# Quantified Lot of A123 20Ah Cells for PHEV I1



## IamIan (Mar 29, 2009)

As part of a PHEV project I am doing on my 2000 Model year Gen-1 Honda Insight I bought 55 pouch cells of the A123 20Ah type.

My NiMH battery pack is fine ... and data suggests it will be for many years to come ... but I wanted to start my project before it was needed ... I tend to take a while with my projects , so I would rather be done early than not be ready ... and if done early ... I will benefit from the better battery specifications and I'll retire the NiMH pack to other projects.

Sense the OEM BCM in the Gen-1 Insight tries to only use the middle ~4Ah from it's OEM 6.5Ah NiMH battery pack ... a A123 20Ah cells replacement has the potential to give more than 3x that usable capacity in the same vehicle space and weight ... the OEM is 12+ year old battery technology ... so the progress is not entirely surprising.

It is best to use well matched cells in the battery build ... so I wanted to test the 55 cells first to do that matching ... the testing would also allow me to be better able to estimate the packs potential for balance separation over use and over time ... so instead of BMS or no-BMS just being an opinion piece or trying to weed through the various testimonials on both sides ... I figured I would quantify the cells I am working with instead ... Data over opinion and testimonials.

My setup was a PowerLab8 PL8.
I used their OEM software with FirmWare Version 3.31.

As a Bidirectional DC-DC converter the PL8 allowed me to pump the Discharge Wh from Test of Cell A into battery bank B , which I then could recycle that wh for the next charge test... not 100% efficient ... but much better than a resistive heating element.

As a battery Bank B to recycle wh from and to , I used 2 junk yard civic NiMH battery packs I have that have been reconfigured into a 14.4V nominal a bit over 100 Ah capacity pack.

To compensate for the less than 100% efficiency I have a 3A Bench Power Supply set on CV to refill losses to the battery bank B.

Step #1> Initial Discharge
Step #2> Full Cycle: Charge , Rest , Discharge , Rest , Charge
Step #3> Repeat 1 & 2 for all 55 cells
Step #4> After 2 months from that cells charge from 2 , do Initial Discharge
Step #5> Full Cycle: Charge , Rest , Discharge , Rest , Charge
Step #6> Repeat 4 & 5 for all 55 cells.
Step #7> Export Data into spread sheets for analysis

Charge Rate was CC-CV at 10A to 3.65V and c/20 current or at most 30 minutes for the CV phase.

There was a 60 minute rest period between each phase.

Full Discharge Wh of capacity at 10A rate CC to 2.80V
Best Cell 60.071 Wh
Worst Cell 52.101 Wh
55 cell Average 58.537 Wh

Cycle Efficiency Wh Input / Wh Output
Best Cell 94.53%
Worst Cell 88.95%
55 cell Average 93.587%

Average Self Discharge Rate over 2 Months
Best Cell 13.81 mWh / Day
Worst Cell 690.13 mWh / Day
55 cell Average 53.890 mWh / Day ... without the worst cell ... which was way worse than any of the others ... the 54 cell average was 42.108 mWh / Day

Interestingly ... The Lowest Wh capacity cell is also the worst % efficiency and the worst 2 Month Average DailySelf Discharge Rate.

Also Interestingly ... the highest Capacity cell was also the Highest Cycle Efficiency Cell ... but was not the lowest Self Discharge Rate Cell ... Although it was far bellow the average at only 36.48 mWh / Day

The Exponential Voltage increase is easily seen at the end of the charge phases ... the Exponential Voltage drop is easily seen at the end of the discharge phases ... the Logarithmic voltage stabilizing is easily seen toward the end of the rest periods... and dV is easily seen at the beginning of 10A charge or discharge events.

I did a round trip cycle efficiency instead of just a simple Internal Resistance Ohms ... My thought is that it is more inclusive and gives a better over all picture than just a snap shot of Ohms would ... but the data is there if I ever want to go back to it.



If I sort by the 50 Best Wh of capacity cells I get:
Weakest cell in the series chain is the limit of the whole pack to avoid cell reversal.
So a peak 50 cell pack potential capacity of about ~2,874 Wh.
An Average cell efficiency of ~93.673%
Difference from high to low cell is ~4.07%
This is the potential per cycle out of balancing effect.
An average 60 Day Self Discharge Rate of ~42.136 mWh / Day
Difference from High to low cell is 59.773 mWh/ Day
This is the potential per day out of balancing effect.
 
If sorted by the 50 Best Cycle Efficiency cells I get:
Weakest cell in the series chain is the limit of the whole pack to avoid cell reversal.
So a Peak 50 cell pack potential capacity of about ~2,802 Wh
An Average cell efficiency of ~93.827%
Difference from high to low cell is ~1.53%
This is the potential per cycle out of balancing effect.
An average 60 Day Self Discharge Rate of ~42.171 mWh / Day
Difference from High to low cell is 58.672 mWh/ Day
This is the potential per day out of balancing effect.
 
If sorted by the 50 lowest Self Discharge Rate Cells I get:
Weakest cell in the series chain is the limit of the whole pack to avoid cell reversal.
So a Peak 50 cell pack potential capacity of about ~2,802 Wh
An Average cell efficiency of ~93.745%
Difference from high to low cell is ~3.45%
This is the potential per cycle out of balancing effect.
An average 60 Day Self Discharge Rate of ~39.677 mWh / Day
Difference from High to low cell is ~44.54 mWh/ Day
This is the potential per day out of balancing effect.
 

I find it interesting how close the results are ... once the worst 5 cells are removed.

Personally I think I'll be going with the 50 best cycle efficiency cells:

I don't think the extra ~72wh from the peak Wh pack is enough to be meaningful.
I think the less than 60 mWh/Day of potential Self discharge pack balance issue is so slow that it would take years to be an issue , and any time a properly balanced charge is done it resets that drift clock.
Although the average pack efficiency is not significantly any better ... The narrower gap in efficiency reducing the potential gap between cells on a per charge basis I think is potentially useful to reduce the burden load , or need for a BMS.

I also like the idea of putting the highest most efficient cells toward the center of the pack and the slightly lower efficient cells toward the outside edges of the pack ... this will just be one more tiny step to try and balance the thermal load in the complete pack. 

My testing shows, that even if someone put the weakest ( but not DOA ) cells together into the weakest pack. My data set from my lot of cells suggests the worst they might have seen would be about ~5.6% efficiency balance separation per cycle , a ~2,600 Wh pack capacity , and ~677mWh/Day Self Discharge balance separation. 

That is only ~7.2% less usable capacity. 

A BMS will easily keep pace with the ~677mWh/Day. I think it would be pretty difficult to have some kind of driving conditions that the ~5.6% potential per Cycle balance separation would be able to get ahead of a BMS either. It's only ~3 Wh per full cycle.

For those who would have run with no BMS on this pack ... that's their option ... the separation rate is fairly slow ... and sense a Higher SoC cell has more internal resistance than a low SoC cell ... there is a small amount of built in self balancing effect.

Myself ... I like the idea of a pack monitoring system for a LVC and a HVC for each of the cells ... With that monitoring and safety system in place I should be able to prevent and catastrophic events ... and as a PHEV , if needed I can still run on the ICE without the HEV side at all.

For a Grid charger , I am considering using a per cell individual charger ... That will balance each cell without any risk of a mismatched bleed load... The alternative would be just a basic CC-CV dumb charger.

With the LVC and HVC and a well matched pack to start with ... I should be able to go without a grid charge balancing event a minimum of several weeks if not several months ( with the SoC variation in internal resistance ) .... and still not have any significant chance of any major issues... because of this , I am considering the dumb charger and then just the occasional balancing maintenance event.

The attached files show some of the above ... Each graph is sorted by it's type ... so Wh of capacity cells are sorted from high to low ... cycle efficiency cells are sorted from high to low ... etc... I did exclude the single worst cell from the Self Discharge graph , it grossly screwed the results of the graph because it was so far different from all the others.


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## major (Apr 4, 2008)

Thanks for sharing, Iam. You have obviously done much work on this.



IamIan said:


> ... and sense a Higher SoC cell has more internal resistance than a low SoC cell ...


Please provide a reference source or the data (graph or such) that supports this. 



IamIan said:


> ... there is a small amount of built in self balancing effect.


How does this happen?

Regards,

major


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## tomofreno (Mar 3, 2009)

major said:


> Thanks for sharing, Iam. You have obviously done much work on this.
> 
> Please provide a reference source or the data (graph or such) that supports this.
> 
> ...


 I think he is just referring to the typical charge curve which shows changing resistance with SOC, especially on the exponential part of the graph of cell V versus Ah. I don't think changing resistance can help with cell balancing though, as the same charge still goes into each cell in a series string, it just requires more work to put that charge into some cells (ones with higher ir) than others, due to more energy dissipated as heat in the higher ir.

Nice characterization of the cells!


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## IamIan (Mar 29, 2009)

major said:


> Thanks for sharing, Iam. You have obviously done much work on this.


Thanks.
Alot more yet to do.
I tend a bit toward the over analysis side.



major said:


> IamIan said:
> 
> 
> > ... and sense a Higher SoC cell has more internal resistance than a low SoC cell ...
> ...


It is a common phenomenon in many Electro-Chemical Cells that the Internal Resistance will vary with SoC ... It should , the chemical composition is changing as the individual molecules change their proportions relative to each other.

An example of this effect from the EPA tests the OEM NiMH battery in the Gen-1 Insight they found the graph attached bellow... in that case the lowest internal resistance SoC point is near the middle of the SoC band ... bellow that SoC point the Internal resistance increased ... and above that SoC point the Internal Resistance increased.

More specifically with this batch of A123 cells that I have.

The PL8 applies charging power to a cell at a frequency ... it is not a 100% true DC charging ... The frequency is slightly adjustable ... in the case of the testing I did above , it was done at a frequency of 62.5khz... the PL8 uses this to estimate the internal resistance of the cell being tested... similar to the way other high frequency battery testers estimate the internal resistance of a cell.

For the same cell in the sample graph above ... # SHA11A0900409
The PL8 measured a ~2.07% difference of internal resistance ... or increase from empty SoC to full SoC ... not much , but it is a difference.

Part of another project is I wanted to better quantify this effect for this batch of A123 pouch cells ... but I haven't done that yet... So I didn't want to present specific data on that until I have more specific quantified date about it.

I also plan to eventually test and quantify the specific heat of this batch of cells ... which given the cycle efficiency would allow me to more accurately estimate the rate the cells will warm up during use or cool off while sitting in the cold.

It's just a hobby ... so testing always takes a back seat to Real-Life stuff... and I tend toward over analyzing.



major said:


> IamIan said:
> 
> 
> > ... there is a small amount of built in self balancing effect.
> ...


When the Internal Resistance of a cell varies over different SoC ... the efficiency of that cell is also varying ... it might not track as a one to one relationship with internal resistance but they do correlate in a general sense.

So at a SoC point where the internal resistance is lower the efficiency of the cell will be higher ... and vise versa ...at a SoC point where the internal resistance is higher the the efficiency will be lower.

Similar to how resistors in series with different resistance will convert different amounts of energy to heat.

For example ... looking at the more complete picture of the variation shown from the EPA testing of the NiMH battery pack ... if for example one of the 120 cells were at say the 70% SoC point or higher where they show the internal resistance is higher than if there is say another 1 of the 120 cells at the 50% SoC point where the internal resistance is lower... with all of the cells in series they all see the same current amps ... but those cells that are at a higher internal resistance will convert more of that energy to heat than those cells that are at a lower internal resistance... with more of the energy converted to heat less of the energy is left to drive the chemical energy storage of the charging battery... which allows for during the charging event for the lower SoC and lower internal resistance cell to catch up a bit in it's chemical energy SoC ... effectively acting as a built in mini-balancing effect.

Unfortunately the same mechanism does the exact opposite on the discharge side ... where the NiMH battery shows a increase in internal resistance at lower SoC ... so to get the same amps out of that cell which is at the SoC point that it has a higher internal resistance means the cell will heat up more ... which comes from a larger % of the chemical energy it is converting to electricity , being converted to heat ... larger anyway than the cell that is at a SoC point where the internal resistance is lower.

So if a person spent a great % of the battery operational time in the direction of the built in small balancing effect ... it helps them ... if they spend more operational time in the other side it hurts them.

To get a more clear idea of how the change in Internal Resistance ... or electro-chemical efficiency tracks with SoC for these A123 cells would require me to complete that other testing project I haven't completed yet... but I haven't seen any evidence yet to suggest the effect does not exist in these cells ... it is just a question of how much it is? ... and what is the shape of the effect over the SoC window?


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## Ziggythewiz (May 16, 2010)

I would expect the apparent IR to rise when charging and rise when discharging. My CALBs can easily demonstrate less than 1/3 the resistance at high SOC compared to lower SOC when discharging.


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## IamIan (Mar 29, 2009)

tomofreno said:


> I think he is just referring to the typical charge curve which shows changing resistance with SOC, especially on the exponential part of the graph of cell V versus Ah. I don't think changing resistance can help with cell balancing though, as the same charge still goes into each cell in a series string, it just requires more work to put that charge into some cells (ones with higher ir) than others, due to more energy dissipated as heat in the higher ir.
> 
> Nice characterization of the cells!


I'll agree it depends on the specific relationship between Internal resistance and the cell's efficiency ... which may not be a 1 to 1 relationship.

And I'll agree it can work both for and against balancing ... in some cases the two balance out ... in some cases it hurts more than helps ... and in some it helps for than hurts.

And I'll agree it can be a very small effect.

And I'll say I'd expect it to also depends on the shape of the difference over the SoC band.

But I haven't yet seen evidence to suggest there is zero change in cell efficiency as the chemical composition of the cell changes with different SoC.


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## GerhardRP (Nov 17, 2009)

Nice work Ian, Thanks.
For the question of balancing, it the the charging current efficiency that matters. Do you have the data for Ahr's in and out during the full cycle?
I am also in favor of over-analysis, so can you share the raw data spreadsheet for others [me] to play with?
Gerhard



tomofreno said:


> I think he is just referring to the typical charge curve which shows changing resistance with SOC, especially on the exponential part of the graph of cell V versus Ah. I don't think changing resistance can help with cell balancing though, as the same charge still goes into each cell in a series string, it just requires more work to put that charge into some cells (ones with higher ir) than others, due to more energy dissipated as heat in the higher ir.
> 
> Nice characterization of the cells!


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## major (Apr 4, 2008)

IamIan said:


> An example of this effect from the EPA tests the OEM NiMH battery in the Gen-1 Insight they found the graph attached bellow... in that case the lowest internal resistance SoC point is near the middle of the SoC band ... bellow that SoC point the Internal resistance increased ... and above that SoC point the Internal Resistance increased.
> 
> More specifically with this batch of A123 cells that I have.
> 
> ...


Thanks for the reply. The graph is for a different chemistry so I doubt it relates well. And the PL8 is measuring impedance at 62kHz and guessing at DC resistance. I wouldn't put faith in a 2% number. But all this is irrelevant with regards to SoC. As Gerhard notes: 


GerhardRP said:


> For the question of balancing, it {is} the charging current efficiency that matters.


 Which was my concern. You are drawing SoC conclusions based on energy efficiency. 

As Gerhard suggested, take a look at the charge (Ah). It would be interesting if you can actually show a mechanism for this "self balancing".


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## IamIan (Mar 29, 2009)

GerhardRP said:


> Nice work Ian, Thanks.
> For the question of balancing, it the the charging current efficiency that matters. Do you have the data for Ahr's in and out during the full cycle?
> I am also in favor of over-analysis, so can you share the raw data spreadsheet for others [me] to play with?
> Gerhard


Yes I have the Ahr's In and Out ... but ... why would Ah be better than Wh?

