Capacity Mapping (Optimal Charge-Discharge Voltages)

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DrkAngel
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Capacity Mapping (Optimal Charge-Discharge Voltages)

Post by DrkAngel » Sat Oct 05, 2013 8:48 am

Moved from Homemade Battery Packs

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Tests
Dell Media Bay LiPo (unbranded)
Samsung ICR18650-22p
Samsung INR18650-R25
Samsung INR18650-29E
Sanyo 18650F
Sanyo 2600mAh (red)
SONY US18650VTC4
Sony Laptop Media Bay LiPo
Thunder Power Extreme 5000mAh
WinForce 5700mAh "20C" RC Lipo
Winners Circle RC Lipo 2000mAh


Lithium Cobalt - Laptop recycled cells

There is some debate and much confusion about optimal charge voltages.
Reputedly, restricting working voltages can greatly prolong-maintain lifespan-capacity.
I have noticed excessive losses in capacity due to .... abuse?

Possible abuses are:
Excessive discharge rates
Excessive charge rates
Excessive charge voltage
Excessive DOD (Depth Of Discharge)

All are potentially damaging!
As with most everything, heat is the enemy!
Lithium is a fairly unique battery technology, at moderate rates, heat production is nearly non-existent.
Anything that produces heat creates "damage"! (Pushes cell beyond "optimal")

As for charge-discharge rates.
I try to limit charges and discharges below .5C, 15Amps from a 30Ah pack.
One thing I noticed is that this .5C should be from the actual present capacity, rather than the original. When the capacity of my 26Ah recycled Laptop Lipo build dropped below 18Ah, I noticed the pack getting warm when charging at 10A. Likewise, standard output, with the diminished capacity, began producing noticeable heat.
Once heat begins being produced during normal use, damage is progressive and accelerated.

Prolonging good capacity is doubly important.
I have decided to test optimal charge and discharge voltages.

As determined by these previously built capacity maps, (See - Capacity Map - By Charge mAh) 3.72V appears to be maximum DOD for the Sanyo 18650's and 3.78V for the Lipo.

These DOD voltages are for a resting voltage, discharge voltages are much lower due to voltage sag.
With cells at max DOD, apply normal throttle discharge.
This will exhibit the max DOD "working voltage".

Sanyo 18650 labeled 3.6V 2600mAh
Lipo labeled 3.7V (2x2160mAh)

Image

Final factor is optimal charge voltage. Finding the capacity-lifespan saved by lowering charge voltage.
Normally this might take 2 or more identical packs and many months of actual use, to get any measurable results.
To speed up the process I decided to test 3 sets of identical cells at 3 differing charge voltages.
Based on the capacity maps, I decided to use 4.15V, 4.10V and 4.05V.

Tests will be run concurrently with 18650 2600mAh Sanyo and Dell recycled 2160mAh Lipo.
Discharge will be .5C for 1 hour.
Recharge will be with 3 voltage adjusted power supplies.
18650's will be charging while Lipo discharges and vice versa.

All cells will be capacity tested matched and recorded.
I intend on running several cycles per day, 25? per week per each cell, on the side, while I work.
Noticeable results after 50 cycles?
1 hour resultant discharge voltages will be charted for each cycle.
Capacity test will be performed every 50? cycles, and results posted.

Too much work?
Once determined, optimal voltage might double the lifespan of the pack.
Sanyo cells are among the most commonly available and results should be valid and applicable for a multitude of builds.
More importantly, for me, the lipo results will apply nicely to the hundreds of 6 packs I've acquired.
Knowledgeable performance optimization and expectations from many packs, for many years, sounds worth the initial bother.
I do hope others are capable of benefiting also.

Based on capacity map ... ensuring that bulges of capacity are included:
2160mAh Lipo optimal charge voltage is expected to be 4.15V.
2600mAh 18650 Sayno optimal charge voltage is expected to be 4.05V.
This compares reasonably with the iMax charge voltages of 4.2V for "Lipo" and 4.1V for "Li-ion".
Hopefully this might explain the recent rapid deterioration in a Sanyo 18650 build that I have been charging to 4.20V.

Perhaps most enlightening will be the differing results from the Lipo cells at 4.05V and 4.15V.
This voltage difference excludes - includes a substantial bulge of energy capacity!

Preliminary results will be posted as soon as there are any noticeable variations.

