Oh dear … 
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Cluster
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Haven’t they been testing these here for several years? It sounds like they decided not to report it until there was a software fix.
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Here is the full article without the paywall if anyone wants to read it.
What do you think of the possibility of having member photos in a member gallery somewhere? It would be good to have a sort of commons where images could be shared and reused.
Spot on.
When I’m not catching PT my daily driver is an EV, based off my experience I am almost certain that the issue is caused by BCC’s end of trip rapid charging system, which would explain why this issue caught HESS off guard.
When it comes to batteries, the biggest generator of heat is how quickly energy moves in and out of the battery. Generally most EVs have a maximum charging speed that’s sort of in the ballpark of the max power output of the motor (my car charges at ~90kW, with a single 125kW motor) - however because the vehicle only uses a fraction of the motor’s power when driving normally, it’s not a massive generator of heat. When I’m charging my car on a 40 degree day and pulling max power for 10-30 minutes, my battery can get to over 40-50 degrees which makes the cooling kick in, diverting power away from the AC. It still blows cold air, but it’s noticeably warmer for a few minutes when you leave a charging station on a stinking hot summer day and takes about 5-10 mins to ‘recover’ when I leave a charging station, as once I’m on the highway again I’m only using 20-40% power output to maintain 110kmh.
For these HESS models my understanding is they have two motors with a combined max power output of 320kW, however the ‘flash charging’ at the end of each trip is a whopping 600kW which generates an incredible amount of heat. Because they’re charging so often, I suspect the battery is becoming heat soaked (known as ‘rapidgating’) where the battery doesn’t completely get back to ambient temperature by the time it’s charged again which generates even more heat, so throughout the day with these cycles the battery temperature slowly gets higher and higher until a point where it’s stealing cooling power from the cabin.
Europe is prone to high summer temperatures just like us, but I would guess that the reason Brisbane is unique is due to the ultra high speed charging system as opposed to most BRT systems in Europe which have the luxury of constant overhead power. Having a small battery and dumping 600kW into it every 30 minutes or so is an insane heat generator and any cooling system would struggle to deal with that on a very hot day.
The issue this poses is more severe than the article suggests, the batteries getting to a temperature where cabin cooling is being affected shows that they are basically hitting a thermal ‘limit’ where the battery protection is starting to do it’s thing. From memory last summer in Brisbane was relatively tolerable in terms of max daytime temperatures, I’d be interested to see how it goes with temperatures pushing past 40 degrees if it’s already struggled now. The other issue is that if all they’ve done is adjust the balance of power between cabin and battery cooling the laws of thermodynamics suggest there has to be a trade off somewhere else. Either they have to tweak the cooling software to allow the battery to run hotter (unlikely, this affects battery life), reduce the charging power at the end of every trip to try and reduce the amount of heat generated (impacting turnaround times) or allow more power to be consumed by the cooling system (impacting range).
The good thing is this is likely a uniquely Brisbane Metro issue, the existing fleet of non-metro BEV buses being trialled by Kinetic, Transdev, BCC, etc are only charged one or twice a day (generally slowly overnight) which means the heat issue is negligible. The other good thing is that this should really only be an issue on the hottest of days in summer, BCC/HESS could implement a system where they reduce charging power (and in turn, heat generated from charging) by around 30% on really hot days which will slightly affect turnaround time but not pose a huge issue (about 8.5 minutes per charging stop vs 6 minutes).
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Brisbane isn’t the only fast charging version of the LighTrams in operation though - Geneva and Nantes operate the fast charging version of the vehicle as well. Temperature-wise, Geneva can get close to 30°C in peak summer I believe (apparently they almost hit 40°C a few years ago - a record for the city), and Nantes mid to high 20s I think?
That’s true, and they appear to use the exact same hardware as in Brisbane, however my understanding is the implementation is different. The systems in Geneva and Nantes both have the vehicles regularly topping up for 15-20 seconds at a time at various stops along each route, so it’s still drawing 600kW but only for a very short amount of time, more often.
I haven’t been able to find exact specs, but comments online about the system in Nantes suggests that in addition to charging while underway, they also charge at the end of the route, but only at 400kW instead of 600kW. Whether that’s all they needed or whether they decided to limit it to 400kW to prevent heat issues is unclear.