Wh is the unit of energy chemical , electrical , heat, etc ... not Ah ... 1Ah at 3.6V is 3.6Wh ... the same 1Ah at 3.0V is only 3.0Wh ... if one is only looking at the Ah it obscures the actual joules or wh of energy ... so I'm a bit confused by why Ah would be a better determinate? ... if anything it seems like an inferior determinate.

The above % Efficiency numbers are based on Wh , in and out.

As for the raw data ... I doubt I can just add it here to a post ... it's about 290 MB , and about 700 files ... thousands of lines per file ...  ... sorry that seems kind of daunting to convert all of that... call me lazy I guess.

If it is enough for your needs I converted the Summery Spread sheet file to an excel format for MS Word ... It has the Ah in and out you were asking about for the same phase of testing that I used the Wh to determine Wh cycle efficiency ... I attached that bellow.

Feel free to check it out and let me know if you notice any errors I might have made ... or if you see any interesting relationships.



major said:


> Thanks for the reply. The graph is for a different chemistry so I doubt it relates well. And the PL8 is measuring impedance at 62kHz and guessing at DC resistance. I wouldn't put faith in a 2% number. But all this is irrelevant with regards to SoC. As Gerhard notes:
> Which was my concern. You are drawing SoC conclusions based on energy efficiency.
> 
> As Gerhard suggested, take a look at the charge (Ah). It would be interesting if you can actually show a mechanism for this "self balancing".


The graph I showed was just an effort to explain the concept , you asked about... I know it is not for this chemistry or these specific cells ... but like I already wrote ... I have not yet done that other test to quantify that aspect for these cells.

I agree about the impedance and it guessing at the DC resistance ... but that is still in my point ... any measure even a dV under a known amps of current is still an impedance measurement ... it doesn't tell you how much of that ohms is from the chemical reaction opposition ( by charging the cell converting electrical energy to chemical energy ) or how much is from the actual resistance ( converting electrical energy to heat )... ohms of impedance are just dV opposition to a given current.

Which is why I would have to complete that other more detailed experiment to actually quantify it.

Sorry I was not more clear ... I'm not drawling SoC conclusions based on Energy Efficiency ... I'm saying that if Cell #1 is at say 88% energy efficiency and Cell #20 is at 94% energy efficiency ... than I see that difference in efficiency as a potential mechanism for creating a SoC drift ... because a lower % of energy efficiency mean that less of the applied electrical energy is making the round trip to chemical energy and back ... that difference in efficiency can be from differences in the cells themselves ... or differences in conditions , like SoC , Temperature, etc ... it is not the only mechanism ... but I think it is a mechanism ... how much it is ... I haven't done that testing yet to quantify it.

I know a pack of series cells all charged and discharged together ... with nothing to correct for it ... do get out of balance with each other in terms of SoC over time ... I've seen this for Lead Acid cells , NiCd, NiMH ... I don't see any evidence yet to suggest the mechanism does not exist in these A123 cells ... the question to me becomes what are the contributing influences that disrupt the pack balance and what are the influences that contribute to maintaining the pack balance.

I know differences in Self Discharge Rate is one mechanism that can influence to disrupt pack balance... I know a cell tolerant of over charging ( like lead acid ) can be a mechanism to help maintain the pack balance.

I have not yet quantified it ... but I suspect that like other electrochemical cells the variation in cell efficiency can also be an influence ... as that efficiency changes under different conditions , including SoC , etc ... I suspect the influence can potentially change as the efficiency changes... even if it is not a 1 to 1 relationship.

Sorry ... maybe I'm just blind to it at the moment ... But I don't see how Ah ( not a unit of energy ) will be a more useful determinate than Wh ( a unit of energy )??

If I know the Wh of energy a cell holds , I can do SoC based on Wh ... and I suspect it is more accurate SoC than one based on Ah ... which is not a unit of energy and just looking at Ah ignores the difference between [email protected] and [email protected] ... a difference that Wh SoC does not ignore.


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## major (Apr 4, 2008)

IamIan said:


> Yes I have the Ahr's In and Out ... but ... why would Ah be better than Wh?..........Sorry ... maybe I'm just blind to it at the moment ... But I don't see how Ah ( not a unit of energy ) will be a more useful determinate than Wh ( a unit of energy )??
> 
> If I know the Wh of energy a cell holds , I can do SoC based on Wh ... and I suspect it is more accurate SoC than one based on Ah ... which is not a unit of energy and just looking at Ah ignores the difference between [email protected] and [email protected] ... a difference that Wh SoC does not ignore.


SoC = State of Charge. Not SoE, State of Energy. Using charge is the convention in the industry. It is the way batteries and cells are rated, tested and sold. That should be reason enough for you. I am sure there are plenty of technical reasons as well, but don't feel like getting into all that with you. They're your cells. Test them however you want. But using non standard metrics makes it difficult to compare to the work others have done.


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## tomofreno (Mar 3, 2009)

IamIan said:


> Yes I have the Ahr's In and Out ... but ... why would Ah be better than Wh?
> 
> Wh is the unit of energy chemical , electrical , heat, etc ... not Ah ... 1Ah at 3.6V is 3.6Wh ... the same 1Ah at 3.0V is only 3.0Wh ... if one is only looking at the Ah it obscures the actual joules or wh of energy ... so I'm a bit confused by why Ah would be a better determinate? ... if anything it seems like an inferior determinate...


 SOC is State of Charge – the proportion of the cell’s Ah charge capacity the cell is charged to. So maybe you could use SoE, State of Energy, rather than Wh SoC since you are talking about energy not charge?

During charging the intercalated lithium is ionized, leaves the cathode and diffuses to the anode through the cell. The cathode material converts from LiFePO4 to FePO4. This phase change occurs at 3.4V, so 3.4V is now driving lithium back to the cathode from the anode. Electrons flow from the cathode through the charger to the anode neutralizing the lithium ions diffusing into the anode. The neutral lithium atoms intercalate in the anode.

What appears externally as differences in resistance of cells, i.e. less current per volt applied, may be due to differences in diffusion of lithium ions out of the cathode and/or diffusion into the anode, resulting in variances in the voltage of cells during charging which are all at similar SoC. One known effect on cell resistance is the buildup of lithium carbonate on the electrodes if the electrolyte breaks down due to overheating of the cell. This makes it harder for the lithium ions to get in/out of the electrode. It also leaves less volume in the films for lithium, so decreases the capacity. I assume structural differences in the electrode films also contribute somewhat to differences in resistance.

At any rate, as long as the same electron current is flowing from cathode to anode in each cell during charging, the same number of lithium ions should be flowing to the anode in each cell, i.e. they should all be charging at the same rate, i.e. adding the same charge per unit time to each cell, resulting in the same number of lithium atoms being intercalated in the anode. Differences in cells may result in more energy required to move charge from cathode to anode during charging, but should not affect the SoC. This is why a charge, or Ah, counter on a battery pack is simpler to understand than an energy, or Wh, meter. At least for me.

If there are differences in energy required during charging, it will likely take more energy to move charge from anode to cathode during discharge, so you will get less energy out of this cell – it will sag more in voltage than others, so less energy per electron out. It will then affect the vehicle range, as of course it is energy, charge at some potential, that is required to move the vehicle not just charge. So I can see why you would be concerned with energy.

There are so-called side reactions that can occur in the cell. I assume these may possibly affect SoC if they occur, but I don't know anything about them.


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## IamIan (Mar 29, 2009)

major said:


> SoC = State of Charge. Not SoE, State of Energy. Using charge is the convention in the industry. It is the way batteries and cells are rated, tested and sold. That should be reason enough for you. I am sure there are plenty of technical reasons as well, but don't feel like getting into all that with you. They're your cells. Test them however you want. But using non standard metrics makes it difficult to compare to the work others have done.


I'll take your word for it ... that , that is the industry standard... but that isn't how I've heard and read people talking about SoC.

I almost always hear people referring to SoC as a % indication of how far a rechargeable battery is ... from empty to full ... 0% SoC = Empty ... 100% SoC is full... 50% SoC is half full ... etc... 

For example:
If someone drove their BEV 20 miles from 100% SoC to 50% SoC they would often expect to be able to go another 20 miles under the same conditions if they went all the way down to 0% SoC ... this usage is a % of total energy point of view ... not Ah.

That person if thinking about SoC as Ah ... should writing an expectation of the top 50% SoC to take him significantly further than the bottom 50% SoC ... because top 1/2 Ah SoC has more energy than the bottom 1/2 Ah SoC does ... .but that is not how I read and hear people using the term.

However ... I still don't see how that changes the initial concept ... If Cell #1 is at 88% energy efficiency ... and Cell #10 is at 94% energy efficiency ... than even if you only want to look at Ah ... 1Wh of electricity at 88% efficiency converts less of that 1Wh to chemically stored energy in the cell than a 94% efficient cell ... 

88% of 1 Wh is fewer Ah than 94% of 1 Wh ... at any voltage.

If the % efficiency between cells is different it still results in a difference in the amount of Ah ... and thus ... even if you want to use SoC to only consider Ah it still results in a mechanism for changing the balance of a pack.



tomofreno said:


> SOC is State of Charge – the proportion of the cell’s Ah charge capacity the cell is charged to. So maybe you could use SoE, State of Energy, rather than Wh SoC since you are talking about energy not charge?


That would seem the industry standard ... as above ... but ... not how I see people using the term SoC ... and it seems more complicated to me.

If anything Ah SoC seems to me to make things more complicated... now if SoC is only for Ah ... 10% SoC is not necessarily = to 10% SoC ... because 10% at the bottom is the smallest 10% SoC and 10% SoC at the top is the largest 10% SoC ... it is not even linear ... with the voltage curve of the cell it means a fairly complicated % of remaining battery energy or distance.

I'm not arguing what is or isn't 'industry standard' ... but I think it is more complicated and less useful method ... and it isn't how I read and hear people talking about SoC... and even with that convention , I don't see how it would change the expected effect of a difference in cell % of energy efficiency on pack balance.



tomofreno said:


> At any rate, as long as the same electron current is flowing from cathode to anode in each cell during charging, the same number of lithium ions should be flowing to the anode in each cell


I don't see how or why??

Each individual molecule requires energy to do a chemical reaction to convert to a different molecule ... each of those steps you listed for the anode , cathode , electrolyte ... they take energy ... Joules or Wh take your pick of units.

For example:
[email protected] = 2.8Wh
[email protected] = 3.6Wh
about ~29% more energy ... but still just 1 Ah.

For your claim to be correct it seems to require a ~29% energy difference to have zero effect ... even though the Molecules are chemically identical ... somehow one chemically identical molecule needs ~29% more energy to make that same chemical reaction than another chemically identical molecule.

I don't see how or why I should expect ~29% more energy to be needed for the same chemical reaction of chemically identical molecules.

Maybe I'm just missing something ... but I just don't see how or why that would be the case.



tomofreno said:


> This is why a charge, or Ah, counter on a battery pack is simpler to understand than an energy, or Wh, meter. At least for me.


What ever works for you.

It seems much more complicated to me.



tomofreno said:


> So I can see why you would be concerned with energy.


Glad I'm not too difficult to understand.


It is not always one of my strengths.


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## IamIan (Mar 29, 2009)

If it is useful ... attached is another graph of the Ah cycle Efficiency vs the Wh Cycle Efficiency.


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## tomofreno (Mar 3, 2009)

IamIan said:


> I'll take your word for it ... that , that is the industry standard... but that isn't how I've heard and read people talking about SoC.
> 
> I almost always hear people referring to SoC as a % indication of how far a rechargeable battery is ... from empty to full ... 0% SoC = Empty ... 100% SoC is full... 50% SoC is half full ... etc...


 Yes that is correct. But they are not considering energy at all, only how much charge they have, i.e. how many electrons they have left to flow out of the batteries, regardless of what potential they are at. That is because it is much more straight-forward to count charge into and out of the pack since you don't have to consider what voltage the pack is at, which is almost continually varying while driving due to varying load on the motor and discharge current as a result.



> For example:
> If someone drove their BEV 20 miles from 100% SoC to 50% SoC they would often expect to be able to go another 20 miles under the same conditions if they went all the way down to 0% SoC ... this usage is a % of total energy point of view ... not Ah.


 Agreed. They are ignoring the energy per charge, or rather assuming it is constant. I agree it is not. But in practice you find that the difference, due to decreasing pack V, does not make a big difference in range per a given amount of charge because the voltage of a LiFePO4 cell doesn't change very much for a given load throughout most of its SoC range.



> However ... I still don't see how that changes the initial concept ... If Cell #1 is at 88% energy efficiency ... and Cell #10 is at 94% energy efficiency ... than even if you only want to look at Ah ... 1Wh of electricity at 88% efficiency converts less of that 1Wh to chemically stored energy in the cell than a 94% efficient cell ...


 No, the charger just has to do more work to move charge into the pack because that cell with higher resistance (lower efficiency) will have a higher terminal voltage than ones with lower resistance. The charger does the extra required work by developing higher output voltage. The electrons then enter the pack with greater energy than if the internal resistance was lower. The extra energy is dissipated in the resistance. The stored energy per charge is the same as it would be if the cell had lower resistance.



> 88% of 1 Wh is fewer Ah than 94% of 1 Wh ... at any voltage.


 No, Wh is energy, Ah is charge. The energy of an electron discharged from the pack is the product of its charge, 1.602e-19 Coulomb, and the actual (sagged) pack voltage at discharge.



> If anything Ah SoC seems to me to make things more complicated... now if SoC is only for Ah ... 10% SoC is not necessarily = to 10% SoC


 Yes it is, because we are only talking about charge, not energy.



> ... because 10% at the bottom is the smallest 10% SoC and 10% SoC at the top is the largest 10% SoC ... it is not even linear ... with the voltage curve of the cell it means a fairly complicated % of remaining battery energy or distance.


 Yes, the energy per charge discharged from the pack may vary slightly with SoC, but sag of pack voltage will be a much larger effect. If you drive at 1C constant discharge current from 90% SoC to 30% SoC, the energy per charge discharging from the pack will be about the same over that entire range.



> I don't see how or why??
> 
> Each individual molecule requires energy to do a chemical reaction to convert to a different molecule ... each of those steps you listed for the anode , cathode , electrolyte ... they take energy ... Joules or Wh take your pick of units.


 Yes, the change from LiFePO4 to FePO4 takes 3.4V. The energy stored is the product of that and the total charge moved from cathode to anode.



> For example:
> [email protected] = 2.8Wh
> [email protected] = 3.6Wh
> about ~29% more energy ... but still just 1 Ah.
> ...


 You shouldn't. To charge a cell the charger just needs to supply enough potential (~3.4V) to drive that phase change from LiFePO4 to FePO4 plus any voltage across internal cell resistance. The energy or work expended doing that is the product of that approximate 3.4V and the charge on the electrons pumped to the anode by the charger, plus the energy dissipated in the cell resistance.


----------



## IamIan (Mar 29, 2009)

tomofreno said:


> Agreed. They are ignoring the energy per charge, or rather assuming it is constant. I agree it is not.


Which was the the point I was trying to make there ... the way I have experienced many people use the term SoC ... is one where they describe energy ... not Ah.



tomofreno said:


> No, the charger just has to do more work to move charge into the pack because that cell with higher resistance (lower efficiency) will have a higher terminal voltage than ones with lower resistance. The charger does the extra required work by developing higher output voltage. The electrons then enter the pack with greater energy than if the internal resistance was lower. The extra energy is dissipated in the resistance. The stored energy per charge is the same as it would be if the cell had lower resistance.


How closely cell resistance or cell impedance relates to cell efficiency ... I suspect they are related ... but I don't know yet how closely they are.