Note:
Very likely, DOD is as important, or more important, than charge voltage!
But charge is every cycle, while deep discharge is seldom, or hopefully, never.
Last edited by DrkAngel on Sun May 21, 2017 11:25 pm, edited 8 times in total.
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There, shallow draughts intoxicate the brain,
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Re: Determining Optimal Charge Voltage

Post by DrkAngel » Sat Oct 05, 2013 8:49 am

DrkAngel wrote:Lithium Cobalt - Laptop recycled cells

Final factor is optimal charge voltage. Finding the capacity-lifespan saved by lowering charge voltage.
Normally this might take 2 or more identical packs and many months of actual use, to get any measurable results.
To speed up the process I decided to test 3 sets of identical cells at 3 differing charge voltages.
Based on the capacity maps, I decided to use 4.15V, 4.10V and 4.05V.

Tests will be run concurrently with 18650 2600mAh Sanyo and Dell recycled 2160mAh Lipo.
Discharge will be .5C for 1 hour.
Recharge will be with 3 voltage adjusted power supplies.
18650's will be charging while Lipo discharges and vice versa.

All cells will be capacity tested matched and recorded.
I intend on running several cycles per day, 25? per week per each cell, on the side, while I work.
Noticeable results after 50 cycles?
1 hour resultant discharge voltages will be charted for each cycle.
Capacity test will be performed every 50? cycles, and results posted.
Still refining method.
Step 1

Verify 3 pairs of cells of same age batch and capacity (mAh)
Step 2
Charge pairs to 4.05V, 4.10V and 4.15V then attach in series.
Step 3
1 hour ~.5C Discharge - 18650's (5200mAh) with 2.50A 12V fan
1 hour ~.5C Discharge - Lipo (4320mAh) with 2.10A 12V ? (AC inverter with 25w? fan - will determine proper drain with digital A meter)
Step 4
Recharge with MeanWell set to 12.30V
Initially, all cells will recharge to original voltages, (4.05, 4.10, 4.15V), variance in bulk recharge will indicate cell deterioration!
When noticeable variance occurs, cells will be "trimmed" to original voltages, at staged intervals.
Step 5
At 25-50 cycle intervals, mAh for each pair will be retested.
From 3.72V for the 18650 and from 3.78 for the Lipo, to 4.05V for each pair, individually tested.
This will be the deterioration comparison.
Then additional charge for 4.10V and 4.15V pairs will be noted.

After enough cycles, the full charge capacity of the 4.15V cells is expected to decrease below the full charge capacity of the 4.05V.
Rate of deterioration from each voltage should allow accurate approximation of useable lifespan!

This is expected to be a long term project ...
But with an electric shut off timer and CV (constant Voltage) charger, can be run unattended and repeated cycles run as a side project with minimal attention or interruption of other projects.

I would invite others to run the same test with their cells (brand) of choice.
RC Lipo is popular, and might differ greatly from my test cells.
Due to it's chemistry and charge methodology LiFePO4 types are unlikely to provide ... usable results - These test are tailored for Lithium Cobalt cells.
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Determining Optimal Charge Voltage

Post by dnmun » Sat Oct 05, 2013 9:25 am

have you done any research on battery chemistry and the documented information available on charging lifepo4 and lipo? i cannot follow what you are trying to do or the graph that you presented.

what information do you seek to discover and how does your experimental procedure allow you to gain access to that information? how will you analyze it? has your testing already been done and is now part of the available literature?

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Re: Determining Optimal Charge Voltage

Post by dogman dan » Sat Oct 05, 2013 12:18 pm

I was feeling stupid there for a moment, looking at that graph.

If I follow it right, you are going to use the same discharge rate, but look at discharged voltage dropping over time to determine which of the three top of charge voltages works best.

Makes sense to me. Why charge to only 4.1v if 4.15 v is just as effective. I have been using 4.1v a lot with my new lico from HK. Mostly I'm doing that because it's somewhat safer to charge to 4.1v if I will be bareback bulk charging. If I plan on an extra long ride, I charge it to 4.2v, but manually watch it do the last half hour with a cellog.

Charging and storing at 4.2v with the last set of lico, I still got 2 years of good use, and one more of low capacity use. The big drop in capacity happened after 2 years, despite a lot of storage at 4.2v per cell. 2 years not so bad for such cheap lico IMO.

