nuckolls.bob(at)aeroelect
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 Posted: Sun Oct 04, 2020 11:10 am Post subject: Li-Ion versus LiFePO4 |
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At 01:10 PM 10/4/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "bobnoffs" <icubob(at)gmail.com>
without any mod the 'idiot light' comes preset to warn below 13.0 volts.
in a lead acid set up this would catch the alternator soon after it went
off line and a lead acid would have most of its charge left. when a lipo
drops below 13 volts a lot of its charge is already been used. |
Are you perhaps conflating Li-Ion with LiFePo4
chemistries?
Check out this plot https://tinyurl.com/y6o5olae
These curves are examples of the discharge characteristics
of the wildly popular lithium cells offered in the vast
majority of ads on the 'net.
As you can see, the discharge characteristics are
exceedingly different than for LiFePO4.
To achieve 100% charge you must push energy into
these cells at 4.2 volts or so. 3 cells in series
would give us a 'bus voltage' of 12.6v . . . a
tad low. Their end of service voltage of 3 volts
would power our goodies at 9V . . . waaayy too
low.
Okay, 4 cells in series gives us a bus voltage
of 16.8 volts. Yeah . . . I suppose you could
configure a system that would run happily at
that level. MOST modern avionics wouldn't care.
But your battery contactors, light bulbs and
legacy 14v accessories would care. At end of
service we would see 12v . . . just fine but
yes, it would make your existing LV warning
useless.
But are you aware of any BMS supported, engine
cranking batteries offered to the automotive
or aircraft communities that are fitted with
the Li-Ion chemistry?
LiFePo4 is a marriage made in the lab.
A 4-stack array offers full charge and end
of service voltages are quite compatible
with the lead-acid world. That's why all those supplier are
able to offer plug and play lithium upgrades
to virtually everyone . . . including those
who choose to cheat death in those
funny kites with air-thrashers on the
front.
Bob . . .
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