You seem to be assuming that different cell efficiencies have no impact on pack balance ... I have plans to test this to quantify it ... and I suspect differences in efficiency do have an influence ... I have not done my testing yet to quantify it one way or the other.

Do you have testing data that shows what you seem to be claiming ... that cells with different efficiencies ( and no other compensating mechanism ) has no impact of pack balance?



tomofreno said:


> > 88% of 1 Wh is fewer Ah than 94% of 1 Wh ... at any voltage.
> 
> 
> No, Wh is energy, Ah is charge. The energy of an electron discharged from the pack is the product of its charge, 1.602e-19 Coulomb, and the actual (sagged) pack voltage at discharge.


I know Wh is energy that is part of what I was describing.
88% is less than 94% ... Wh or Ah 88% is still less than 94%
88% of 1Wh is less than 94% of 1Wh.
The Ah portion from 88% of 1Wh is less than the Ah portion from 94% of 1Wh.

Also ... keeping in mind the context of this quote of mine you reference ... This was from a part of my post where I was replying to major ... and saying that weather is was Wh or Ah a difference in efficiency of the cell is a difference in the efficiency of the cell.



tomofreno said:


> > If anything Ah SoC seems to me to make things more complicated... now if SoC is only for Ah ... 10% SoC is not necessarily = to 10% SoC
> 
> 
> Yes it is, because we are only talking about charge, not energy.


No ... it isn't ... And you agree with this in you next quote ... where you list the next part of the paragraph that was part of this same description of mine.

Also ... we are not only talking about charge... we've been talking about charge , energy , how people use the term SoC for both Charge and Energy ... etc.



tomofreno said:


> Yes, the energy per charge discharged from the pack may vary slightly with SoC, but sag of pack voltage will be a much larger effect. If you drive at 1C constant discharge current from 90% SoC to 30% SoC, the energy per charge discharging from the pack will be about the same over that entire range.


This is next sentence part of the same description of mine where I was talking about the same concept ... you disagree with this same concept above and then agreeing with it here ... doesn't make any sense??

Here you agree with me that the energy per charge .. .ie the energy ( distance one can drive , etc ) from the top 10% SoC might not be = to the energy from bottom 10% SoC ... 10% may not = 10% ... which Is exactly the same concept I was describing in the previous quote you broke apart and both disagreed with it and agreed with it.



tomofreno said:


> Yes, the change from LiFePO4 to FePO4 takes 3.4V. The *energy stored* is the product of that and the total charge moved from cathode to anode.


(Bold Added)
Exactly why I had issue with your previous statement ( shown next ):



tomofreno said:


> At any rate, as long as the same electron current is flowing from cathode to anode in each cell during charging, the same number of lithium ions should be flowing to the anode in each cell


LiFePO4 to FePO4 *ENERGY* ... not current ... the same current can have different energy ... and if it has different energy ... It shouldn't have the same number of Lithium Ions.



tomofreno said:


> IamIan said:
> 
> 
> > For example:
> ...


Exactly ... energy needed ... it is not just current.

I'm glad you now seem to agree that I shouldn't expect the same number of Lithium Ions from different amounts of energy just because the current was the same.


----------



## IamIan (Mar 29, 2009)

sorry to add to an already long previous post ... but I forgot to include what I think might be a useful concept / point to point out.

Looking at the previous graph I posted showing both Ah Cycle Efficiency and Wh Cycle Efficiency.

The two do not track exactly as a 1 to 1 relationship ... but their is what seems like some level of correlation.

In the idea of effects on a battery pack in series ... of my 55 cells my lowest Ah Cycle efficiency cell was 87% the highest was 97% ... these cells in series all see the same amp rate ... but the lower Ah Cycle efficient cells will returned less of it per cycle ... as long as their is a difference in cell efficiency I still see it as a potential mechanism for pack balance drift... that % Efficiency I also expect to change the closer to full or the closer to empty a cell is... and other factors as well.

So for those that prefer to look at in terms of Ah I give the above ... myself I think Wh is easier for me ... but if Ah are easier for you ... there you go.


----------



## GizmoEV (Nov 28, 2009)

IamIan said:


> LiFePO4 to FePO4 *ENERGY* ... not current ... the same current can have different energy ... and if it has different energy ... It shouldn't have the same number of Lithium Ions.


Why not? One electron can move with different amounts of energy. Use a spectroscope and look at a fluorescent light and you will see different color bands of light. This is the result of electrons changing different energy levels. Not a different number of electrons for a given brightness line but the same number.

Batteries store coulombs not Watt-hours, that is why they are rated in amp-hours. Take two batteries with the same Ah capacity, say 10Ah, one has a nominal voltage of 1.5V and the other 3.0V. If they are both at 0%SOC and you put 10Ah into them they both will be at 100%SOC even though the 3.0V cell took 30Wh of energy and the other took only 15Wh. It doesn't matter if people misuse SOC or not. SOC is based on Ah.

I will never trust a Wh meter, especially as a % of capacity, to determine what the SOC of my pack is. An Ah meter, on the other hand, I do trust. Assuming of course that its accuracy is sufficient. Yes the Ah count faster near the end but so does the gas gauge in my car. The top usually moves much slower than the bottom in every car I have driven.


----------



## IamIan (Mar 29, 2009)

GizmoEV said:


> > LiFePO4 to FePO4 *ENERGY* ... not current ... the same current can have different energy ... and if it has different energy ... It shouldn't have the same number of Lithium Ions.
> 
> 
> Why not? One electron can move with different amounts of energy. Use a spectroscope and look at a fluorescent light and you will see different color bands of light. This is the result of electrons changing *different energy levels*. *Not a different number of electrons* for a given brightness line but the same number.


(Bold Added ) You gave one answer yourself ... if it were only the electric current ... than the same number of electrons would always produce the same effect ... your light shows this is not the case ... if it is a different ENERGY ... it can result in a different energy level ... even for the same number of electrons ... ie amps or Ah ... but this only goes so far ... molecules have finite energy limits ... but I can have trillions of more energy but not have changed the number of electrons ... the amps ... or the Ah.

Another answer would be ... any one molecule to have a given chemical reaction requires a certain amount of energy ... not amps ... energy... chemical energy is quantifiable for known chemicals , reactions, and conditions.

If you know enough about the exact details of the chemicals involved and the conditions ... you can define that number of joules or Wh , or whatever unit of energy you like ... for each individual chemical reaction of each individual molecule.

This is true for the energy content of Hydrogen Oxygen reactions and is true for the 100% Full battery , or any chemical reaction ... each one of it's molecules have a finite amount of energy per reaction.

The amount of Ah does not by itself tell you the number of Lithium Ion ( which is a product of a chemical reaction ) ... for that you need energy ... I can have different amounts of energy from the same Ah ... vastly different amounts of energy ... thousands , millions, billions or more different amount of energy and still have the same 1 Ah ... It is not possible for significantly different amounts of energy for the same number of molecules to have the same chemical reactions to give you the same number of Lithium Ions just because you happen to be using the same 1Ah... that 1 Lithium Ion can not contain , carry , nor store any arbitrary amount of energy ( 10x, trillion times , etc ) you want , just because it is still the same 1Ah.... thus is it energy not current that determines the number of Lithium Ions.



GizmoEV said:


> Batteries store coulombs not Watt-hours


Incorrect.

Batteries are chemical reactions ... each individual molecule that has a chemical reaction has a quantified amount of energy ... batteries like any other chemical energy storage device store chemical energy ... in their chemical bonds and structure.

This is true for sugar , beef, wood, and batteries ... energy is stored in each molecule by the chemical bonds and structure.



GizmoEV said:


> It doesn't matter if people misuse SOC or not. SOC is based on Ah.


I specifically did not disagree with and took major and others at face value when they said that , that is the convention ... It does make sense ... even if it is not how I see and hear people using the term SoC.

What defines a term is how it is used ... Cool and hot don't just mean temperature anymore ... etc ... I used the term as I had often seen many people use the term... that is why it matters in the context of this particular discussion here.

I do find it funny how insistent people are being about Ah SoC ... beating me over the head for something they know people use it to describe energy ... and even though I am not disagreeing with Ah SoC ... but also they seem to have no issue using Ah or SoC , as a measure or gauge of the amount of energy needed to go __ Miles under __ Conditions.... oh well ... to each their own... but yes that I do find amusing.



GizmoEV said:


> I will never trust a Wh meter, especially as a % of capacity, to determine what the SOC of my pack is. An Ah meter, on the other hand, I do trust. Assuming of course that its accuracy is sufficient. Yes the Ah count faster near the end but so does the gas gauge in my car. The top usually moves much slower than the bottom in every car I have driven.


You are completely free to use any method you like ... whatever works for you.

I prefer Wh ... moving a given vehicle a given distance under given conditions requires a given amount of Wh .of energy .. We don't calculate wind resistance in Ah ... it's power Watts and energy Wh ... we don't calculate rolling resistance in Ah ... it's power W and energy Wh ... etc ... but that's just me ... I'm not here , nor do I want to convince people to see the world the way I do ... that was not the intention of this thread ... you are welcome to use any method you like ... whatever works for you ... but I may not agree with you or use the same methods myself.


----------



## PStechPaul (May 1, 2012)

I also prefer using watts and watt-hours. For instance, suppose you have a battery pack that is 72 volts nominal, and you charge it with 10 amps for 10 hours, you will have 100 Ah of charge and 7200 Wh of energy storage. If you know that your vehicle uses about 333 Wh/mile you can easily predict that you can go about 21 miles with that SOC.

Now suppose you upgrade your battery pack to 144 volts nominal. The same 100 Ah of charge will now be 14400 Wh of energy, and your car can go 42 miles. Of course, if your fuel gauge reads 0-100%, you will need to recalibrate it when you change the battery pack, just as you would if you changed the gas tank in your ICE car.

In an ICE car, the gas tank is often shaped somewhat like an inverted triangle, so if the float reads the height of the fuel, each increment corresponds to more volume at the top of the tank than at the bottom. This is analogous to batteries, where most of the energy is stored at the highest voltage, and when the voltage drops significantly there is little energy left. 

I think this is because the battery chemistry is related to the reduction and oxidation potentials for the electrodes, so it has a fairly specific standard value. Since most of the reaction for either charging or discharging occurs near this potential, the same Ah of charge corresponds to different Wh of energy for each chemistry. For more info see:
http://www.chemguide.co.uk/physical/redoxeqia/introduction.html#top
http://en.wikipedia.org/wiki/Battery_(electricity)
http://www.chem.wisc.edu/deptfiles/...odules/electrochemistry/05potential/18_52.htm

For a capacitor, the amount of energy is 0.5*C*V^2, so a fixed current will result in a linear rise of voltage, but as the voltage increases the amount of power needed to maintain the charge current increases exponentially. A similar effect occurs in batteries, but it is more complex because it involves a chemical reaction which is affected by temperature and local effects such as gas bubbles which depend on time and other factors. 

It seems that the standard measure of battery capacity has been the ampere hour, but the actual energy storage is more properly in watt-hours. The Ah measure depends on the nominal voltage, so it may be about 3.3V or 3.6V for Lithium cells, and 12 to 13.2V or so for a common lead-acid battery. When trying to determine effective cost differences, it is easier and more meaningful to compare $/Wh, especially if the average current draw is known and the Peukert factor can be used for true Wh capacity. And an even more meaningful figure may be the cost per Joule over the lifetime of the battery, in which case LiFePO4 can be shown to be more economical. Of course you also should include the actual environmental cost of manufacture and disposal, as well as the energy required to move the weight of the battery pack.


----------



## GizmoEV (Nov 28, 2009)

IamIan said:


> (Bold Added ) You gave one answer yourself ... if it were only the electric current ... than the same number of electrons would always produce the same effect ... your light shows this is not the case ... if it is a different ENERGY ... it can result in a different energy level ... even for the same number of electrons ... ie amps or Ah ... but this only goes so far ... molecules have finite energy limits ... but I can have trillions of more energy but not have changed the number of electrons ... the amps ... or the Ah.


Now you are going in circles. You said,


> the same current can have different energy ... and if it has different energy ... It shouldn't have the same number of Lithium Ions.


And I disagreed with you. Then you agreed with me?



> The amount of Ah does not by itself tell you the number of Lithium Ion ( which is a product of a chemical reaction )


Yes it does. An Ampere is a specific number of electrons/second. Multiply that by time and get Ah and you have only a quantity of electrons. If you convert the hours to seconds you will see that the time unit cancels out. Each Li Ion accepts a set number of electrons. Since there is a fixed number of Li ions in the battery (assuming none plate out or otherwise get sequestered out of use) there is a fixed number of electrons available. It matters not at what energy they have to be moved. Consider a battery with only 100 Li ions. When they have all moved from one plate to the other the battery is either at 100%SOC or 0%SOC. Again, it matters not what the voltage was when this transfer took place. The state of charge of the battery is independent of voltage. The voltage along with Ah determines the energy capacity of the battery, yes, but not the SOC. You can only approximate SOC with Wh. With Ah it is as good as the measurement method.



> What defines a term is how it is used ... Cool and hot don't just mean temperature anymore ... etc


Just because the "general public" misuses a term doesn't change its definition. The meaning of cool and hot are very specific within a given context. Taking the meaning used in one context and applying it to another doesn't work. Putting SOC in the same category as a "slang" term like cool and hot doesn't help its misuse.



> ... I used the term as I had often seen many people use the term... that is why it matters in the context of this particular discussion here.


So why didn't you use it the way many people use it, the proper way?



> ... but also they seem to have no issue using Ah or SoC , as a measure or gauge of the amount of energy needed to go __ Miles under __ Conditions....


You are assuming it is a measure of energy. Gallons of gas isn't a measure of energy either, it is a volume of something. It is just that it is consumed within a relatively narrow band of rates, just like the number of electrons flowing from one terminal in a battery to another with side trips to do something considered useful. Using an Ah/mi figure is merely a measure of how quickly the "tank" empties. In the case of an EV's "fuel gauge" measuring Ah is significantly more accurate as far as SOC is concerned if one wants to know what the true level of the battery is. It works at any temperature or pressure (voltage). The lower the voltage the faster they get used up for a given power output.

When it comes to comparing one vehicle to another then comparing Ah/mi doesn't work because Ah is like a clear tube on the side of a gas tank. You can't compare levels between different dimensioned tanks. That is where Wh/mi makes more sense.



> I prefer Wh ... moving a given vehicle a given distance under given conditions requires a given amount of Wh .of energy .. We don't calculate wind resistance in Ah ... it's power Watts and energy Wh ... we don't calculate rolling resistance in Ah ... it's power W and energy Wh ... etc ...


That is true but we don't measure distance in gallons of gas either. It is a measure of how full our tank is. Ah is what is used to measure the "fullness" of our batteries, not the energy they are storing at a given point.



PStechPaul said:


> I also prefer using watts and watt-hours. For instance, suppose you have a battery pack that is 72 volts nominal, and you charge it with 10 amps for 10 hours, you will have 100 Ah of charge and 7200 Wh of energy storage. If you know that your vehicle uses about 333 Wh/mile you can easily predict that you can go about 21 miles with that SOC.
> 
> Now suppose you upgrade your battery pack to 144 volts nominal. The same 100 Ah of charge will now be 14400 Wh of energy, and your car can go 42 miles. Of course, if your fuel gauge reads 0-100%, you will need to recalibrate it when you change the battery pack, just as you would if you changed the gas tank in your ICE car.


No, the fuel gauge will read just fine with either pack provided you didn't change the Ah capacity of it. If it was designed to use Wh only for its 0-100% range then yes it would have to be updated.




> It seems that the standard measure of battery capacity has been the ampere hour, but the actual energy storage is more properly in watt-hours.


