Another 7am start beckoned before a cloudless drive across the desert. We all met up to pack the van at the aforementioned time, and after following up with a quick breakfast and essential cup of coffee, the convoy left the hotel and rejoined the Pan-American Highway mere metres from the hotel’s entrance.
Today was set to be a long drive of 300 miles, and while this should be within our range, our recent observations seemed to suggest otherwise, so we opted for a short intermediate charge in Moquegue, around 150km north of Tacna. Talking of the range problem, we do now have a theory which seems to fit all of our data, although it is not a certainty yet so please bear with me if it changes upon further investigation!
Essentially, we have noticed a range decrease since Quito amounting to somewhere around 10%. After looking at how the state of charge (SoC) decreases, which is akin to looking how the petrol needle in your car goes down as you drive, we have noticed that the fastest drop occurs in the first 15% of the battery life. So, upon leaving a destination, the SoC plummets rapidly to around 85%, and thereafter steadies out to a normal rate of decrease. In those first 15%, our projected range can be as low as 300km after which it steadies out to around 450km, still 50km short of our normal range under good driving conditions. So, what could be causing such behaviour?
The first thing that would affect our overall range is driving style and terrain. In North America, the roads were typically very gentle and well paved, and we could pretty much cruise at 60mph for hours on end without stopping. In addition, we were very carefully watching our speed, not just for energy reasons, but also to avoid being pulled over by the strict American and Canadian police!
In contrast, our driving since Quito has been on very mountainous terrain and as the roads have been generally good (and the policing is lax on occasion), we have taken to driving and accelerating a little faster than before! Why did we not notice this in Central America though? This can be attributed to much lower average driving speeds due to the rain, potholed roads, and of course the fact that we were doing shorter legs typically so we were never concerned about our range.
However, while this may make a difference, it doesn’t explain why the first 15% drops so rapidly or why it’s got apparently worse since Quito. We have looked at all the log files of previous data, but these are inconclusive as you can never have 2 identical drives without driving the same road, so a direct comparison is actually very difficult. Furthermore, we have stripped the car down to its bare components and we can find absolutely nothing which could cause such behaviour, so what could be happening at the beginning of all these drives?
To answer this, you need to really look at the fundamentals of what we are doing each day, and what environment we are in. You also need to know a little about how batteries work, so let’s start from the beginning! Essentially, batteries store energy as a chemical potential, and when a current is requested from the battery, the molecules inside undergo a chemical reaction which releases energy in the form of electricity.
Because all batteries have an internal resistance, as current flows through the cells, a very small but not insignificant amount of energy is converted into heat. Another crucial point to note is that this chemical reaction is greatly affected by temperature; it’s slow at low temperatures, and faster at high temperatures. This means that when your batteries are cold, the internal resistance is higher which means to get the same power out of your batteries, you draw a higher current due to the higher internal resistance, and so you suck more power. This is why in cold conditions, your petrol car has difficulty starting because the battery inside just does not have enough power to crank the engine. If you have an electric car, then this is why you see a range reduction during cold weather. So far so good I hope!
Now, up until Quito, we have been charging the car in fairly warm conditions outside, or in a garage. However, in Quito, the nights get cold, as is also the case in the deserts which we have been passing through since Quito. Our suspicion is that, even though the batteries are charging overnight which releases small amounts of heat, albeit very minimal, they are actually getting colder than at any other point we have experienced.
Following this train of thought, we always leave early in the morning before the weather has really warmed up enough to warm the batteries, and our driving first thing in the morning is fairly stop/start as we get out of the city, and this is typically a big drain on the batteries even under normal conditions. However, as we drive, the batteries warm themselves up to a stable temperature and the range begins to improve.
So, there you have, in short, the RGE theory on why we were seeing a range decrease! In tomorrow’s blog I will explain a little more how we demonstrated that this was the case by doing a drive which exhibited an even better than normal range, but for now, back to today!
The drive was on perfect roads with spectacular weather, and breathtaking scenery. Really very similar to all our other driving in Peru; while all this coastal desert is much the same, it’s incredibly beautiful and I would recommend doing a drive in this part of the world if you can! However, the first 300km to Moquegue was very uneventful apart from an impromptu stop in the desert.
Why did we stop in the desert? Well, running parallel alongside the road, around 200m away, was a row of electricity pylons stretching off into the distance. We noticed that they didn’t have any cables running between them and were safe enough to climb. “Easy”, we thought, “they don’t look so big; let’s climb them!” so, after stopping on the side of the deserted road (no pun intended) we walked over to them, anticipating a great view a great view from the top.
However, reaching their base we realised that they were a lot taller than we had thought from the road, and a lot harder to climb! However, not to back out from a challenge, we did climb up a little bit; perhaps 10 metres or so, but that was enough for us! We quickly shimmied down, ran back to the car, and carried on with what we are good at; driving!
About 20km from the failed pylon attempt, we arrived in the surprisingly green town of Moquegue. We had a contact here from Salvador who had offered us a place to charge the car for an hour or so, but as it turned out, we couldn’t get hold of him! So, we had to make an impromptu decision as to where to charge.
The answer came as we were driving into town in the form of a big box, marked with a lightening bolt and a man being electrocuted, that was on the wall of a petrol station! For good reason, we are taught as kids to not go anywhere near these high voltage electricity boxes, however, for us these little boxes are sources of sweet electric nectar! If you know how to do it safely, which we do, you can draw lots of power to charge your car from these boxes, so we drove into the petrol station to see what we could organise.
The petrol station attendant, replete in grubby baseball cap and greasy overall was a little bewildered! The first source of confusion was why a car like the SRZero was in a place like Moquegue, and the second source of consternation was why on earth a car would need to plug into an electricity supply! So we explained to him that the car was electric and all the other missing pieces of the puzzle, and very quickly he was inviting us to plug in at our leisure!
As it so happened, we only needed a short charge, so while the car was drinking its juice, we were eating some rather bland local takeaway while sitting on the petrol forecourt. Whoever thought that RGE was all about fast cars and luxury, think again! We are just as happy sitting and eating on the floor of a petrol station which smells of manure as we are eating canapes in the home if the British Ambassador!
Anyway, with us having finished our food, we took the car off charge and headed back on our journey. The drive into Tacna went very quickly as we drove fairly fast into the slowly fading daylight. We arrived at a very reasonable time, and we were soon able to call our contact here to give us directions to his hotel.
But for the second time in one day, and only the third on the entire trip, our contact was unreachable. However, with Peru running off the higher power 220 volt electricity standard, finding a suitable place to charge, unlike the northern part of our trip, is actually very easy. So, all we did was follow a cab to an alright looking hotel, book some cheap rooms, and ask the manager if we could charge the car. They were more than happy to help, even giving us a discount on our rooms, and before long the car was charging once more! As it turned out, we didn’t actually need the intermediate charge as we had enough energy to travel the entire distance, which was a good thing as it further reenforced our suspicion that there is in fact nothing wrong with the car!
As is usual nowadays, we were fairly exhausted after dinner, and it was around 9.30pm that consciousness slipped away! That being said, we were looking forward to our early start and our entry into Chile the following day…the penultimate country of the RGE adventure!