# Battery dimensioning

By Enrico Melotti *** **Initial parameters**

The first step to design a battery pack is to fix some variables:

- Voltage:

We decide to use **144V** battery pack, created with common LiFePO4 cells type, usually used in EV conversions.

- Resistent (Drag) Power:

The main source of Resistent Power is the aereodynamic resistance (drag).

After few evaluations we consider about **8 kW** at **80 km/h** (see **Note 1** in the footer).

**Number of cells**: The number of cells is really simple to obtain:

144V (our battery voltage) / 3,2v (nominal voltage of each cell) = **45 cells**

**Battery capacity**:

The battery capacity is a bit more difficult to determine, because it depends on more than one variable.

Some of these are:

**Max Discharge rate**:The discharge rate, or “C” rate, required by the motor is obatained by this formula:

Peak Power of the motor / Nominal capacity of the battery pack

The Peak Power considered is

**66KW**The datasheet specifes

**2C**optimal discharge rate - to**5C**max rate.**Driving style**:Depends on the driver. We decided a normal driving style with good acceleration and not excessive speed.

**Range autonomy**:The range depends on driving style and capacity. We focus our attention in the

**100-150 Km**range.

After this introduction, our choice is among two battery cells: **A=100Ah** and **B=160Ah**.

**Differences**:

Weight: A = **140 Kg** | B = **260 Kg**

Volume: A = **89 liters** | B = **160 liters**

Price estimate (1,2$ per Ah): A = **5500<math>** | B = **8600</math>**

Max C rate: C = 3

Max Continuous amperage = Cell capacity x C: A(100Ah) = **300 A** | B(160Ah) = **480 A**

Note 1: You may compare this result against the Powertrain dimensioning sheet we are using for the conversion and currently [tracked in the repo] (https://github.com/iaiaGi/iaiaGi_ZEV_Kit/tree/master/Projects/Kevin/Mechanical_Dimensioning)