Correct but Ah capacity is NOT an energy value. It is a "number of electrons" value.



> The Ah measure depends on the nominal voltage,


No, Ah measure is independent of voltage. It is energy capacity which is dependent on Ah and voltage.



> When trying to determine effective cost differences, it is easier and more meaningful to compare $/Wh, especially if the average current draw is known and the Peukert factor can be used for true Wh capacity.


And that is why the $/Wh figure is used to compare batteries of differing chemistries. When comparing identical batteries, however, $/Ah works just fine too. That is why many (most?, all?) LiFePO4 vendors show cost as a $/Ah value.


----------



## IamIan (Mar 29, 2009)

GizmoEV said:


> Now you are going in circles. You said,
> 
> And I disagreed with you. Then you agreed with me?


I agreed with a specific part of what you said, not all of it.
I'm sorry if that was confusing... not my intent.
I am not going in circles ... my position is the same... 1Ah does not give a set number of Lithium Ions.



GizmoEV said:


> > The amount of Ah does not by itself tell you the number of Lithium Ion ( which is a product of a chemical reaction )
> 
> 
> Yes it does.


I disagree.



GizmoEV said:


> An Ampere is a specific number of electrons/second. Multiply that by time and get Ah and you have only a quantity of electrons.


Agree.



GizmoEV said:


> Each Li Ion accepts a set number of electrons.


Disagree.

It is the chemical reaction of the molecules that give off the Lithium Ion. 

Each of those molecules that has a chemical reaction has a energy associated with that reaction ... not a specific set Ah amount.



GizmoEV said:


> It matters not at what energy they have to be moved.


I disagree.

It is the chemical reaction of the molecules that give off the Lithium Ion. 

Each of those molecules that has a chemical reaction has a energy associated with that reaction ... not a specific set Ah amount.



GizmoEV said:


> Consider a battery with only 100 Li ions. When they have all moved from one plate to the other the battery is either at 100%SOC or 0%SOC.


Agree.

Caution:
But not a Linear 1 to 1 over the % from 0 to 100.

Because each Lithium Ion comes from a Chemical reaction of a molecule ... each of those is a specific energy.



GizmoEV said:


> The state of charge of the battery is independent of voltage.


Only so long as SoC is only used for Ah ... and not for energy ... Lithium Ions from chemical reactions that need energy ... Distance traveled under specific conditions ... etc.

Once people start using the term SoC to describe Energy ... than they are describing and talking about energy , not Ah ... even if they are still using the term SoC.



GizmoEV said:


> Just because the "general public" misuses a term doesn't change its definition. The meaning of cool and hot are very specific within a given context. Taking the meaning used in one context and applying it to another doesn't work. Putting SOC in the same category as a "slang" term like cool and hot doesn't help its misuse.


But understand that usage ... and allowing the conversation to move on ... is more useful ( I think ) , than beating the dead horse ... over and over and over again , day after day after day.



GizmoEV said:


> So why didn't you use it the way many people use it, the proper way?


I did use it the way many people use it.
As a % of SoC indicating a % of the battery between empty and full.

When I wrote that I think a % of the batteries Wh from empty to full is a better method ... it was pointed out to me that the term SoC is industry standard only for Ah ... I understood the explanation given , and did not disagree with it ... I offered an explanation for why I had used the term as I had ... which is how many people use the term ( as a % of the battery from full to empty ) ... and ever sense then the dead horse keeps being beaten over and over again.



GizmoEV said:


> > but also they seem to have no issue using Ah or SoC , as a measure or gauge of the amount of energy needed to go __ Miles under __ Conditions....
> 
> 
> You are assuming it is a measure of energy.


It is a measure of energy. 
If you define the conditions and the distance traveled you define a quantity of energy.



GizmoEV said:


> Gallons of gas isn't a measure of energy either, it is a volume of something.


It is a measure of chemical energy.

One Gallon of a specific mix of gas under specific temperature and pressure will have a specific number of a specific mix of molecules. Those molecules when they undergo the chemical reaction with Oxygen in the air yield a specific amount of energy. For crude purposes people give it an average number like ~36kwh per gallon of gas. But it does vary. E10 for example is a different mix of molecules in that same gallon and under the same temperature and pressure would still have a different energy content, because it has different molecule mix.

Chemical reactions are driven by and give off energy... when one knows the chemicals involved and the reactions involved , one can know the amount of energy per molecule.



GizmoEV said:


> Using an Ah/mi figure is merely a measure of how quickly the "tank" empties.


That is how people use it ... but the action they are describing is energy.

Energy , by definition of the term , is the capacity to do work ... ie force over a distance ... when there is a force either one you applied or the force of gravity or the force or rolling resistance or the force of wind resistance ... and you move any distance ... you have a specific amount of energy ... If you want your car to go __ Miles under specific conditions ... it is a specific amount of mechanical energy you use.

Energy and Ah are not the same thing ... and for me ... I think using a term like Ah/Mile only leads to confusing people about what energy is and what an Ah is... which is why I prefer Wh/Mile.

Again you are welcome to use any method you like ... but going a specific Distance under specific conditions requires a specific amount of Energy , not Ah.



GizmoEV said:


> In the case of an EV's "fuel gauge" measuring Ah is significantly more accurate as far as SOC is concerned if one wants to know what the true level of the battery is. It works at any temperature or pressure (voltage). The lower the voltage the faster they get used up for a given power output.


Use whatever you like.

But ... I disagree ... I think this usage leads people be confused about what is and Ah and what is Energy.

If I know the Wh capacity of my battery ... and I know the Wh I've used from it ... 1Wh = 1Wh ... 1Wh of energy from the bottom allows me to do 100% exactly the same amount of work as 1Wh from the top... This is not the case for Ah ... From my point of view ... using Ah not only confuses people about what energy is and what an Ah is ... but it is also more complicated ... Because I can't do the same amount of work.



GizmoEV said:


> When it comes to comparing one vehicle to another then comparing Ah/mi doesn't work because Ah is like a clear tube on the side of a gas tank. You can't compare levels between different dimensioned tanks. That is where Wh/mi makes more sense.


Agree.

And +1 more reason I prefer to use the % of Wh capacity of my batteries.



GizmoEV said:


> No, the fuel gauge will read just fine with either pack provided you didn't change the Ah capacity of it. If it was designed to use Wh only for its 0-100% range then yes it would have to be updated.


read fine yes ... but that wasn't my point in that quote... I'll try again.

The amount of work ( ie distance under conditions ) one can do ... 1Ah or 1%Ah at the bottom , one will be able to do , will be considerably less work ( ie distance under conditions ) ... than 1Ah or 1%Ah at the top can do.

This isn't the case for Wh ... 1Wh or 1%Wh at the top will be able to do exactly the same amount of work ( ie distance under conditions ) as 1Wh or 1%Wh at the bottom.


----------



## PStechPaul (May 1, 2012)

One way to think about this is to look at what happens with a single 3.3 volt cell charged at 1 amp for 1 hour, and then two cells in series, also 1 amp and 1 hour. In the first case, there was a movement of (say) 1000 electrons from the cathode to the anode of the single cell, while with two cells 1000 electrons moved in BOTH cells, so it is the equivalent of 2000 electrons, or twice the energy.

Depending on cell chemistry, there will be a certain characteristic voltage required to perform the RedOx reaction, and the cell voltage must have at least this voltage for actual charging to occur. There may be some current flow below this voltage, but generally a deeply discharged battery will quickly reach its nominal voltage and then current will rise as the reaction spreads over the surface of the electrodes. Then the charging voltage will rise at a given charging current because of internal resistance and chemical reaction effects.

It may be better to calculate the SOC from the current and the nominal voltage of the cell, rather than the measured voltage of the cell, because the actual power includes some portion which is not stored but instead is dissipated as heat or in chemical reactions such as gassing which do not contribute to stored energy. But when the cell is fully charged, almost all additional applied power is wasted, so you need another way to determine SOC. For LiFePO4 cells, I think the most accurate method is to use coulomb (or Ah) counting and stop charging when the specified capacity of the battery is reached. Since the chemistry determines the nominal voltage, it will be a constant, so Ah or Wh will be equivalent. However, Wh measurement is more useful if you don't know the pack voltage, which should never be the case.


----------



## GizmoEV (Nov 28, 2009)

IamIan said:


> > Originally Posted by *GizmoEV*
> > _Each Li Ion accepts a set number of electrons._
> 
> 
> ...


Then you need to go back and restudy chemistry. This isn't something we get to vote on. It is dictated by the laws of nature. A give set of reactants in a given reaction transfer the same number of electrons every time.



IamIan said:


> It is the chemical reaction of the molecules that give off the Lithium Ion.
> 
> Each of those molecules that has a chemical reaction has a energy associated with that reaction ... not a specific set Ah amount.


The Ah amount is the same because, regardless of the energy level it is done at, the same reactants and products are involved.



IamIan said:


> When I wrote that I think a % of the batteries Wh from empty to full is a better method ...


You didn't write that. It was *PStechPaul.*



IamIan said:


> It is a measure of energy.
> If you define the conditions and the distance traveled you define a quantity of energy.


So then you agree that Ah/mi is a useful term since it then relates to a distance traveled and relates to a quantity of energy for a given battery pack. Just like mi/gal of gasoline, diesel, propane, etc.



IamIan said:


> It is a measure of chemical energy.
> 
> One Gallon of a specific mix of gas under specific temperature and pressure will have a specific number of a specific mix of molecules. ...


Just like Ah/mi for a given battery pack.



IamIan said:


> That is how people use it ... but the action they are describing is energy.


Yep, just like mi/gal.



IamIan said:


> Energy and Ah are not the same thing ... and for me ... I think using a term like Ah/Mile only leads to confusing people about what energy is and what an Ah is... which is why I prefer Wh/Mile.


If the voltage at which the Ah are given then it can be used to compare vehicles. Wh/mi is definitely preferred. When working with a "fuel gauge" on an EV, however, Ah/mi is much more accurate of an indicator of how full the battery is. This is because it will count accurately regardless of the temperature, voltage, current, etc. at which the battery is being drained. Wh will count too slowly under heavy loads if there is significant voltage sag. Ah will track quite well.



IamIan said:


> But ... I disagree ... I think this usage leads people be confused about what is and Ah and what is Energy.


That is fine but don't take a clearly defined term and misuse it just because you think people are confused. That just exacerbates the problem.


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## GizmoEV (Nov 28, 2009)

PStechPaul said:


> One way to think about this is to look at what happens with a single 3.3 volt cell charged at 1 amp for 1 hour, and then two cells in series, also 1 amp and 1 hour. In the first case, there was a movement of (say) 1000 electrons from the cathode to the anode of the single cell, while with two cells 1000 electrons moved in BOTH cells, so it is the equivalent of 2000 electrons, or twice the energy.


That is because the charge current is happening at twice the voltage for two series cells as it is for the single cell. Of course twice as many electrons have flowed. Twice as many reactions took place too. In both cases, however, the SOC of the batteries changed by exactly the same amount. That is also why a "fuel gauge" must be tied to Ah and not Wh. Once it is set to the particular number of Ah which constitutes the full to desired empty point, adding more batteries in series doesn't mean a new calibration has to be done. What will be noticed, however, is that the battery doesn't drain as fast with the larger pack assuming the same driving conditions are considered. This is consistent with maintaining the same Wh/mi figures. There is more energy stored in the larger battery pack so naturally it takes longer to go from the 100%SOC to the cutoff point.

If, however, the Ah size of the pack is changed, along with the voltage, then the Ah depletion rate will also change. For example, my Gizmo has a 2p20s pack of TS-LFP100AHA cells. This gives me a 200Ah pack at 64V nominal. Under light driving conditions I can drive 1 mile on 2Ah of pack capacity which corresponds to 128Wh/mi. Assuming my system could handle the voltage increase I could reconfigure my pack to be 1p40s for a 100Ah pack at 128V nominal. If I drove with the same light driving conditions my Ah consumption would be cut in half to 1 mile on 1Ah of pack capacity for the same 128Wh/mi energy consumption rate.

This underscores the need to always include, or ask, what the nominal pack voltage is if an Ah/mi figure is given. It does not, however, give license to misuse how SOC is determined. Two wrongs don't make a right. [I heard, however, that two wrights make an airplane. ]



PStechPaul said:


> It may be better to calculate the SOC from the current and the nominal voltage of the cell, rather than the measured voltage of the cell, because the actual power includes some portion which is not stored but instead is dissipated as heat or in chemical reactions such as gassing which do not contribute to stored energy. But when the cell is fully charged, almost all additional applied power is wasted, so you need another way to determine SOC. For LiFePO4 cells, I think the most accurate method is to use coulomb (or Ah) counting and stop charging when the specified capacity of the battery is reached. Since the chemistry determines the nominal voltage, it will be a constant, so Ah or Wh will be equivalent. However, Wh measurement is more useful if you don't know the pack voltage, which should never be the case.


SOC is calculated by the current but the voltage is irrelevant. That is why gauges like the ZEVA-II doesn't need to know the pack voltage. The CycleAnalyst I use in my Gizmo only needs pack voltage to calculate Watts and Watt-hours. It does not even measure Watts or Watt-hours, it only measures voltage and time: voltage of the pack and voltage across the shunt.


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## magudaman (Mar 29, 2009)

This is a monster of a thread! I really love the test done in the first post, great data. I must chime in and say that I have never heard of amp hours used for state of charge, and is instead watt hours. This is industry standard for cell phones, laptops, and commercial electric cars.


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## major (Apr 4, 2008)

magudaman said:


> I must chime in and say that I have never heard of amp hours used for state of charge, and is instead watt hours. This is *industry* standard for cell phones, laptops, and commercial electric cars.


Look at the battery industry. Here is an example: http://www.trojanbattery.com/ They list the specification for all their batteries and they always use Ampere hour for capacity. I cannot see any mention of Watt hours. 

The battery industry standard for rating is Ampere hour, which is charge.

edit: Calb uses Ah and even includes it in their cell part #. http://en.calb.cn/product/?id-116.html


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## magudaman (Mar 29, 2009)

major said:


> Look at the battery industry. Here is an example: http://www.trojanbattery.com/ They list the specification for all their batteries and they always use Ampere hour for capacity. I cannot see any mention of Watt hours.
> 
> The battery industry standard for rating is Ampere hour, which is charge.
> 
> edit: Calb uses Ah and even includes it in their cell part #. http://en.calb.cn/product/?id-116.html


I guess I am think more of when a cell is in a product it is all watt hours. It seems amp hours really is really just a legacy rating system. It doesn't really tell you much about a battery. The first thing I am looking for when shopping for new cells is wh/kg, specific power watts/kg, and lastly wh/Liter. You are correct manufactures don't usually provide watt hours which is a PIA


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## Nordic (Mar 28, 2012)

Thanks IamIan for posting the data on your cell tests.

I have assembled a pack of 15s A123 20AmpHr cells for use on my ebike and I have similar results to your tests. The purpose of the tests was to have a baseline to measure future changes in the pack and to verify that it was performing at or near cell spec.
These cells were from Victpower marked made in USA and do not show signs of being used. The negative (-) plated copper tab though is riddled with small holes. I am not sure why but think it was done to provide a fuse of sorts in case of shorts.(at the sacrifice of the tab and rendering the cell unrepairable). I use a mid pack 60 Amp fuse link in the pack itself to prevent a short across the pack output from killing the cells.


I did not test the capacity of each cell on its own but as an assembled pack. WattHrs, Volts and AmpHrs were recorded over time measured with a Turnigy Wattmeter, Volts and Amps agreed with a Fluke 83 to within 1%. No BMS was used, I balanced each cell manually. Load was resistive.