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Re: Determining Optimal Charge Voltage

Post by DrkAngel » Sat Oct 05, 2013 12:30 pm

dnmun wrote:have you done any research on battery chemistry and the documented information available on charging lifepo4 and lipo? i cannot follow what you are trying to do or the graph that you presented.

what information do you seek to discover and how does your experimental procedure allow you to gain access to that information? how will you analyze it? has your testing already been done and is now part of the available literature?
Project is for determining the optimal charge voltage for Lithium Cobalt laptop recycled cells, 18650's and Lipo.

Graph is a charge capacity map of Sanyo 18650 cells and unknown (Dell) Lipo cells.
It clearly indicates maximum DOD, and demonstrates potential optimal charge values.

As clearly stated(?) the object of the test is to determine the degree of degradation to LiCo cells by charging to various voltages. Real world application is to use optimal charge voltage so as to prolong or extend usable life.
Immediate question is - I fear I am capacity damaging Sanyo 18650 cells by charging to 4.20V and how much can this capacity damage be reduced by charging to 4.15V, 4.10V, 4.05V?
A little learning is a dangerous thing;
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There, shallow draughts intoxicate the brain,
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Re: Determining Optimal Charge Voltage

Post by dnmun » Sat Oct 05, 2013 1:09 pm

how can it damage capacity to charge to full voltage?

by charging to 4.1V then you are just charging it up to 90% charged.

cell damage is on excessive discharge rates or leaving it fully charged from my understanding.

i wondered if you had found anything in the literature when you did your research. that was why i asked.

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Re: Determining Optimal Charge Voltage

Post by DrkAngel » Sat Oct 05, 2013 2:21 pm

dnmun wrote:how can it damage capacity to charge to full voltage?

by charging to 4.1V then you are just charging it up to 90% charged.

cell damage is on excessive discharge rates or leaving it fully charged from my understanding.

i wondered if you had found anything in the literature when you did your research. that was why i asked.
It is a common assertion that using 80% of capacity will double cycle life.

Most laptops charge to near 4.10V as opposed to 4.20V ... as a life extending measure?

As demonstrated in the graph, charging the Lipo beyond 4.15V increases capacity a negligible amount.
The Sanyo 18650's has it's last bulge of capacity below 4.05V.
Any reduction in charge voltage increases battery life.
I am merely attempting to ascertain the optimal voltage for the cells I use.

Battery University Chart.
'How to Prolong Lithium-based Batteries - Battery University' - batteryuniversity_com_learn_article_how_to_prolong_lithium_based_batteries.jpg
'How to Prolong Lithium-based Batteries - Battery University' - batteryuniversity_com_learn_article_how_to_prolong_lithium_based_batteries.jpg (48.98 KiB) Viewed 10649 times
I would gladly sacrifice 10-15%+ initial capacity to prolong usability to 200-300%.

Additional Battery University Graph
lithium2.jpg
lithium2.jpg (27.25 KiB) Viewed 10649 times
So, after I determined how much capacity was added by increasing charge voltage it appears ...
My Lipo can increase lifespan to 150% by a .05V reduction in charge where negligible additional capacity is stored, or to 300% but losing a substantial bulge, maybe 25%+, of capacity, by charging to 4.05.
Sanyo 18650's, more clearly, can prolong life 300% (3x) by charging only to 4.05V, after the last substantial capacity bulge.

Image

Now this is embarrassing!
I'm afraid that this further investigation has rendered my test ... unnecessary?

4.05V for my Sanyo 18650's! 3x expected lifespan!
4.03V for my recycled LiPo! 3x+ expected lifespan! Or 4.125V @ 1.5x lifespan for trips etc.
\
See - Battery University.com How to Prolong Lithium-based Batteries
Last edited by DrkAngel on Sat Dec 26, 2015 7:20 am, edited 2 times in total.
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Determining Optimal Charge Voltage

Post by Jolly Jumper » Sat Oct 05, 2013 5:31 pm

Thanks good info.
Recently i have read that NeilP got from his now decomposed Turnigy nano pack only ~8000miles 13000km. when he now charge to 4.08-4.09 ~85% he could double that with his new buyed pack!

I guess this is 1:1 applicable for all lithium chemistry batteries.
So we can conclude Lithium batteries like it in the middle of there capacity. my calculator is telling me its better to buy 5Ah more and use the pack from 20% to 85% of ther capacity. this should more than double the cycles than use 15% to 95% with 5Ah fewer in pack. :mrgreen:

Storing not used cells @40% in cold <0°C is too something i must remember.

