Transport Evolved

[DaveD]

Ah, OK. My apologies for my randomization of the discussion. Carry on! :biggrin:

 

[JRP3]

Still interesting information about the Tesla pack that I don't remember hearing before. One battery researcher has mentioned that he feels the Tesla pack design is overkill as far as safety is concerned, but it's hard to complain about that.

 

[DaveD]

It may seem like overkill today, but it's important to remember that when the battery was being designed, there were stories in the news on a regular basis about LiIon batteries in laptops/cell phones/cameras catching on fire, sometimes physically harming their owners. I clearly remember that when the Tesla Roadster was announced, the naysayers were squawking about how the people in a Roadster would be "burned alive in the ensuing LiIon battery fire" should a Roadster get into a fender bender. Certainly, they were grossly exaggerating of the risk of that happening, but Tesla went out of their way to have a solid design so that something like that has a small chance of happening.

 

[TEG]

Years later, and millions of EV miles, we have had 0 stories of Roadsters battery packs catching fire, right?
(At least none that I can recall hearing about.)

(But there was an issue with the 12V Aux battery wiring in 2010s that they had to sort out, but that had nothing to do with Li-Ion...)

 

[JRP3]

In fact I've never heard of any lithium battery EV catching fire during or soon after an accident, all fires that I'm aware of other than the crash tested Volt were from parked vehicles that were plugged in and charging. I don't know how many LEAF's and iMiev's have been crashed but there must be a good number by now.

 

[Norbert]

In fact I've never heard of any lithium battery EV catching fire during or soon after an accident, all fires that I'm aware of other than the crash tested Volt were from parked vehicles that were plugged in and charging. I don't know how many LEAF's and iMiev's have been crashed but there must be a good number by now.

Also the two other somewhat recent ones involving a Volt, including the one prompting Duke Energy to tell all EVs to stop charging, were later found to have started elsewhere in the garage.

 

[vfx]

Overkill was the watchword back in those days. The old HPC came with a separate fire detector that would be above the unit. Agreed that was the time to be cautious. I'm sure the idea of making money on Roadsters had something to do with loosing some safety features.

What will probably happen in the future is some bean counters at a car maker will make an EV without some safety component to save pennies and it will catch fire. Lawsuits, a blow to the EV movement and then laws will be written to require such features in all EVs.

 

[mpt]

Absolutely! And, those features will include mandatory fire suppression systems, a wired link to the local fire department, 2' thick fire suppression doors, at least 100' fire break around the building and a big red button in each room of the house to ensure the garage can be isolated at the first sniff of smoke.

...Or am I just being a little sensitive?

 

[DaveD]

Weren't we just discussing overkill?

 

[JRP3]

I think Nikki is spreading incorrect information again, regarding "draining" the battery after an accident by puncturing it. They have to be talking about discharging the pack, not the electrolyte, since the battery is made up of many individual cells and you could not drain each individual cell without completely disassembling the pack. There may be liquid electrolyte, not much though, but it is flammable. However it is not necessarily toxic, some electrolyte you can actually drink, not that I'd recommend it.

It seems as if the battery coolant may be flammable as well, depending on what is used, so that may need to be drained.

 

[TEG]

Dana Battery Cooling Technology Featured on Volt

...The battery cooling technology, which is new to the automotive market, prevents the Volt's lithium-ion battery from overheating by enabling efficient heat transfer between the battery pack's 200-plus cells. This occurs as battery coolant circulates around individual plates located between the cells...

Cooling Fins Help Keep Chevrolet Volt Battery at Ideal Temperature


Volt pack details

...The battery cooling system circulates a pre-mixed DEX-COOL® which is a 50/50 mixture of DEX-COOL® and de-ionized water...

 

[TEG]

Electric cars require firefighter training in new safety tools | Detroit Free Press | freep.com

...That Volt caught fire because NHTSA did not know to drain the Volt's battery. The battery case had been punctured, spilling coolant, which caused a short that in turn triggered a fire, GM spokesman Rob Peterson said Monday.

The automaker is working to give NHTSA its tool to drain Volt batteries, Peterson said. The tool should be available at dealerships next year, eliminating the need for the GM team to visit in the case of a crash.

GM has had to send out employees to drain batteries only a few times this year, he said, since the automaker has sold only about 5,300 Volts so far...

 

[JRP3]

Apparently a water/anitfreeze mix can catch fire, especially if it's pressurized and spraying: http://www.nfpa.org/assets/files//PDF/Research/RFAntifreezeSprinklers.pdf
Ideally a non conductive and less flammable antifreeze can be used in the future, though I'm not sure in this case the antifreeze actually caught fire. Another reason to prefer a battery chemistry that does not need liquid cooling, one less thing to go wrong.

 

[VolkerP]

I'd like to see CO2 as coolant agent in car HVAC. Must redesign to accommodate for higher pressure, though.
I am not sure if it is feasible to run pressure-proof tubing through the pack.

Does Tesla use the coolant loops to heat the pack, too? That wouldn't be feasible with CO2, methinks.

 

[JRP3]

Yes they heat the packs as well as cool them. Or are you asking if they use a different mechanism to heat the packs than to cool them? I doubt it as it would add cost and complexity to have separate systems.

 

[doug]

I'd like to see CO2 as coolant agent in car HVAC. Must redesign to accommodate for higher pressure, though.
I am not sure if it is feasible to run pressure-proof tubing through the pack.

Does Tesla use the coolant loops to heat the pack, too? That wouldn't be feasible with CO2, methinks.

Don't confuse coolant with refrigerant. CO2 can be used as a refrigerant. In temperate climates, Tesla could probably get away with mostly water for coolant, though the antifreeze typically also helps keep the water pump lubricated among other things.

 

[VolkerP]

Thanks Doug, coolant and refrigerant surely do different jobs here. CO2 is used in heat pipes, will that work to cool the pack?

JRP3, I assume the "different mechanism" to heat the pack is implemented sending electric current through the cells. Do you mean the coolant agent is heated then circulated through the pack?

 

[JRP3]

That would be my assumption. Use the same medium to heat or cool the pack as needed, but I could be wrong. They could use direct resistance heating but if you already have liquid coolant in place why not use it for heating as well.

 

[JRP3]

More silliness from Nikki, though I guess just parroting Honda market speak about their braking software, she should know better: No braking software is going to "vastly improve" the range of any vehicle.

 

[GSP]

Thanks Doug, coolant and refrigerant surely do different jobs here. CO2 is used in heat pipes, will that work to cool the pack?

JRP3, I assume the "different mechanism" to heat the pack is implemented sending electric current through the cells. Do you mean the coolant agent is heated then circulated through the pack?

In the Teslas and Volt the refrigerant is used to cool the water ethylene glycol (WEG) coolant, and the coolant cools the cells.

The Volt can also switch to an air to WEG heat exchanger in moderate temperatures to reduce the energy needed to cool the cells. I can't remember if Tesla does this also.

The Volt cells are heated by a high voltage resistive heating element that warms the WEG. I think Tesla also uses this method to heat their cells.

GSP