Re: Got 4Ah, not 5Ah, battery 18V (20V) - done right thing?

On Sat, 18 May 2024 12:46:42 -0700, Bob La Londe <none@none.com99>
wrote:

On 5/17/2024 5:56 PM, Jim Wilkins wrote:

"Bob La Londe"  wrote in message news:v28jc3$2cs45$1@dont-email.me...
 
On 5/17/2024 2:41 PM, Jim Wilkins wrote:

...

 
I think its more likely adjustment of the internal BMS depending on how
the larger battery is configured to make it larger.  For instance if it
has an extra bank of cells it can 100% certainly deliver more current.
Just like tying two car batteries in parallel gives you more current
capacity.  I expect larger cells might also be capable of more current
if the conductors are sized accordingly.
Bob La Londe
CNC Molds N Stuff
 
-------------------------------------
Beyond the BMS limits, the capacity and internal resistance depend on
details of the chemical formulation and physical structure, such as
particle size, which may be trade secrets. I've read that they can be
traded off depending on the intended load current, higher resistance for
greater capacity and vice versa.
https://www.linkedin.com/pulse/what-does-c-mean-lithium-ion-batteries-bruce-feng
 
Marine batteries are similar, the high capacity deep cycle ones for
trolling motors aren't recommended for engine starting current.
 
 
 

>
I think you are over thinking it.  Sure changes in technology can make a
difference, but often larger battery packs are just larger.  Quite often
when you dig into various mid to good quality battery packs you find
they have the same cells from the same manufacturer.  Assembly quality
is an issue, as is the choice and programming of the BMS, but the cells
are the same.
>
I have a bit more experience with marine deep cycle lead acid batteries,
and I don't think its as big of a deal as you think.  I've even run
combined usage with the base ground battery doing double duty as the
cranking battery and the ground battery for the trolling motor.  I've
done it for years, and other anglers I know have done it for years
before me.  Its a way to run a larger trolling motor when battery space
is limited.  I did run four batteries in my current 20'10" bass boat
because I have the room for them.  In my newest smaller acquisition
there is no space for 4 batteries, but I noticed it has a 36V trolling
motor on the bow.  They have just been running it on 24V.  Runs fine.
Just less power.  I'll be converting it to the dual usage cranking
battery configuration as soon as I have enough play money to buy all new
matching batteries for that one.  Could they get better life if
configured differently.  Maybe.  That all is a bit of a tangent though.
>
>
>
--
Bob La Londe
CNC Molds N Stuff

  With cylindrical lothium batteries the cells are all pretty much the
same physical size regardless of their published capacity. All pretty
much induatry standard 18650 format. The difference between battery
PACKS of different capacities will be either the composition of the
cells or the number of banks. If limitted to the number of banks
capacity differences will be the cell capacity X1. X2, X3, or X4 -
with the physical size reflecting the difference.
Battery cell composition - different chemistries or different
construction, will give less distinct "multiples" af power and no
change in physical size. An 18/20 volt battery is composed of 5 cells
in series, 0r 2 series sets of 5 arranged in parallel, or 3 sets in
parallel - etc. For a 4Ah and 5Ah to be composed of the same cells the
5Ah battery would be  1/4 larger than the 4Ah - and would be capable
of producing 1/4 more capacity AND maximum current (assuming the
connector links are sized appropriately and heat shedding is adequate)

 With lead acid batteries things get more interesting. The grid
design, link design, lead alloy, and acid capacity all come into play
(along with the separator material) before even taking case size into
account. (or acid strength). Basically the weight of lead in a battery
is a pretty good predictor of capacity - but whether that weight is
arrives at by plate thickness or plate density makes a BIG difference
- primarily by the difference in "paste" capacity.

Deep Cycle, SLA (Starting Lighting and Accessory) or Marine
(combination) are all designed and built differently.Whether flat
plate or coiled.
Real good "deep cycle" batteries are most often "pure lead" while
antimony or calcium alloys are generally used in SLA and Marine
batteries. Marine batteries are generally built to withstand more
vibration without degrading ling connections or dislodging the paste -
through both plate design and separator material. Some cheaper
batteries address the plate material issue by providing deeper "acid
wells" below the plates to allow more shed material to accumulate
without shorting the plates - at the expense of smaller plates - while
at the other extreme you get starved acid, or AGM (absorbed glass mat)
batteries there there is NO SPACE between the separator and the plate
- meaning no plate material can effectively leave the plates - and
ONLY the rquired amount of acid is contained in the battery - allowing
for maximum plate vol;ume and mass for the battery case dimension. AGM
batteries are highly vibration resistant, and pure lead versions make
ideal deap cycle batteries although not NECESSARILY suited for high
current output.

When sizing a "battery bank" endeavour to use the highest capacity
cells you can get, connected in series, rather than higher voltage
batteries connected in parallel - for a 36 volt pack use 6 big 6 volt
batteries in series rather than  2 packs of 3 12 volt batteries. The
6X6 is ONE BATTERY while the 6x12 volt solution is actually TWO
BATTERIES in parallel - with the associated load sharing and
interconectivity issues involved.


The same can be said with Lithium (or other chemistry ) Large cells
connected in series makes a much better traction battery than a couple
bushels of 18650 cells or double A cells bunched together into a
battery pack