*1st and 2nd Charge-Discharge cycles*
Charged to 3.6 V per cell at 5 Amps CC.
Discharged at approx *5* Amps, Stopped when lowest cell hit 2.8 VDC
Results of two complete cycles
WattHrs 920, 927
AmpHrs 19.04, 19.133 

*3rd and 4th Charge-Discharge cycles*
Charged to 3.6 V per cell at 6 Amps CC.
Discharged at approx *10* Amps, Stopped when lowest cell hit 2.8 VDC
Results of two complete cycles
WattHrs 900, 903
AmpHrs 18.7, 18.84 


I allowed the pack to rest one hour after Discharge, then I discharged the lowest voltage cell again to 2.8 V and the highest voltage cell to 2.8 V and compared the difference in Watt and AmpHrs taken from the two cells and found it to be about 2.5%

Average charge efficiency of the four Charge\Discharge cycles was 93%
Temperature rise during Discharge at 10 amps nominal was about 4 Deg C above ambient.

My application does not require more than 20 amps continuous and 30 amps burst so I am satisfied with the results and will not test at high currents.


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## GerhardRP (Nov 17, 2009)

magudaman said:


> This is a monster of a thread! I really love the test done in the first post, great data. I must chime in and say that I have never heard of amp hours used for state of charge, and is instead watt hours. This is industry standard for cell phones, laptops, and commercial electric cars.


I have always read that the Coulombic efficiency of lithium ion batteries is greater than 99% and is independent of temperature, charging and discharge rates to the extent that internal resistance doesn't interfere with cutoff timing. This fact makes the number of Coulombs remaining a good SOC indicator. 
This paper has some interesting graphs:
http://www.cse.anl.gov/us-china-wor...ePO4 battery performances testing for BMS.pdf
Also Google around for Ragone plot to see the variation of energy available from a battery as modified by the power level at which it is withdrawn. A SOC meter based on energy would have to account for the anticipated power level, while a charge based system would not.
Gerhard


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## IamIan (Mar 29, 2009)

GizmoEV said:


> Then you need to go back and restudy chemistry. This isn't something we get to vote on. It is dictated by the laws of nature. A give set of reactants in a given reaction transfer the same number of electrons every time.


I agree it isn't something we vote on ... but the facts don't agree with you ... You should heed your own advise and go do a review.

It's called Chemical *Energy* ... not Chemical *Ah* ... Go Look it up , sense you obviously just refuse to believe me.

The Chemical Bonds and reactions for a given set of reactants in a given reaction have a specific amount of chemical ENERGY... either released or absorbed... each molecule having a chemical reaction.

If the theory you keep trying to defend were correct ... than that same 1Ah quantity of electrons would always give the same Quantity of chemical reactions ... to always give the same quantity of Lithium Ions ... weather is was 1Ah as part of 1 mWh of energy ... or 1 Ah as part of 1 TWh of energy ... and sorry ... it doesn't work that way ... the chemical reactions have a finite and limited amount of chemical ENERGY ... for each individual chemical reaction of molecules.



GizmoEV said:


> > When I wrote that I think a % of the batteries Wh from empty to full is a better method ...
> 
> 
> You didn't write that. It was *PStechPaul.*


 Sorry you missed it ... but ... my short summary stands.

This sentence I wrote , was a tiny summary of a much larger number of words and comments.

This concept described in that part of the summery you reference there I did refer to in several posts above ... even before PStechPaul's first post on this thread ... that one sentence part of the summary was not a word for word quote of everything I said ... nor was it intended to be such a word for word quote... but a short summary.

If you want to go see it ... feel free to go re-read:
Post #9 , 12 , 15 , 16 , 18 Above.



GizmoEV said:


> So then you agree that Ah/mi is a useful term since it then relates to a distance traveled and relates to a quantity of energy for a given battery pack. Just like mi/gal of gasoline, diesel, propane, etc.


I'm sorry if I gave the impression I did not think it was useful.

I agree it can be a useful term ... I think it is less useful than Wh/Mile ... which is actually energy per mile ... ie the action being described ... some of the reasons for that are listed previously ... but if it is between Ah/mi and nothing ... yes Ah/Mi can be useful.

However ... the person who is using it in that context ... is still describing energy ... and using the incorrect term ( Ah ) to do so ... if they choose to for whatever reason ... sure go ahead ... but it can lead to confusion and people misunderstanding and using terms to describe the wrong thing.



GizmoEV said:


> If the voltage at which the Ah are given then it can be used to compare vehicles. Wh/mi is definitely preferred. When working with a "fuel gauge" on an EV, however, Ah/mi is much more accurate of an indicator of how full the battery is. This is because it will count accurately regardless of the temperature, voltage, current, etc. at which the battery is being drained. Wh will count too slowly under heavy loads if there is significant voltage sag. Ah will track quite well.


If you are describing a technical issue with having a equally % accurate Wh meter vs one for Ah ... that is worth considering when one makes the choice.

However ... that does not mitigate the issues raised above with using Ah to describe an action that is my definition energy... which Ah alone is not.

If I have two meters that are equally accurate for Wh or for Ah ... the Wh as being an actual measure of energy I think it better to use than Ah ... the 1st 1Wh from the battery will be able to do the same amount of work as the last 1Wh from the bottom ... the otherwise equal Ah meter , can not make the same claim , because 1Ah is not a specific amount of energy ... for any action one wants to think about or discuss involving energy ... be it driving __ distance or anything else.



GizmoEV said:


> That is fine but don't take a clearly defined term and misuse it just because you think people are confused. That just exacerbates the problem.


I've described and addressed this multiple times already ... that is not what I thought ... nor what I did ... read above.

Will you also stop using Ah ... or SoC based on Ah ... to describe an action that is by definition Energy?

Such as Ah/mile ... is a misuse of the term Ah to describe an action that is an amount of energy... that action is a quantified amount of Wh of energy to go that mi ... using Ah is a misuse of the term.

Ah is a clearly defined term ... Energy is a Clearly defined term.

Why does your request about clearly defined and misuse of terms not apply to yourself?

- - - - - - - - - - - - - - - - - 



Nordic said:


> Thanks IamIan for posting the data on your cell tests.


You're Welcome.

Best of luck on your project.... I think testing like you did is always a good 1st step.


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## major (Apr 4, 2008)

GerhardRP said:


> I have always read that the Coulombic efficiency of lithium ion batteries is greater than 99% and is independent of temperature, charging and discharge rates to the extent that internal resistance doesn't interfere with cutoff timing. This fact makes the number of Coulombs remaining a good SOC indicator.
> This paper has some interesting graphs:
> http://www.cse.anl.gov/us-china-wor...ePO4 battery performances testing for BMS.pdf
> Also Google around for Ragone plot to see the variation of energy available from a battery as modified by the power level at which it is withdrawn. A SOC meter based on energy would have to account for the anticipated power level, while a charge based system would not.
> Gerhard


Thanks for posting this Ger.



> I have always read that the Coulombic efficiency of lithium ion batteries is greater than 99% and is independent of temperature, charging and discharge rates to the extent that internal resistance doesn't interfere with cutoff timing.


I also have read of the high 99-plus or "nearly 100%" Coulombic efficiency. Iam's tests show several points lower. You may have cited a possible reason in the cutoff timing, or possibly that it may take a number of cycles to bring up that number.



> This fact makes the number of Coulombs remaining a good SOC indicator.


SOC = State of Charge so it is the remaining Coulombs. 



> This paper has some interesting graphs:
> http://www.cse.anl.gov/us-china-wor...ePO4 battery performances testing for BMS.pdf


This paper or presentation is quite detailed and appears very well done. I believe that Dr. Lu's objective is much the same as IamIan's. Note how often Dr. Lu uses SOC for the basis of graphs and displaying test results in a logical manner, along with using the charge parameters. He seldom uses energy.

SOC = State of Charge. State of Charge. See the third word in that phrase? Charge. Charge is Coulombs or Ampere hours. I can not understand how it can be interpreted any differently.

I realize that Iam and some people are concerned with energy and don't really care about charge. Fine. And if someone wants to use energy as a basis for a battery "fuel gauge", fine. Do so. But please do not call it "SOC" or State of Charge. It is not. Call it State of Energy (SOE), or Wh level, or something else. Please.


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## IamIan (Mar 29, 2009)

major said:


> I also have read of the high 99-plus or "nearly 100%" Coulombic efficiency. Iam's tests show several points lower. You may have cited a possible reason in the cutoff timing, or possibly that it may take a number of cycles to bring up that number.


It is also possible that it is the specific cells I have that are under performing for one reason or another.

It is also possible that the total charge was a tiny bit more put in than the cell was able to store ... this part at least should show up when I later get around to the various % of full cycles efficiency testing.



major said:


> This paper or presentation is quite detailed and appears very well done. I believe that Dr. Lu's objective is much the same as IamIan's. Note how often Dr. Lu uses SOC for the basis of graphs and displaying test results in a logical manner, along with using the charge parameters. He seldom uses energy.


Further agrees with what you already stated above about the industry standard.



major said:


> SOC = State of Charge. State of Charge. See the third word in that phrase? Charge. Charge is Coulombs or Ampere hours. I can not understand how it can be interpreted any differently.


That's one reason why your explanation made sense to me.



major said:


> I realize that Iam and some people are concerned with energy and don't really care about charge. Fine. And if someone wants to use energy as a basis for a battery "fuel gauge", fine. Do so. But please do not call it "SOC" or State of Charge. It is not. Call it State of Energy (SOE), or Wh level, or something else. Please.


I'll stand by what I wrote to you before ... I have no issue with that industry standard.

Along the same line of thinking ... I would suggest people who describe an action that is by definition energy shouldn't be using non-energy terms as units of measure of that action ... if you are describing an action that is energy then call it energy ... or Wh , or some other unit of energy.

Out of curiosity ... would you also want those people not to use other 'charge' based terms ?? ... like charging and discharging ... would you rather they be using terms like energizing and de-energizing?


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## Nordic (Mar 28, 2012)

IamIan said:


> It is also possible that it is the specific cells I have that are under performing for one reason or another.
> 
> It is also possible that the total charge was a tiny bit more put in than the cell was able to store ... this part at least should show up when I later get around to the various % of full cycles efficiency testing.


My tests also show about 93% charge efficiency. I did not record the temperature rise during charging but did notice a small rise above ambient. Since they heat during both discharge and charge cycles there must be something less than 100% conversion efficiency. I had about a 4 deg C rise on discharge. Given the mass (15 Lbs) of the cells this means a fair bit of energy went into heating and not in to the load on discharge. The specified internal resistance alone would not seem to account for this as it would only produce 2.7 Watts of heat at 10 amps.


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## major (Apr 4, 2008)

IamIan said:


> It is also possible that the total charge was a tiny bit more put in than the cell was able to store ...


That would be an issue with cutoff timing.



IamIan said:


> Out of curiosity ... would you also want those people not to use other 'charge' based terms ?? ... like charging and discharging ... would you rather they be using terms like energizing and de-energizing?


Isn't it used correctly now? You charge the battery by supplying charge to it, as current, a rate of charge. The battery or cell manufacturer recommends this rate as C/4 or such. And you discharge the battery by taking charge out of it. Here again, recommendations are in the form of C-rates.* And by the way, C is capacity which is the maximum charge.

Terms like energizing and (de-energizing) are not appropriate because they are often used for turning on and turning off circuits and devices. If you want or need to talk about the power or energy associated with charging or discharging a battery, then do so, but speak about the power or energy as such and don't confuse it with charge.

* Interesting to note that there is such a thing as E-rate. "Similarly, an E-rate describes the discharge power. A 1E rate is the discharge power to discharge the entire battery in 1 hour." From: http://mit.edu/evt/summary_battery_specifications.pdf
So it would seem that my suggestion to use SoE is not that far fetched


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## PStechPaul (May 1, 2012)

Here is a good discussion of the Ah and Wh conventions:
http://electronics.stackexchange.co...e-hours-but-electricity-usage-measured-in-kil

Nothing new that has not already been presented here, however, but one post noted:



> Now that I look at my cell phone battery, I notice that it has all three ratings printed on it. It is a Lithium-Ion battery whose nominal voltage rating is 3.7V. It's energy capacity is marked as 4.81 Watt-Hours. It's electric charge rating is 1300 milliAmp-Hours.


I think the Ah term is somewhat of an anachronism based on long-time standard 6 volt and 12 volt automotive and plating batteries, where the usage and charging measurement was mostly based on current. In "olden days", wattmeters and Wh meters were rare and/or expensive, while ammeters were common. 

The automotive fuel gauge is also not a true indicator of available energy or volume, but a percentage of "full". Most vehicles have fuel tanks based on the nominal consumption of the ICE and a range of about 300 miles or so, although some commercials brag about 500 miles on a tank (but only because it's a BIG tank). The gauge is simply a reminder of when it's time to refill (or recharge). But when you go to the pump or the recharge station, you pay for the equivalent energy.

The ultimate gauge might actually show the expected miles of range based on the SOC and the average Wh/mile. When I'm driving, my main concern is how far I can go before I need to refuel. And AFAIK, many newer vehicles, especially hybrids and EVs, have a multipurpose instrument panel that can display that information as well as many other metrics.


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## IamIan (Mar 29, 2009)

Nordic said:


> My tests also show about 93% charge efficiency. I did not record the temperature rise during charging but did notice a small rise above ambient. Since they heat during both discharge and charge cycles there must be something less than 100% conversion efficiency. I had about a 4 deg C rise on discharge. Given the mass (15 Lbs) of the cells this means a fair bit of energy went into heating and not in to the load on discharge. The specified internal resistance alone would not seem to account for this as it would only produce 2.7 Watts of heat at 10 amps.


The question there is what is the specific heat of the cells... After all ... 15 lbs of Copper do not heat up the same number of degrees C as 15 Lbs of Aluminum do , when given the same wh of heat energy input... same is true for any material that has a different specific heat capacity than another material.

- - - - - - - - - - - 



major said:


> That would be an issue with cutoff timing.


That is one potentially.

It also occurs to me that there could also be an influence with the difference between the rate of diffusion in the cell vs the rate of charge and or energy being applied to it.



major said:


> Isn't it used correctly now?


Sometimes yes ... other times it is not.

For example:
People will describe and talk about the kwh of electrical energy they paid for ... the utility doesn't charge by the Ah ( for good reason ) ... or how energy efficient their charger is wall to battery ... or MPGe numbers when calculated based on energy ... or how far they can drive on a full charge or a half charge ... etc ... It seems like the convention for people to use terminology like charging and discharging even when they are describing and talking about the energy going in , going out, stored, etc.



major said:


> And by the way, C is capacity which is the maximum charge.


It always seemed to me the C was a more generic , just abbreviation of capacity ... and not always referring to charge.

So a person using Ah of capacity would abbreviate is with the C ... like you described in your example ... and the person using Wh of capacity would also abbreviate it with the C ... as the C itself was only an abbreviation for capacity , which itself is not specific to only one usage of the word capacity.



major said:


> Terms like energizing and (de-energizing) are not appropriate because they are often used for turning on and turning off circuits and devices. If you want or need to talk about the power or energy associated with charging or discharging a battery, then do so, but speak about the power or energy as such and don't confuse it with charge.


So what do you suggest the person use as a term for when they are measuring the kwh from the wall going into the battery? ... if they aren't to confuse it with charge , then it seems they shouldn't be describing their action as charging the battery... even if they are applying energy to the battery to bring it from say a lower SoE to a higher SoE.

Or ... For when someone refers to __ Miles on __ Charge ... those __ Miles is describing energy , not charge ... in that context they are describing the energy from the battery... even though many people use a term like discharging even when talking about the energy and not the charge.

etc.



major said:


> So it would seem that my suggestion to use SoE is not that far fetched


Not far fetched at all ... it seemed to make perfect sense as an energy based variation of the convention for SoC.


