Blogs!

Our individual groups from the electrical systems has created blogs to update our weekly progress!

Solar PV System
Motor and Drive System
Battery and Charging System
Telemetry System

Click to check out their blogs now!

Q & A on SunSPEC 4

1.       What are the major electrical & mechanical systems in a solar car?

A solar car consists of TWO parts:

A.      Electrical Systems

a.       Solar PV system

b.       Motor and driving system

c.       Battery and charging system

d.       Telemetry system

e.       Auxiliary system

B.       Mechanical Systems

a.       Body & Shell structure

b.       Steering System

c.       Braking System

d.       Cooling system

2.       To design a solar car, what are the factors you should consider? Focus on weight, shape, strength and others?

For an efficient solar car to be built, several factors are to be considered. It should be light-weighted, to consume less energy. The material of car body must be strong and resistant to collisions. To create aerodynamics, the shape of the car must be as streamline as possible. Arrangement of solar cells are also a factor of designing a solar car so that we can harvest the maximum sunlight.

3.       What are the commonly available battery used in a solar car? What is your choice, and what are the reasons for choosing it?

The commonly available batteries include, Lithium-Ion (Best), Lithium Polymer and Lithium Iron Phosphate and Lead Acid battery. Our team has chosen Lithium-ion batteries for SunSPEC4. In particular, NCR18650B is used because of its high energy density, stable power output and durability. For the same amount of energy in kwh, it is the lightest as compared to other types of batteries.

4.       What is Voltaic cell and Battery?

In redox reactions, electrons are transferred from one species to another. Energy is released a spontaneous reaction, which can be used for work. To harness this energy, oxidation and reduction are required. The reactions are conducted in separate containers, a wire is used to drive the electrons from one side to the other. In doing this, a voltaic cell is created. Commonly used redox agents are Copper and Zinc. Battery can be formed by connecting a series of cells together.

5.       What are the basic technical specifications of a cell?

The basic technical specifications of a cell includes capacity in mAh, voltage in volt; energy density kJ/kg, weight in gram, operating temperature range.

6.       Table the technical specification of NCR18650A & NCR18650B. Include Vmax, Vmin and weight.

	NCR18650A	NCR18650B
Rated Capacity	Min. 2900 mAh	Min. 3200 mAh
Capacity	Min. 2950 mAh Typ. 3070 mAh	Min. 3250 mAh Typ. 3350 mAh
Nominal Voltage	3.6 V	3.6 V
Charging	CC-CV, Std. 1475 mA, 4.2V, 4 hrs	CC-CV, Std. 1625 mA, 4.2V, 4 hrs
Weight (max.)	46.5 g	48.5 g
Min. Voltage	2.5 V	2.5 V
Max. Voltage	4.2 V	4.2 V
Temperature	Charge:                   0 to 45 °C Discharge:                -20 to 60 °C Storage:                -20 to 50 °C	Charge:                   0 to 45 °C Discharge:                -20 to 60 °C Storage:                -20 to 50 °C
Energy Density	Volumetric:                 620 Wh/l Gravimetric:               225 Wh/kg	Volumetric:                 676 Wh/l Gravimetric:               273 Wh/kg

7.       In WSC 2015, regulation: Li-ion battery is limited to 60kg. How many S and how many P can be configured using NCR18650A / NCR18650B?

Using NCR18650A: 35S, 36P =35x36x2.9x3.6 = 13.245kwh

Using NCR18650B: 34S, 36P =34x36x3.2x3.6 = 14.100kwh

8.       How do you determine/decide the battery voltage level of the solar car?

By the motor maximum voltage level. Higher the better.

9.       What is the technical information of 30S15P NCR18650A battery bank used in SunSPEC3?

Total Weight: 30 x 15 x (46.5/1000) = 20.925 kg

Maximum voltage: 30 x 4.2 = 126 V

kwh:  15 x 30 x 3.6x 2900 = 4.701 kwh

10.       Why battery management system is required in the battery system?

As part of the WSC regulation requirements.

A Battery Management System (BMS) is used to balance the cell voltage and to protect the cells from overcharging and discharging.  Without a BMS, the high voltage battery pack is at risk of operating outside its Safe Operating Area (SOA) which could cause overheating/explosion or a breakdown of the entire battery system. With this system it obliterates the risk, by monitoring each cell and maintaining the operations within the SOA. The system could also disconnect the battery pack if the voltage or temperature limit has exceeded.

11.   Draw a typical state of discharge curve of a NCR18650A (3A). (Volt vs Time)

     

12.   Draw a typical state of discharge curve of a NCR18650B (3A). (Volt vs Time)

13.   Compare and comment on the curve in Q11 and Q12.

Both discharge at 3A, curve Q12 stop at 1 hour, and curve Q11 stop at 55minute, this indicates that the cell in Q12 has higher energy.

14.   Why state of discharged curve with (Volt vs %) is preferred?

By having the x-axis as percentage, it is easier for us to predict the remaining battery capacity in the cells against the voltage.

15.   What is the current drawn from the battery if the load is at 3kw, while the battery voltage is at it minimum of 85 volts?

Current: 3000/85 = 35.29 A (Means: Current can shoot up at low voltage operation)

16.   Please select a flexible electrical cable to carry the above calculated current in Q15. What is the cable AWG – size?

According to the AWG table, cable size AWG 9 is required.

17.   Table the current carry capacity of SWG & AWG.

18.   How many battery box/es can be installed in the cruiser class solar car?

According to the World Solar Challenge Rules and Regulations, item 2.22.14, only two battery boxes are allowed on the cruiser solar car. 

Team 3 Eco Meter Results

For our team, we obtained data from the half cell solar panel. These are the graphs that we have extracted from the data that we attained from yesterday.

Top Right: Graph of I-V(Parallel) ; Top Left: Graph of P-I-V ; Bottom Left: Graph of I-V(Series)

Resistance(Series): 3.25 ohm

Resistance (Parallel) : 66 ohm

Below is our capture of the solar internal characteristic of the solar panel using the multisim.

The Isc is 0.905 Ampere. The series and parallel resistance values are the ones that we have calculated above from the respective graphs.

However, our readings are not 100% accurate because the sensor unit was not activated.

SunSPEC4!

SunSPEC4 is a solar car from Singapore Polytechnic.

Our team consists of lecturers and students from the School of Electrical & Electronics Engineering and School of Mechanical & Aeronautical Engineering.

SunSPEC4 will be participating in the upcoming World Solar Challenge 2015!

Stay tune for more updates!