Battery Charge failures as
a result of a ground fault
Introduction:
It seems that charging failures mostly occur in rainy conditions or in
California, after you wash your car.
It goes without saying that once I got my car to Vancouver Island it did not
take long for me to get the dreaded "isolation error"
After a lot of trouble shooting and some reverse engineering I was led to
the HWS circuit and a signal called LeakyV.
Now LeakyV which must mean leaky voltage is the output of a circuit which
measures a voltage leak or potential between the chassis of the car and the
battery pack.
This circuit is much more complex but not very different to the ground fault
circuit in your bath room where you plug in your razor or hair dryer.
Water being the common factor here too. So the idea is that if there is a
voltage potential to the chassis of your car and ground or your hair dryer
and ground you want to trigger an alarm or shut the power off. In the case
of your car it shuts down the charging system which is an interesting
compromise that allows you at least to perhaps limp home.
Work around #1:
After a bit more trouble shooting I was able to determine that if you
unplugged the high voltage connector from the HWS/LeakyV circuit the car
computer would not detect the error and would charge normally. Good work
around but not safe I said.PLEASE TAKE NOTE. NOT SAFE.
Discovery #1 :
When I pulled the batteries from my car the first time as an exploration to
figure out what was going in the battery pack, we learned a lot of things
but made one significant discovery, thanks Bill. I had built a fancy high
voltage impedance tester as part of my initial trouble shooting and
discovered then that the impedance of the pack high voltage to the chassis
was around 60k ohms. A minimum industry standard from what I could determine
was 120K ohms. No wonder it was failing. When we started to disconnect the
pack it was not long before we had an impedance of over 900 meg ohms. Yea
problem solved, well not really. Thanks to Bills tenacity he poked around
with a ordinary ohm meter and found that where the paint was chipped inside
the case mostly underneath the batteries you could measure a short to
ground. Hint #1. Further with a battery placed in a slot with chipped paint
and using the high voltage impedance meter we also found a low impedance
from the battery post to chassis ground. Ah ha we said. using blue weather
shield tape we were able to eliminate the short. So what did we do .... put
the car back together of course. Bill was not convinced. The charging worked
for a little while but soon I was back to unplugging the HWS/LeakyV circuit
to charge again. Bill was right.
Discovery #2 :
It was not long before through some good fortune and the help of Darren that
we sourced some used batteries and a plan was set to replace a bunch in my
pack. This time armed with 2 part epoxy garage floor paint and another
friend I dropped the pack and completely cleaned the case inside and out in
preparation for painting. This was the next ah ha moment.
Lots of chipped paint and paths to ground which led to the discovery that
the entire case is coated inside and out with a conductive copper coating
essentially a giant ground.
The inside coating is isolated from the batteries by a barrier coat, with
lots of chips and scuffs from vibrating after 70,000 miles and careless
removal and installation of batteries by me and the previous owners friend
who had tried to fix it once before. Now the big questions are where is the
path to chassis ground from the battery case and why are all the bolts in
the case completely isolated from the battery case so that there is no
possible path to the chassis. See pictures 3 & 4 attached. Picture 3 shows
the rubber isolation mounts of the main bolts I thought they were for
vibration damping. But if you look at picture 4 you will see that each of
the bolt mounts have a black ring around them the conductive copper coating
is purposely isolated. There is no connection to ground.
Discovery # 3 :
There is a bonding strap that goes from the fire wall to the battery case
where the high voltage cables go to the battery. This strap serves no
obvious purpose except to trigger the ground fault circuit after 10's of
thousands of miles.
Was it designed specifically to do that or is that an
unintended consequence of wanting to create an RF shield around the
batteries and the battery ECU or create a path to ground in the case of an
accident or serious mechanical failure. Somebody at Toyota may know, but I
don't think they are letting on. If anyone else has any suggestions happy to
hear. In the mean time this may be a work around but I am not recommending
you use this information for anything other than quiet contemplation.
Final footnote:
The conductive path from the battery posts to the chassis ground is not
completly as a result of moisture after all fresh water is mostly
non-conductive. Whats really happening is that a soup is being created n the
battery tray after many years of charging and driving. The soup is a mixture
of moisture, off gassed electrolyte, road dirt and dust. This creates a
lovely film over all the batteries and in the bottom of the tray which is
conductive and creates a conductive path across the tops of the batteries,
down the sides of the batteries and the restraining brackets to the tray.
Any abrasian, cracks or chips then provide a direct path to the chassis
ground through the bonding strap. Except for this bonding strap the battery
case is purposefully completly isolated from the chassis and by the barrier
inside the tray from the batteries.
Cleaning the batteries is your next step
Pictures 7 & 8 shows my nice epoxy coated tray that may be 100% isolated now
but runs without a bonding strap.