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## IamIan (Mar 29, 2009)

PStechPaul said:


> The ultimate gauge might actually show the expected miles of range based on the SOC and the average Wh/mile. When I'm driving, my main concern is how far I can go before I need to refuel. And AFAIK, many newer vehicles, especially hybrids and EVs, have a multipurpose instrument panel that can display that information as well as many other metrics.


Or use one's known CdA , weight etc ... combined with a mapping program of the hills , and traffic ahead ... combined with a weather app ... to collectively be able to more accurately be able to predict under all those known conditions how far will the energy in this battery go... or will they make that distance?... etc.


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## major (Apr 4, 2008)

IamIan said:


> major said:
> 
> 
> > Isn't it used correctly now?
> ...


You agree that certain terms are misused. I can't stop that. I was simply attempting to alert you to the situation. I think you'll appreciate "charge" a lot more when you get into testing and using series connected cells and balancing them.



major said:


> Which was my concern. You are drawing SoC conclusions based on energy efficiency.
> 
> As Gerhard suggested, take a look at the charge (Ah).


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## IamIan (Mar 29, 2009)

major said:


> You agree that certain terms are misused. I can't stop that. I was simply attempting to alert you to the situation. I think you'll appreciate "charge" a lot more when you get into testing and using series connected cells and balancing them.


Fair enough.

I'll try and be more mindful about the specific terminology I use ... it's technically correct usage instead of how people may use it ... although sadly given the reactions I've seen here ... I suspect I will still have clashes again , no matter what efforts are made ... oh well ... it is what it is I guess.

As for the potential of more appreciating 'charge' ... maybe ... I don't dislike charge , I'm not 'anti-charge' or anything like that ... but I see issues with how it is sometimes used ... I know the chemical bonds and reactions are about chemical energy ... I know any work I want to do , be it move a car or run a light or whatever , is again about energy ... I know I pay for it by units of energy ... etc ... so , I wouldn't say I won't appreciate it more ... but those things that are energy don't go away , no matter what I appreciate ... it is just how things work ... and will always be there.

- - - - - - 

The second quote you reference ... I already discussed (Post#9 above)... that wasn't what I was doing ... If you were just using it as a reference to what your concern was, yes I recognize you expressed that concern... I hope my previous explanation better clarified that.


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## GizmoEV (Nov 28, 2009)

IamIan;327545
It's called Chemical [B said:


> Energy[/B] ... not Chemical *Ah* ... Go Look it up , sense you obviously just refuse to believe me.
> 
> The Chemical Bonds and reactions for a given set of reactants in a given reaction have a specific amount of chemical ENERGY... either released or absorbed... each molecule having a chemical reaction.
> 
> If the theory you keep trying to defend were correct ... than that same 1Ah quantity of electrons would always give the same Quantity of chemical reactions ... to always give the same quantity of Lithium Ions ... weather is was 1Ah as part of 1 mWh of energy ... or 1 Ah as part of 1 TWh of energy ... and sorry ... it doesn't work that way ... the chemical reactions have a finite and limited amount of chemical ENERGY ... for each individual chemical reaction of molecules.


Yes, chemical reactions involve energy but they also involve the same number of electrons for a given reaction. Your statements are implying very strongly that the number of electrons involved is different depending on the *terminal voltage* you are measuring. That is why I said to go back and review the chemistry. The terminal voltage does not matter, the voltage at the reaction point(s) does but you can't get that measuring at the terminals. That is the problem with using Wh for SOC. You measure terminal voltage and current and use those to calculate Watts. Since each chemical reaction uses the same number of electrons each and every time state of charge is very accurately measured by counting electrons.

At least it looks like major's explanation on why SOC is not an energy value made sense to you. Just like number of inches of gasoline, or gallons, in a rectangular tank isn't an energy value but it correlates directly to an energy value.


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## IamIan (Mar 29, 2009)

GizmoEV said:


> Yes, chemical reactions involve energy but they also involve the same number of electrons for a given reaction.


I know you keep repeating this ... I still disagree with it ... see above for previous explanations.

chemical reaction do not just 'involve' energy ... it is energy that is stored in the chemical bonds of a structure ... it is energy that is needed to form chemical bonds and structures ... a given chemical reaction has a finite amount of chemical ENERGY for each chemical reaction that happens.



GizmoEV said:


> Your statements are implying very strongly that the number of electrons involved is different depending on the *terminal voltage* you are measuring. That is why I said to go back and review the chemistry. The terminal voltage does not matter, the voltage at the reaction point(s) does but you can't get that measuring at the terminals. That is the problem with using Wh for SOC. You measure terminal voltage and current and use those to calculate Watts. Since each chemical reaction uses the same number of electrons each and every time state of charge is very accurately measured by counting electrons.


My statements consistently and repeatedly disagreed with the idea that a fixed number of electrons ( ie Ah ) always results in a fixed number of Lithium Ions ( ie the number of molecules reacting ).

I know you keep claiming the part I put in red above ... I still disagree... as I've tried to explain previously.

Sense you've made it clear you just won't accept my descriptions ... I'll try by providing some references bellow ... weather you accept them or not ... is up to you.

From Wikipedia:


> In chemistry, *Chemical energy* is the potential of a chemical substance to undergo a transformation through a chemical reaction or, to transform other chemical substances. Examples include batteries and light bulbs. Breaking or making of chemical bonds involves energy, which may be either absorbed or evolved from a chemical system.


If you prefer a more academic source:
From Physics for Scientists and Engineers 7 , page 753 , on the right hand side of the page:


> Pitfall Prevention 27.2
> Batteries do not supply electrons
> A battery does not supply electrons to the circuit. It establishes the
> electric field that exerts a force on electrons already in the wires and
> elements of the circuit.


Also from the same physics text book when describing chemical Ionic bonds:
on Page 1258:


> When the electron makes a transition from the E  0 state to the negative energy state associated with the available shell in the atom, energy is released. This amount of energy is called the electron affinity of the atom. For chlorine, the electron affinity is 3.6 eV. Therefore, the energy required to form Na and Cl from isolated atoms is 5.1  3.6  1.5 eV. It costs 5.1 eV to remove the electron from the Na atom, but 3.6 eV of it is gained back when that electron is allowed to join with the Cl atom.


Note: 1eV is a tiny unit of energy ... specifically about ~1.6x10^-19 Joules

This chemical reaction ... Although the details and mechanisms change between the different types of chemical bonds and structures ... it is still a finite amount of ENERGY to make that chemical bond , or to break it ... Battery Chemistry is not and exception ... this is how chemistry works.

Like you said before , it is not open to vote ... like it or not ... each chemical reaction to form or break bonds is a specific amount of ENERGY... not Ah... 1Ah worth of electrons , does not tell you how much energy it was ... it could be 1mWh or 1TWh or any other amount of energy... and still be that same 1Ah.

I could get that 1.5eV of energy for the above listed chemical reaction from various different amounts of Ah ... because the Ah doesn't define a fixed amount of energy... but the chemical reaction and the chemical bonds involved , breaking and forming ... do define a specific amount of energy.

Each Lithium Ion represents a chemical reaction ... each one of those chemical reactions requires a specific amount of energy to break and form it's chemical bonds and structure ... not a specific Ah or number of electrons ... but a specific amount of energy.



GizmoEV said:


> At least it looks like major's explanation on why SOC is not an energy value made sense to you. Just like number of inches of gasoline, or gallons, in a rectangular tank isn't an energy value but it correlates directly to an energy value.


I disagree ... a specific quantity of a specific mix of gasoline does define a specific amount of chemical energy ... Just like any chemical reaction.

SoC and Charge are not energy ... they do not correlate directly to energy ... energy and charge are different things... using Ah or SoC to measure or indicate energy is a misuse of Ah or SoC.

I'm sorry you misunderstood ... I did not intend to infer that SoC is an energy value ... I was referring to people use the term SoC when they are describing energy ... and in that usage it would be better to use Wh an actual unit of energy ... they use the term SoC to indicate the % of potential work that can be done in a battery of some state ... which the ability to do any work is by definition, energy.

It made sense to me Major's explanation that it is an industry standard to use Ah for SoC and that SoC is about charge ... not about energy ... not about the potential to do work ... not about the ability to do any action that is by definition energy ... this swings both ways ... Wh shouldn't be used for SoC or Ah ... and SoC and Ah are the wrong term to describe actions that are , by definition energy.


----------



## GizmoEV (Nov 28, 2009)

IamIan said:


> chemical reaction do not just 'involve' energy ... it is energy that is stored in the chemical bonds of a structure ... it is energy that is needed to form chemical bonds and structures ... a given chemical reaction has a finite amount of chemical ENERGY for each chemical reaction that happens.


When I said "involve" I meant it the way you stated it that energy is stored in the bonds. Maybe I should have said "associated with" in stead. I am not saying that energy is not even in the picture, just that it is not as directly connected to what you are claiming it is when you are measuring voltage at the terminals.



IamIan said:


> My statements consistently and repeatedly disagreed with the idea that a fixed number of electrons ( ie Ah ) always results in a fixed number of Lithium Ions ( ie the number of molecules reacting ).


Then please explain this reaction which goes on in a LiFePO4, specifically a TS-LFP cell: 

LiFePO4 → Li+ + FePO4 + e-

The electrolyte does not participate in the reaction, it is only a carrier to move the ions between the electrodes. In that reaction there is one electron which plays bumper cars with the others in the circuit around to the other terminal of the battery. The Li+ ion is carried across the "chasm" by the electrolyte to intercalate into the anode. There is a great pictoral representation of this (for discharge) in "Nonaqueous Liquid Electrolytes for Lithium-Based Rechargeable Batteries" by Kang Xu, published in Chemical Reviews, 2004, Vol. 104, No. 10 on page 4305. http://www.tinhoahoc.com/Battery/cr030203g.pdf. Another resource is http://chargecar.org/blog/main/Battery_Tech_Talk.



IamIan said:


> Like you said before , it is not open to vote ... like it or not ... each chemical reaction to form or break bonds is a specific amount of ENERGY... not Ah... 1Ah worth of electrons , does not tell you how much energy it was ... it could be 1mWh or 1TWh or any other amount of energy... and still be that same 1Ah.


That is true, each chemical reaction has a specific energy associated with it. The problem is you are still measuring terminal voltage not "reaction voltage." That is why the Ah is what is needed to determine SOC. It eliminates the error of measurement associated with other "resistive" forces besides the reaction which charges/discharges a battery. That is what I mean when I say the voltage doesn't matter. If you want to know the energy it took to charge a battery then you need the voltage but the energy it took does not equal the energy that was stored by the battery during that event. An Ah out or in will always be an Ah out or in. The references you gave to the energy of forming a bond between Na and Cl atoms supports this.



IamIan said:


> I could get that 1.5eV of energy for the above listed chemical reaction from various different amounts of Ah ... because the Ah doesn't define a fixed amount of energy... but the chemical reaction and the chemical bonds involved , breaking and forming ... do define a specific amount of energy.


I never said that the Ah defined a fixed amount of energy. I said that the SOC of a cell could only be determined accurately with Ah. I did say that an Ah is related to a specific amount of energy depending on conditions, namely voltage at which it was transferred at. No different than saying a gallon of something doesn't define a fixed amount of energy. Until you know what that something is, an energy value cannot be determined.



IamIan said:


> I disagree ... a specific quantity of a specific mix of gasoline does define a specific amount of chemical energy ... Just like any chemical reaction.


This is what is confusing about what you are saying. You give specifics of a liquid fuel and it equates to a specific amount of energy but you don't take a specific number of Ah at a specific voltage and equate it to energy but to get the Wh you want you need the Ah and voltage. Here is the correlation between the two things as I see it:



A gallon (or any volume measurement) is analogous to an Ah.
The type of "stuff" in that gallon which can give us the info to calculate an amount of chemical energy is analogous to knowing the voltage at which an Ah was measured.
 


IamIan said:


> SoC and Charge are not energy ... they do not correlate directly to energy ... energy and charge are different things... using Ah or SoC to measure or indicate energy is a misuse of Ah or SoC.


Take one of my TS-LFP100AHA cells for example. Suppose it is at 90%SOC. Suppose further that it will not be discharged beyond 20%SOC. This means there are 70Ah which are available to be removed from the cell. Based on my CycleAnalyst measurements on my pack I have determined that 3.2V is actually a very close voltage to use for calculations. With that information can't the available energy in that cell be calculated as follows: 70Ah*3.2V=224Wh? This is why I don't understand the statement you made above (in red).



IamIan said:


> It made sense to me Major's explanation that it is an industry standard to use Ah for SoC and that SoC is about charge ... not about energy ... not about the potential to do work ... not about the ability to do any action that is by definition energy ... this swings both ways ... Wh shouldn't be used for SoC or Ah ... and SoC and Ah are the wrong term to describe actions that are , by definition energy.


I agree. Saying 2Ah/mi is meaningless unless more information is available. Just like saying mi/gal. Saying that my truck gets 15mi/gal is largely meaningless. Most people assume that would be gallons of gasoline but they don't even worry about what type of gasoline. It could be diesel, LPG, LNG, or a host of other fuel sources. Telling you that my Gizmo "uses" 2Ah/mi and my battery pack is 64V, does give enough info to determine the proper energy consumption rate.



IamIan said:


> From Physics for Scientists and Engineers 7 , page 753 , on the right hand side of the page:
> 
> 
> > Pitfall Prevention 27.2
> ...


Batteries do not supply a *net* number of electrons to the circuit. But electrons do leave one terminal and enter the other, though they are not the same electron. The electrons (or holes if you prefer) do move. I had to do those calculations in my undergrad Physics program.

My guess is that we are a whole lot closer to the same understanding about this than it appears. I think we have the same understanding on the following:


SOC or charge is not energy
There is an energy associated with any chemical reaction.
We seem to be looking at the "elephant" from different directions on:


I say a gallon of gas isn't energy but it is known how much energy it contains and you are saying it is energy.
I say an Ah isn't energy but if the voltage is known it can be determined how much energy it represents and you are saying that it doesn't correlate to energy.
I say a given chemical reaction involves a specific number of electrons and you are saying that it doesn't.
Are the two lists above correct?


----------



## IamIan (Mar 29, 2009)

Skipping some of the parts for the sake of brevity ... if you really want them individually addressed let me know.



GizmoEV said:


> My guess is that we are a whole lot closer to the same understanding about this than it appears. I think we have the same understanding on the following:
> 
> 
> SOC or charge is not energy
> ...


A Few corrections on the last items:

3rd Item:
What I was disagreeing with about the gallon of gasoline ... was that it seemed to me like you kept claiming that knowing how much of the chemical to react we had was not enough to know it's energy content any more than the energy content of 1Ah worth of electrons ... and it was that , that I was disagreeing with ... knowing the amount of a chemical for a given chemical reaction does exactly tell you how much energy content it has... unlike knowing how many Ah you have does not by itself tell you the energy content.

4th Item:
I was saying Ah alone does not correlate to energy ... if you change it so that Ah and volts together correlate to energy ... that is a completely different claim... and one I have no issue with.

5th Item:
Me and the physics book and other chemistry books say the chemical reaction of chemical bonds is a specific amount of energy ... a specific number of electrons is not a specific amount of energy ... somehow it seems to me like ... you look at this and conclude that you get fixed chemical energy results from any amount of energy you like as long as it is the same number of electrons ... Me and the text book disagree with that ... the chemical reaction has specific energy ... The Chemical reaction and chemical bonds are not any arbitrary amount of energy as long as the number of electrons is the same.

