Fires in electric-assisted cars

[moldyoldy]

Moderators, move this thread as necessary.

For those of you who read German, check out the Focus.de article in the Auto section on fires in battery-operated vehicles, from Porsches to Motorbikes. The batteries discussed were Lithium-Iron-Phosphate, Lithium-Polymer, and Lithium-Ion, The point for us flashaholics is to pay attention to the proper use of our Lithium-xxx cells and to use a charger with the correct charging algorithms.

http://www.focus.de/auto/ratgeber/s...ch-wird-die-elektromobilitaet_aid_774866.html

A brief synopsis of the Focus.de article follows:

ie: A Porsche GT3 that used a Lithium-Iron-Phosphate battery pack for the electric starter to save weight was destroyed when the battery pack caught fire during charging in a garage (photo included). An investigation by Auto Bild implicated the battery pack as the source of the fire. Porsche is withholding comment, but claimed that an incorrect battery charger was being used.

ie: The firm Fisker-Karma produces a hybrid vehicle Karma that caught fire in a garage. NHTSA is still investigating as to what started the fire. however the firm recalled over 200 vehicles to change out the battery packs.

ie: In May 2012 in Shenzhen China <<where many of our flashlights are made>>, 3 Chinese citizens died when their Elektro-Taxi E-6 was hit from the rear which immediately triggered a fire in the Lithium-Iron-Phosphate main battery. Chinese authorities are still investigating.

According to a battery expert at the Ulm (Germany) research center ZSW, there are 3 elements in a Lithium-Ion battery that are pertinent: The Cathode - which in the case of the Lithium-Iron-Phosphate battery is not critical since this cathode material cannot thermally decompose. The carbon-based Anode can react under certain circumstances (and overheat). The Electrolyte is an organic solution which can catch fire either by opening the cell, or if some other component overheats.

ie: The Chevrolet Volt has had problems with fires. In one case, the Lithium-Ion battery pack caught fire after a crash test. In another case a Volt caught fire 21 days after the crash test. In that case, the operator was not paying attention after the crash, did not discharge the battery pack per protocol, and coolant leaked out leading to the Lithium-Ion battery pack overheating. In another case, NHTSA and Chevrolet technicians conducted a variety of tests on the T-shaped battery pack (in the Volt). In one case, the battery pack caught fire a couple hours after test. In another case, the battery pack caught fire 7 days after a test.

ie: the electric-assisted bicycles called Pedelecs have also suffered damage to the bikes and to the riders. In one case, a Lithium-Polymer battery was seriously overloaded and overheated. when the rider attempted to put out the fire, the fire flared and the rider was seriously burned. However in this case, an investigation showed that the battery pack was manipulated/changed by the owner when the battery management pack was jumped which monitored the charge state of the cells and temperature. Worse still, the owner used a non-standard charger.

The general feeling amoung battery experts is that battery packs developed by small companies will most often be implicated as a fire source, not from large companies. The larger companies spend a lot of money in crash tests and sealing the battery in a well-protected housing. In the case of a collision, battery power is instantly cut off.

Comments were made at the end that there is simply insufficient long-term experience with the Lithium-Ion technology.

<<Edit: I understand that an accident which somehow deforms the battery compartment can cause a fire. However the time delay in the fire starting after the incident is very disconcerting!>>

 

[jtr1962]

Most of these fires fall under the category of "not being used as designed". You can't prevent stupid people from doing stupid things. In the end, as a whole electric vehicles are far safer than their gas-powered counterparts. During the time period where these fires occurred, how many gasoline-powered vehicles exploded in collisions? Probably hundreds but I can't find figures anywhere. Besides that, a gas-powered vehicle is harmful even when being used as designed due to the toxic exhaust. I'm 100% sure these electric vehicle fires will be studied and the next generation will be even safer. I'm actually surprised at the fires in vehicles using LiFePO4 cells. This is an inherently safe chemistry. The fires were probably caused by the battery being short-circuited during a collision. Better design (cutting off power plus reinforcing the battery compartment) can prevent that.

 

[AnAppleSnail]

Better design (cutting off power plus reinforcing the battery compartment) can prevent that.

Designing a battery to do that is difficult or expensive - take your pick. One of the main obstacles to electric-cars becoming more common very quickly is the cost of producing them. Whether that cost comes from simple battery production or smaller volumes doesn't matter much yet.

To make a battery that can power a car fail-safe in a collision requires dozens or hundreds of 100% reliable fuses (Or other circuit breakers). Let's say that fusible links (Or smart circuit breakers) tie the cells in the battery together, and are designed to let go at 200% of the unsafe load (Or pick some other margin). Now each of these components must be fitted into the battery pack, tested to reliability (It won't strand anyone, will it?), and added to production costs of that part. Every cell will need to be separated, and cells may even have to be reduced in size to maintain some "maximum likely discharge event." This does not address something exciting like a conductive spike through the battery, but that is a very rare event. Addressing that requires geometrically small cells and still more complexity in the battery.

If we use smart circuit breakers, there is "dark load" on the battery. Even when the car is parked and 'Off' while I'm gone on a business trip, the battery will consume power sitting in a parking garage. There are certainly control architectures that would allow a full battery-sleep, but these require rebuilding many of the car's electronics that assume constant power, even when the car is "off." Radio settings, electric seat settings, etc, all depend on having power. We come once more to "More money or more development time" which comes down to more money.

Gas-powered vehicles caused a lot of destruction when they were new. I am told (Thirdhand, mind you) that the owners of cars were held liable by courts for damage caused by them - they were responsible for training their neighbors' horses not to startle at the car. And newspapers described early car crashes as "The vehicle rearing up and dashing into innocents." Fundamentally different technology is nothing new anymore. New vehicles cause damage, Social media causes teen depression, books (no, television, no, it's computers) cause obesity, and so on.

 

[moldyoldy]

The question regarding fires in conventionally-driven cars was partially answered in the article: "... yearly in the US there are about 287,000 fires causing 400 deaths...". <<Loose translation is mine>>

Unfortunately comparative statistics to cars with battery packs was not provided.

Worse stiill, I have reservations about the US car-fire statistic provided. Averages can be very misleading.

 

[gadget_lover]

I'm always saddened to see reports like this. They tend to spook the buying public who don't bother to look up the rest of the statistics. I commuted daily for much of 40 years and have seen dozens of car files (or burned out hulks) on the freeways and yet you seldom see any mention of the general problem in the news. The exception is when a major freeway is backed up for miles as people watch the flames. Then it makes the news. 🙂

Lithium based batteries are prone to fires when misused. So are diesel, gas, natural gas and hydrogen. I hope this does not dissuade people from buying the new technologies.

As far as the need to make them safe from overload, the technology is already there. There are circuits that can isolate each set of cells when they malfunction. My 10 year old Prius has that technology, even though it is NiMH based. Each set of cells can be isolated if the cells inside fail.

Daniel

 

[alpg88]

i feel just fine driving a car with 270v li ion pack in the trunk.