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0. 12:23 AM - Please Make a Contribution to Support Your Lists... (Matt Dralle)
1. 11:18 PM - Re: lithium facts (Jim Kale)
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| Subject: | Please Make a Contribution to Support Your Lists... |
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I have been studying lithium batteries for several years, when and where I
can find information. I am not a chemist, or electrical battery engineer.
Just a guy who uses lots of lithium batteries. I use them to power large
radio control models aircraft. Common RC models these days use batteries
similar to the type you would use in a homebuilt airplane. The RC models I
fly typically use 4 cell, 14.4 nominal volt batteries. They are discharged
at the rate of about 30 to 150 amps and get totally drained in about 10
minutes. Us modelers have also found that stopping the discharge at about
20 to 30 percent capacity remaining helps keep the cells cool and increases
their life substantially.
I have seen some lithium batteries catch fire in flight and the RC model
(normally fairly expensive - a few hundred dollars and normally built from
wood or plastic) goes down in flames.
All of the multi cell lithium batteries I use are charged with each cell in
the battery pack getting charged individually from a very special charger
normally called a balancing charger. That means if you have 4 cells, there
are 5 wires coming from a balancing charger that independently charges and
monitors each cell while it is charging. I believe that some of the high
end lithium batteries in use today have some balancing technology built into
each cell and these special batteries may be charged form a common source
like an alternator, with a single total charge voltage, sort of like the
lead acid battery charging we are all familiar with . Inside each cell or
these special lithium batteries, the automatic circuitry keeps each
individual cell at a controlled charge current and the proper float voltage
when the cell is topped off at the proper voltage for the chemistry being
used. All of this automatic control inside each cell, just means there are
many potential failure points. If any individual cell, or its automatic
charge circuitry goes bad, the whole battery may fail in a mild manor (just
quits working) or catastrophic manor (fire).
All of this automatic cell monitoring is very expensive. Failures may be
dangerous, or just very expensive.
The bottom line is if you want to switch to lithium batteries, you should
have your charge system designed by some highly qualified folks. Just
buying and installing a lithium battery can be very expensive at best, or
very dangerous at worst. Let the home builder beware. You can bet Boeing
spent some very large sums of money for that lithium battery that caught
fire in their 787 Dreamliner. Catastrophic failure is always possible no
matter how much you spend for hardware.
I work as a flight training systems instructor for a USAF squadron that
flies helicopters. For the past 50 years or so, the military forces used
Nickel Cadmium batteries in their aircraft. These batteries costs about 8
times as much as lead acid batteries, and required many man hours of service
and tests every 4 months. Recently we switched to sealed lead acid
batteries (Gel Cells). Now we pay about 5 times less than the NICADs costs,
and they don't need any regular maintenance. We just use them till they
don't come up to standards, and replace them. Much like you maintain your
car. A giant leap backwards, and we save lots of money and get better
reliability and performance, not to mention improved safety (those NICADs
had a tendency to melt down every now and then.) It doesn't get much better
than that. Of course, the quality and performance of sealed lead acid
batteries has improved by leaps and bounds over the last 50 years.
Jim Kale
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Jan de
Jong
Sent: Thursday, November 6, 2014 5:28 AM
Subject: Re: AeroElectric-List: lithium facts
--> <jan_de_jong@casema.nl>
On 11/5/2014 9:22 PM, Robert L. Nuckolls, III wrote:
> <nuckolls.bob@aeroelectric.com>
>
> At 12:46 2014-11-05, you wrote:
>> <jan_de_jong@casema.nl>
>>
>> Well, all I can say - I'm amazed.
>> I wonder why I never read anything anywhere but 3.6V to 3.7V - with
>> dire warnings about exceeding much...
>>
>> By the way, these people show 90% charge at 3.6V (100% at 4.2V):
>> http://www.powerstream.com/LLLF.htm
>
> Check out this page . . .
>
> http://tinyurl.com/2349lq2
>
> and the links cited thereon. Isidor Buchmann is
> about as knowledgeable as they come about batteries
> exceeded only by his generosity for sharing what
> he knows.
>
>
> Bob . . .
>
Interesting.
It remains difficult to know when generic "Li-ion" data applies and when
specific data is needed for one of the cathode chemistries: "LCO", "LMO",
"LFP", "NMC", "NCA", "LTO"
see
http://batteryuniversity.com/learn/article/types_of_lithium_ion
http://batteryuniversity.com/learn/article/lithium_based_batteries
What I am guessing at the moment:
- the aging mechanisms and lifetime statistics are similar
but some are more robust than others
- the maximum cell voltage (4.2V) applies to all
- charging method and charging phases are similar
but they have different capacity vs. final charging voltage curves
charging LFP beyond 3.6V doesn't add much, charging LCO beyond 3.8V to
4.2V adds most of the charge
see http://www.powerstream.com/lithuim-ion-charge-voltage.htm
(the average force required to get an ion into a crystal location is
different)
- they have different (slow) discharge voltage curves (LFP flat at about
3.2V, LCO steadily decreasing from 3.9V)
I could be wrong.
Jan de Jong
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