Very proudly, I am now able to say that the team has persevered through really difficult conditions and has been able to successfully repair the car! It shows that even when there are immense and seemingly insurmountable challenges, with some real grit and determination, pretty much anything can be achieved. Corny though this sounds,this is a message we’re really trying to get out so as to inspire children to take up science and technology subjects to attack and conquer the challenges we as a society are going to face in the future; it feels great to be able to walk the walk as well as talk the talk, I have to say!
So now I will expand on some of the details which explain what went wrong with the car. Let’s start with the fire which occurred last week Thursday, a few hours after the SRZero was removed from the container. Before explaining how the fire occurred, it is necessary to examine some other aspects the car’s environment. Firstly, the car was held in a container for 10 days prior to being released. Research conducted after the fire showed that the average temperature in a sealed container is between 40 and 50 degrees celcius. However, in the tropics, the temperature (and hence the humidity) inside the container would have been significantly higher than the average scenario. Add to this the fact that the air was sea air as the container was stored at a port and transported by sea, so therefore heavily laced with salt as well.
Another crucial factor was the weather in Cartagena on that fateful Thursday. The early morning had brought a strong storm off the Caribbean Sea and had lashed the city with very heavy rains. So heavy was the rain in fact, that large parts of the city were flooded, and the affected areas made the national news later that day. The heavy rainfall had the effect of reducing the day’s temperatures, and we all remember the evening being significantly cooler than normal.
Now, consider that the car started completely normally inside the container, and then a few hours later while sitting outside doing nothing, suddenly caught fire. It truly was a perplexing mystery, but we think we have the answer. Here we go! Apologies for the very technical explanation to follow…
While the car was imprisoned in the car for such a long time, the high moisture and salty air permeated everything it could in the car. While we had designed each component to be waterproof, we suspect that one box containing a BMS slave board had somehow become corrupted and let in some of this air. One piece of evidence for this was the corrosion on some of the screws inside the box – each of them had rusted to some degree while screws in all the other boxes had not. However, this in itself would not have caused a problem for the electronics as the circuit board was covered in a protective coating, and each of the terminals on the connectors in the box were isolated from each other.
And this is where the temperature change between the container and the outside air became important. As the air inside the slave box slowly cooled, at some point it must have reached its dew point, the temperature at which it condenses, thereby precipitating out droplets within the slave box. Our suspicion after inspecting the damaged system is that one of these salty droplets (much more conductive than fresh water) caused a short between 2 or more of the measurement wires going to the cells. This short would not have lasted for long as the heat would have evaporated the water very quickly, but we suspect that the short lasted just long enough to burn through the wires’ insulation thereby creating a permanent short circuit between adjacent wires which were all at a different potential.
Anyway, this short circuit caused intense heating which caused further burning of the the insulation surrounding the cable of individual wires. This caused the flames and smoke which Toby saw and very skilfully extinguished before any major damage could be done. Regardless of why the fire started, we had some damage which we had to fix, and after the run around to find a garage in which to fix the car (which can be read about in previous blogs) we had everything fixed as it should be pretty quickly.
However, the car still would not work even when all the fire damage had been fixed, and we spent several days in pure frustration trying to ascertain exactly what was wrong. And when we couldn’t find anything wrong with any component, and with the car still not starting, we started trying to experiment with various components to see if the problem would go away. This way, we hoped to find what was causing the problem in the first place. At this point I would like to thank the huge amount of people that commented on the blog or emailed me personally with their ideas as to why the car wasn’t working. Thank you for all your suggestions, however, just like our ideas, none of them served to demonstrate what the problem was!
However, today we found something which made the car work just as before…and it was something very strange. When we removed a certain feature of the battery management system (BMS) the car worked perfectly. So bizarre is this phenomenon, that we will continue investigating why this problem occurred and what its nature is, because even now with the car driving again, we still have no idea as to why we saw the symptoms we saw. The feature that we removed essentially allowed the car to ascertain the voltage of each individual cell, and to shut down the car if any cell got either dangerously low or dangerously high. Considering that the car had NEVER shut down due to either an over or under voltage, we deemed it safe to remove this feature. Not ideal, but it gets us back on the road!
So once we deemed everything operational, we tested the car, and it drove fine! It was a great feeling and we were thoroughly chuffed with ourselves! After getting the car working, we finished our overhaul and started puting the car back together, polishing it as we went along. And just a few hours later, the car stood there fully rebuilt and in excellent condition to tackle the rest of the world’s longest road! We are now ready to continue our travels, and we cannot wait to get back on the road. Meanwhile however, I have to cut this blog short as the boys are dragging me off the computer to go out and celebrate!
To be fair, after all the hours of hot, sweaty, dirty and frustrating work, we really deserve it!