Recently seen a thermal run away on a seneca where battery is in the nose. Glad
i was not in the air with it.!!!!!!
Sent from my iPhone
On 28 Apr 2012, at 16:35, "Jan de Jong" <jan_de_jong@casema.nl> wrote:
>
> I believe that a 12 V LiFePO4 battery is quite safe if used with care.
> It does not have a thermal runaway mode, but will burn, not explode, if
> mistreated
to an internal temperature of about 800 C (well above the melting point
of aluminium).
> By the way, LiFePO4 is not for low temperatures; one example increases
> internal
resistance (4 mOhm) below 10 C as follows: 20 mOhm at 0 C, 40 mOhm at -10 C
etc.
>
> How I intend to use with care:
>
> 1. Charge with a CC/CV regime, just like a lead-acid battery.
> CC: small alternator, charging current guaranteed less than 2C
> CV: maximum charging voltage 14.5 V; less is ok but the maximum SOC will be
> less
than 100%
>
> 2. Cell balancing is much slower and worse than with a lead-acid battery
> (because
a fully charged cell largely stops passing current).
> Mitigation:
> - long stays at CV interrupted by shallow discharges - normal starter battery
use actually
> - apply an external shunt (3.70 V) across each cell to speed up balancing
> if/when
needed
> Monitor:
> - all cell voltages must remain below 4.00 V; remedy: stop charging
>
> 3. Replace if ever discharged to below 20% SOC
> Monitor:
> - battery voltage must remain > 12.8 V; remedy: if needed carry on
> discharging,
but do not recharge, replace
>
> 4. Have 2
>
> I designed a "monitor & top equalizer" for attachment to a Shorai LiFePO4
> battery.
It has just two indications: 1. a cell has a shunt operating, 2. a cell
has a shunt operating but even so its voltage exceeds 4.00 V.
> According to the battery suppliers no equalizing or monitoring is needed -
> which
may be right ofcourse. Neither of the indications may ever show. On the other
hand - they do sell balancing chargers...
>
> Attached a typical charge curve for a LiFePO4 cell (author unknown). See the
current drop when a SOC of 100% is approached.
>
> Jan de Jong
>
>
>
>
>
> <40138chargeprofile.jpg>
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