When first discussing what topic, we would cover in our project, we knew it would be something to do with environmental issues and how to decrease their never-ending consequences. And…after discovering that transport takes a big role in the global annual CO2 emissions, we ended settling with that same area. After a while we came upon Bluesky Energy and their GREENROCK saltwater batteries which inspired us to start creating our model which would represent the innovation that the transport industries are in need. This will lead directly to the objective of the project which is encouraging the transport industry to renovate them selves as fast as possible.
However, before we start explaining how our model works, we need to cover how the same components would work on a conventional electric car, and we will talk about the motor first.
Although not every electric car will have the same motor the 3-phase induction motor is the most common among the EV industry. Like all electric motors the induction motor is composed of 2 major components the rotor and the stator. For understanding how any electric motor works we will first need to understand some rules and laws which I will explain now.
The stator of an induction motor will have 3 set of coils which are then connected to each other by an alternating current this is what will give the name of the motor as we will have 3 phases accounting for 3 sets of coils. We know according to the Oersted experiment that whenever we have electric current flowing, we will have a magnetic field surrounding it. This will happen in the 3 sets of coils; we will have a magnetic field surrounding them however it’s important to understand how alternating current works. Alternating current will travel back and forward along time, periodically inverting the polarity of the circuit. So, as the polarity of the current flowing through the 3 coils reverses the polarity of the magnetic field created by the coils will reverse as well. However, the 3 phases wont change polarity at the same time so this will mean the magnetic field will rotate as the phases change their polarity creating a rotating magnetic field or RMF, there is more depth into this but we don’t have time to cover everything. This rotating magnetic field RMF will continue to rotate provided that alternating current is flowing through the sets of coils. The rotor being made of good conductors and being inside the stator will interact with the RMF. Before João explains what type of interaction will happen between them you need to understand 2 fundamental laws. Firstly, we have the Faraday’s laws. The Faraday´s First Law on electromagnetic induction states that any changes in the magnetic field of a coil of wire will cause an electromotive force to be induced in the coil. This force is called induced emf and if the conductor circuit is closed, the current will also circulate through the circuit and this current is called induced current. Faraday´s Second Law on electromagnetic induction states that the magnitude of emf induced in the coil is equal to the rate of flux change that links with the coil. The flux linkage of the coil is the product of the number of turns in the coil and the flux associated with the coil. With these laws we understand that if the rotor is inside the RMF it’s magnetic field will constantly suffer changes and thus an induced alternating current will be created inside the rotor. Moreover if we If we have an electric current flowing on a closed circuit, according to the Oersted experiment another rotating magnetic field will be created this time on the rotor.The second fundamental law is the Lenz’s law, and it states that the direction of the current induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes the initial changing magnetic field that produced it. This will mean the RMF of the rotor will have an opposite polarity to the RMF of the stator. As the rotor RMF will have an opposite polarity it will try to catch up to the stator RMF and thus creating a constant rotation.
As the induction motor being an AC motor, we opted for a simpler motor which wouldn’t require an inverter to work. We ended up settling with a common brushed DC motor. Although more complex DC motors will have sets of coils as stators just like in the induction motor, simpler and smaller dc motors, like the one we are using use, will have permanent magnets as stators. These permanent magnets will then create a magnetic field inside of the stator. The rotor which stays inside of the rotor is composed of many components of it’s own. First, we have the copper windings, these are connected to a commutator which will be in direct contact with 2 spring loaded brushes. These brushes will be the ones who the electric current will flow through. Since we will have an electric flowing through the copper windings it will create an induced magnetic field as we seen in the Oersted Experiment. This magnetic field will interact with the one of the stator, consequently making all of the rotor rotate. Each time the brushes make contact with different commutator segments the polarity of the circuit will reverse which will reverse the polarity of the induced magnetic field as well. This reversing of the polarity will continue to happen creating a continuous rotation of the rotor. So, while the induction motor relied on its alternating current to reverse the polarity of the induced magnetic field to then make it rotate the DC motor runs on a constant voltage, so it needs the commutator and the brushes to “manually” reverse the polarity of the circuit.
