Today I opened the battery pack of the Leaf to see how it held up when
the vehicle above it was on fire.
I now understand why the fire started in the auxiliary battery pack in
the trunk.
Believe it or not, it was caused by rainwater.
Ironical as it is that a fire starts from rain water, I can come to no
other conclusion.
Or actually - it was caused by incorrect weather-proofing.
See, the auxiliary battery was directly connected (cell-to-cell) by a 97
wire umbilical cord from the
auxiliary pack in the trunk to the Leaf's battery pack. For that wire
bundle, there was a 3" hole cut in
the side of the Leaf's battery box under the car, close to the point
where all BMS sense wires converge
on the side of the box, very close to the rear tire.
I found a layer of water inside the Leaf Battery box, heavy corrosion
(so it was not from the last days or weeks,
this has been going on for about a year at least) and a thick layer of
white corrosion on the Alu BMS enclosure,
it looked as if it was a cake with too much frosting.
And lots of burned wires inside and a very unhealthy looking BMS and
contactor set.
In other words, the rain splashed up by the rear tire entered the
battery box through the hole for the wiring
(which did have weather-proofing on it, but it is extremely difficult to
close such a big hole and so many wires)
and it pooled inside, corroding everything and sloshing around until it
destroyed enough of the BMS sensing
circuits or wires that the BMS started to malfunction and something
happened that started destroying the cells,
either the BMS continued charging while some cells were already full, or
the BMS allowed continued driving 
even though the cells were already empty or the owner noticed that the
car would not charge somehow (because the
BMS malfunctioned and would not allow charging) and he needed it, so he
hooked up an external charger
without the BMS protecting the now imbalanced pack, causing the fire
when some cells were pushed way over
their boundaries.
The cells in the horizontal stack have a steel end plate with open frame
across them. They looked like balloons,
puffed up almost an inch in the middle, bending the end plate and
stretching things to the breaking point.
I made sure to put the battery box cover back on and re-engage all
bolts, so that if corrosion and stress causes
bolts to break and nuts to become projectiles, at least they will be
caught by the sheet steel of the box.

I originally opened the box in hopes to at least salvage the BMS and
other parts and then see if the cells would be
able to be revived, but the interior of the Leaf Battery box looked
pretty hopeless.
So - a warning to all who use a Leaf (or other) BMS with their cells:
These computers are *not* able to withstand
outside environment, they are not water-proofed as they are completely
weather-protected inside the Leaf battery box.
Also, there is close to 400VDC present across the PCB (printed circuit
board), so any moisture in the BMS will cause
serious leakage currents, which cause migration and deposit of metal,
which causes short circuits across the PCB,
resulting in the moisture being the cause of the failure of the cells
that the BMS needs to protect.
In this case, even resulting in fire in the vehicle as well as burned
wiring in the Leaf Battery box, besides the corrosion
due to the presence of water.

Cor van de Water 
Chief Scientist 
Proxim Wireless 
  
office +1 408 383 7626                    Skype: cor_van_de_water 
XoIP   +31 87 784 1130                    private: cvandewater.info 

http://www.proxim.com

This email message (including any attachments) contains confidential and
proprietary information of Proxim Wireless Corporation.  If you received
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_____________________________________________
From: Cor van de Water 
Sent: Friday, October 14, 2016 6:00 PM
To: 'Electric Vehicle Discussion List'
Subject: Leaf with interior fire, probably due to auxiliary battery
extension in the trunk

I saw a burned-out Leaf in a tow yard and asked what caused the interior
fire
(The contents of the motor bay are fine, so if anyone is interested in a
2011 Leaf motor, inverter, front suspension, brake controller, ..., then
let me know!
The front bumper and radiators and lights are gone.)

It had an after-market secondary battery pack added in the trunk,
probably by a hobbyist or someone building a prototype.
There was a 97 wire loom coming out of the Leaf battery pack that fed
into the auxiliary pack in the trunk, plus two high voltage/high current
wires for the power.
The auxiliary pack consisted of 18650 style cells in a wooden box in the
trunk. The maker of this FrankenLeaf apparently wanted to avoid a BMS
for the aux pack
and thus wired all the Aux cells in parallel to the Leaf's 96 cell
series string.
My strong suspicion is that the failure occurred due to the Leaf BMS not
being capable to balance the difference in self-discharge between the
18650 cells, because good quality cells have low discharge, but
cheap/faulty cells might have high self-discharge and a large variation
from cell to cell. The result of imbalance is that cells get
over-charged or -discharged although the Leaf BMS should protect from
that, but other causes of failure may be a cell shorting, causing the
attached Leaf's module to dump all its energy into that failure, or an
auxiliary charger that was not under control of the Leaf's BMS, so it
could continue to charge until the car caught on fire....
Anybody know who was the owner of this black 2011 Leaf with auxiliary
battery pack, the fire probably happened in north Sunnyvale, California?

Cor van de Water 
Chief Scientist 
Proxim Wireless 
  
office +1 408 383 7626                    Skype: cor_van_de_water 
XoIP   +31 87 784 1130                    private: cvandewater.info 

http://www.proxim.com

This email message (including any attachments) contains confidential and
proprietary information of Proxim Wireless Corporation.  If you received
this message in error, please delete it and notify the sender.  Any
unauthorized use, disclosure, distribution, or copying of any part of
this message is prohibited.


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