This should go into the ES WIKI

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Re: Determining Optimal Charge Voltage

Post by wb9k » Sat Oct 05, 2013 6:35 pm

Good lesson at the middle of all this. An A123 pack that is never taken above 80% SOC will absolutely live longer than one that is taken to 100% SOC every time. It would appear this is true for many, if not all Li chemistries. It's a compelling reason to overbuild the pack a bit in a large EV where changing out the battery is a major undertaking. In a bike, one would have to weigh the performance penalties (which are probably more severe in a bike than in a car) against the long term cost benefits of one approach vs the other and decide for themselves.

The implications are more significant for HEV's than for PHEV's. An HEV that can be set to have a target SOC well below 50% will enjoy a very long life if the rest of the design is robust.
dh
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Re: Determining Optimal Charge Voltage

Post by DrkAngel » Sat Oct 05, 2013 7:40 pm

As demonstrated by this graph, an initial loss in usable capacity by lowering charge voltage is offset by the continued sustainability of capacity from the lower voltage charged cells. With the bonus of many more cycles.
Of course, I am recommending voltages below 4.2V only, but the graph does demonstrate a similar increase in usable cycles as related to lower charge voltages.

Image
Also of interest is that the graph demonstrates a difference in capacity between various voltages.
The capacity increase between 4.20V and 4.25V is noticeable.
Most impressive is the minimal capacity increase from charging between 4.25V and 4.30v, but the increase in damage is spectacular!
But again, the capacity increase from 4.30V to 4.35V is greater.

Just a further justification for Capacity Mapping ... within usable voltages.
A little learning is a dangerous thing;
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Re: Determining Optimal Charge Voltage

Post by dnmun » Sat Oct 05, 2013 7:46 pm

so why do laptop lipo packs get charged to 4.2V all the time? are they just not informed like you are?

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Re: Determining Optimal Charge Voltage

Post by DrkAngel » Sat Oct 05, 2013 8:01 pm

dnmun wrote:so why do laptop lipo packs get charged to 4.2V all the time? are they just not informed like you are?
Maybe they want you to have to buy new batteries twice as often?

Maybe they want to give you best initial performance ... a quickly deteriorating battery is a good reason to buy next years model?

All the dozens of Dell laptop Lipo I open up after charging are charged to ~4.08V, similar with HP, Dell and Gateway 18650 packs I build from. I've never found any laptop charged cell at 4.2V ... except from a bad pack with other cells below 4.0V.
Last edited by DrkAngel on Fri Oct 11, 2013 8:17 am, edited 1 time in total.
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Re: Determining Optimal Charge Voltage

Post by dnmun » Sat Oct 05, 2013 8:14 pm

well see that is a problem for me right away since every laptop cell i have pulled from a dell pack or the other laptop packs was charged to 4.2V so i don't know how one you have is somehow different from mine. so now you are gonna say mine were overcharged.

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Re: Determining Optimal Charge Voltage

Post by DrkAngel » Sat Oct 05, 2013 10:12 pm

More increased capacity-lifespan due to reduced charge voltage.
Proper Care Extends Li-Ion Battery Life
V Cycles_1.jpg
V Cycles_1.jpg (47.59 KiB) Viewed 10473 times
V Cycles_2.jpg
V Cycles_2.jpg (47.07 KiB) Viewed 10473 times
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Determining Optimal Charge Voltage

Post by wb9k » Sun Oct 06, 2013 8:46 am

Not sure what the argument is about. 4.2 works without immediately noticeable detrimental effects, but it does shorten lifespan. In consumer electronics, designers quite often opt for better performance out of the box in the form of longer runtimes, but this comes at the expense of battery longevity--hardly a heartbreak for the manufacturer who is happy to sell you another one that will perform great for a little while. Fig 3 above tells the story quite succinctly.
dh
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Re: Determining Optimal Charge Voltage

Post by DrkAngel » Sun Oct 06, 2013 10:07 am

Some of the advantages of recycled laptop cells include:
Up to double the energy density of LiFePO4, and variants = 1/2 the weight and size for the same capacity
Low, low cost

This allows the building of comparatively massive capacity packs.
My next build will shoehorn 9s12p 2600mAh 18650 Sanyo cells into an eZip oem "RMB" battery case.
That is 33.3V 31.2Ah, (1038.96Wh or 1kWh+), replacing 24V 10Ah SLA (240Wh x 50% efficiency = 120Wh)
That is an 866% capacity increase ... with a ~40% weight savings
4 hour (.25C) run time with better performance than the oem at 1/2 hour (1C)!
Now am I willing to sacrifice some of that extra capacity to extend pack life?
You Betcha!

