Calculate the size of battery packs that are made by single cells
All kinds of battery packs are assembled from single cells, we can adjust the size of battery pack according to the space requrement from customer.
For example, to make a 48V20Ah LiFePO4 battery pack, we use 3.2V 10Ah LiFePO4 cells for assembling, the pack structure will be 16S2P. 2P means every 2 of 3.2V10Ah cells will be made to a 3.2V20Ah cell module, 16S2P means here will be 16 sets of those 3.2V20Ah cell modules put in series configuration. We always use 3V for calculation, but the real pack volt is 16*3.2=51.2V.
Calculating the size of cell pack:
Take BP-HK-10A (10Ah LiFePO4 cell) type for example, the original size is 60*12*190mm (Length*Width*Height, without terminal tab). When do assembling, we need to consider the space increasing when cells build together, so we add 2mm at length side (60mm+2mm), add 1mm at width side (12mm+1mm). For height we add 10mm(190mm+10mm), because we need to weld tabs though converting boards and adding wires for cells connection, the height increased.
So that the 3.2V20Ah cell module will have the size of below:
If we put those 16 cells modules together into a metal box, arrange them as 2 line 8 column, the size will be:
Lengh (8 column): 26*8= 208mm;
Width (2 column): 62*2= 124mm;
Height : 200+5=205mm. For the height, if we only use welding for wires connection of series config, here will be only about 5mm increasement. If customer want to use wires with connectors for "plug-unplug" connection, we should leave like 30~50mm space for those big wires and connectors(Like for 75A constant current, anderson PA75 connectors which size are big).
Assuming the thickness of BMS is 12mm (Most of 12S or 16S type BMS will have this 12mm thickness). We always put BMS/PCB at the top of pack, we also use about 2~3mm isolate materials to separate BMS from batteries as heat isolation.
So, Height increased again: 205mm (cell packaging height) +12mm (BMS thickness) + 3mm (isolate materials) =220mm
BMS can also be placed at the Length side (the 208mm side) if needed, so length will incrase to 208+15=223mm, but height will still keep 205mm.
Put this cell pack and BMS into metal case, it needs some extra foams for vibration protection, so size will be incrased, also the metal sheet of metal case have some thickness, so the size will grow as below:
Foams will lead to about 4~6mm increasement in size , the metal sheet of case will lead to about 4mm increasement in size too.