Project 1 Mechanical design of battery pack
Given Cell datasheet of ANR26650M1-B below.
Cell Datasheet or Specification required for designing the battery pack:
| Cell Model |
ANR26650M1-B |
| Cell Name |
Nanophosphate® High Power Lithium Ion Cell |
| Diameter | 26 mm |
| Height | 65 mm |
| Weight | 76g |
| Nominal Capacity | 2.5 Ah |
| Minimum Capacity | 2.4 Ah |
| Nominal Voltage | 3.3 V |
| Power | 2600 W/kg |
| Standard Charging | 2.5A to 3.6V CCCV, 60 min |
| Fast Charging | 10A to 3.6V CC, 12 min |
| Maximum Continuous Discharge | 50A |
| Cycle life (@20A & 100% DOD) | >1000 cycle |
Cell parameter calculation:
Cell Volume = `pir^2h`=`pi d^2/4h`=`pi*(26m)^2/4*65m`=`3.45X10^-6m^3`=3.45cc.
Cell Energy = Nominal Voltage X Nominal Capacity=3.3*2.5=8.25Wh.
Cell Energy Density, = Cell Energy/ Cell weight= 8.25/76=108.55Wh/kg.
Battery pack Designing.
Given, Battery Pack Energy Capacity required = 18kWh.
Assuming Battery pack Voltage = 72V.
Battery pack capacity= Energy/Nominal Volatge = `18k/72` = 250Ah.
No of Cell in Series = Nominal Battery Voltage/Nominal Cell Voltage= `72/3.3`=21.818~22nos.
No of Cells in parallel = Battery pack Capacity/Nominal Capcity=`250/2.5`=100nos.
Total no of cell in the Battery pack = 22*100=2200nos.
Battery Pack Configuration = 22S100P
Nominal Battery pack Voltage = 22*3.3V=72.6V.
Battery Capcaity = No of Cells in Parallel X Cell Nominal Capacity = 100*2.5=250Ah.
Battery pack Energy Capacity = Nominal Battery pack Voltage X Battery Capacity = 72.6X250=18.150kWh.
Battery pack Volume = Total no of cells X Single Cell Volume = 2200X3.45cc=7590cc.
Battery pack weight = Total no of cells X Singles Cell Weight = `2200X76X10^-3`=167.20kg.
CONSTRUCTION:
The above are the just calculation for electrical demand and body of the battery pack. Accroding to the above calculation, we need to construct the battery pack for battery configuration of 22S100P ie. 22 cells are connect in series those 22 cells set are made of 100 more combination that are finally connected in parallel. While make such connection we need leave definite gap between the each cell such they can eliminates the heat generated during the charging and discharging by natural or force cooling system. For spacing use some none conductive material such that they don't shorting between the neighbouring cells. Following are the types of packing the battery pack.
- Linear Type - The strap will both come off the top when there are an even number of cells and one off the top the other off the bottom when there is an odd number of cells. Connector for electrical connection and wrap for mechanical packing.
- Multi Row Cells - Two ways to start packing them either by cubic or by face centered cubic or nested.
- Nested Type Cells
Linear type
Multi Row Type
Nested Type Cells
Face Centered Type cells
Example of spacerand electrical connection
Example of electrical connection made
After placing the cells to make an electrical connection by spot welding the conducting strip. For making series connection the below image shows the method to connect them in series. To avoid the consuming the larger area made connection one layer by other such that reduces area but increases the height.
After constructing the all the 100 set of 22 series combination. Connect all those set to make 100 parallel configuration here also spacers are used. If it consumes wider space they can be placed one over the other such that they make better configuration as below.
Finally after build the required configuration external terminals and other battery management circuits like Cell balancing, thermal management, cooling or coolent flow were made as per the thermal management required.
After all electrcial connection mechanical support are designed such that they are fixed to firm structure either by any shrinking wrap or by thermo setting plastic or by hard metals.
