Conversion Process - Electrical -
Battery fire Forensics and prevention finding.....
Please note this article is the
August 2008 findings of this case.......
The article is from Bill Moore - EV World Insider
Battery Fire Forensics
Early in June 2008, an engineer with Central Electric Power Cooperative of
Columbia, South Carolina was driving a Toyota Prius that had been converted by
Boulder, Co-based Hybrid's Plus to a PHEV 15 plug-in hybrid. The day was hot,
the maximum temperature got up to 98 F (36.6 C). After driving an
estimated 40 miles, he noticed the Prius' engine beginning to rev at high RPMs
and a warning light come on. He pulled onto the shoulder of the road and
inspected the vehicle, assuming the acrid smell coming from the vehicle was the
engine over-revving. He pulled back onto the road and drove a few more miles
before noticing the warning light again and a strong smell of burning fabric,
which quickly filled the cabin with smoke. Pulling off the road, he got out of
the vehicle and noticed the right side of the rear cargo compartment was on
fire, which eventually consumed the vehicle, igniting an intense forensics
search as to the cause. The results of that research are now available in the
following PDF:
Report of Investigation: Hybrids Plus Plug In Hybrid
Electric Vehicle. The 33-page report prepared
for the National Rural Electric Cooperative Association and the U.S. Department
of Energy's Idaho National Laboratory by eTec in Phoenix, concludes...
Here is the summary
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.
A timely reminder to do the right thing when it comes to dealing with high
current connections in our conversions. I also highly recommend using a torque
wrench on battery terminals (bolt style terminals) to ensure they are
not over tightened causing internal damage. Once again, remember any connection
will work to start with but it's the longer term connection issues that will
cause problems. This can result from all the things mentioned in this report.
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