Got it. So then in situation where the intent is to use them for a temp controlled shipping container (very low average loads) the
LVD should still be set to honor the 2.7V manufacturer spec for 100% DOD ( or a little higher if desired to extend life) regardless
of battery temperature. Since the only loads are on average very low then it makes the design easier not having to account for peak
> -----Original Message-----
> From:
[hidden email] [mailto:
[hidden email]] On Behalf Of Bill Dube
> Sent: Saturday, October 31, 2009 8:53 PM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] LiFePO4 discharge characteristics
>
> It is the voltage that causes the damage. The LifePo4 cells are much
> less sensitive to low voltage than the older metal oxide cells,
> however. (The old metal oxide cells would simply not recover from
> being taken below about 2.5 or 2.0 volts.) Reverse voltage is what
> you _really_ want to avoid because it does a lot of damage.
>
> Once the cell is below 2.5 volts, there is hardly any energy
> left so you might as well stop the discharge there. Electronics
> generally does not want to run below 2 volts, so they sound the alarm
> around 2.5 volts.
>
> To keep from false triggering, the low voltage sensing for
> LiFePO4 should allow brief excursions below 2.5 volts to perhaps as
> low 1.0 volts, perhaps even a bit lower.
>
> Bill Dube'
>
> At 09:28 PM 10/30/2009, you wrote:
> >Hey Lee you out there? Or anyone who can answer this question for me?
> >
> >Since the typical discharge curves for the LiFePO4 batteries is way
> >more flat than for lead acid, there is a very sharp drop once
> >they reach ~95% DOD. So looking across the temperature
> >characteristics the voltage takes a dive or tanks at or below the 80% DOD
> >level for colder temps (-25*C to -40*). The question is, in
> >designing an LVD for these things, if you were operating at -40
> >degrees could you actually let the voltage tank as far down as it
> >can go (meaning never activate the LVD) since the actual capacity
> >in the cell (if it were at room temp) is still more than 80% DOD?
> >
> >Is it the absolute voltage that causes cell damage and subtracts
> >from its useful life, or the depth of discharge?
> >
> >(OK so 2 questions ;-)
> >
> >Mike
> >
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