As I understand it, the self-discharge for LiFePO4 cells is effected by
a host of conditions, including state-of-charge.
As I recall, it hits a minimum at something like 60% SOC.
Abnormally high self discharge is never a good sign, regardless.
Bill D.
On 4/20/2014 4:04 PM, Cor van de Water wrote:
Since about 6 months I have been testing the self-discharge of
a bunch of blue CALB LiFePO4 cells.
The good news is that after half a year of sitting, their
average voltage has changed from the (parallel) charge voltage
of 3.00V (meaning that they were charged to approx 10% SoC to
allow me to see how quickly they would fall off again, as the
voltage changes are larger to wards the extreme ends of the
charging curve) (after which I disconnected them to measure the
individual self-discharge of just each cells by themselves by
occasionally connecting a DVM to check and record voltage by hand)
to a self-discharged voltage of between 2.78 and 2.86V.
The current highest cell has the lowest self-discharge, losing
only about 80mV in that half year, while the fastest self-discharging
cell has lost almost double that voltage - 140mV
Note that this is not from the original 3.00V but from their state a
few weeks after I disconnected them, when I started recording voltages.
So, while the sitting of a cell over a half year (in winter)
apparently removes less than 10% of the charge, there definitely is
a marked difference in self-discharge between cells of almost 100%
higher discharge for the worst cell than the best cell in this sample
set of 16 cells.
I thought this might be of interest to some here.
Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203
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