Homemade Battery Packs

This thread caters to the hard core do-it-yourselfers.
Designed to explore simplified super budget battery building.
Of course most BUILDS are time and/or labor intensive.
But I have built 25.9V 24Ah (actual capacity) packs for $40 and 33.3V 30Ah (1kWh actual capacity) pack for $90.
Over the years I've streamlined methods to reduce build time and improve durability but unless you need to save money ...

You might want to purchase new cells, build yourself, add a compatible BMS and find a charger ... in which case I would recommend purchasing a pre-made pack with matched components.

Plenty of good tips and ideas here though.
Check the index in #1 post of this thread.

Note: even new cells should be tested for:
self-discharge;
IR (Internal Resistance);
and
actual capacity.
Any variance in any of these factors will require the continuous use of a BMS or thorough testing and precise sorting.
Good brand name cells from retailers of impeccable reputation might be considered "pre-tested".
I have seen such encouraging claims as "all cells shipped in batch will be IR matched"."

Self- discharging cells are the bane of any battery build and must be tested for and eliminated ... IMO.
The alternative is a good BMS that constantly bleeds down all the "good" banks that aren't infected with self-discharging cells ... idiotic IMO!!!.

--- RC Lipo Day ---

Gathered up all my RC Lipo packs for full testing - evaluation.

12 - 3s 2000mAh (10C) Winner Circle
1. Charged and balanced @ 4.20-4.21V per Cell
2. All cells have set for 60+ hours with no notable self discharge

9 - 4s 2000mAh (10C) Winner Circle
1. Charged and balanced @ 4.20-4.21V per Cell
2. All cells have set for 60+ hours with no notable self discharge

9 - 3s 5700mAh (20C) WinForce
1. Charged and balanced @ 4.18-4.19V per Cell
2. All cells have set for 60+ hours with no notable self discharge

Today
Quick testing for comparative IR
then:

Rigging 9 Best 3s WC in series 27 x 4.20V = 113V* and discharging with 2 60w light bulbs (120w) for a 1000mA discharge rate
Might switch to 1 60w light bulb after 1st hour (500mA) for more precise and safer discharging

Rigging 7 Best 4s WC in series 28 x 4.20V = 117.6V* and discharging with 2 60w light bulbs (120w) for a 1000mA discharge rate
Might switch to 1 60w light bulb after 1st hour (500mA) for more precise and safer discharging

Rigging all 9 3s WF in series 27 x 4.20V = 113V* and discharging with ... 300w? Halogen flood - not metered yet for actual w usage

Will post pictures and some results later today.

* Caution! 50V+ DC can be very dangerous! Use safety precautions, be aware, rubber gloves(?) etc.

DrkAngel said:

--- RC Lipo Day ---

Gathered up all my RC Lipo packs for full testing - evaluation.

12 - 3s 2000mAh (10C) Winner Circle
1. Charged and balanced @ 4.20-4.21V per Cell
2. All cells have set for 60+ hours with no notable self discharge

9 - 4s 2000mAh (10C) Winner Circle
1. Charged and balanced @ 4.20-4.21V per Cell
2. All cells have set for 60+ hours with no notable self discharge

9 - 3s 5700mAh (20C) WinForce
1. Charged and balanced @ 4.18-4.19V per Cell
2. All cells have set for 60+ hours with no notable self discharge

Today
Quick testing for comparative IR ...

Click to expand...

Got busy today and don't want to risk getting busy or distracted during discharge testing.
Was able to ...
1st equalize all cells in batches to 1/100th V!
run a comparative IR test on 30 packs - 99 cells. (2 minutes per pack )



3s 2000mAh (10C) packs labeled with voltage at 1 minute into a 1.1A discharge, cells individually rated a few second later.

4s 2000mAh (10C) packs labeled with voltage at 1 minute into a 1.25A discharge, cells individually rated a few second later.

3s 5700mAh (20C) packs labeled with voltage at 1 minute into a 3.4A discharge, cells individually rated a few second later.

Packs are of various use, and misuse, but I'm hoping discharge capacity test will prove out a definitive relation of comparative IR to capacity among cells of same manufacture.

Discharge tested the 3s 2000mAh (10C) packs.
They clipped together in series nicely.
I added a cell level low voltage alarm to presumed weakest pack.
Discharged At 1A (2 60w light bulbs) for 1 hour then an additional 90 minutes at 500mA (1 60w light bulb) for a total 1750mAh test discharge.
Surprisingly, although cells are several years old and some slightly used, all tested packs showed similar residual voltages after 1750mAh of rated 2000mAh discharge. Noted cell static voltages at 1500mAh and 1750mAh.
Ended test to move on to 4s packs testing.



