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Calculate the size of battery packs that are made by single cells

For battery packs assembled from pouch cells, we can adjust the pack size to suit customer requirement, by put cells in different arrangement.

For example, to make a 24V50Ah LiFePO4 battery pack, we use 16 of 3.2V 25Ah LiFePO4 cells for assembling, the pack structure will be 8S2P, it means every 2 cells in parallel and 8 of them in series config. We always use 3V for calculation, but the real pack volt is 8*3.2=25.6V. The 3.2V 25Ah pouch cell have the size of 140*8.5*240mm (L*W*H, without tab), when we put 16 cells in stack as all 16 cells in one row, and use some extra foam for protection, the new size will be:

Length: (140mm +2mm tolerance) + 2mm*2 (foams) +1mm*2 (PVC sheets)+ 0.5mm*2 (shrink film) = 147mm
Width: (8.5mm+0.5mm tolerance) * 16 pcs + +1mm*2 (PVC sheets)+ 0.5mm*2 (shrink film) = 147mm
Height: (240mm +2mm tolerance) + 20mm (cell tab and welding etc) + 2mm*2 (foams) +1mm*2 (PVC sheets)+ 0.5mm*2 (shrink film) = 267mm.

The finished shrink film cell pack will have the size of 147*147*267mm.

If we build the BMS into this battery pack, assume BMS thickness is 12mm, necessary foam is 3mm, when put BMS at length direction, length will be increased to 147mm+12mm+3mm=162mm. The new pack size will be 162*147*267mm.

If put the BMS at height direction, the new height will be 267mm+12mm+3mm=282mm. The new pack size will be 147*147*282mm.

When built into metal case, please consider the reasonable space for holding the shrink film battery pack. For bigger battery packs, please consider to directly use the battery module structure.

Above steps will give customer a general idea of how our batteries packaged. For the exact size calculate, please contact us and we can help you well.

What is LiFePO4 battery

LiFePO4 battery, or LFP battery, the full name is the lithium iron phosphate battery, which belongs to one kind of rechargeable lithium batteries, battery takes LiFePO4 as cathode materials.

For original LiFePO4 have low electric conductivity, many battery manufacturers make efforts on improving original LiFePO4 materials, like nano-technology, metal-doping, carbon-coating etc. Bestgo-Power takes metal-doping and carbon-coating to update original LiFePO4 materials for battery manufacturing.

What is depth of discharge (DOD)?
DOD, short for the Depth of Discharge, is used to describe how deeply the battery is discharged. If we say a battery is 100% fully charged, it means the DOD of this battery is 0%, If we say the battery have delivered 30% of its energy, here are 70% energy reserved, we say the DOD of this battery is 30%. And if a battery is 100% empty, the DOD of this battery is 100%. DOD always can be treated as how much energy that the battery delivered. For lithium batteries we do not suggest fully discharge them to 100% DOD, it would shorten the cycle life of batteries.
What is state of charge (SOC)?
SOC, short for the State of Charge, is used to describe how full a battery is. When a battery is fully charged, we can say that the SOC of this battery is 100%. SOC can be used to describe how fully the lead acid battery charged, cause lead acid battery always need to be fully charged for storage. Later nickel batteries and lithium batteries also take SOC to describe energy reserve. Here is a formula describing the relationship of SOC and DOD, that is “SOC = 100% - DOD”.
What is the Amp-hour (AH)?
The Amp-hour (Ah) is used for describing how much energy that battery can store in. The volume of the constant current (in amps) multiple with time (in hours) then got Amp-hour (AH) as battery capacity. For example, if a Bestgo-Power LiFePO4 cell, marked as “10AH @ 3C discharge, 25°C”, it means in 25°C condition, if discharge this battery with current no more than 30A (10AH, 3C), this battery can offer 10AH energy, like 30A current for 1/3 hour, or 5A current for 2 hours.
What is CC/CV mode?
Constant current / constant voltage (CC/CV) charging mode is a effective way to charge lithium batteries. When a lithium battery is nearly empty, we take constant current to charge it. We need to make sure that charging current should be lower than the max charging current that battery can accepted. With constant charing the voltage of battery is slowly upping, when battery volt reaches the max charging voltage, charger would make sure charging voltage fixed as "constant voltage" and reduce the charging current. When battery is fully charged this state would be stopped.
How to extend the battery cycle life?
Signal cell (battery) is an independent unit which contains a complete chemical reaction environment inside. For nominal usage we need to make sure that cells / batteries are under specified conditions that data-sheet described. For lithium batteries, we suggest to take consideration of working temperature, and do not fully charged to 100% SOC and do not fully discharged to 100% DOD when using, by this way the cycle times of LiFePO4 could be effectively extended.