Project 1 Mechanical design of battery pack
Creating a detailed battery pack drawing along with an enclosure involves a combination of electrical and mechanical considerations. Designing a safe and functional battery pack requires expertise in electrical engineering and knowledge of safety standards. The following is a basic representation to get started.
Assumptions:
1. Cell Configuration:The ANR26650M1-B cell is a cylindrical lithium-ion cell. Assuming a nominal voltage of 3.6V per cell and a typical capacity of 5,000mAh, the pack will consist of cells connected in series and parallel to achieve the desired voltage and capacity.
2. Voltage and Capacity: Assuming the cells are connected in a series to achieve the desired voltage, we need to calculate the number of cells required. For an 18 kWh pack, considering the nominal voltage of 3.6V per cell, the total number of cells (N) can be calculated using the formula:
\[N = \frac{\text{Total Energy (Wh)}}{\text{Nominal Voltage (V)} \times \text{Capacity per Cell (Ah)}}\]
\[N = \frac{18,000 \text{ Wh}}{3.6 \text{ V} \times 5 \text{ Ah}}\]
This would give you the total number of cells in a series.
3. Pack Configuration: Once you have the number of cells in series, you can decide on the parallel configuration to achieve the desired capacity. The pack will have multiple groups (parallel sets) of cells connected in series.
4. Enclosure Material:The enclosure should be made of a material that is durable, heat-resistant, and electrically insulating. Common materials include plastic or metal, and the design should consider factors such as heat dissipation and protection against external elements.
5. Cooling System: Depending on the application and power requirements, you may need to incorporate a cooling system, such as fans or heat sinks, to maintain the temperature of the battery pack within safe limits.
6. BMS (Battery Management System): A Battery Management System is crucial for monitoring and balancing individual cells, protecting against overcharging, over-discharging, and ensuring overall safety. Make sure to include space for the BMS within the enclosure.
7. Connectors and Wiring: Consider the type of connectors and wiring that will be used to connect the battery pack to the application. Ensure that these components can handle the expected current and voltage.
Nanophosphate High Power Lithium Ion Cell ANR26650M1-B:
ANR26650M1-B Technical data:
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Cell Dimensions
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26 x 65 mm
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Cell Weight
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76 g |
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Cell Capacity (nominal/minimum) (0.5C Rate)
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2.5/2.4 Ah
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Voltage (nominal)
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3.3 V |
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Internal Impedance (1kHz AC typical)
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6mΩ
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| Power |
2600 W/kg
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Recommended Standard Charge Method
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2.5A to 3.6V CCCV, 60 min
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Recommended Fast Charge Method to 80% SOC
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10A to 3.6V CC, 12 min
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Maximum Continuous Discharge
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50 A |
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Maximum Pulse Discharge (10 seconds)
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120 A |
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Cycle Life at 20A Discharge, 100% DOD
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>1,000 cycles
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Operating Temperature
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-30°C to 55°C
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| Storage Temperature |
-40°C to 60°C
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About cell:
The LithiumWerks ANR26650M1-B is the next generation of A123 Systems' pioneering 26650 cylindrical cell, now with greater power and energy density and lower impedance. This versatile lithium ion cell is suitable for a wide variety of applications and system designs.
About module:
A battery management system (BMS) is any electronic system that manages a rechargeable battery (cell or battery pack), such as by protecting the battery from operating outside its safe operating area, monitoring its state, calculating secondary data, reporting that data, controlling its environment.
About Battery pack:
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.
EV design - Battery calculation:
Assumptions:
Battery energy = 18 kwh
Voltage (to run the vehicle) = 400V
(i) Energy = 18 kWh
(ii) Number of cells (N) = energy / (nominal voltage*capacity)
N = 18000 / (3.3*2.5)
N = 2182
We need a minimum of 2182 cells to get 18 kWh energy, now based on that, we need to decide configuration – series and parallel.
In series configuration capacity remains the same and voltage will be the sum of individual cell voltage.
In a parallel configuration, the voltage remains the same and capacity accumulates.
And we assumed 400 Volts are need to run the vehicle.
The nominal voltage of one cell is 3.3 V
Number of series cells required to produce 400 V (Ns) = voltage required / nominal voltage of one cell
Ns = 400 / 3.3
Ns = 121.21 = 122
122 cells are connected in series will generate 400 voltage and the capacity of the whole module will be 2.5 Ah
Now we need to find the number of cells which will be connected in a parallel configuration
Np (cell in parallel) = total cell / Ns
Np = 2182 / 122
Np = 17.8 = 18
Hence we take 18 cells for each parallel row, although it is exceeding the required capacity, that is negligible.
Cell architecture = 122 Series and 18 Parallel = 122S18P
(iii) Battery capacity:
We know parallel configured cell multiplies individual cell capacity so,
Capacity = parallel cell row*individual cell capacity
Capacity = 18 * 2.5
Capacity = 45 Ah
(iv) Current supplied by the battery
We have already calculated battery capacity which is 45 Ah means it is going to supply 45 A current per hour. which can be considered as C-rate.
(v) Range:
Let’s powertrain energy consumption = 100 Wh/km at 70% powertrain efficiency
Range = Capacity / energy consumed per kilometre
Range = 18000 / 100
Range = 180 km
So,our vehicle will be able to cover around 180 km with current parameters.
(vi) Internal Resistance of Battery:
The entire resistance encountered by a current as if it flows through a battery from the negative terminal to the positive terminal is known as internal resistance of battery.
(vii) Battery Dimensions:
ANR26650 cell has 26mm diameter and 65mm height. On the basis of that we need to decide battery size of battery casing.
Length of casing (L) = number of cells at series*(cell diameter (26) + margin at both side of cell (4)) + clearance at side (diameter of edged cell + margin)
L = 122*30 + 60
L = 3720 mm
Breadth of casing (B) = number of cells at parallel*(cell diameter (26) + margin at both side of cell (4) + clearance at side (diameter of edged cell + margin)
B = 18*30 + 60
B = 600 mm
Height of casing (H) = 65+35 (Height of cell + margin for wiring ,Cell holders and metal strips)
H = 100 mm
(viii) Weight of battery pack
Cell weight = 76g
Number of the cells = 2182
Battery pack weight (W) = cell weight*number of cells + weight of accessories
W = 76*2182 + 4.5 = 165.8 + 4.5 = 170.3 kg
Conclusion:
Lithium Ion and Lithium Ion Polymer batteries are a great power source for some applications but they require preventive protection during discharging and charging.