As indicated by the red line on the graph below, the last capacity bulge ends at 4.05V.
If I charge to 4.05V instead of 4.20V the cells will lose 900mAh of capacity or 18% of it's usable capacity.
However, according to the previous charts and graphs this will increase lifespan to 300%!
Instead of daily cycles for 1 year, pack should provide 3 years of daily cycles.
Capacity loss would be for the 1st 3 months ... after that the lower charged version would maintain a higher capacity!

Image
More difficult to justify are the recycled laptop Lipo, represented by the blue line.
I build 7s12p 25.9V 25.92Ah eZip rebuilds.
Charging to 4.15V instead of 4.20V sacrifices 300mAh.
An 7% loss in capacity for a ~150% resultant lifespan ... the best bargain by far!
But not happy ... I would really appreciate a much larger lifespan increase.
Problem is, just below 4.15V there is an substantial and unexpected bulge of capacity.
Nearly an 1100mAh, 21% additional sacrifice by charging to the next lower optimal capacity point - 4.02V.
A 21% capacity loss, to increase lifespan from 150% to 300% is no where near as efficient as available from the Sanyo 18650's.

18650 = 300% increase from 18% initial capacity loss. vs Lipo = 200% increase from 21% additional capacity loss.

Of course it looks better if total is figured from the initial 4.20V!
A 300%+ usable lifespan from a 28% initial capacity loss.
My 1st Lipo build using these recycled laptop has performed excellently for the past 3 years - 6000+ miles.
Initially, for 2 years, I charged to 4.20V.
Then due to discharge mapping results I began charging to 4.10V.
My more recent capacity maps, derived from mAh per .02V of charge (shown above) indicate 4.15V or 4.02V as optimal.
The choice represents as ~24 initial Ah with a 2 year service life or ~18 initial Ah for a 4 year service life.
Daily use "needs" should probably determine the choice?

Oh!
Amazingly, and contrary to many "experts" the Lipo I use, recycled from Dell "secondary bay" battery packs still show excellent measured capacity.
A recent 4320mAh pack measured better than 90% of rated capacity, with all cells equalized within 2/100th V at max DOD.
My point?
Sorry ... cells were date stamped 2004 ... 9 years old and still in excellent condition!!!
Most "experts" insist that age greatly damages capacity-lifespan.
Last edited by DrkAngel on Fri Oct 11, 2013 8:22 am, edited 2 times in total.
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Determining Optimal Charge Voltage

Post by wb9k » Sun Oct 06, 2013 3:23 pm

DA, this is an interesting concept you have running here with the "capacity mapping". Perhaps you have data to do this already, but if you want to really be convincing, perform your tests at a wide range of C rates (simulated drive cycles would be even better yet) and ambient temperatures to demonstrate that the patterns don't change when the real world doesn't line up so pretty with your test. It may make a great deal of difference in the patterns that emerge.

Other things to consider:

These are recycled cells, presumably all exposed to similar conditions and purchased as a lot (please correct me if I'm wrong). Patterns in the charge curves can be imposed by the life a repurposed cell had before you got it. With used batteries, knowing exactly what you've got sitting before you is everything. What is the average SOH across them, did they see hard use before, have they ever been exposed to any kind of abuse? One can certainly not take for granted that every used Lico they may encounter has double the energy density of a brand new LiFePO4 cell. You have to test the cells at hand to know that kind of thing. Where I'm going here is that in addition to testing under various conditions, you should test cells at widely ranging states of health and ages to the maximum extent possible. Include some brand new cells if you can get them.

Finally, while there are advantages to metal oxide chemistries over LiFePO4, let's not gloss over the very real safety disadvantages of metal oxide cells. They're not for the unvigilant.
dh
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2008 Prius with Hymotion L5 PCM
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Under construction: 2008 Miles ZX40ST truck with altered DC drivetrain
Departed: 2002 VW Jetta TDI which was run for a time partly on WVO.
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"You can tell I'm a troublemaker, because I plug in my car."

