Cameron and Mattias having a look at the old alternator prototype
Cameron, Nina and Mattias have spent most of their time working on the alternator. Cameron and Nina are both exchange students: Cameron comes from Monash University, Australia, and Nina from University of Ljubljana, Slovenia. Our last exchange student – Christophe from the University of Technology of Troyes, France – has been focusing on mechanical systems. Mattias comes from Råneå.
The alternator is the thing in Baldos II that transforms the mechanical energy from ICE into electrical energy by charging the electric double-layer capacitor. It is a type of generator that only produces Alternating current (AC). We already have one of these in the car, but that one has a maximum efficiency of around 80% and was designed to be an electrical motor (i.e. doing the exact opposite of an alternator). The aim for this year has been to surpass those 80% – with some efforts it could reach up to 90%. This 10 % difference would increase the efficiency of the whole vehicle with 12,5% – which is a significant raise for an already high performing vehicle like Baldos II.
The construction of the alternator is probably the single process that has suffered most from massive design changes at late stages. This is a stepwise description of what has happened.
Equipment to do copper coils by hand
First attempt: The start off point for the whole project was to create a sound magnetic field. An alternator typically consists of two things. First, magnets rotating together on a “rotor”, creating a magnetic field that spins around an axis. Second, copper wire coiled and attached on a “stator”, which responds to the changes in the magnetic field by producing current (i.e. electricity). The initial idea was to modify a prototype alternator (which was built but never completed during last year’s project) to create such a superior magnetic field.
First setback: While doing calculations on the efficiency, the trio discovered that the alternator they were about to build would generate 50 V already at 700 rpm. Since the ICE would run at somewhere around 5-7000 rpm, the voltage would be far too high. Also, the old prototype was a rather fragile construction, and the round shape of its magnets was far from ideal.
Second attempt: So, Cameron, Nina and Mattias abandoned the alternator from last year and started out with their own prototype. They also found some bar magnets and decided to use those as a guide for the whole design.
Initial (left) and final (right) rotor design
Second setback: But after a while working with the bar magnets they got cold feet. By putting bars in a circle (see the image on the left) they received open spaces on the outer rim of the rotor. These spaces would have a relatively low magnetic field strength and thereby produce very little current. The only way to make these gaps negligible would be to run the alternator at extreme rpm:s.
Third attempt: There was no way out but to change the shape of the magnets, and thereby the whole design of the alternator. A big issue was to get a hold of such permanent magnets – it was already quite late in the production process. Luckily Vacuumschmelze supported us with new ones (a big thank you to Stork Drives as well, who supplied us with an Incremental Rotary Encoder). These magnets were shaped like circular sectors, and the efficiency calculations suddenly looked a lot more promising than before.
Third setback: So far the trio had only concentrated on optimizing the magnetic field, but after a while they realized that they had neglected the second part: the copper windings. When they compared their design to their efficiency calculations it was clear that there simply wasn’t enough space to fit in all the necessary copper.
Fourth attempt: Fortunately there was a way to solve this. All of their previous work focused on a single rotor (magnets)/double stator (copper) approach. If they instead switched to double rotor/triple stator it would allow more room for copper. The fuel efficiency calculations gave thumbs up, the computer model stated that everything would fit in physically, and even producing the parts appeared manageable. So that’s where we are today.
The final rotor design in the CNC
Although it was painful, Mattias, Nina and Cameron are happy to have passed through all of these stages. As they see it there’s no way they would’ve reached any results with their initial approach, but now they’ve gone through their solution so many times that they feel quite confident in it.
This is what we call the “Alternator paradox” – to balance the need to investigate and improve a design solution theoretically with the time needed to produce it. Among engineers there’s often an inherent aspiration to achieve excellence; but it has to be put in relation to when it’s time to stop developing and start doing. This issue accompanies everyone in the project, and is vital for the final output of the team.
According to the latest calculations, the alternator will reach a stunning efficiency of 94,5%. But will it be completed? The coming days, evenings and nights will tell us.
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