- - - - - - - 

Just an add on for Item #5 ... if this helps any... I feel like I'm being redundant.

In the text book example of the Na and Cl ... if an electron comes by that only has 0.5 eV of energy to offer ... it doesn't have enough energy for that chemical reaction.

If the claim that the number of electrons itself tells you the number of chemical reactions were true ... than the text book quote about the amount of eV of energy needed for the chemical reaction would have to be false ... because the text book claims a required amount of energy for that reaction.


----------



## GizmoEV (Nov 28, 2009)

IamIan said:


> 3rd Item:
> What I was disagreeing with about the gallon of gasoline ... was that it seemed to me like you kept claiming that knowing how much of the chemical to react we had was not enough to know it's energy content any more than the energy content of 1Ah worth of electrons ... and it was that , that I was disagreeing with ... knowing the amount of a chemical for a given chemical reaction does exactly tell you how much energy content it has... unlike knowing how many Ah you have does not by itself tell you the energy content.


What I said was that a gallon is not a measure of energy, it is a measure of volume. You need to know what is in that gallon to then be able to calculate the energy. Just like an Ah worth of electrons is not a measure of energy. You need to know the potential to be able to calculate the energy. That is why I said that an Ah and a gallon of fuel is analogous. With no more information than that you cannot know the energy involved but you CAN know how full the "tank" is if you know its capacity.



IamIan said:


> 4th Item:
> I was saying Ah alone does not correlate to energy ... if you change it so that Ah and volts together correlate to energy ... that is a completely different claim... and one I have no issue with.


I never said that an Ah was energy. What I did say was that to determine SOC of a LiFePO4 battery was that knowing the voltage was irrelevant. I even gave the reaction for charging a LiFePO4 cell showing that for each Li atom moved from one plate to the other that one electron was involved. That is why it is not necessary to know the voltage. That is why voltage is irrelevant in determining SOC, State of Charge, at no point did I claim that it was State of Energy. A LiFePO4 battery with 100 Li atoms available for charge transfer means that when one electron is pulled out of one side and an electron is shoved in the other side the the battery has changed SOC by 1%. The voltage doesn't matter even though all that is known is that the voltage was enough to move the one Li atom from one plate to the other.

Just like you said that a gallon equates to a known amount of energy, I said that an Ah equates to a known amount of energy for a given battery pack.



IamIan said:


> 5th Item:
> Me and the physics book and other chemistry books say the chemical reaction of chemical bonds is a specific amount of energy ... a specific number of electrons is not a specific amount of energy ... somehow it seems to me like ... you look at this and conclude that you get fixed chemical energy results from any amount of energy you like as long as it is the same number of electrons ... Me and the text book disagree with that ... the chemical reaction has specific energy ... The Chemical reaction and chemical bonds are not any arbitrary amount of energy as long as the number of electrons is the same.


Go back and look carefully over the context of my responses. I have been talking about State of *Charge*. That was the issue and that is what I was addressing. I pointed out issues with using energy to determine SOC and why it wasn't a very good way to do it. I never concluded or stated that the amount of energy was the same as long as the number of electrons was the same. I did say that for a given chemical reaction, such as LiFePO4 → Li+ + FePO4 + e-, that the number of electrons did stay fixed and that was why it is a better measure for determining State of Charge.



IamIan said:


> Just an add on for Item #5 ... if this helps any... I feel like I'm being redundant.


Same here.



IamIan said:


> In the text book example of the Na and Cl ... if an electron comes by that only has 0.5 eV of energy to offer ... it doesn't have enough energy for that chemical reaction.


This comes from a false assumption you made about what I was saying. I did not say that it takes any voltage, even no voltage, or that it varies. I said it is irrelevant in determining SOC change. Obviously if the voltage is not enough for the desired reaction to happen then the reaction won't happen. But in the case of a battery, if the voltage isn't enough then there will be no current flow anyway.

Remember I referred to the ZEVA fuel gauge? It has no knowledge of the voltage of the pack it is monitoring. The user calibrates it to full and then to the desired empty point. Once this has been done it will work regardless of the pack voltage. It could be calibrated to a single 100Ah cell, then any number of 100Ah cells cold be strung in series and that same gauge will be spot on for SOC of the battery pack even though the amount of energy transferred would be vastly different. That is what I have been saying all along.



IamIan said:


> If the claim that the number of electrons itself tells you the number of chemical reactions were true ... than the text book quote about the amount of eV of energy needed for the chemical reaction would have to be false ... because the text book claims a required amount of energy for that reaction.


Not at all. If the required amount of energy weren't there then the electron flow wouldn't happen either so none would be counted. Again you are reading into my statement that the voltage is irrelevant without looking at the context of that statement. The ZEVA gauge is a perfect example of where voltage is irrelevant because with out a potential difference no current would flow thus no reactions from which to count electrons.

The LiFePO4 pack in my Gizmo has been discharged at temperatures between -3°C to around 30°C. I can assure you that if I counted only Wh, when the pack was cold I would easily discharge my pack beyond my desired cutoff point. By counting Ah to determine SOC that problem is eliminated entirely.

While my Wh/mi remains relatively constant for a given set of road conditions my Ah/mi rate varies from around 2.5Ah/mi with a cold pack down to a little below 2Ah/mi with a warm one under similar road conditions. With a warm pack, >~18°C, 3.2V/cell is a good average voltage to use for energy calculations. As the pack temperature drops much below this the average voltage also drops so 3.2V/cell becomes a little optimistic. This was empirically determined with the pack starting at different temperatures.

An interesting result of the voltage under load being noticeably affected by pack temperature is that when I have left on a trip which takes about 1.5 hours. The pack can be ~5°C when I leave and when I get back the temperature has risen to around 20°C (case temp after stabilizing). These runs are usually done at about 50mph on the main road. The voltage under load will either climb or stay steady during the run as the batteries warm up.


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## IamIan (Mar 29, 2009)

@GizmoEV:

All references to SoC are irreverent to the 3 issues being discussed in #3 , #4, and #5.

We have already dealt with SoC previously ... Please stop beating the dead horse.

Reminder:
Issue #3: Is not about SoC.
#3 was about the difference between talking about __ Amount ( Gallons or Ah ) , of ___ Material ( Fuel A , or electrons ) ... and how that difference in material ( Fuel A or Electrons ) allows you to know more or less about the energy content of that amount ( Gallons or Ah ).

#4 was not about SoC.
It was about the difference between referring to energy and only using Ah ... or using Ah and Voltage together.

#5 was not about SoC.
Was about weather a specific amount of Ah always results in the same number of Lithium Ions ( chemical reactions ).

- - - - - - 

In reference to Issue #3:



GizmoEV said:


> What I said was that a gallon is not a measure of energy, it is a measure of volume. You need to know what is in that gallon to then be able to calculate the energy. Just like an Ah worth of electrons is not a measure of energy.


I'm sorry if I misunderstood you , or if I was not better describing the point I was trying to make.

I was not arguing that a gallon is not a measure of volume.

I was describing a scenario were we did know what was in that gallon ... __ amount ( gallons ) of __ Material (Fuel A) ... just like knowing __ amount (Ah) of __ Material ( Electrons ).

The Difference is that __ Amount of electrons that passed by still doesn't tell you the energy ... you're still stuck as Ah ... while knowing the ___ amount of a known Fuel A , does tell you the specific energy potential... be it Hydrogen, Oil, Coal, Sugar, etc.

- - - - - - - - 

In Reference to Issue #4:



GizmoEV said:


> > 4th Item:
> > I was saying Ah alone does not correlate to energy ... if you change it so that Ah and volts together correlate to energy ... that is a completely different claim... and one I have no issue with.
> 
> 
> You need to know the potential to be able to calculate the energy. That is why I said that an Ah and a gallon of fuel is analogous. With no more information than that you cannot know the energy involved but you CAN know how full the "tank" is if you know its capacity.


This #4 of mine is in reference to other comments of yours ( not about the Gallon issue which was #3 ) ... such as the following which do not include reference to voltage you made here.



GizmoEV said:


> So then you agree that Ah/mi is a useful term since it then relates to a distance traveled and relates to a quantity of energy for a given battery pack.


Ah can be a useful ... yes.
Relates to a distance traveled ? ... capacity to do work is by definition energy ... not just as Ah.
Relates to a Quantity of energy for a given battery pack ? ... not just as Ah.

As I wrote in my #4 correction ... if you want to change the claim as you have more recently to Ah and Voltage together ... that is a completely different claim ... one I have no issue with.

- - - - - - - - 

In Reference to Issue #5



GizmoEV said:


> What I did say was that to determine SOC of a LiFePO4 battery was that knowing the voltage was irrelevant. I even gave the reaction for charging a LiFePO4 cell showing that for each Li atom moved from one plate to the other that one electron was involved. That is why it is not necessary to know the voltage. That is why voltage is irrelevant in determining SOC, State of Charge, at no point did I claim that it was State of Energy. A LiFePO4 battery with 100 Li atoms available for charge transfer means that when one electron is pulled out of one side and an electron is shoved in the other side the the battery has changed SOC by 1%. The voltage doesn't matter even though all that is known is that the voltage was enough to move the one Li atom from one plate to the other.


Issue #5 Not about SoC

Your description here ... seems to assume that the energy of each 1 electron put in ... is always exactly = to the energy needed for the chemical reaction that releases 1 Lithium Ion ... as I wrote to tomofreno back when this particular issue started ... I don't see how to why.



GizmoEV said:


> Go back and look carefully over the context of my responses. I have been talking about State of *Charge*. That was the issue and that is what I was addressing. I pointed out issues with using energy to determine SOC and why it wasn't a very good way to do it.


Issue #5 Not about SoC



GizmoEV said:


> I never concluded or stated that the amount of energy was the same as long as the number of electrons was the same. I did say that for a given chemical reaction, such as LiFePO4 → Li+ + FePO4 + e-, that the number of electrons did stay fixed and that was why it is a better measure for determining State of Charge.


Issue #5 Not about SoC

I do not disagree that there is an electron involved in the chemical reaction ... what I have been describing is a different issue ... is that the number of Ah ( electrons ) , that go into the battery does not by itself specifically tell you exactly how many Lithium Ions ( chemical reactions ) there are.

As I have already posted ... it is well known that chemical reactions define a specific amount of energy ... input or output ... in order to form and or break the chemical bonds ... that's the way it works ... the Ah of electrons is not a specific amount of energy ... thus an unknown amount of energy can not act as a determinate to tell you how many chemical reactions ( each a specific amount of energy ) happen.



GizmoEV said:


> Obviously if the voltage is not enough for the desired reaction to happen then the reaction won't happen. But in the case of a battery, if the voltage isn't enough then there will be no current flow anyway.


This Voltage claim disagrees with the Ah determinate quantity of Lithium Ions being discussed... that Ah determinate claim is that __Ah always results in the same known quantity of Chemical Reactions ( Lithium Ions ).

Look again at the text book quote ... Energy is needed for the chemical reaction ... weather or not it happens is not determined just by voltage ... even with enough voltage to produce a flow of electrical current there may not be enough energy for the chemical reaction.

It is false to assume that you only get current flow when you have enough voltage on that current to produce the chemical reaction that produces more Lithium Ions ... to increase the SoC for example ... I can provide examples of it not being the case if you like.



GizmoEV said:


> Remember I referred to the ZEVA fuel gauge? It has no knowledge of the voltage of the pack it is monitoring. The user calibrates it to full and then to the desired empty point. Once this has been done it will work regardless of the pack voltage. It could be calibrated to a single 100Ah cell, then any number of 100Ah cells cold be strung in series and that same gauge will be spot on for SOC of the battery pack even though the amount of energy transferred would be vastly different. That is what I have been saying all along.


Issue #5 Not about SoC



GizmoEV said:


> IamIan said:
> 
> 
> > If the claim that the number of electrons itself tells you the number of chemical reactions were true ... than the text book quote about the amount of eV of energy needed for the chemical reaction would have to be false ... because the text book claims a required amount of energy for that reaction.
> ...


As long as the claim itself continues to specifically exclude volts ... Ah alone by themselves being the determinant ... than it is not reading into it at all to assume you are concluding volts are irrelevant ... that is part of the Ah determinate claim ... as far as I know that continues to be the claim ... that volts and energy are irrelevant ... the Ah alone always allow you to determine a specific quantity of Lithium Ions ( chemical reactions ) produced ... the energy of that Ah is irrelevant to the number of Lithium Ions ( chemical reactions ) as long as it is still the same quantity of Ah ... That is the claim I am disagreeing with.

It is false to assume that you can only get current flow when you have enough energy to produce the chemical reaction that produces more Lithium Ions ... to increase the SoC for example ... I can provide examples of it not being the case if you like.

- - - - - - - - 



GizmoEV said:


> The LiFePO4 pack in my Gizmo has been discharged at temperatures between -3°C to around 30°C. I can assure you that if I counted only Wh, when the pack was cold I would easily discharge my pack beyond my desired cutoff point. By counting Ah to determine SOC that problem is eliminated entirely.


You've made your personal preference for Ah very clear multiple times ... I don't care what your personal preference is ... use whatever you like.



GizmoEV said:


> While my Wh/mi remains relatively constant for a given set of road conditions my Ah/mi rate varies


Whatever you like , is your preference.

The Ah variation is one reason I dislike it ... but that's just me.

Another reason ... just my personal preference ... that I dislike it ... As I have mentioned before the reference to a potential to do some amount of work ... and using Ah to measure it ... I dislike that usage ... it implies that this thing being described ... potential to do work ( which is energy ) can be measured in Ah... or a rate of energy ( power ) can be measured in amps.


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## GizmoEV (Nov 28, 2009)

The context of every claim I made was with respect to determining SOC of a cell (more specifically the change of SOC of a cell), a LiFePO4 cell to be specific. Taking it in other directions outside of this and making assumptions which weren't valid will give apparently conflicting results. None of the references you made contradicted what I have said. They all agreed with what I said.

Like it or not, Ah counting is still the most accurate way to determine SOC change of a cell.


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## IamIan (Mar 29, 2009)

GizmoEV said:


> The context of every claim I made was with respect to determining SOC of a cell (more specifically the change of SOC of a cell), a LiFePO4 cell to be specific. Taking it in other directions outside of this and making assumptions which weren't valid will give apparently conflicting results. None of the references you made contradicted what I have said. They all agreed with what I said.
> 
> Like it or not, Ah counting is still the most accurate way to determine SOC change of a cell.


As I have repeatedly said many many times now ... I did not disagree with Major's post about the industry standard for SoC is Ah ... That specific issue has not been in disagreement for over 15 days and about 35 posts now.

I have not disliked it ... it is just SoC ... and Ah is the standard for it.

What I dislike ... and have described several times ... is when people describe something that is , by definition energy , then use Ah or SoC ( based on Ah ) to measure that capacity to do work ( energy )... that dislike is not about Ah being used for SoC.

The other discussions of other issues went in other directions away from SoC , some time ago... I'm sorry if you somehow misunderstood and thought this was still about Ah being used for SoC.


----------



## major (Apr 4, 2008)

A timely post elsewhere  



Elithion said:


> Yes and no. Depends on whether you're talking about charge efficiency (which is 100 % for Li-ion) or energy efficiency (which, naturally, is always less than 100 %).
> 
> How can that be?
> 
> ...


----------



## IamIan (Mar 29, 2009)

major said:


> A timely post elsewhere


Thanks.

That would seem to be the common conception ... based on how I read people describe it.

But ... 100% Charge Efficiency does not agree with what I have actually measured ... even in the unlikely event that all my readings were in the low part of the +/- range of the PL8 ... and my meter was also off by very nearly the same amount , so I wouldn't see it when I first tested the PL8's themselves... even in that seemingly unlikely event ... I would still be under 100% charge efficiency... high 90's yes ... but 100... no.

