Project 1 Mechanical design of battery pack

EV-BATCH-17

Battery pack capacity: 18 kWh

Cell: ANR26650M1-B

Prepare a detailed battery pack drawing along with its enclosure. State your assumptions.

AIM:

To prepare a Mechanical design of battery pack using ANR26650M1-B cell model.

THEORY:

A battery pack is a set of any number of (preferably) identical batteries or individual battery cells. They may be configured in a series, parallel or a mixture of both to deliver the desired voltage, capacity, or power density. The term battery pack is often used in reference to cordless tools, radio-controlled hobby toys, and battery electric vehicles.

Components of battery packs include the individual batteries or cells, and the interconnects which provide electrical conductivity between them. Rechargeable battery packs often contain a temperature sensor, which the battery charger uses to detect the end of charging. Interconnects are also found in batteries as they are the part which connects each cell, though batteries are most often only arranged in series strings.

When a pack contains groups of cells in parallel there are differing wiring configurations which take into consideration the electrical balance of the circuit. Battery regulators are sometimes used to keep the voltage of each individual cell below its maximum value during charging so as to allow the weaker batteries to become fully charged bringing the whole pack back into balance. Active balancing can also be performed by battery balancer devices which can shuttle energy from strong cells to weaker ones in real time for better balance. A well-balanced pack lasts longer and delivers better performance.

For an inline package, cells are selected and stacked with solder in between them. The cells are pressed together and a current pulse generates heat to solder them together and to weld all connections internal to the cell.

Object:

To design the battery pack which has 18 kwh using ANR266050M1-B cell modu

DATA SHEET:

LFP batteries technology and applications

To prepare a Mechanical design of battery pack using ANR26650M1-B cell model.

THEORY:

A battery pack is a set of any number of (preferably) identical batteries or individual battery cells. They may be configured in a series, parallel or a mixture of both to deliver the desired voltage, capacity, or power density. The term battery pack is often used in reference to cordless tools, radio-controlled hobby toys, and battery electric vehicles.

Components of battery packs include the individual batteries or cells, and the interconnects which provide electrical conductivity between them. Rechargeable battery packs often contain a temperature sensor, which the battery charger uses to detect the end of charging. Interconnects are also found in batteries as they are the part which connects each cell, though batteries are most often only arranged in series strings.

When a pack contains groups of cells in parallel there are differing wiring configurations which take into consideration the electrical balance of the circuit. Battery regulators are sometimes used to keep the voltage of each individual cell below its maximum value during charging so as to allow the weaker batteries to become fully charged bringing the whole pack back into balance. Active balancing can also be performed by battery balancer devices which can shuttle energy from strong cells to weaker ones in real time for better balance. A well-balanced pack lasts longer and delivers better performance.

For an inline package, cells are selected and stacked with solder in between them. The cells are pressed together and a current pulse generates heat to solder them together and to weld all connections internal to the cell.

Advantages and disadvantages of LFP batteries

The main advantages of the LFP batteries are:

• Durability
• Long lifecycle
• Low cost
• Excellent safety

The main disadvantages of the LFP batteries are:

• More tolerant to conditions of full charge and is less stressed at higher voltage for a long time.
• lower nominal voltage which reduces the specific energy
• Higher self-discharge than other types Li-ion batteries, which causes balancing issues with aging

APPLICATIONS OF ANR26650M1-B Cell:

Commercial Solutions

1. a) Advanced lead acid replacement batteries for:
2. b) Datacentre UPS
3. c) Telecom backup
4. d) IT backup
5. e) Autonomously guided vehicles (AGVS)
6. f) Industrial robotics and material handling equipment

7.g) Medical Devices

Government Solutions -

1. a) Military vehicles
2. b) Military power grids
3. c) Soldier power
4. d) Directed energy

Grid Solutions

1. a) Frequency regulation
2. b) Renewables integration
3. c) Reserve capacity
4. d) Transmission and distribution

Transportation Solutions

Hybrid, plug-in hybrid and electric vehicle battery systems for:

1. a) Commercial vehicles
2. b) Off-highway vehicles

BATTERY PACK DESIGN:

The purpose of a battery pack is to provide a convenient integrated power source for portable applications. The advantages of using custom designs are outlined in the section on Benefits of Custom Packs. The pack may fulfil several functions:

1. It enables higher voltage or higher capacity batteries to be built up from low voltage, low capacity cells.
2. It houses a cell or a bank of cells together with the associated interconnections in a single convenient pack.
3. It accommodates any necessary monitoring and electronic protection devices or circuits within the pack.
4. It can accommodate additional circuitry such as indicator lights, heaters, cooling ducts and solar panels. 5. It matches and meshes with the cavity in the product which the battery is intended to power providing both electrical and mechanical interfaces. 6. It can provide unique electrical and mechanical interfaces to ensure compatibility both of the battery with the intended product and the charger with the battery.

Following Factors are considered while we design a battery pack:

1. a) Capacity and Voltage:

With a simple series chain of cells, the battery capacity in Amp Hours is the same as the capacity of the individual cells since the current flows equally through all the cells in the chain.

High battery voltages are achieved by adding more cells in a series chain. The voltage of the battery is the voltage of a single cell multiplied by the number of cells in the chain. This does not increase the Amp Hour capacity of the battery, but it increases the Watt Hour capacity, or the total stored energy, in proportion to the number of cells in the chain.

Battery capacity can increase through adding more parallel cells. This increases the Amp Hour capacity as well as the Watt Hour capacity without increasing the battery voltage. For batteries with parallel chains the capacity of the battery is the capacity of the individual chain multiplied by the number of parallel chains.

Whereas cell voltage is fixed by the cell chemistry, cell capacity depends on the surface area of the electrodes the volume of the electrolyte, - that is, the physical size of the cell. If at all possible, the number of cells in a pack should be minimised to simplify the design and to minimise potential reliability problems. Fewer cells require fev support electronics. Thus, parallel chains should be avoided by specifying the highest capacity cells available.

NOTE: Cells with different capacities or cell chemistries should not be mixed in a single battery pack.

1. b) Cell Configuration:

The ultimate shape and dimensions of the battery pack are mostly governed by the cavity which is planned to h it within the intended application. This in turn dictates the possible cell sizes and layouts which can be used. Pris cells provide the best space utilisation, however cylindrical cells provide simpler cooling options for high power batteries. The use of pouch cells provides the product designer more freedom in specifying the shape of the batt cavity permitting very compact designs. The orientation of the cells is designed to minimise the interconnections between the cells.

1. c) Battery Electronics:

Besides the cells many battery packs now incorporate associated electronic circuits. These may be protection devices and circuits, monitoring circuits, charge controllers, fuel gauges, and indicator lights. Electronics for high power multi-cell packs also include cell balancing and communications functions. The packs may also be design to deliver more than one voltage from the basic cell combination, although applications requiring multiple voltage sources are more likely to make provision for this within the application. In addition to the basic battery support electronics the battery pack may include other functions such as heaters to extend the lower working temperature solar cells to keep the battery fully charged. These circuits in turn have their own control circuits. Space, fixing poin and methods and interconnections need to be allocated for all these electronic circuits.

1. d) Software:

Software is a major component of Lithium batteries, particularly for automotive applications. Control systems are required to keep the cells within their specified operating range and to protect them from abuse. Fuel gauging needs complex algorithms to estimate the state of charge (SOC). Communications with other vehicle systems are needed for monitoring the battery status and controlling energy flows.

1. e) Internal Interconnections:

Low power cells are usually connected together using nickel strips which are welded to the cell terminals or the case. Soldering is not recommended since the soldering process is apt to apply large, uncontrolled amounts of heat to the battery components which may damage the separators or the vents which are normally made of plastic. Modern computer-controlled resistance welders allow much more precise control of the welding process, both limiting the amount of heat applied to the battery and localising the heat to a small desired area. Welding also provides a stronger, low resistance joint. The interconnecting strips often have complex shapes and profiles which may be stamped out of flat strip in a progressive die. High power cells may use solid copper bus bars or braided straps. The electronic components are usually mounted on a conventional printed circuit board (PCB). Flexible PCBs may cost more than rigid PCBs but they can be used to reduce the overall product costs. Not only do they save weight and space but they also provide more packaging options and they simplify physical interconnections and assembly operations as well as eliminating the need for connectors. Connectors may in fact be specified to facilitate assembly. and disassembly if the design requires that individual battery components need to be changed or serviced but there is usually a cost and reliability penalty associated with such designs.

