coleafrado said:
WetEV said:
I'm not sold on the requirement for a TMS.
For an commuting and around town car, no TMS is cheaper, simpler, more reliable and safer.
Yet I seem to be a tiny minority on this issue. The bad example of the early Leafs along with FUD from Tesla fans have likely doomed the idea.
The lithium-ion batteries are widely used for electric vehicles due to high energy density and long cycle life. Since the performance and life of lithium-ion batteries are very sensitive to temperature, it is important to maintain the proper temperature range. In this context, an effective battery thermal management system solution is discussed in this paper. This paper reviews the heat generation phenomena and critical thermal issues of lithium-ion batteries. Then various battery thermal management system studies are comprehensively reviewed and categorized according to thermal cycle options. The battery thermal management system with a vapor compression cycle includes cabin air cooling, second-loop liquid cooling and direct refrigerant two-phase cooling. The battery thermal management system without vapor compression cycle includes phase change material cooling, heat pipe cooling and thermoelectric element cooling. Each battery thermal management system is reviewed in terms of the maximum temperature and maximum temperature difference of the batteries and an effective BTMS that complements the disadvantages of each system is discussed. Lastly, a novel battery thermal management system is proposed to provide an effective thermal management solution for the high energy density lithium-ion batteries.
I wouldn't really call it FUD. It may be uneducated, but their thesis is essentially correct.
Thermal management comes in all shapes and sizes. Tesla's approach is considered the most risky, with fragile inter-cell cooling on thousands of cells, but LG and CATL's approaches are much more basic - they just embed refrigerated plates below and above each set of prismatic cells. Just like an off-the-shelf refrigerator - and even though refrigerators work at substantially higher pressures, when was the last time you experienced one leaking? I agree that there is added cost, but the benefit/cost ratio is so high that it can only be a value-add. There was a lot of concern that cooled packs would leak and cause fires - has a single case of coolant leakage leading to fire ever been identified?
FUD it is. Educated FUD, but still FUD, and still not correct.
Yes, multiple fires. Yes, often after accidents with physical damage to the pack. Hitting road debris. Damage to an passive pack isn't likely to result in a fire. Damage to a water cooled pack is likely to result in a fire. The good news of this is that the fires are often delayed. The bad news is that sometimes they are not.
coleafrado said:
Contrast that risk with the guaranteed degradation damage inflicted on tens to hundreds of thousands of TMS-less Leafs. Having no TMS basically only works with a short-range EV because the odds of anyone using it on a roadtrip is miniscule. Expecting people to tolerate no TMS on a long-range EV is just asking too much. Especially in the land of the American road trip!
Again, notice that I said "
For an commuting and around town car". Not everyone does road trips, and not every car is likely to be a road tripper.
coleafrado said:
You can just do the math: if killing a car's battery with heat causes $5000 in damage, and has a 10% likelihood of happening over a ten year span without any thermal management, everything else equal you should be willing to pay up to $500 more for a car with a TMS. (The odds are WAY higher than that number for a Gen 1 or 2 Leaf.) Does that sound like a lot? The overall unit cost for a TMS in a Bolt or Kona has been estimated around $100 - all it takes is 15-25 kg of stamped aluminum and some plastic tubing. And maybe a $10 pump. All the programming and temperature adjustment stuff is software in the VCM -> marginal cost is zero.
That would be useful math if that was a useful model of the value and cost of a TMS. It isn't.
Start with a hot place, say Furnace Creek, CA. The TMS will have a setpoint temperature of say 30C or 35C, the air temperature will be as hot as 45C, and a passively cooled battery will be somewhat warmer. So realistically, the TMS battery will be as much 20C colder, so will last up to 4 times as long. Ok, but not that long as most of the year isn't that hot. Perhaps twice as long. Battery will be below 70% before the end of the warranty (say 8 years/100k miles). There is a significant value of a TMS in Furnace Creek. Average car lasts 12 years.
Move to cool coastal WA. Air temperature almost never exceeds the setpoint of the TMS. Like wise, battery temperature only rarely exceeds the setpoint, and usually by very little. Added battery life just about zero, might even be negative. Battery life will be 2 to 3 times the warranty life. Car is likely dead for other reasons before the battery hits warranty limits, and will be useful for about 5 times the battery warranty. Very few cars make it to 40 years with no major repairs.
Various people have modeled this, and drawn lines where TMS has the same cost as the cost of decrease in battery life of having a passive battery. Most of the population of the USA would be either clearly better off with no TMS or close to break even. Yes, is complex.
The cost of the TMS is also much higher than your estimate. A larger or separate AC cooling unit is needed to cool both the battery and the cabin. This isn't free. Add in reduction of range, added weight and added energy cost. Expansion tanks and redundant pumps. Radiators and wiring.
coleafrado said:
Anecdotally, the long-run resale value of cars with proper TMS is higher. I get that this is a personal position for you, but it's really quite irrational.
Resale value isn't very useful information, as there are lots of things that make up a car. Battery isn't the only issue.
It is personal because I don't like to see misinformation win. Happens too often.
