When DIY Li-Ion battery bank goes bad !

[theoldwizard1]

You can watch the whole video here

The key take away is "when that one battery blew, it shot a flame out 3 feet !"

Those cells were some type of Lithium Cobalt Oxide (LiCoO2) cells, which are the most common because they have high energy density and moderate cost (because they are very high volume; Down right cheap when purchase as recycle, even recycled from never used products).

Lithium Iron Phosphate (Li FePo4) batteries will not explode and burn even when over charged or over discharged. This is the technology used in Battle Born batteries and other Lithium batteries found in RVs.


The good news is, this DIY battery bank is HUGE ! 700 cells !! This has been the only reported failure.

Moderator edit to re-size picture to forum recommended limit of 640px maximum width.

[MrWizard]

He said the individual cell that blew fire
Had no Mfg markings, and blamed it as being weak and his fuses for not blowing
Granted he should have tested his fusing
But the whole centre pack died, one cell did not cause that
To much heat was the probable cause of that

[theoldwizard1]

MrWizard wrote:
interesting video
probable cause "HEAT"

i NOTICED he put 100 cells in parallel ( he referred to each pack as (1) cell, (in reality each pack was a 3.7v 300amphr battery consisting of 100 cells) ...

Reminds me of the Boeing 787 battery issues !

The stupidest thing Boeing did was to not vent the battery compartment to the OUTSIDE. In the event of some failure that produced smoke, it was kept inside the plane, same as this guys design.

[MrWizard]

interesting video
probable cause "HEAT"

i NOTICED he put 100 cells in parallel ( he referred to each pack as (1) cell, (in reality each pack was a 3.7v 300amphr battery consisting of 100 cells)
then put the 'packs' in series
he also built them in series, sandwiched together
and the failed 'pack' was the center pack, no airflow no cooling,
IT got to hot, and degraded to the point of failure

Tesla batteries are built in a different configuration
a 444 cell Tesla battery is only (1) layer thick, approx 12"*12"*4"

5.2 KwHrs 233 amphrs 24v, a 6s74p configuration, IIRC is 6 in series and paralleled 74 times, (74 * 6-cell 24v)

the safest way to build , for 24v, 7 cells in series makes one small 24v battery (6 or 7 depends on which cell chemistry is being used)
then parallel multiple 7 cell batteries, to get the total ampHrs
if a cell goes bad, the fuse link for 'that series', takes all 7-cells out of the build
meaning there is never an imbalance in the number of cells in series
but the large Battery looses (1) small battery pack, instead of just one individual cell

a single flat pack 6s74p Tesla, or multiple 7-cell packs parallel
allowed for more even heat dissipation, less chance of overheating

it is 'easier' to construct a large battery, the way he did it
lots of cells in parallel, then series wire the parallel packs

it is NOT the best way, even if spaced apart to allow for heat dissipation, because if a few cells go out in a pack it still , that pack still has to pass the full amps load of the other packs, meaning each cell in the failing pack has to carry more amps, and increase cascade failure rate

[2oldman]

theoldwizard1 wrote:
Those cells were some type of Lithium Cobalt Oxide (LiCoO2) cells,... Down right cheap when purchase as recycle, even recycled from never used products).

Of course, that's why they do it. Probably best just to spend the money and be safe.