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Re: Determining Optimal Charge Voltage

Post by DrkAngel » Sun Oct 06, 2013 4:29 pm

You seem to be asking for a discharge profile?
Laptop cells are designed for discharges rates below 1C.
I did produce discharge profiles at an optimal-minimal discharge rate, I found the results to be very interesting ... but sadly lacking.
See - Lithiums - mAh/100th V - Discharge Tests
Charge capacity mapping is so much more accurate and useful!

Before building packs I do thoroughly test and evaluate every cell.
I have developed and refined simple and effective procedures ...

Step 1
I bulk charge all cells to just above working voltage, then I allow cells to set several days and remove any with bleed down.

Step 2
Then I "Bulk" capacity test all cells - Method 2 preferred.

Step 3
Any unfamiliar brand, I choose a good sample and run a Charge Capacity Test to build a capacity map.
This test is performed by discharging cells to maximum DOD, then charging in 2/100th V increments, recording mAh required for each step. This gives an accurate map of each portion of capacity added at each fraction of a volt.

Previously, I have built capacity maps based on Discharge - mAh /100th V.
While interesting, the discharge map was flawed due to voltage sag and IR.

Step 4
Finally, I Match up the best cells for pack build. Equal total mAh per bank works nicely.

So far, and preferably, each pack is constructed from cells of same brand and oem rated capacity and results have been excellent.

I've been building eBike battery packs from recycled laptop cells for 6+ years and am continually finding-developing better methods.
The thread Homemade Battery Packs is a reasonably complete documentation of my progress.
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There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Determining Optimal Charge Voltage

Post by DrkAngel » Wed Apr 16, 2014 7:25 am

I did a quick summation of my capacity mapping theory-methodology for another thread and realized it would be a benefit in this thread.
DrkAngel wrote:
I tend to map cell capacity then keep usage within the beefier areas.

I began testing by mapping mAh /100th V discharge - too time consuming and inaccurate, IMO.
Voltage graph shifted almost .1V lower than actual rest voltage.
See 4th graph ("Recycled Li-ion" - red) for direct comparison.

Image
RC LiPo displayed a noticeably lower area of good capacity
Image

So I decided to remap using a mAh/10thV

Tools -
MeanWell 24V bulk charger (19.8 - 29.8V adjustable)
30V 4 digit volt meter, 100ths capable
Ah meter

I discharged my 25.9V recycled Lipo pack to 24.5V.
Then precisely equalized the cells at 3.50V.
I applied charge with MW (MeanWell) set to:
25.20V (3.60V) - full charge required .27Ah
25.90V (3.70V) - full charge required .53Ah
26.60V (3.80V) - full charge required 3.87Ah
27.30V (3.90V) - full charge required 3.15Ah
28.00V (4.00V) - full charge required 4.60Ah
28.70V (4.10V) - full charge required 4.10Ah
29.40V (4.20V) - full charge required 1.85Ah
(Ah is capacity between each .10V)

Telling, but lacking resolution.
So I mapped in 2/100thV increments. (50th V)
1st discharging to a stable 3.50V per cell
Then setting MeanWell to 2/100thV higher (3.52 etc), then charging through a mAh meter and recording mAh required to stabilize voltage at higher voltage.
Then repeating test in 2/100thV increments.
These non-RC Lipo displayed a strange capacity bulge near 4.12V, so I repeated the same test with another sample ... with very similar results.
(Rated optimal use at >3.75-4.05 to 4.15 for trips.)
Image

Li-ion 18650 (laptop cells) look optimal with a >3.70V to 4.05V for an estimated 300% lifespan.
Image
An alternate source displays very similar results in a more familiar graph style.
Image

Every formulation is different and you should test you own cells.
Discharge to a stable lowest voltage you want to test.

After finding no noticeable capacity at 3.5V, I began starting my tests at 3.6V.

Results show barren and rich regions of energy capacity. At the upper (4.2V) regions 1/10thV reduction in charge voltage can double usable cycles with a ~10% loss in capacity, a similar doubling for each 10thV reduction.
It seems deterioration is more determined by voltage than Ah.

Every 1/10thV of additional charge cuts usable life in half! = reasonably proven and generally accepted.
Every 1/10thV of additional discharge also cuts usable life in half? = reasonable assumption!