The other component that we will talk about will be the battery.
A battery is made out of:
The anode and cathode store the lithium, and when the charging or discharging process happens, the electrolyte carries positively charged lithium ions inside the battery through the separator.
[When the ions are released from the:
When the ions are being released from the anode or from the cathode, a charge will be created in one of the current.
This battery behaves in a similar way as the battery that we already mentioned in this presentation, which is the GREENROCK Saltwater battery, which I will now explain.
The GREENROCK Saltwater battery is based on a sodium-ion technology that behaves similarly to lithium-ion batteries.
As you can see here, it has the same components of a lithium-ion battery [(cathode, anode, current collectors, electrolyte, and separator) and charging and discharging methods are the same as well (charging: cathode to anode; discharging anode to cathode)]. The only difference is that it is based on sodium ions, not lithium ions like Tesla’s battery. Also, every material used is non-toxic and environmentally friendly.
This battery does not have a pretty big market, having only sold 250 batteries in 2017 for around 850 - 1100 euros per kWh. It is sold directly to the customer and it is a good option for people that live far from civilization, where power doesn’t usually reach.
With the curiosity of replicating a battery that also is powered by saltwater, we decided to create our own saltwater battery. This example consists of:
The dissolved salt in the water separates into positive and negative ions, which makes the electrical conductivity [(which means that if a material is more conductive the less resistance it shows to current flow)] of the salted water considerably higher than normal water. [The resistance then translates into energy dissipation, which in this case, is heat.]
In this battery there will also be an exchange of electrons between them, one being negatively charged and the other one positively charged. With this, one of the metals will attract the positive ions and the other metal will attract the negative ions, so, we can call this a redox reaction.
If we connect a cable, we will be able to see voltage between the two metals (which should be around 0,8 V), but when we did experiments with the battery, the values were different.
The first battery that we did was the battery that I explained in the 2nd Term, which gave us around 0.7 V, not that different to the number that we saw when doing the research about the battery, but it was not enough to power the motor, so we tried different methods.
In the second battery that we did, we decided to try and replicate a voltaic pile with our components [(in case you do not know what it is, it is plates of zinc and copper with a paper soaked with a liquid in the middle stacked on top of each other)] and that gave around 1.2V, which still is not enough to power the motor.
In the third battery however, although we did the same voltaic pile, we used vinegar as an electrolyte instead of salt water, which gave us around 2.2V, which, in theory, is enough to power the motor, but when we tried to connect the battery to the motor, there wasn’t any movement.
We even tried a fourth battery, which is the third battery with more stacks, and it gave us a total of 3.2V, and there was still no movement. This is due to the internal resistance of the battery, which we didn’t know was a problem.
Internal resistance in the simplest way possible is the resistance that is created by the electrolyte within the cell between the two electrodes. In our case, the electrodes are the copper and the zinc. When we tried to connect the battery to the multimeter just by itself, it gave us 3.2 V as said before, and this number gives us the electromotive force of the battery. On a closed circuit, where the battery was connected to the motor, we read 0.05V on the multimeter, which gives us the voltage of the circuit. We’ve also taken a look at the values of electric current in the circuit, and it turned out to give us 0,0015A, which is a very low number. If we do the math, it turns out that the internal resistance of the materials is around 2100 Ohms per cell. This number is usually high, and if we take a look at this graph, we can prove that this always happens with voltaic piles using two electrodes. In the graph, we can see that even if we have the smallest amount of electric current on the circuit, we will still have a lot of voltage drop.
This is the main reason why we could not bring a complete model for you today, but we have some ideas in how we can solve this. We have seen articles online, that suggest that we can decrease the internal resistance by:
We are trying to correct this problem, but we had a sequence of unfortunate events associated with the arrival of the raw materials which led to the construction of the model taking more time than we expected.
With that, our project comes to an end. We have been educated about a big number of things, and although we are a little disappointed for not being able to show you guys the working model, we will be working on improving the car and battery until the end of the year to hopefully make it work. We would also like to thank all the teachers involved in this subject, as we've been given the opportunity to do this in our last year before university.