nuckolls.bob(at)aeroelect
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 Posted: Tue Mar 14, 2023 11:55 am Post subject: What's all this Lithium Specific Battery Charger stuff anyho |
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At 12:24 PM 3/14/2023, you wrote:
| Quote: | The NOCOs are way overpriced. Bob's example does a better job at 1/6th the price.
Bob, have you found a similar charger for lithium batteries? |
There are lithium and then there are LITHIUM batteries.
I've oft pondered the contradictions in performance
claims by the various purveyors of lithium products.
There are dozens of batteries that are simple
assemblies of cells stacked 4-high proposed
for service in a 14v system. They claim
to be drop-in replacements for wet or SVLA
products.
Okay, if the thing is claimed to live happily
in a lead-acid environment, then what's
this "special lithium charger" stuff all about?
Then there are products that offer battery
management systems within the battery itself.
The term "BMS" does not offer an industry
wide description of form and function.
Products that seek to assure consumers of
100% compatibility with the lead-acid world
often include electronics adding substantially
to the cost of the battery! Yet, there are as
many (if not more) products offered with NO
built in electronics. Some do offer a
cell-balancing connector. Ebay and Amazon
are replete with cell-balancing modules
that cater to the DIY battery-array market.
I'll call your attention to the figures here
on my website:
https://tinyurl.com/mw4fz3pf
One figure illustrates a family of capacity
vs. charge voltage plots for an A123
LiFePO4 cell. Note the battery performance
when charged at various termination voltages
ranging from 3.3 to 3.7 volts. In a 4-stack
array intended for 14v systems, these voltages
correspond to system voltages of 13.2 to 14.8
volts.
Note that cell capacity is essentially maxed
out with a charge voltage of 3.4 Volts/Cell
(13.6V system) with no significant improvement
above that.
The other image is a snapshot of specs for
a well known variety of LiFePO4 cells that
state a max charging voltage of 4.2 until the
current drops below 100mA. This would be a system
voltage of 16.8 Volts!
Perhaps this offers a reason for the success
of the many bare-foot, 4-stack engine cranking
products out there. As long as system voltage
is greater than 13.6 (but less than 16. ,
the battery has a high order probability of
a useful life.
So, what's all this lithium specific charger
stuff about? The charger we've been discussing
in this thread tops out at just under 15V. No
red flags there.
In the BMS camp for lithium products, we're
told that the battery is a plug-n-play replacement
of the EXISTING wet or SVLA battery. Rest assured
that the BMS will protect your substantial investment
from alternator malfeasance . . . except that its
not clear to me that the legacy lead-acid system
set up to charge and 14.2 to 14.8 volts is something
to be worried about.
So that's a long introduction to my response to
your question. Unless someone has DATA to suggest
otherwise, I'm of the not-so-humble opinion that
lithium specific chargers are in the same class
as battery desulfators. There are dozens of patents
on desulfation processes NONE of which are accompanied
by repeatable laboratory grade tests that demonstrate
efficacy of their claims.
I've got a EarthX battery on the bench that's
be maintained by one of my venerable BatteryMinders
for about 10 years. That reminds me, I think I'll
run a new cap and load check on the little feller.
Don't have an airplane to run it in but it's jump
started a dozen or so vehicles over the years!
The one thing I've not yet mentioned is the 'cell-
balancing' feature suggested in some battery
management philosophies.
Cell balancing becomes a significant concern as
the cells age. If the internal impedance and/or voltage
vs. charge current one layer in the 4-stack array
rises significantly over the others, it's capacity has
been depressed. So while its brothers are still actively
taking on more Joules of energy, the 'weak sister' is
at risk for exacerbated damage due to over-charging.
A cell balancing system places a dummy-load resistor
across a compromised layer of cells to reduce the
risks to the cells.
Given what we've observed of the lithium art and
science over the last decade, I'll suggest that cell
balancing is probably not applicable to aircraft
applications. Keep in mind that the majority market
for batteries is populated with customers who routinely
deep-discharge their batteries and flog 'em until they
don't get up and hunt any more.
We airplane guys are intently interested in
CAPACITY of a battery compared against DESIGN
GOALS for Plan-B endurance in battery only
ops. The rule of thumb for battery replacement
is to take it out of service at 80% of new
or when battery-only endurance goals are not
satisfied.
In both SVLA and Lithium worlds, a battery is
likely to still be cranking an engine when it's
time to replace and before cell balancing becomes
a significant issue.
That's kind of a long winded answer to your
question but hopefully gives you understanding
that supports future decisions.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
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