Discharge tested the 4s 2000mAh (10C) packs.
They clipped together in series nicely.
I added a cell level low voltage alarm to presumed weakest pack.
Discharged At 1A (2 60w light bulbs) for 1 hour then an additional 30 minutes for a total 1500mAh test discharge.
Noted cell static voltages at 1500mAh.
Ended test at 1500mAh due to closing time. One notable cell at extra low voltage. Labeled 97 on 3rd pack from top on left, note extra line on cell indicates was originally at very low voltage. 97 in pack above suffered similar low voltage at one time, but seems to have recovered nicely.



Will spreadsheet up the results and post soon.

So far...
These 2000mAh 10C cells seem to still maintain a large percentage of their original rated capacity (1 cell, stressed by low voltage, of reduced capacity)
These cells map as very compatible with the Dell recycled Lipo I've been using.



3.7V as "empty" to 4.12V as "full" - to provide optimal capacity at notably improved lifespan.
(I intend on a test hybrid eZip pack)

#2 9s8p 2160mAh (33.3V 17.28Ah) laptop Lipo
paralleled with
9s1p 2000mAh (33.3V 2Ah) RC Lipo
for a total
33.3V 19.28Ah = 642wh of mixed hybrid cells
For PA (Pedal Assist) use on several of my multi voltage capable eBikes - (~25mph) and light duty on 36V controllered Snow Beast - (geared down for more torque, 24V = <14mph - 33.3V = ~18mph( .
And to test evaluate RC + Laptop Lipo discharge capabilities.

Click to expand...

Casualties ... so far ...
1 cell of 3s 2000mAh Winner Circle Lipo
2 cell of 4s 2000mAh Winner Circle Lipo - 1 discovered during discharge test

1 cell of 2s 5700mAh WinForce Lipo
2 cell of 3s 5700mAh WinForce Lipo (1 puffer & 1 duffer)

I will separate packs for individual cell recovery-recycle

Power tool build
Impetus for testing these packs was to evaluate for constructing 18.5V (5s) 2000mAh 20A capable Packs to rebuild 18V 1.2Ah NiCd Ryobi power tool packs - 5s2p laptop Lipo will not fit. 4s with 1 bad cell split and add 1 cell to 4s and 2 cells to 3s or Halving a 4s pack to marry with 2 3s packs should provide 2 good prototypes. - (18.5V x (2A x 10C) = 20A 370w)
Yes, will convert and boldly label charging station for Lipo charging - bulk charge design so am carefully matching cells! (balance plug attached but inside pack, will require opening for periodic balance charges)

WinForce 3s 5700mAh (20C) discharge test
3s x 9 = 27s1p
Had no 300w Halogen floods so I had to use a 500w.
500w / ~110V = 4.5A ... 4.5A / 5.7Ah = ~ .8C discharge rate
70 minute discharge (6 pks - 18cells ±3.60V) but discharge diminished by early,3 packs, removal.
Full term (6 packs) are being iMax charged, not "balance charged", at ~ .4C to confirm recharge to same starting cell level equalization.



2 cells of poor "comparative IR" dropped out early.
Oddly ... voltage recovered and equalized properly after discharge removed.

This seems to indicate that the "poor" cell can output the same mAh, at tested discharge rate, as the better cells ...
but that the mAh are only available at a lower voltage ... summing up to lesser wattage - actual capacity, from the cell! ... ?
Whether happenstance or some design function???

Will try to expound later.
Got 1st snow today and still have to prep the Snow Beast!

DrkAngel said:

WinForce 3s 5700mAh (20C) discharge test

2 cells of poor "comparative IR" dropped out early.
Oddly ... voltage recovered and equalized properly after discharge removed.

This seems to indicate that the "poor" cell can output the same mAh, at tested discharge rate, as the better cells ...
but that the mAh are only available at a lower voltage ... summing up to lesser wattage - actual capacity, from the cell! ... ?
Whether happenstance or some design function???

Click to expand...

With some recently tested packs ...

Type "poor"
Monitored cell level discharges seem to confirm a comparative IR as a reasonable (Yardstick method) indicator of actual capacity.
While voltage sag lets 1 cell hit LVC earlier, actual static voltage might still be equal with the better cells in series.
This seems to indicate that poor IR cell still outputs a similar percentage of its capacity as the good IR cells.

