Prius A123 Battery Fire Report

[cstaszak]

Randomly stumbled onto this: Toyota Prius A123 car fire investigation report 2008 - Wikileaks

It's a very interesting report with many photos and worth taking the time to look through. The moral of the story is to make sure any aftermarket battery is installed properly!

Summary
A Toyota Prius converted to a Plug-In Hybrid Vehicle configuration was destroyed by fire. The likely cause of the fire is improper assembly of bolted joints with electrical lugs. These joints became loose causing excessive heating which led to the rupture of individual battery cells which resulted in significant short circuiting of the battery ultimately resulting in the vehicle fire. The batteries were designed so that a spacer should have been placed between the fuse blade and the electrical lug so that the plastic battery cover would not be in compression. Compressed plastic has a tendency to creep which would result in loss of clamp load on the fastener. Inspection shows that the brass washers that were intended to be the spacers were instead installed underneath the bolt head (between the bolt and the lug which served no purpose). Additionally, there was no locking mechanism (lock washer, safety wire, adhesive, etc.) that prevented the bolt from backing out of the nut. It is likely that the bolted joint became loose over time and during regular vehicle operation which resulted in a high-resistance connection causing those components to increase in temperature.

A123 Systems’ design guidelines appear to be violated in several areas which may have contributed to the severity of this incident.

[jammin012]

VERY INTERESTING. Firefighter friend of mine would love to see this.

[Scummer]

Interesting... wrong assembly caused the fire. Human error.

[sorka]

I'm stunned that the conversion system didn't employ multiple temperature monitoring points along with a warning system should any part of the battery exceed a safe temperature. These are Li-Ion batteries for christ sake! They need to have auxillary cooling and monitoring systems to ensure safety. Tesla has gone through great expense engineering these safety systems. Obvioulsy the company that made this batter didn't. Very sloppy.

[jelloslug]

I have seen terminal stud damage like that on fork lift motors with poor connections. You also get the same results.

[efusco]

Wow, impressive write up and fire.
The thoughts of a DIY PHEV conversion have just taken a few steps backward for me...one loose connection can cause a catastrophic failure like that...yikes. And a DIY project would have none of the above mentioned protections such as temp sensors and all.

I hope the new Hymotion conversion has taken this situation into account in the new design.

[miscrms]

Very interesting report, thanks for posting!

Rob

[sparkyAZ]

Originally Posted by efusco

I hope the new Hymotion conversion has taken this situation into account in the new design.

From the investigation, there were a number of obvious problems in the Hybrids Plus conversion battery design:
1.) clamshell plastic in compression without appropriate load distributing washer (incorrect mechanical assembly)
2.) parallel batteries built with full sheet nickel buss bar instead of individual fuseable links.
3.) known flammable foam used in the pack construction.
4.) lack of a safety mechanism to prevent conductive ejected battery material from breaching the electrical isolation between the battery pack and the vehicle chassis.
5.) marginal thermal sensing design.

This underscores the amount of Engineering and upfront failure analysis that has to go into proper battery pack design. The DIY projects may or may not incorporate the appropriate safeguards.

It's important to remember that Hybrids Plus and Hymotion are two very different companies. Both companies use the A123 LiIon cells in their pack design, but Hymotion is a wholly owned subsidiary of A123 systems while Hybrids Plus is not.
I have a feeling that Hymotion would not violate their parent companies own design guidlines with regard to pack design. However, the internal construction of their conversion unit seems to be a closely guarded secret at this point. Aside from the high up-front cost at this time, I think I'm going to wait until I can see a complete teardown or at least get a look at the electrical construction inside the Hymotion unit.

[Flying White Dutchman]

maybe because 123 is a company from GM ( if i am not mistaking or is it chevron )
this fire did the electric car deal no good..

[snakeman]

Originally Posted by Flying White Dutchman

maybe because 123 is a company from GM ( if i am not mistaking or is it chevron )
this fire did the electric car deal no good..

Yes, and they shot Kennedy too.

Seriously, not everything is a grand conspiracy. I'll grant you that if I were the Ford dealership that the car was towed to originally, I'd probably be taking lots of pictures to show my customers what happens when you buy those spooky foreign cars, now let me show you a Taurus.....

However, the report seems to clearly point to a sloppy mechanic doing the final assembly that was the 'straw that broke the camel's back' to a design that had a few problems in it that are perfectly clear in hindsight but probably weren't during original design. The good thing is that it looks like they did a good job of trying to learn from their mistakes and show that they had done so with this report. Also, the report was a really good insight into the conversion that I found interesting to read. Thanks to the OP for sharing it.