric vehicle. The batteries are recharged from the dedicated charging unit.

TYPES OF BATTERIES

The types of rechargeable batteries used in Hybrid Electric Vehicles and All-Electric Vehicles [EV] are Lead-Acid batteries,Nickel-Cadmium Battery (NiCd or NiCad), Nickel Metal Hydride [NiMH] batteries and Lithium-ion [Li-ion] batteries. Each battery type has its own advantages and selection of these batteries depends on where it is used so that maximum benefit can be obtained.

LEAD ACID BATTERIES

It was invented by Gaston Plante, a French Physician in 1859. To convert chemical energy to electrical energy sponge metallic lead and lead peroxide are used in Lead Acid batteries. It is the oldest and the first rechargeable batteries available.

Some of its advantages are low cost, longest life cycle, it can withstand slow, fast and overcharging, available in all sizes and shapes, wide capacity range, low self-discharge-which is lowest among rechargeable batteries, high discharge rate, can be recycled and reused in new batteries.

Some of its disadvantages are energy density is low, poor weight-to-energy ratio, not environmental friendly, transportation restrictions on flooded lead acid, limited number of full discharge cycles.

NICKEL-CADMIUM BATTERY (NiCd or NiCad) BATTERIES:

Waldemar Jungner invented Nickel-Cadmium battery in 1899. The rechargeable NiCd battery is composed of nickel hydroxide in the positive electrode, cadmium in the negative and potassium hydroxide as electrolyte.  A typical lead-acid battery has cell voltage of roughly 2V, which then steadily comes down as it is depleted whereas NiCad batteries will maintain a steady voltage of 1.2v per cell up till it is nearly completely depleted.

Some of the advantages are low internal resistance, wide range of sizes and performance options are available, high charge and discharge rate, lighter, more compact and higher energy density than lead acid batteries, self-discharge rate is lower than NiMH batteries.

Some of the disadvantages are expensive than lead acid, extremely toxic-causes environmental pollution, high self-discharge, low energy densities compared to newer systems.

NICKEL METAL HYDRIDE[NiMH] BATTERIES:

The Nickel Metal Hydride Battery was patented by Standford Ovshinsky, founder of Ovonics. Hydrogen absorbing alloys are used as the active element at the negative electrode and Nickel -hydroxide at the positive electrode.

Some of the advantages are higher capacity than NiCd, environmental friendly-no toxicity issue, wide operating temperature range, transportation and storage is simple.

Some of the disadvantages are load discharge is high, generates heat during fast charge, sensitive to overcharge.

LITHIUM ION[Li-Ion] BATTERIES

NiMH and Li-ion came into view in 1990s and Li-ion became the most promising and the fastest growing battery system. Lithium offers the largest energy density and is the lightest of all the metals. Due to safety issues attempts to develop Lithium-rechargeable batteries failed. Thus, there was a shift from Lithium to Lithium-ion, it is safer but lower energy density than Lithium metal. The Sony Corporation in 1991 commercialized the first Lithium-ion battery. The electrodes are made of lightweight lithium and carbon. The Lithium-ion has energy density twice that of Ni-Cad Batteries.

Some of the advantages are no memory and no regular discharge is needed – hence low maintenance, high energy density, can handle more charge/discharge cycles, much lighter than other rechargeable batteries,

Some of the disadvantages are protection circuit is required to maintain voltage and current within safe boundaries, very expensive to manufacture, sensitive to high temperatures.