Gordon,
We use a "CellPro" PowerLab 8 to initially balance, and cycle our
LiFePO4 packs in groups of eight cells (or less.)
http://www.store.revolectrix.com/Products/Cellpro-PowerLab-8-EC5-version/Cellpro-PowerLab-8_3299
About $250 and you will realize that you have been sleeping under a
rock. Amazing device. 1300 watt
Get the USB interface module ($22) so you can easily collect and plot
the data while you are testing and cycling the cells. Get the CPBP9P-10
battery pigtail so you can easily wire up the individual cell taps.
(Tough to wiring it up to the cells without the proper connector, so for
$3, get a pigtail.)
We use a deep cycle 12 volt battery with the CellPro to provide the
input charging energy, (plus a modest 12 volt charger,) and to also
provide a reservoir for the CellPro to dump the energy from the Li-Ion
cells under test.
>>>> Charging, balancing, and using a pack with used/mixed cells <<<<
You have what you can afford, so sometimes you build a pack out of
cells that aren't well matched. First, put them on the CellPro and cycle
them in groups to find any defective or low capacity cells. Cycle all
the cells, and then cycle them once again to gauge what the self
discharge is for each cell. Toss any that have large self discharge as
that is a sign that they have internal damage, and will prove impossible
to keep in balance in the car.
Get all the cells fully charged. Then assemble the ones that proved
good on the CellPro into a pack.
>>>> "Foil covered cells" <<<<
These cells with a thin metal, plastic covered, outside are "pouch"
type cells and need to be constrained before they are used. They
basically are a hermit crab without its shell. _You_ need to provide the
shell. If you try to use them without a proper case, they will have low
performance, and a very short life. They require a case that presses
them into a giant sandwich at a very specific pressure range. It can be
done, but it is tricky stuff to build the proper case.
Bill D.
On 3/14/2021 6:47 PM, Gordon Wong via EV wrote:
Sorry if this message is not in the flow - I am a digest-only subscriber.
I have been helping John through this via direct email for maybe a couple
of weeks, and it was Willie who said it most accurately.
John's pack has probably never been properly balanced and an fire early on
due to improper mounting of the cells didn't help. Instead of the usual
thick plastic case on these prismatic LFP cells there was (by this
particular manufacturer) a relatively thin transparent plastic film around
the metal case (apparently an electrode) of the cells according to his
description. The cells must have been mounted in a sheet metal battery box.
Very likely the replacements for the burnt cells were not matched in
voltage when installed. And I think the BMS was only configured via CAN to
the charger to prevent overcharging. As far as I know the BMS was *not*
configured to shut down the motor inverter either via CAN or using the
(active low) Discharge Enable line on the Orion BMS.
It seemed logical to suggest a one-time bottom balance as this mix of old,
new and perhaps damaged cells might never top balance within a reasonable
timeframe and I didn't want to hear of the car being test-driven with an
unbalanced pack. I suggested 2.8v as a reasonably safe bottom but the
manufacturer spec sheet apparently stated 2.5v.
My idea was to expedite the balancing process by starting at a low SOC and
let the BMS stop the charge when the lower capacity cells came up to 3.6
something or whatever the BMS was set to.
Then short drives would rout out rather quickly any cells that were still
significantly lower in capacity. And I emphasized before going much
further to enable that very important *other* function of the BMS, the one
which should at least alert the driver if not outright stop the motor
inverter. I believe that this oversight reverse-charged some of the
cells.
For individual cell charging I suggested a commonly available bench power
supply and John did take delivery of a (5A or 10A?) unit but apparently it
failed before very long.
- Gordon Wong
PS John is a member of the Vancouver EV Association as am I. He is some 80
miles to the east. I haven't seen Roger Stockton for a couple of years.
He's running a Leaf now and I think he is still part of Delta-Q. All are
welcome to come visit VEVA via Zoom (Tuesdays 7-9 Pacific and Saturdays
10-12) - register at veva.ca.
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20210313/3879f974/attachment.html>
_______________________________________________
UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
ARCHIVE: http://www.evdl.org/archive/
LIST INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org
_______________________________________________
UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
ARCHIVE: http://www.evdl.org/archive/
LIST INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org
