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Old November 15th 18, 01:42 AM posted to rec.aviation.soaring
Graham Drinkell[_2_]
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Posts: 12
Default LiFePO4 chargers

At 20:09 14 November 2018, wrote:
On Wednesday, November 14, 2018 at 2:56:35 PM UTC-5, kinsell

wrote:
On 11/14/18 9:03 AM, moshe... wrote:
On Tuesday, November 13, 2018 at 11:11:52 PM UTC-5,

kinsell wrote:
On 11/13/18 6:08 PM, bruce... wrote:
Mark, When K2 was fairly new on the market I contacted

them asking
if=
Battery Tender Jr. is okay and safe, they replied that it is perfectly
oka=
y and nearly the same as their charger. I also contacted Battery

Tender
Jr.=
with the reverse question and they said the BTJr is fine for

LiFePO4. I
us=
ed the BTJr for years on my K2 with no issues. They're about $25

on
intern=
et sites.


Have you measured the amount of charge you're getting into

the K2's?
=
It
will be considerably less than the rated amount due to using

lead-ac=
id
charger.

Also, if K2 has cell balancing capability, it won't be used

because
yo=
ur
Battery Tender doesn't put out enough voltage to make it

work.
=20
Many simple lead-acid chargers reach up to around 14.2-14.8

volts.
Tha=
t voltage would suffice to charge an LFP battery to well above 90%
capacity=
if it stays there for a while. If it quickly shifts to "float" at 13.5V
o=
r so then it won't do well in charging LFP. So simpler is better in

this
c=
ase. Measure what your charger does. And disconnect it after

several
hour=
s, don't leave it on "float".
=20

=20
Hate to break this to you, but at $24, the Battery Tender Junior

is one=
=20
of the cheapest chargers on the market, and is fully featured

with a=20
float mode.
=20
14.2 volts wouldn't begin to charge an LFP to "well over 90%" as

you=20
claim. If you found a charger that delivers 14.8 volts under

load, then=
=20
it would overcharge an SLA and would be considered defective.
=20
If you're going to spend big bucks for an LFP, you ought to get a

proper=
=20
charger for it. Still waiting to hear just how much charge the

K2's got=
=20
in them from a BTJ.
=20
-Dave


That's the conventional wisdom, but see experimental results he
https://www.powerstream.com/lithium-phosphate-charge-
voltage.htm
- well above 90% capacity even at a bit lower than 14V!

A cheap dumb 14.x volt fixed-voltage source with limited current

output
(an=
d perhaps aided by the battery's BMS) would charge an LFP just

fine. I'm
n=
ot saying that's the ideal charger, but in a pinch it would work well
enoug=
h. I am not happy with the several chargers I have that push SLAs

well
abo=
ve 14V (even above 15V), but they may be handy for LFPs.
Personally, I would fly a model aircraft with a lipo battery. Full

size, definitely not! They deform at high altitudes, with the
possibility of fracturing cells? The best bet is to use military spec
batteries that work in space?