If you want to see whether a cell will last a long time you have to test it
in damaging conditions - full charge and high temps.

Cycling does nothing useful beyond allowing the cell to spend more time a
conditions that are not damaging at all. That's not really useful, but is
is what you will get from most low cost purveyors. When I tried to survey
vendors I got nowhere even finding out the test conditions.

If you could get tests that actually stress the cells you still have to
make comparisons between various cells to see if they are consistent in
withstanding the difficult conditions, or a particular brand or design is
better than another.

Your best bet is to go with a vendor and manufacturer that has a good
reputation, and that is likely not a low cost solution.

I am not sure about previous discussions and you may know this: Peukert's
Law is not applicable to Li ion cells in any way. It only relates to lead
acid cells.

If you nave not listened to lectures by Jeff Dahn you should to understand
how Li ion cells are damaged.
http://tinyurl.com/y395ahod
This 2013 lecture is worth spending time with on what causes Li ion cells
to die:
https://www.youtube.com/watch?v=pxP0Cu00sZs

On Thu, Mar 14, 2019 at 6:20 AM Dan Baker via EV <ev@lists.evdl.org> wrote:

> I have been communicating with a couple sellers now on Aliexpress.  Prices
> seem quite varied and reviews are mixed on these batteries.  I suspect
> there isn't a lot of standards or testing on actual claimed capacities.  I
> would like to try a 12v pack or 2 before buying more and perform some tests
> to verify capacity.  Has anyone done this testing before?  I assume the ah
> rating is based on a 1amp draw for x amount of claimed hours.  So would I
> hook up a 12 watt load (LED bulbs?) and watch pack voltage till it drops
> till below 12v?  Or would I measure it till the BMS protection cuts in -
> (9-10v?).  Some reviewers have found packs listed at 100ah capacity to
> actually have only 30ah cells inside, lots of misinformation.
>
> Thank you,
> Dan
>
> On Tue, Mar 12, 2019 at 1:01 PM Jay Summet via EV <ev@lists.evdl.org>
> wrote:
>
> >
> >
> > On 3/12/19 9:59 AM, Dan Baker via EV wrote:
> >
> > > If I don't charge with my Sevcons and use the included individual 12v
> > > chargers, would there still be worry of connecting too many in series?
> > Is
> > > it charging,discharging or both the issue when connecting in series?
> >
> > That depends entirely upon the battery model/manufacturer and the specs
> > for that specific battery.  If there is an issue, it would most likely
> > be an issue for both charging and discharging.
> >
> > The thing to watch out for is if the batteries have a MOSFET (solid
> > state switch) that is used to disconnect the battery when charging (done
> > charging, voltage too high) or when discharging (voltage too low).  In
> > many cases, the MOSFETS are not rated for super high voltages. It may be
> > twice the working voltage or much higher (24,36 or perhaps 60 volt
> > rated).  If your series pack goes above the MOSFET rating, it is likely
> > to fail spectacularly (short closed in the worst case) when it is asked
> > to disconnect the battery.
> >
> > If the batteries use relays or contractors, they may or may not be rated
> > for higher series voltages, you need to verify.
> >
> > In short, the electronics that are making these batteries "drop in
> > replacements" for a 12 volt battery are designed to work at that voltage
> > level...with perhaps  a 2x or 4x safety factor (24 to 48 volts), but the
> > system was not designed for high voltage (72-144 or higher) to be seen
> > by the battery.
> >
> > The BattleBorn batteries for example use 60V electronics, and are rated
> > to be used in series up to a 48 volt system (They were designed this way
> > to be a drop in replacement for 12, 24, 36 and 48 volt solar power
> > systems....but many "auto starter" or RV replacement batteries gave no
> > thought about using more than one in series, or if they did, it was only
> > up to a 24 or 48 volt level.)
> >
> > Jay
> >
> > _______________________________________________
> > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> > http://lists.evdl.org/listinfo.cgi/ev-evdl.org
> > Please discuss EV drag racing at NEDRA (
> > http://groups.yahoo.com/group/NEDRA)
> >
> >
> -------------- next part --------------
> An HTML attachment was scrubbed...
> URL: <
> http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20190313/9f300d12/attachment.html
> >
> _______________________________________________
> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> http://lists.evdl.org/listinfo.cgi/ev-evdl.org
> Please discuss EV drag racing at NEDRA (
> http://groups.yahoo.com/group/NEDRA)
>
>

-- 
Michael E. Ross
(919) 585-6737 Land
(919) 901-2805 Cell and Text
(919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Tablet,
Google Phone and Text
-------------- next part --------------
An HTML attachment was scrubbed...
URL: 
<http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20190314/fc51bc2b/attachment.html>
_______________________________________________
UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
http://lists.evdl.org/listinfo.cgi/ev-evdl.org
Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)

Reply via email to