1. f) External Connections:

The type of terminals or connections to the external circuits depend on, the current to be carried, the frequency with which the battery may be connected and disconnected and the design of the design of the circuit to which the battery will be connected. For low power circuits, gold plated contacts are the terminals of choice for connectors which are subject to frequent insertions. Gold is hard wearing; it has low contact resistance and doesn't oxidise. Flying leads with spade terminals or snap on studs are also used for low power applications. Metal tabs are also used on pouch cells.

Terminals for high power applications are usually threaded metal studs to ensure a reliable connection. Safety requirements on high voltage batteries may also dictate shrouded terminals to prevent accidental exposure of the operator to dangerous voltages or of the battery to short circuits. Keyed or terminals or connections are also advisable to prevent connection to incorrect chargers or loads.

1. g) Thermal Design:

Thermal management is a major issue in high power designs, particularly for automotive applications. See details in the Thermal Management section. As part of the battery system, it may be necessary to provide air- or water-cooling ducts, pumps or fans and heat exchangers for high temperature working or heaters for operating in low

temperature environments. The layout of the cells should be conducive to managing heat flows within the pack.

1. h) Battery Packaging:

The battery casing has to provide the mechanical and electrical interfaces to the product it is designed to power as well as to contain all the components outlined above.

The simplest and least expensive packaging for small batteries is shrink wrap or vacuum formed plastic. These solutions are only possible if the battery is intended to be completely enclosed by the finished product.

The simplest and least expensive packaging for small batteries is shrink wrap or vacuum formed plastic. These solutions are only possible if the battery is intended to be completely enclosed by the finished product.

Injection mounded plastics are used to provide more precision packs. For enclosed packs designs using a minimum of materials are based around which a plastic frame holds the components in place thus minimizing the cost, the
weight and the size of the pack. The overall product cost can be further reduced by using insert moldings in which the interconnection strips and the terminals are molded into the plastic parts to eliminate both materials and assembly costs. Over molding may also be used to encapsulate and protect small components or sub-assemblies.

In some designs the battery pack forms part of the outer case of the end product. The colors and textures of the plastic must match the plastics of the rest of the product even though they may come from a completely different supplier. These designs are usually required to incorporate a mechanical latch to hold the battery in place. Again,

this latch as well as the terminals must interface with plastic parts from a different supplier so high precision and tight tolerances are essential. ABS polymers are the materials typically used for this purpose.

necessary for batteries made up from pouch cells which are vulnerable to physical damage. Automotive battery packs must also withstand abuse and possible accidental damage so metal casings will normally be specified. The metal pack casing also serves to confine any incendiary event resulting from the failure of a cell or cells within the battery and to provide a measure of protection for the user. At the same time the case must also protect the cells and the electronics from the harsh operating environments of temperature extremes, water ingress, humidity and vibration in which these batteries work.

i) Other Considerations:

Thermal effects need to be taken into account and, tolerances must allow for potential swelling of the cells. Some Lithium pouch cells may swell as much as 10% or more over the lifetime of the cell. For this reason, potting is not recommended. In low power designs groups of pouch cells may be shrink wrapped but for higher power application:

plastic or metal frames may be used both to provide physical protection of the cells as well as to allow for swelling. The battery pack should not normally be airtight or sealed since many batteries release hydrogen or oxygen during operation which could cause bursting of the pack or an explosion if the gases are allowed to accumulate. Lithium cells do not emit gases under normal circumstances, but in the case of failure and thermal breakdown, inflammable gases may be vented by the cells. Some form of ventilation or purging should be provided to avoid these problems.

Prepare a detailed battery pack drawing along with its enclosure. State your assumptions

calculations are done in excel sheet attached below

conclusion:

thus we have designed battery pack sucessfully which 18kwh capacity and consisting of ANR26650_m1B