I’d be curious to see whether any other regions are pulling the full 600kW at the end of the route for 6 minutes. The Brisbane Times article is also lacking important information about what kind of temperatures air con was actually being diverted for battery cooling - was it 30 degrees? 35 degrees? 38 degrees? Was it for the entire route or only right after UQ Lakes and RBWH when they’ve just been charging without time for the batteries to cool down yet?
I’m not in any way suggesting this is a major issue with the Metros, but by BCC’s own admission, the battery cooling system wasn’t keeping up on hot days and stealing power from the climate control system which means something isn’t quite right. I think realistically HESS will (or maybe already have) done some testing to further optimise charging rates and cooling and hopefully a compromise will stop it from happening in future.
Edit: According to Hitachi’s case study, end of trip charging in Nantes is 400kW for 4-5 minutes vs 600kW for 6 minutes in Brisbane. That could already be the difference?
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Well, I’ve only caught it a few times as both the M169 and the M2, but I haven’t ever noticed any major fluctuations in air conditioning temperatures when I caught it. I never caught any of the services from their terminus, but I did get it a few times from Boggo Road, and it felt like any other service temperature-wise.
When M1 comes online, I expect to be using it more often so I can feel for any continuing temperature changes.
I’ll keep saying it - in-motion charging with trolley wires would have averted these issues, and also helped prolong battery life and produce a solution with longer legs. Except for a few space constrained bits of busway, most of it is quite capable of accommodating wires, and they don’t have to be 100% contiguous from start to finish. Also would have been able to roll out standard rigid or articulated electric buses with trolley poles for in-motion charging in these sections of the network. We don’t have to string wires up everywhere, just in enough places where it does the most good.
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Looks like Geneva uses the higher 600kW version, but the 600kW charge duration looks to be a much shorter 20sec. I think that is the big difference with the Brisbane version of TOSA/Grid-eMotion vs others - the much longer duration of the 600kW charge.
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Is there a fire risk from the battery charge cycle and ambient or built up heat?
Let’s say for example if we had a 45 degree heat day.
What material is the battery made from?
The batteries are a lithium-titanium-oxide (LTO) battery. I’m not a battery expert, but according to the below link, LTO batteries are safer, better for fast charge purposes, and have superior temperature tolerances to other lithium ion-type batteries.
LTO Batteries: Benefits, Drawbacks, and How They Compare to LFP.
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Not really, the battery cooling ‘stealing’ the passenger air con is the first step in quite a few protection systems. If that’s not sufficient, the vehicle will dramatically reduce charging speed as needed to control the temperature, and if that’s not enough either it will go into ‘limp mode’ and cut down motor and regenerative braking power too. If all else fails, the battery will basically completely shut down to protect itself. there’s multiple layers of redundancy, and if all goes wrong they’re still very unlikely to go into thermal runaway and catch fire. A crazy amount of engineering goes into this technology.
As Nathan linked, the metros use LTO batteries which are less energy dense (not as much stored energy should one of the metros actually catch fire, which would be incredibly rare) but also rated for an incredible amount of charge and discharge cycles, well over 10,000 before you even need to think of replacing them. They are also rated to withstand a much wider range of temperatures than traditional LFP batteries you’ll find in passenger EVs.
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I raised this at the meeting with the Brisbane Metro team today. They said that the software changes, plus having patron operated doors rather than opening all doors automatically at every station, should resolve the air-conditioning issues without causing dwell times to increase at chargers. It sounded like the main issue was just the doors automatically opening at every stop.
Of course this is speculative to a certain extent since it hasn’t been put to the test. They will be monitoring during the next summer.
I noticed this last Sunday when. I caught it that the doors need to be manually opened. It seems to delay the platform screen doors from opening at KGS though.
So, what will happen during peak periods on hot days, when every door will be opened by passengers at most stops anyway?
I think they’re not being completely honest.
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I think we have a white elephant!!
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This is a reasonable point. If the bus carries 150 people, is it reasonable to think that any door will be left closed?
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I had this happen a few weeks ago getting off at KGS: only the front KSG door opened.
Also: maybe they can cool the Adelaide street tunnel to like 12 celcius and cool the buses halfway through their routes? /jk
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