And even if the CV to 3.6V phase slightly over charged my cells ... which I will better know when I complete my various % of capacity levels cycle tests ... but ... 100% charge efficiency also does not agree with the measurements from the paper previously posted earlier in this thread ... which showed 99+% ... but not 100% ... on post #29.

Perhaps the 100% is just commonly used simplification for a more accurate statement like ... can be as high as just under 100% ... or in the high 90's ... etc.

- - - - - - 

As for the part about all the electrons piling up on one terminal ... not my personal preference ... written that way reads too much like someone describing the functionality of a capacitor ... which is not the main mechanism of the chemical reactions in the battery.... but that's just my preference.

- - - - - - - 

Although I suspect that from it's context ... and maybe I'm taking too much of a leap ... but it seems like the way it was described was more meant to be easily read and understood in that threads context ... than a 100% technically accurate description of what happens and how it happens.


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## Ziggythewiz (May 16, 2010)

IamIan said:


> But ... 100% Charge Efficiency does not agree with what I have actually measured
> 
> Perhaps the 100% is just commonly used simplification for a more accurate statement like ... can be as high as just under 100% ... or in the high 90's ... etc.
> 
> As for the part about all the electrons piling up on one terminal ... not my personal preference ... written that way reads too much like someone describing the functionality of a capacitor ... which is not the main mechanism of the chemical reactions in the battery.... but that's just my preference.


Yes, yes, and yes. Nothing's 100%. If it were there would be no mechanism for degradation.


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## major (Apr 4, 2008)

Ziggythewiz said:


> Nothing's 100%.


Are you 100% sure about that?


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## WarpedOne (Jun 26, 2009)

Heating is always 100% efficient...


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## Ziggythewiz (May 16, 2010)

WarpedOne said:


> Heating is always 100% efficient...


Unless noise, light, or anything else is produced.


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## WarpedOne (Jun 26, 2009)

Nope - sooner or later noise, light and everything else turns into heat.


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## Ziggythewiz (May 16, 2010)

Well, if you want to essentially define energy as heat, then yes, everything is heat, but for heating to be 100% efficient 100% of that heat has to go to the target. If any is flowing (including as light or sound) through walls, windows, or a contact surface it's not going where you want it.


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## WarpedOne (Jun 26, 2009)

Sure.
But in priciple, heating is 100% efficient where everything else in principle cannot be.


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## major (Apr 4, 2008)

Let’s get back on topic. 
Imagine a tiny battery. It has only one Lithium ion. I put in one electron. Fully charged. I take one electron out. Discharged. 100% charge efficiency. Not 100% energy efficiency. I would have had to put more work into the battery to charge it than the work I was able to do by discharging it. But the charge or Coulombic efficiency was 100%.
Now scale that up to 100 Li-ions, or 1,000,000 or whatever. Same principle applies. Now yes, maybe there are some alternate paths, or self-discharge, or leakage, or side reactions. But in a good Lithium cell these are very small. Look at Dr. Lu’s graph.


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## IamIan (Mar 29, 2009)

major said:


> Imagine a tiny battery. It has only one Lithium ion. I put in one electron. Fully charged. I take one electron out. Discharged.


The only thing I'd add to that as a clarification ... for my own personal preference or 2 bits ... generally speaking.

When you put 1 electron into the battery you also loose 1 electron ... and when you pull 1 electron out you also get 1 electron in ... the amps of electrical current flow are generally the same magnitude on both anode and cathode ... the electrical circuit is complete ... one is a flow of electrons in a direction toward the battery the other is a flow of electrons in a direction away from the battery.

Of course there can be minor exceptions for a variety of reasons and mechanisms ... but the majority of the chemical reactions do not result in any significant change in the net total amount of electrons in the battery ... charged or discharged.

Like I said ... just my own 2 bits / personal preference on how I would add a bit more to it... Hopefully to prevent a misconception.

- - - - - 

But ... I do agree... there is good evidence that the side reactions are minor influences and a good cell should have a very high charge cycle efficiency.


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## IamIan (Mar 29, 2009)

After the Initial Cell testing I did for the intent of being able to match up the best team of cells ... I moved on to some other cell testing... which was part of the reason I got the cells , to do the experiments and get more data... the testing / data is interesting / fun for me ... and it might prove to be informative / useful for the PHEV project as well.

One aspect that seemed interesting to me ... is the minimum sustained / trickle current rate for the cells.

There are some people who insist that LiFePO4 cells can not sustain a slow trickle charge rate ... but I see a problem with those claims ... the cells do have a self discharge rate.

The issue with it is that when the OEM A123 tells you that the cells have a known self discharge rate ... about ~3% in 1 year @ 25 degrees C ... up to about ~8% @ 40 degrees C in 1 year... that comes down to a sustained trickle rate in order to counter that effect... ~8% of 20Ah is ~1.6Ah per year ... or ~133mAh per Month ... or ~4mAh per day ... or a sustained trickle rate of around ~180uA .... the ~3% self discharge rate would be a sustained trickle rate of around ~67uA.

That is a extremely slow trickle / sustained rate ... so it does make sense why people would think it was nearly zero ... and fairly useless in any practical sense ... even the higher ~180uA would take about ~230 days just to flow ~1 Ah of charge through the cell.

But when looking at the OEM Self Discharge rate guide there is a curve to it ... ie the self discharge rate is faster in month 1 then it is in month 6 ...month 6 is faster than month 12 ... etc ... where things like the ~3% to ~8% are the cumulative loss over the entire 12 months.... that curve to the rate may eventually flatten into a straight line ... but at least in the beginning there is a curve to the self discharge rate.

And this lines up with the Self Discharge rate testing I did for my 55 cells.... for example ... one specific cell over the 1st 2 months had an average self discharge of ~37.87 mWh per day ... but the same cell over a 12 month period had an average self discharge rate of only ~9.8 mWh per day.

So I was curious about how high the self discharge rate would go as someone gets closer and closer to no rest period after charging.... ie a sustained trickle charge.

I also figured I would check / try and quantify the change ... if any ... at different SoC / SoE / Cell Voltages... I suspected the higher SoE would have a higher self discharge rate... maybe even get up to 1mA... even though 1mA ie C/20,000 , is still fairly useless in any practical sense.

- - - - - - - 

So I started testing.

At first it seemed to be going as expected ... CV to 1mA was getting longer and longer ... the curve of the amps seemed to continue to suggest that there was a sustained trickle charge point out there ... it seemed like I just had to go to a higher SoE / terminal voltage to get it up to at least 1mA... then the data was a bit odd ... and not as expected.

CV 3.0v 2A to to 25mA took ~16 Minutes ... went bellow 1mA Graph
CV 3.1v 2A to to 25mA took ~28 Minutes ... went bellow 1mAGraph
CV 3.2v 2A to to 25mA took ~45 Minutes ... went bellow 1mAGraph
CV 3.3v 2A to to 25mA took ~7Hours ... went bellow 1mAGraph
CV 3.31v 2A to to 25mA took ~14 Hours ... went bellow 1mA Graph
CV 3.32v 2A to to 25mA took ~47 Hours ... went bellow 1mA Graph
CV 3.33v 2A to to 25mA took ~24 Hours ... went bellow 1mA Graph
CV 3.34v 2A to to 25mA Took ~18 Hours ... went bellow 1mA Graph
CV 3.35v 2A to 25mA took ~27Hours ... went bellow 1mA Graph
CV 3.36v 2A to 25mA took ~50 Hours ... went bellow 1mA Graph
CV 3.37v 2A to 25mA took ~24 hours ... went bellow 1mA Graph
CV 3.38v 2A to 25mA took ~19 Hours ... went bellow 1mA Graph
CV 3.39v 2A to 25mA took ~23 Hours ... went bellow 1mA Graph
CV 3.40v 2A to 25mA took ~16 Hours ... went bellow 1mA Graph
CV 3.41v 2A to 25mA took ~15 Hours ... went bellow 1mA Graph
CV 3.42v 2A to 25mA took ~11Hours ... went bellow 1mA Graph
CV 3.43v 2A to 25mA took ~8 Hours ... went bellow 1mA Graph

Note:
The Time listed is just for the CV phase of charging.

At this 3.43v point the discharge was showing I was near the top of the cell SoE / SoC ... not wanting to risk over charge the cell quiet yet ... at least until I do other testing ... I plan to eventually come back to continue the CV series up to higher voltages ... still I am confidant in saying that it does seem that any potential for a sustainable trickle charge ... is well bellow 1mA ... even on a cell charged nearly to top SoE / SoC.

I was not initially expecting the bumps ... or for the CV time to go up and down as it did .... interesting... something else to look into.

Eventually after other testing ... I might try another round of testing by putting all 55 of the cells together in parallel ... in order to try and use that way to amplify the sustainable trickle charge rate ... at least for detection / verification ... that method might allow me to go down to around ~18uA per cell with still having a fairly good amount of precision ... but considering how low that is ... I don't see it being of any use in application... that would just be out of curiosity ... as any rate this slow is even more useless than C/20,000 is.

- - - - - - 

The only other thing of mini-note is kind of what was already known ... the lower end current at a end CV voltage point ... the less from that voltage the cell will settle ... meaning ... by going down to 1mA in the CV phase ... the rested terminal voltage did not drop as much as it does when I normally go down to ~500mA ~C/40 as a termination current for the CV... like I said , a mini-note kind of already known / expected.


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## PStechPaul (May 1, 2012)

I think it is interesting, and perhaps significant, that CV above about 3.33 volts causes the "bump" in the curve where current remains about the same for a while and then continues a logarithmic reduction to a very low level. It seems that the LiFePO4 has a characteristic voltage that is just about 3.33V and higher voltage may result from some other effect such as capacitance. Another effect may be self-heating which changes this voltage level, and it may take some time for the temperature to stabilize at various areas of the cell. And something else to consider is noise or instability of the charging source, which may be such that the cell draws current in a non-linear manner which could skew the I/E relationship.

Bottom line, though, seems to indicate that there is no need for a float charge because the capacity is only reduced 5% to 12% over 2 years.


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## IamIan (Mar 29, 2009)

PStechPaul said:


> Another effect may be self-heating which changes this voltage level, and it may take some time for the temperature to stabilize at various areas of the cell.


I would have suspected self heating to be a very minor influence at a 2A charge rate... but yeah ... that could be involved in the bump.



PStechPaul said:


> And something else to consider is noise or instability of the charging source, which may be such that the cell draws current in a non-linear manner which could skew the I/E relationship.


Source was stable to +/-1mA and +/-1mV.
I would have thought that would be fairly stable ... but yeah ... an instability could also be involved in the bump.



PStechPaul said:


> Bottom line, though, seems to indicate that there is no need for a float charge because the capacity is only reduced 5% to 12% over 2 years.


Agreed.

Even if one wanted to do it , the 'safe' levels to do it at ... are very low ... at this point I suspect down bellow ~200uA.


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## GerhardRP (Nov 17, 2009)

The changes you see are consistent with the discharge curve here: http://www.diyelectriccar.com/forums/showthread.php/zakpak-calb-ca-a123-cell-group-76578.html . 70% of the capacity charges at 3.27V while the other 30% charges at 3.35V. Capacity data from your graphs. I am thinking that there are two regions in the battery with very slightly different crystal structures.


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## IamIan (Mar 29, 2009)

IamIan said:


> Eventually after other testing ... I might try another round of testing by putting all 55 of the cells together in parallel ... in order to try and use that way to amplify the sustainable trickle charge rate ... at least for detection / verification.


I finished going through this ... for my lot .. with 50 cells in parallel ... I was still not able to see a sustainable 'trickle charge' rate that would be any higher than what one expects to see just from the very small Self Discharge rate (A123 graph that shown previously).

Although not practical (at all) ... this does show at least in theory a trickle charge method could be used to charge or even balance correct a multi-cell pack ... it is also possibly one mechanism that allow a series of these cells to 'self correct'.

Concept Example:
At temperatures that give 2% self discharge per year ... that would mean one cell at 15Ah charged is loosing charge at roughly ~34uA rate ... and another cell also at 2% self discharge per year temperatures ... but currently at 16Ah charged is loosing charge at roughly ~36uA rate... Thus a extremely weak (decaying) self correcting (and balancing) mechanism... it would take 1 whole year at this rate to 'balance' or 'correct' ... a small difference of less than ~8mAh out of the 1Ah difference between the 15Ah and 16Ah cells in the above example... making it of course completely insignificant and impractical.

Caveat:
Unfortunately for the (impractical) example above ... it also assumes equal self discharge rates among all the cells at a given temperature ... and in all likely hood real world cells will likely vary slightly ... which would complicate the above even more than the impractical-ness it already was.

- - - - - - - - - - -

There are also a few other minorly interesting things (to me anyway) I found ... from the last of my planned tests ... both related to the Peukert like effects (during CC phase).

#1> 
When a CV phase is included (top or bottom) I was not able to detect any significant amount of total difference (Ah or Wh) at different Amp rates ... all it seemed to do was shift the Ah or Wh point of the transition from CC to CV ... the sooner the CV phase stared the longer it took... either charge or discharge.

#2> 
As expected , it did change the Ah/Wh transition point from CC to CV ... a Smaller % SoC/SoE on input ... and a larger remaining % SoC/SoE on output... but the effect was pretty small .. changing discharge rate from 10A to 75A only moved the the SoC/SoE a bit less than ~10% ... doing the same 10A to 75A on charge SoC/SoE only moved a bit less than ~5%.

#3> It was interesting to see how very closely the SoE and SoC % changes mirrored each other in either charge or discharge at the different rates ... Although the SoE was consistently a tiny bit higher the difference was in the insignificant (instrumentation limits) range.

#4> The Peukert like effect only presented in the direction of the increased rate ... but I was not able to detect any significant change in the other half of the cycle that did not have a increased rate ... Soo a 10A to 75A rate change on charge has the above kinds of effects on the CC to CV point during charge ... but no significant effect was found on the discharge side of that cycle that didn't change in rate ... and the opposite as well ... if the discharge goes from 10A to 75A it sees the above effects on the discharge part of the cycle .... but no significant effects were detected on the charge side of that cycle that didn't change in rate.

#5> I've been satisfied with how well they stood up to rates (100A+) both charge and discharge sides of the cycle ... and even to both sides in the same cycle... giving me a satisfactory buffer (~30%) beyond what I will be asking the cells to do in their eventual application usage the vast majority of the time (greater than 3 standard deviations).


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## IamIan (Mar 29, 2009)

GerhardRP said:


> I am also in favor of over-analysis, so can you share the raw data spreadsheet for others [me] to play with?
> Gerhard


Better late than never?

32MB Zip File Link ... is about as small as I was able to get the raw data files ... it is too much data for a single spread sheet file (more than limited number of columns and rows)... The zip file contains the raw data as txt files ... and I also included basic pic of the test setup and copies of the pdf manuals of the testing instrumentation used and the basic A123-20Ah pdf.

Although I'm satisfied with what I got for results from the testing if anyone else wants to use the raw data for their own analysis feel free.


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## IamIan (Mar 29, 2009)

Here is some other (I found interesting) results... I don't think I posted these yet here.

I did partial charging followed by discharging... so the bellow graphs are for that much of a cycle ... Not necessarily the efficiency at that specific point itself .. be it SoC or SoE.

And I posted it elsewhere on the forums .. but I figured I would tac it on here as well .. a graph showing the change in internal resistance (and type) at different temperatures , and SoC. That was done by the bellow.
From:
LiFePO4battery performances testing and analyzing for BMS
By:
Dr. Languang Lu
At:
Department of Automotive Engineering,
Tsinghua University


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