I really have to beg to differ about CALBs.
My Focus has 45 CA180 cells that have been on the road for about five
years without BMS. Once a year, sometimes twice, I pump a few amp hours
into the lowest cells with with a radio control type charger.
That usually involves about five cells.
I do have a homemade battery monitor with a display, expanded voltage
scale, that I use to keep a eye on the pack while driving. And, I do
datalog each cell all the time while driving and charging. In the
charging sweet spot, about 3.4 volts, all 45 cells are in a tight range
of about 25 mV. I consider that basically magic!
My battery monitor also will stop the J1772 if any single cell voltage
gets too high.
So, that my experience with CALB cells,
Tom
On 8/6/2018 7:51 PM, Alan Arrison via EV wrote:
I guarantee that the inferior Chinese cells will change capacity as
they are cycled and not by just a few percent.
Running them without a BMS is a recipe for disaster. Damaged cells at
best, a fire at worst.
All the Chinese cells are junk, especially the CALBS.
Al
On 8/6/2018 7:48 PM, David Nelson via EV wrote:
On Tue, Jul 31, 2018 at 9:25 PM, Tom Hudson via EV
<ev@lists.evdl.org> wrote:
Those two were ZERO VOLTS, and show ZERO OHMS resistance.
Is this a common failure mode of lithium-ions (or the CALB
modules)? I'm
thinking that I'd better set up some kind of fusing between the
buddy pairs
because if one of the pair fails in this way, it's going to present
a dead
short to its buddy -- and nothing good is going to come of that.
I don't know how common of a failure mode that is but I suspect it
could happen. If they were placed upside down (terminals facing down)
there is evidence that that has corroded the internal contacts to the
terminal bolts but that caused an open circuit situation, not a dead
short.
Internally the cells are made up of several layers which are
"buddy-paired" at the terminals. I put 20 buddy pairs of TS-LFP100AHA
cells in my Gizmo back in January 2010 and they are still going
strong. While the probability of any given cell failing goes up with
the number of cells I claim that a 200Ah cell made up of the same size
materials as the 100Ah cells would also have a higher probability of
failure. Definitely give each cell a cycle test and if you have the
time a capacity test. I would recommend that you then pair them up
where the capacity of the pairs ends up being nearly identical. I did
a rudimentary version of this for my Gizmo and it has worked out just
fine.
Some claim that you have to have the cells at exactly the same SOC
before connecting the buddy pairs. Theoretically this doesn't make
sense and I have also tested it and practice shows it really doesn't
matter. As long as their voltages are similar the initial current
isn't that great. Somewhere in the EVDL archives I posted the numbers
from one of my tests of this. IIRC it maxed at ~100A for a second or
so and quickly dropped to below 20A or so. Charging the cell pair to
3.4V or discharging to 2.8V or so brings the two cells in line with
each other.
The 100% SOC resting voltage of LFP cells from CALB and TS is 3.38V.
Make sure you aren't hammering the cells with 3.6+V on every charge
trying to equalize them. A good set of cells doesn't drift that fast.
I have been running my pack top balanced without attached BMS boards
for several years with no issues. I recently sold the Gizmo and I
don't trust the new owner to be able to be the "human BMS" so I am
going to be reinstalling the BMS boards I have. Furthermore, it is an
unknown how much the cells will drift as they age. They have been fine
so far but I'm not driving it now so can't do my annual voltage check.
I've been charging to 3.465V/cell with my Zivan chargers and the
resting voltage with no load after 12hours has been 3.36V so I know
I'm not overcharging them.
HTH,
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