# [EVDL] A123 ALM 12V7 Batteries Now Charging



## EVDL List (Jul 27, 2007)

*Re: [EVDL] A123 ALM 12V7 Batteries now charging*



> Elithion wrote:
> Lee Hart wrote
> >> All the BMS chips I've seen draw power from all cells
> 
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] A123 ALM 12V7 Batteries now charging*

>
> > Thus, the cells will read over 3 volts for years. The voltage only
> > goes low at the very end of the SOC.
>
>I agree; but it's only true if there is *no load* on the cells.

Again, you are making the incorrect assumption that the internal 
resistance is a strong function of the SOC. In LiFePO4, the internal 
resistance is only a very weak function of SOC. Over 90% of the SOC, 
the load produces pretty much the identical voltage drop. Very little 
increase in internal resistance over the bulk of the discharge.

The fact that there is little change in OCV or internal resistance 
with SOC makes it quite vexing to determine the SOC by the typical 
means of sensing voltage and/or internal resistance. This chemistry 
really _is_ completely different. No marketing. Fact. Name another 
chemistry that has _all_ of these features:

1) Little change in specific power with SOC.
2) Cycle life (to half remaining capacity) of over 10,000 cycles. 
(100% discharge each cycle.)
3) Can be left at zero volts without damage.
4) Has specific power over 3000 W/kg in consumer production. (20,000 
W/kg in specialty production.)

>My
>concern is with designs that *permanently* connect a BMS or some other
>load to the cells. And let's face it -- *most* designs do this! It's
>cheap, it's easy, it's obvious, and the seller doesn't care if it
>murders your cells. He assumes you'll just buy more from him!

There are _awful_ BMS designs out there. The worst of them 
continuously draw large currents unequally from the cells.

The typical BMS in a well-designed commercial product has 
very low continuos operating currents. (Not always, but typically.) 
While it is not all that good for the 26650 M1 cells, they are not 
severely damaged by _tiny_ reversals. Also, the quality control on 
the very mature 26650 M1 cell results in very close capacity and 
thus, they run flat at pretty much the same time in a 12 volt pack, 
generally shutting down the BMS by voltage starvation before cell reversal.

> > It really doesn't matter because the cells are unharmed by going to
> > zero volts.
>
>That is the point of my question. Don't just say it (that's marketing).
>What are the facts? Where is the data?

I have done it myself. Others have done it. They have 
written about it repeatedly on this list. The results are all the 
same. No damage. Many folks have done capacity and internal 
resistance tests before and after running them to zero. (Several on 
this list.) All confirm _exactly_ what I am writing.

The reason you are having such a hard time believing it, and 
saying "This couldn't possibly be so!" is; "This chemistry is 
COMPLETELY different" than any other you have dealt with before." No 
marketing hype. Just a fact.


>I have never deliberately ran an A123 cell dead; but I have to other
>types of lithium cells. They are seriously damaged and even destroyed by
>the experience! So, I don't want to purposely run any A123 cells dead
>without evidence that this is harmless.

See above. LiFePO4 is completely different.


> >>> personal anecdote <<<
> > I have personally discharged a 12 volt LiFePO4 battery to zero
> > volts. (Glove box light left on.) The battery was at zero volts for
> > about two weeks. Since the goal of building that 12v battery was to
> > test it under typical consumer use, I jump started the car with a
> > fully-charged 12 volt lead-acid battery, just like a consumer might
> > do. The jumper cables became noticeably warm from the large current
> > flow into the zero-volt LiFePO4 battery. Started the engine and
> > quickly disconnected the jumper cables, allowing the full 100 amps
> > from the alternator into the LiFePO4 battery. This would have been
> > certain battery death, likely an explosion, and surely a fire with
> > LiPo. Five years and 60,000 miles later, that 12v LiFePO4 battery
> > still working perfectly.
>
>That's pretty impressive! But, it raises some questions.
>
>1. Was there a BMS on that battery?

Yes. A primitive one. Only balancing at full charge.

>Did it detect a low cell, and
> disconnect the load, resulting in 0 volts on the terminals while
> the cells inside were still at some positive voltage?

No.


>2. If there was no BMS, was it just 4 cells in series, connected
> in place of the car's 12v battery? If so, why didn't the first
> cell that went dead get *reversed* by the current continuing
> to flow due to the other cells in series that still had charge?

The 26650 cells are quite well capacity matched as delivered. There 
were six cells in parallel, helping with the statistics, no doubt.
The current draw from the glove box light was likely tiny at the end 
of the discharge. Tiny reverse voltage makes tiny damage.


>3. This was an ICE vehicle? It only takes is a second or two of
> high current to start an ICE. The actual amphours needed is
> trivial; 2 seconds at 400 amps is only 0.22 amphours; less than
> 10% of a single A123 cell's capacity. The cells could have lost
> 90% of the amphour capacity and *still* start the ICE.

Zero volts. With a voltmeter. Zero. Nada. 100% dead.

>4. Did you have an ammeter in the battery? Do you know what the
> current was in or out of the battery? A "100 amp" alternator
> rarely (if ever) supplies 100 amps.

No ammeter. Warm alternator wire is a sure indication of high current 
flow. No accessories on other than the engine.


> > Going to zero volts (but not below!) with LiFePO4 does not harm the
> > cells in any way. It is a fact.
>
>I'll ask again, because all I have are anecdotes with no measurements.
>Where is the test data to show that cells were run down to 0 volts, and
>then tested for capacity, internal resistance, and cycle life?

Look in the EVDL archives. Or do the test yourself.


>If you don't know, just say so. If there is no test data, maybe I have
>to sacrifice some A123 cells to science. 

There will be no sacrifice. They will be just fine.
See above. This chemistry is completely different.


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] A123 ALM 12V7 Batteries now charging*

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## EVDL List (Jul 27, 2007)

*Re: [EVDL] A123 ALM 12V7 Batteries now charging*



> Bill Dube wrote:
> >>> The cells will read over 3 volts for years. The voltage only
> >>> goes low at the very end of the SOC.
> 
> ...


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