"Recycled Li-ion" Red graph, - discharging from 3.72V to 3.70V might have the same available mAh as from 3.70V to 3.00V = 35 times the damage to scrape out the miniscule remaining mAh.

Confirming might take years of testing .... I prefer to just keep my use within the energy rich regions.

Most everyone agrees that deeply discharging is damaging.
Discharging where there is minimal energy = needlessly-wastefully damaging! IMO!
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Capacity Mapping (Optimal Charge-Discharge Voltages)

Post by DrkAngel » Tue May 06, 2014 7:49 am

Latest capacity mapping project involved 2008 and 2010 Laptop 2160mAh cells.
Cells were nicely packaged in 3s2p "bricks".

Using 1 MeanWell S-150-12(V) adjustable power supply, 2 bricks were charged simultaneously using 2 identical mAh meters.
Charging was done in 6/100th V increments which equals 2/100th V per cell.

Charging 6/100th V ... 40 times could take forever ... current slowly degrades until 0 mA as target voltage is reached.
After a bit of trial and error testing, I determined that ...
Charging these 4320mAh banks at +.1V, until charging reduced to .65A, brought rest voltage close to target.
Then I continued charging at .02V above target until charge amperage reduce to .25A.
This brought actual retained voltage to nearly precisely on target.

Saved a whole lot of time sitting and watching and waiting!
Oh! Resulting graph...

Image

Note - 2008 (Red) series mAh meter exhibited a slight "idle charge" ... so graphed line is slightly higher than actual.
Last edited by DrkAngel on Wed May 07, 2014 3:44 am, edited 4 times in total.
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There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Capacity Mapping (Optimal Charge-Discharge Voltages)

Post by TheBeastie » Tue May 06, 2014 7:10 pm

Great work DrkAngle, I have to admit I have become a fan of your informative threads.

One analogy for a battery cells max voltage charge limits that I like to imagine is like how you are blowing up a rubber balloon.
As you pump more air in the rubber balloon the sweat capacity spot is around the middle (3.85) %50
When you keep blowing up that balloon and push those last few gulps of air into that balloon (for around 4.2volts as an example) you can really are stretching the rubber balloon to its limits, and the rubber is getting permanent damage.

Pumping your rubber balloon to absolute peak (just like 4.2volts) every time makes your balloon much more saggy and crappy much more quicker, all that for just 1 gulp of air more capacity....And when the air is finally let out it's not going to come out with nearly as much fluster then if you had blown it up to only 4.05 volts and kept everything nice and tight for as many cycles as possible. Your ballon/battery now has higher internal resistance..

The funny thing about it all is that just like over blowing up an air balloon if you put a high enough voltage into a lipo pack like 5 volts it will eventually burst with hydrogen gas and also a spectacular flame ball..
https://youtu.be/tatq8KcaGY0?t=24
https://www.youtube.com/watch?v=YCWdnjLqVWw

*Add/edit* On the other side of the coin I believe that over discharging your cells below their recommended minimal voltage also kills their life cycles.
The analogy I use for this is a bit like letting a "hot air balloon" get so low in hot air it goes past a point of no return and collapses in on its self and no amount of pulling of the gas flamer really ever quite gets back into the balloon again...In fact with hot air balloons once its gone down they need a special fan to get it going again.. https://youtu.be/FUBxv0CFiHI?t=285

Ebikes.ca have a great chart about it all on their website with their new battery charger..
http://www.ebikes.ca/product-info/cycle ... cycle-life
Last edited by TheBeastie on Thu Mar 31, 2016 9:04 am, edited 13 times in total.
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Re: Capacity Mapping (Optimal Charge-Discharge Voltages)

Post by DrkAngel » Mon May 12, 2014 10:38 pm

Mapped 2 RC Lipo Types

WARNING: map not valid - mapping malfunction!
WinForce 5700mAh
(3.65V - 4.05V as optimal voltages?)
WF RC Lipo.jpg
WF RC Lipo.jpg (44.76 KiB) Viewed 9105 times
And

WARNING: map not valid - mapping malfunction!
Winners Circle 2000mAh
(>3.7V - 4.05V as optimal?)
WC RC Lipo.jpg
WC RC Lipo.jpg (38.55 KiB) Viewed 9105 times
Results might be somewhat skewed by tandem mapping such different capacity cells.

