Question

1. What is the capacity of the accumulator? *

2. In order to increase the capacity of our accumulator, each series cell has 3 additional cells wired in parallel to it; this results in our accumulator containing 576 cells wired in a 144S4P configuration.Each cell has a capacity of 2.5Ah.

3. How much energy (kilowatt.hours) does our accumulator have? * At competition, the energy usage of our electric vehicle is measured to calculate its efficiency over a 22km race.

4. Provide at least 3 reasons why you think we made this decision. * In 2015 and 2016, we used LiPo Pouch cells yet in 2017 & 2018 we made the decision to use Li-Ion 18650 cells.

Question 2 All electric vehicles have a motor controller, this is essentially an inverter which turns the DC input into a PWM output. The motorcontroller we use is the Unitek BAMOCAR-D3-700-400.The bus circuit capacitor of a motor controller has a high capacitance; if this capacitor is not pre-charged before being energised with the full accumulator voltage it will catastrophically explode.

a) Why will the capacitor explode? * HINT: what cannot change instantaneously across a capacitor?

b)List the rules regarding the pre-charge circuit. *

c)Using this rule, what value of resistance will charge the capacitor to at least 540V after 5 seconds? Assume accumulator voltage is 600V. * HINT: you will need to find out the value of the capacitor within the motor controller, consult the manual.

d)What voltage must the motor controller be discharged to within 5 seconds of de-energising? *

Answer 1

1.The total energy of accumulator is given by E = Q× U

Where E= energy

And U = voltage

And Q = electric charge.

4).

• High energy density - potential for yet higher capacities.
  
• Does not need prolonged priming when new. One regular charge is all that's needed.
  
• Relatively low self-discharge - self-discharge is less than half that of nickel-based batteries.
  
• Low Maintenance - no periodic discharge is needed; there is no memory.
  
• Specialty cells can provide very high current to applications such as power tools.