Battery Box


I just got done helicoiling the 6mm taped holes that hold
the battery box lid on the #1 truck. The front and back rows were done
quite awhile ago. But the side rows needed a rivet nut added to them
since they were out of alignment with the holes in the lid due to that
hydrogen thing that happened along time ago. The idea was to get the
battery box leak tight so it won’t leave me stranded with a ground
fault when the truck sits out in the rain at work.

The rivet nut is part number 95105A187 at McMaster.com. If your lid
holes and the threaded holes line up you won’t need it. A 6mm helicoil
will suffice. The side holes will need the 6mm long inserts. The front
and back rows will need the 8mm long inserts, or longer, since the
material is about 4 times thicker.

When it’s all done, then it’s nice to reseal the lid with some weather
stripping that does not stay permanently compressed like the factory
USE stuff does. So I added McMaster p/n 93625K231 (1.5″ wide) to the
bottom of the lid. Factory stuff was 1.25″ wide. It looks to compress
just right with 50 in-lbs of torque on the helicoiled screws. Without
helicoils, the aluminum will strip at 50 in-lbs eventually. This
weather stripping is rated to not compress over time. So it should
hold it’s sealing ability for a long time.

I only had enough weather stripping for 3 of the sides. So when the
next roll comes in I may remove the other stuff I substituted for the
back row.

Also I added 2 large diameter vents to the lid to allow higher volume
airflow through the pack. The 1/2″ pipe that was there before had a
lot of restriction. Now I’m using 1.75″ black plastic pipe adapters
and a 3″ cap to make up the vent assemblies. These are very high
flow and low restriction.

It has rained quite a bit lately so I’ll find out how well it all
works in the next few days.

Here is a completed helicoil repair.

Here is a completed helicoil repair.

Here is a completed rivet nut repair.

Here is a completed rivet nut repair.

The video chips have arrived. The LCD is handling the info just fine.

So far the Lithium and the Nicads are staying within 2 degrees C of
each other under driving conditions. The lithium might be a couple of
degrees higher during charging.

The bench test with only one cells shows everything is ok. I need to
connect up two more cells on the bench to see that it works as if it
were in the truck. Once bench proven, I’ll install everything into the
truck.

My experience with finding ground faults using the voltage method with
a dvm was 100% until this week.

I modified my usual debug pattern and found the ground fault. With the
pack completely assembled, measuring along until I found the fake
ground fault, I would take out one battery connector. Then the ground
fault would go away. Then I’d put back that first connector and take
out another one about 20 cells away. So only one connector was removed
at a time. Removing multiple connectors does not work as I discovered
a long time ago. After a while the real ground fault was at hand. But
only because there was a single break in the pack right before the
real ground fault.

The culprit may have been of my own doing. When I pulled that bad cell
out, there was a major puddle of KOH on the box floor. I had to take
out about 12 cells to clean it all up. And in doing so found an old
dried up koh path that needed attention just to be thorough. Something
like 40 cells were pulled today, wiped off with diluted vinegar and
had the tops brushed off.

Earlier in the week when I had to remove the 27 bluetops for what
appeared to be a ground fault, I must have over stressed a cell, as it
was cracked down the corner for about an inch and had been recently
toped off with water. So it drained alot of electrolyte into the
battery box. As it turns out I must have been careless as there were
two other cells with cracks on the top that I had to leave out. So the
pack is running with 3 less cells.

Man, I have had the ground fault from hell. Sunday there was rain and
the pack was fine. I went through the pack expecting for it to be time
for a full watering. The charger setup has worked great at not boiling
off water very fast. But Monday morning the truck faulted. I put the
fan over the pack to dry it out. This has worked well before, but not
this time. It helped, but not enough.

So Monday, Tuesday, and Wednesday I worked each night hunting down and
killing ground faults. There was a sizable one regarding the 27
bluetop nicads on the drivers side of the pack that I fixed on Monday.
They had lots of KOH on each of their sides. Cleaning them up took
care of that ground fault and allowed the truck to run. Software
showed a bit of ground fault still left, but good enough for now. When
Monday morning rolled around, the truck faulted again. So I took the
10mpg wagon to work. I traced the ground fault to another area. These
were greentops and were nearly clean and in the end didn’t change
anything for all of that work. Still faulting.

The pattern of finding and cleaning up ground faults has not produced
a running truck yet. Bummer. So far I’ve put $125 in gas in the wagon
for the past month in just two tanks. That’s a year’s worth of
electricity at work. They charge me $10/month.

The hard part is that the ground faults seem to move around the pack.
I’ve seen this before. It usually means the ground fault encompasses
many cells. But this time it seems to imply a huge portion of the pack
is ground faulting. So tonight after eating, I think I’ll just watch
the tube and whine since I’m so tired.

The worst part is that the rain has stopped and it’s sunny with blue
sky’s and I’m stuck with a gas hog. This weekend I’m going hunting
with a big gun and am going to kill me a wild ground fault or two….

Here are the 5 Prius packs in my truck. They are wired in parallel. The pack impedance is so low that the rear tires can break loose during heavy regen. Each pack was good for about 1.0kwh. So the pack was good for about 5kwh’s total. Nominal pack voltage was 273 volts. The charger’s software was tweaked to account for this. The dolphin charged the packs fine.

I have an Emeter in my truck. It can get a little as 280 wh/mi under
45 mph. Most of the time it’s 350 wh/mi combined city and 50mph steady
cruising. Pure stop and go traffic is 400-425 wh/mi. 45-50mph is the
sweet spot for my truck. My truck weighs about 500lbs less than yours
because of the lighter pack. So your wh/mi will be higher still. I
also have low rolling resistance tires.

When I first received my truck the 64 ah pack would go 40 miles easy.
I’m confident it would have gone 50 miles if I had needed to.

After owning this pack I don’t put any faith into the resting voltage.
High impedance batterys can fool you badly. A load is very important,
even though lead acid has a fairly linear discharge curve.

The other thing that makes our pack not last long in USE vehicles is a
lack of BMS.

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