Will likely retest separately
Last edited by DrkAngel on Thu May 15, 2014 4:59 am, edited 1 time in total.
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Capacity Mapping (Optimal Charge-Discharge Voltages)

Post by DrkAngel » Wed May 14, 2014 9:06 pm

New, reasonably accurate, capacity map for the ...

WinForce 5700mAh "20C" RC Lipo
WinForce 2 5700mAh.jpg
WinForce 2 5700mAh.jpg (48.27 KiB) Viewed 9061 times
Guess, now ... I'd better retest the Winners Circle 2000mAh
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Capacity Mapping (Optimal Charge-Discharge Voltages)

Post by DrkAngel » Thu May 15, 2014 9:32 am

DrkAngel wrote:New, reasonably accurate, capacity map for the ...

WinForce 5700mAh "20C" RC Lipo

Image
Tried a new method.
Much easier, less time consuming and more ... consistent.
While less exact ... it is more accurate.

Newest Capacity Mapping Method (mAh /200th V) - Li-ion, Lipo, Li-co
(WinForce 20C 11.1V 5700mAh battery pack exampled)

For convenience and to help insure a more general sample, I test a 3s battery.
3 cells in series 10.8V or 11.1V pack.
As a reasonable sampling, I charted for measurements every 2/100ths of a Volt.
With a 3s battery this was measuring in 6/100th volt stages.

Tools
MeanWell 12V adjustable power supply
(Recommend switching SVR1 voltage adjustment pot to a multi-turn pot)
mAh meter
100ths V capable multimeter.
Charting sheet - graph paper

Step 1
Discharge cells to < anticipated maximum DOD.
3.50V has been the lowest voltage, I've seen so far, where any substantial capacity exists.
Equalize voltages between cells.

Step 2
I began charging 2 steps (.12V .04V per cell in series) above desired step voltage, reducing charge voltage to 1 step (.06 .02V per cell) above desired voltage as I estimated desired charged voltage attained.
After several steps, when more substantial capacity was being accepted, I insured static voltage by letting battery set- not charging, for 5 minutes.

Carefully noting the voltage, I adjusted charger .3V higher(.1V per cell).
Applying charge, I carefully noted the amps and the amp change(WF 5700mAh = 1.35A).
After letting battery set, not charging, another 5 minutes, I confirmed resultant voltage and determined that letting amp drain drop to 1.25A was optimal.

Step 3
I stepped charging voltage up .3V on 3s battery and marked mAh required to reach next 1.25A drain level.
Never stopping charge, I just noted mAh then adjusted +.06V for next step.

Accurate map was completed in less than 5 hours of playing Solitaire and watching virus scans run on customers computers

Step 4
Enter data in free graph program

Uploaded WinForce graph file and added a "template" data set for ease of creating your own graph.
Change ".doc extension to .grf = template.grf

Method is reasonably accurate and much more consistent.
Every battery will have a different a charge rate and should be determined at a point of reasonable or median capacity to insure acceptable accuracy.

Update for estimating retained voltage by amperage from higher charge voltage.
Required adjustment and prorating every .10V per cell.
Attachments
Template.doc
(1.67 KiB) Downloaded 94 times
Last edited by DrkAngel on Sun May 25, 2014 9:36 am, edited 2 times in total.
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Capacity Mapping (Optimal Charge-Discharge Voltages)

Post by DrkAngel » Thu May 15, 2014 7:24 pm

Winners Circle RC Lipo 2000mAh Capacity Map
WC2 Lipo.jpg
WC2 Lipo.jpg (70.37 KiB) Viewed 9021 times
These show a better consistent capacity than previous "maps" ... no drastic dips.
Don't have enough for a ebike pack, but might add as a buffer for my laptop cell packs.

Like many of my tested cells, >3.7V to 4.15V looks like optimal discharge-charge points.

Also, might be able to squeeze 4 into a B&D 24V "Firestorm" cordless power tool pack, ...
upgrading from 24V 1.6Ah to 22.2V 4Ah.
Even with the minimal voltage loss the performance increase should be substantial.
Not to mention the 250% capacity ...
and the no voltage loss when setting for a few days ...
and the hundreds of cycles!

The test pack displayed excellent equalization at DOD and full charge.
Just gotta test up a few more packs.
Last edited by DrkAngel on Thu May 15, 2014 8:10 pm, edited 1 time in total.
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - November 2015

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