________________________________
> From: michael.e.r...@gmail.com
> Date: Mon, 30 May 2016 19:17:41 -0400
> Subject: Re: [EVDL] Old packs as powerwalls @L3 EVSE sites to help
> smoothout the grid, +more
> To: hoegb...@hotmail.com; ev@lists.evdl.org
>
> I get a lot of flack for this, but Li - ion cells don't function the
> way PbSO4 and others do. They are essentially bi-stable. You put and
> ion on the cathode (charge it) and it nestles between some platelets of
> graphene within a stable pocket of carbon atoms around it. Until you
> create a potential and current path in the discharge direction nothing
> happens. Before the "until" point there is nothing to cause the ion to
> move, unlike other battery cells. This is called intercalation.
>
> If there is self discharge of a Li-ion cell happening when it is not in
> a circuit, it is a fault in its manufacture. There is a lot of variety
> of manufacturing expertise and quality. We could, any one of us, make
> a functional Li-ion cell in our garage, but it would be unlikely to
> have a long life or good performance.
>
> One good way to treat a new cell is to charge it for long term storage
> is charge to about 50% DOD (or SOC if you prefer). This ensures that
> the degradation that occurs when a fully charged cell sees too high
> temperature. This degradation is a loss of capacity however, not
> necessarily a loss of charge % relative to the whatever functional
> cathode, anode and electrolyte is left. A shitty cell of a particular
> chemistry will be alike to the same cell made well made and formed
> properly of the same chemistry.
>
> At 50% SOC you theoretically are seeing the nominal cell voltage. But
> I warn you that you may not really know the true midpoint cell voltage.
> Spec sheets are notoriously vague to incorrect on this point. Also it
> is not easy tp tell anything about SOC from voltage. a tenth of a volt
> can be a lot of difference in charge, a characteristic of Li-ion
> generally. You might see the voltage change 0.3V from 20% to 80% soc.
> Every change in chemistry can effect this. Do you have LiFePO4? One of
> the combinations of Li with nickel, aluminum manganese, etc.? THe
> nominal can range from 3.2V to 4.2V depending. Do you really know what
> the cells are made of? You said "high voltage after six years, a high
> nominal voltage for one could be a low voltage for another.
Yes I agree (but not 4.2 at old fully charged cells after some storage,
they seems to go back and settle about a bit over nominal, probably a bad
thing :-)
And the sonys I have not done any discharge test on them yet,
But they have about 3.73-3.80V now
Do you / someone know how to read the mfg year out from that code?
The 100Ah lifepo4 on the other hand, they did of course
stay at the nominal voltage, almost as a constant voltage source :-)
As you say we cant really tell based on the voltage for
SOC between 30 or 40 up to 70% , or so.
But I did a discharge test, and got the Ah out, so they where almost full,
And I did not even charge them 100% full before the storage years
So I conclude it is almost "zero" self discharge in some lifepo4, I would say
Also some 25650 DLG-EV cells (K2) 3.3Ah LiFePo4 show the same, but
they have also been short circuit tested until half of the 16p-pack popped
up and disconnected the cells internally, the rest of them was long term
stored, at least 5 years later they still had not gone below 3 volt.
Some of the cells are not ok in capacity, but that I assume was part due
to the extreme abuse, they have had very high internal pressure..
(the bottom of the cells are round..,) and half of the brothers in that
parallel
pack did die and "went" the cap & therefore also open the disconnect switch.
They where also dry inside on the active material layers..
The thundersky we tested DID seem to have some self discharge,
I don't know why if there is some junk in the electrolyte or the separator
or.. I dont know, so then maybe some small leak currents would occur?
Also they did leak "acid" from the vent/cap, bad seal /mfg problems.
Sign: The TS-logo almost disappeared from the clear plastic cap,
end they did come loose, and we also measured very acid electrolyte spill
around the plastic nut.
(The electrolyte seems to form HF-acid when in contact with moist from air,
So I also guess its not good at all to get humid air IN to the cell that way...)
the *very* old Russian NiMh still had some juice left, but not full.
they did seem to operate normal now even after all this years,
if I find one again I can do a capacity plot- test on them to when I build the
tester.
BTW the seller in 1992 told me it was something similar to the thoughts
about the Tesla gigafactory layout in Russia back then, :-) they had their own
nickel mining in one end of the process, battery cells in the other end
and thousands of employees, something like that if I remember correct.
(Cells was probably just a small part of the business, NiMh was not so
common then, and LiIon was not common at all, NiCd was the king of tools
and phones, then Sony/Ericsson started with lipoly some years later, maybe in
-96 or so ?)
Jukka, you might know more about the Russian NiMh producers in the early 90ths?
But the NiMh powercells from the hybrid, that seems to be a different animal,
they also seems to recombine very good when overcharging IF the
temperature is high, about 35-45´Celsius
So one mode that I guess could be damaging to them is: fully charged
cells, ..COLD, and if I then charge them *again*.. the voltage then
seems to go up high before the process takes care about the energy
Therefore I pre-heat them if I need top them of with some Ah before
cutting the lawn with my battery-lawn mover (if the cells have been waiting
some weeks or months, the self discharge seems so high (and uneven) that
they probably needs a bit of re-balancing again besides the energy fill up.
//John
_______________________________________________
UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
http://lists.evdl.org/listinfo.cgi/ev-evdl.org
Read EVAngel's EV News at http://evdl.org/evln/
Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
