Because of my job, my rc plane hobby was put on hold for about 5 years. Now,
I found that I am able to rejuvinate my Ni-Cd batteries but the nickel metal
hydride batteries seemed beyond repair. I invested quite a bit in these Ni-H
batteries and now they appear useless.
What is your experience with these batteries? How do the new LiPO batteries
hold up during long periods of inactivity?
sam as your experienec.
Nimh last at best a couple of years. Nicads can be revivd. LIPOS
generally wont self discharge in much less than a few years. Certainly
with no special storage they are better than 95% charged after an idle
winter..
"...Curent test projecting excellent calendar life: 17% impedance
growth and 23% capacity loss in 15 [fifteen!] years at 100% SOC, 60 deg.
C..."
A123Systems: Technology; press on green "Thousands of Low Rate Cycles"
under image alittle to the right:
I looked up the specs on LiPO batterys and they seem to have the same or
better energy density as Ni-Hd batteries and
the price is the same. Is there any drawbacks to using these new batteries?
LiPo batteries have limited shelf life. They will go bad by themsleves,
even if you are not using them, and they will go bad faster than NiCds
or NiMHs. There are some recommendations that are supposed to prolong
the shelf life of LiPo batteries, like storing them half-charged and
storing them in cool place, but the bottom line is that once you get
yourself a LiPo battery, you have to fly it.
This is utterly completely WRONG.
They have about a 10 yar shelf life, and will generally not lose
anything like the charge that Nickel chemistry will.
There are some recommendations that are supposed to prolong
Total rubbish.
Hi!
Some more information of typical Lithium accumulators:
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"...
When compared to the lithium-ion battery, Li-poly has a greater life
cycle degradation rate. However, in recent years, manufacturers have
been declaring upwards of 500 charge-discharge cycles before the
capacity drops to 80%.
..."
How to prolong lithium-based batteries:
formatting link
"...
A lithium-ion battery provides 300-500 discharge/charge cycles.
...
Aging of lithium-ion is an issue that is often *ignored*. A lithium-ion
battery in use typically lasts between 2-3 years. The capacity loss
manifests itself in increased internal resistance caused by oxidation.
Eventually, the cell resistance reaches a point where the pack can no
longer deliver the stored energy although the battery may still have
ample charge. For this reason, an aged battery can be kept longer in
applications that draw low current as opposed to a function that demands
heavy loads.
...
Figure 1: Permanent capacity loss of lithium-ion as a function of
temperature and charge level.
..."
I didn't know Li-Ion & Li-Polymer were even used in rc planes. I've only
seen LiPO, (which I think stands for Lithium Phosphate) sold for rc plane
power packs. Are we perhaps confusing battery types?
They are much lighter than the NiMh or NiCad for the same output, nearly
half the weight. The advent of LiPos has really let electric flying hit the
mainstream. The biggest downsides are cost ( but they have gotten much more
reasonable lately) and safety. Damaged or mishandled LiPos can and will
burn. That said, I've been an all electric and all LiPo flyer for 5+ years
now with no regrets. I'm also very careful in how I
handle/charge/discharge them.
PCPhill
LiPo AKA LiPoly stands for Lithium Polymer. This is the main battery
type used in electric RC planes.
Once again, to reiterate the _correct_ information I already provided
before:
For extended term storage manufacturers recommend
- storing LiPo packs at 50% charge.
- storing LiPo packs in cool place (one of the recommendations I saw
suggested 32 F = 0 C)
LiPo batteries degrade with time even if not used. The speed of
degradation depends on the specific cell chemistry (and, of course,
storage conditions). High C-rating chemistry usually degrades much
faster than low C-rating chemistry. For example, Thunder Power Extreme
V2 series batteries (now being outphased) had very good C-rating, but
rather short by modern standards shelf life.
Note, that by "shelf life" I don't mean the ability of the battery to
retain the charge (self-discharge rate) or the cycle count in active
use. (Self-discharge rate of LiPo is excellent, much better than NiMH
and even NiCd. Cycle count is also very good). By "shelf life" I mean
the general degradation of the battery when not in use. And this still
remains a weak point of LiPo, even though it is constantly improving.
Thanks for all your responses. I was confusing the Li polymer batteries with
the Li Iron Phosphate ones. After some research it appears these are geared
more for electric motor scooters and motor vehicles. I'm guessing the light
weight of the Li Polymers makes them more suited for rc planes.
The general opinion seems to be that LiPO are a durable time tested battery
with a long shelf life as long as you don't exceed recommended
charge/discharge rates. Perhaps Andrey had a marginal battery and was just
relating his experience with it.
It's sort of right and sort of wrong.
Lipo's need to be charged before storage, leave it discharged and
store it and it probably won't be happy when you get it back. They
self discharge less but below a critical voltage per cell (2.4V I
think) they will become unrecoverable. So fully charging them and
leaving them and they'll be fine, using them till they are flat then
storing them is going to give you trouble..
As has been stated above, the current recommendation is to store them half
charged and in fact some recent chargers provide a charge routine to do this for
you.
I terms of them dying of old age, they will eventually go but my notebook PC has
its original LiOn battery which still works and gives about 75% and is not 5
years old.
Actually there were some reports on RCGroups that seem to demonstrate
that combination of full charge and room (or above room) temperatures
are pretty hard of LiPoly batteries, i.e they do promote faster
degradation. While there are RC products out there that recommend
storing LiPoly in charged state (= fully charged) in their manuals
(Hirobo helis, for example), the manufacturers stated repeatedly that
this is not a good practice. TP datasheet can be found here
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and it explicitly says that the batteries are better stored at 50%
charge. As it has been said here, modern LiPoly chargers support "50%
charge" mode specifically for that purpose.
LiPo's require a bit more care in their care and feeding, but they sure
are nice. Just remember that they've been known to burst into flame
while charging, and charge and store them accordingly. You need to take
an attitude toward a LiPo that you would toward a similarly-sized flask
of gasoline, rather than you would toward a similarly-sized pile of
flashlight batteries.
If it's for an electric powered plane then you just need a charger and
ESC that are made to 'understand' LiPo's and are set up for them, and
follow the due precautions mentioned above.
If it's for a receiver pack then you have a choice between 3.7 volts
(which is too little for all but teeny planes) or 7.4 volts (which is too
much for just about anything without a regulator). Apparently the jet
folks do use LiPo packs for their receivers (I've been approached
professionally to design a regulator), but I have no clue about where to
get a regulator, how much to expect to spend, or who makes good reliable
ones.
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