Today's Message Index:
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1. 08:08 AM - Re: lithium facts (davevon)
2. 10:30 AM - Re: Re: lithium facts (Rick Beebe)
3. 03:46 PM - Re: Re: lithium facts (Robert L. Nuckolls, III)
4. 10:40 PM - Re: Overvoltage crowbar availability? (Justin Jones)
Message 1
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Subject: | Re: lithium facts |
Hi All,
Hope I'm not too late to join in on the discussion, I wish I would have seen this
sooner. Greg over at B&C pointed me in this direction.
I'm in process of redoing the complete electrical system in a Laser 230 aerobatic
airplane. The system had evolved into something that was very heavy, unsafe
and just plain wrong in so many ways...
To save weight I bought an Aerovoltz/Ballistic LiFePo4 EVO2-16 battery. I'm using
a B&C SD-8 with their external regulator and OV protection.
Researching charging voltages for the LiFePo4 chemistry I'm finding a large variation
in recommendations.
The EV (Electric Vehicle) guys claim 3.33v/cell is 100% charged and shouldn't be taken beyond that. http://www.diyelectriccar.com/forums/showthread.php/you-all-destroying-your-lifepo4-cells-65336.html
Then I've seen a couple of places saying 3.65v/cell is 100% charged with a max voltage of 4.2v. http://www.powerstream.com/LLLF.htm
The stock B&C system charges at 14.4v and the OV protection is set 16v. Ballistic
batteries is telling me to charge at 14.4v but don't go over or "bad things
will happen". I'm sure that the OV protection has to be set more than even
a .1v higher that the regulated voltage to prevent nuance trips.
I'm guessing that there's some variation between cell manufactures and their voltage
specs and add to that the battery manufactures/assemblers add their safety
margin which leads to a case like the Aerovoltz/Ballistic having no leeway
between the charging voltage and do not go over voltage...
So is there a definitive answer???
Thank you for your time,
Dave
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=436650#436650
Message 2
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Subject: | Re: lithium facts |
On 01/05/2015 11:07 AM, davevon wrote:
> <davevon@bellsouth.net>
>
> [...]
> Researching charging voltages for the LiFePo4 chemistry I'm finding a
> large variation in recommendations.
>
> The EV (Electric Vehicle) guys claim 3.33v/cell is 100% charged and
> shouldn't be taken beyond that.
>
> Then I've seen a couple of places saying 3.65v/cell is 100% charged
> with a max voltage of 4.2v.
I have an EV that I converted with LiFePo4 cells. While charging I
charge until the voltage hits 3.5v per cell (and I've heard that 3.65 is
the highest safe range but there's little added beyond 3.5v). I then
hold the voltage until the current drops to 0.05C.
After I stop charging the voltage will drop to somewhere around
3.2-3.3v. So maybe that's what the first voltage is about.
> The stock B&C system charges at 14.4v and the OV protection is set
> 16v. Ballistic batteries is telling me to charge at 14.4v but don't
> go over or "bad things will happen". I'm sure that the OV protection
> has to be set more than even a .1v higher that the regulated voltage
> to prevent nuance trips.
Since they're building batteries to replace lead-acid cells, its pretty
silly of them not to protect their batteries from "normal" lead-acid
voltages. If they have 4 cells, 14.4v is 3.6 per cell which should be
fine. The maximum of 4.2 x 4 = 16.8 so bad things shouldn't happen with
an occasional foray above 14.4 except perhaps shortening the life of the
battery.
> I'm guessing that there's some variation between cell manufactures
> and their voltage specs and add to that the battery
> manufactures/assemblers add their safety margin which leads to a case
> like the Aerovoltz/Ballistic having no leeway between the charging
> voltage and do not go over voltage...
>
> So is there a definitive answer???
I've found that there's quite a variation in knowledge about LiFePo4
cells among the people who are selling them and even among those
building them.
--Rick
Message 3
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Subject: | Re: lithium facts |
>>So is there a definitive answer???
>
>I've found that there's quite a variation in knowledge about LiFePo4
>cells among the people who are selling them and even among those building them.
Gee . . . what was your first clue?
I've been sifting the lithium pile of sand for about 4 months.
I'll be writing an article for KitPlanes on some of my findings.
In brief, I believe I am on solid ground with the following
assertions:
LiFePo4 IS the chemistry of choice
The MAX charge voltage for LiFePo4 is 4.2 volts per
cell.
Sift through the spec sheets for commercial offerings
of LiFePo4 and you'll find MOST cells "rated" at 3.7V
charge, 3.3V nominal delivery point.
Here are some exemplar performance curves one particular
cell
Emacs!
Note that charging at 4.2 volts nearly DOUBLES the cell's contained
energy. Stack 4 cells in series to perform in a 14v system and
you would have to charge the battery at 16.8 volts. A tad high for
many 14V bus operated devices . . . and perhaps out of reach for
many voltage regulators.
It's a little different ball game for consumer products that discharge
lithium cells with switchmode power supplies. You can order chargers
rated for EITHER 3.7 or 4.2 volts per cell. There are no caveats
offered for the use of these chargers with any of the COTS lithium
products . . .hence, no big risk . . . but a substantial difference
in cell performance.
3.7 x 4 is 14.8 volts . . . right in the ball park for plug-n-play
replacement of SLVA with Lithium. Yes, STORED energy is 1/2 but service
life gets a real boost . . . and risk for electrically induced damage
to the battery goes way down. The AeroVoltz 3x4 array I tested clocked
in at just over 7AH capacity when charged on a 14.5V bus.
Cells promoted in the wild are burdened with some outrageous
claims for capacity . . . John Q. Public has few tools or skills
to determine if his purchase was righteous or not . . . so the
flim-flammers
get away with it. MOST of the cells I've sampled off eBay were not
worth the postage to get them onto my workbench . . . however,
some are quite good.
Balancing chargers are another story . . . but the bottom line is
that the COTS offerings of lithium drop-ins for SVLA battery
boxes don't come with a lot of hazard to anything but your
pocketbook. As the lithium market matures, we may well be
speaking of 16 volt systems for future airplanes.
Bob . . .
Message 4
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Subject: | Re: Overvoltage crowbar availability? |
Bob,
Do you have any of these new ovp modules available?
Justin
> On Dec 13, 2014, at 19:12, Robert L. Nuckolls, III <nuckolls.bob@aeroelect
ric.com> wrote:
>
> At 20:43 2014-12-11, you wrote:
m>
>>
>> Greetings,
>>
>> It looks like B and C no longer carries the stand-alone overvoltage crowb
ar (at least I think that's where I bought the one in my LongEz).
>> I know Bob is trying to get out of the parts distribution business.
>> Does anyone else know of a source or should I just plan on building my ow
n. (and if you have the link handy to Bob's schematic that would be great b
ut don't search if you don't as I'm sure I can find it...).
>
> There is a replacement for the legacy crowbar modules
> in the works. Boards are laid out and software is
> nearly complete. Probably have some working hardware
> in the next two weeks. B&C can probably still sell you
> the older version as well.
>
> The new one is software based and much more immune
> to nuisance trips. It's also packaged to look more
> like an 'airplane part' than the legacy CBOVM
> modules.
>
> <a76d280.jpg>
>
>
> Bob . . .
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