Severe voltage sag lets the poor cell output the same amps as the good cells.
Poor cell average discharge 3.40V x 5Ah = 17.0wh
Good cell average discharge 3.90V x 5Ah = 19.5wh

Poor cell at ~85% capacity of good cell diminishes pack performance severely!

Type "bad"
Other tested packs quickly showed some poor IR cells as of obvious lower capacity!
"Showed" by rapid discharge voltage loss matched by static voltage loss.

Conclusions ...
IR is a definite factor in battery capacity among same manufacture cells!
Poor IR can either indicate poor capacity (cell discharges at lower voltage) or bad capacity (cell empties early)

Conclusion!
Cells of poor comparative IR (within same brand-model cell) should be eliminated from any build!

Maybe I'll post here to get a better response:

So I put together a new back-up battery pack 48v5Ah 13S2P but with a mixture of eight 2014 "2E12" stamped Samsung 25R from Lilian (SuPowerBattery) in China. I had these in storage for 1.5 years and never used it or charged it. They were held at normal state of charge of 3.61V. I purchased them last July 2014.

Last week, I then ordered 18 other 25R's from ebay from a known seller with feedback of people who confirmed they were legitimate (after taking to vape shops). The date of the 25Rs is stamped "2F34" and means made in 2015 in March.

So anyhow, the first four 2Ps are the older from SuPowerBattery and last nine 2Ps are from eBay.

So they all charge perfectly, and using the Signalabs BMS, they charge up to 4.16V. The first charge after finishing pack build, the first four 2P hit 4.20V and the BMS leds turn on. The rest of the nine 2P were catching up at 4.14-4.16V. After the charge was done, I hooked up a 200-watt light-bulb and let it discharge for 5 hours at 48V. After 5 hours, I measure the first four 2P cells and got 3.16V on each of the first four 2P. On the remaining nine 2Ps from eBay, they are holding at 3.61V.

So what does this mean? Are the eBay cells just holding more capacity and the cells from supowerbattery just lost capacity? Or, are the SuPowerBattery possibly counterfeit? Or vice versa? Is the SuPowerBattery batteries working harder therefore they discharge more?

48V pack voltage after 5 hours of 200-watt lightbulb discharge at the discharge connector through BMS
-----------
|3.16| supowerbattery
|3.16| supowerbattery
|3.16| supowerbattery
|3.16| supowerbattery
------
|3.61| eBay
|3.61| eBay
|3.61| eBay
|3.61| eBay
|3.61| eBay
|3.61| eBay
|3.61| eBay
|3.61| eBay
|3.61| eBay
Last edited by nukezero on Tue Oct 20, 2015 11:36 am, edited 1 time in total. View post history.
nukezero
10 kW
10 kW

Posts: 534
Joined: Tue Jul 02, 2013 5:00 pm
Location: Los Angeles, CA

Older = some degradation - capacity loss
Different batch = possibly different manufacturer, formulation or processing method

Good news - bad news
There is very little capacity below 3.6V!
Hopefully the 3.16V discharge voltage was during discharge?
Discharging to a static 3.16V could be horribly damaging.

Representation for someone who wanted to discharge to 2.65V ...


I believe recommended storage voltage is 3.80 - 3.90V ... ?

DrkAngel said:

Older = some degradation - capacity loss
Different batch = possibly different manufacturer, formulation or processing method

Good news - bad news
There is very little capacity below 3.6V!
Hopefully the 3.16V discharge voltage was during discharge?
Discharging to a static 3.16V could be horribly damaging.

Representation for someone who wanted to discharge to 2.65V ...

I believe recommended storage voltage is 3.80 - 3.90V ... ?

Click to expand...

The 3.16V discharge voltage was static. Meaning, it's after I removed the light-bulb. But get this!! When I plug in my 2Amp charger for about 5-10 minutes, these first four 2Ps, immediately jumped to 3.6V just like the rest of the nine 2P packs. So strange. It sounds like your right. Different batch, different age, the 2P just seem to react a lot more differently.

I'm not sure at this point if it's worth the $40 investment to buy 8 more cells to replace these 8, and trash the old ones, but like you said, there's probably not much charge left at 3.6V or less anyways. This pack was meant to just be a back-up extender pack and not my primary pack.

I ordered a watt meter and going to discharge all my batteries through my 200-watt light bulb with the powerwerx watt meter this week. I'll be highly interested to see how much amp-hours is left in each of my pack.

Recommend you order up 1 or more 1-8s voltage monitor w/alarm and not discharge below 3.40 - 3.50V static voltage.
Set alarm at 3.30V?

VMA (Voltage Monitor Alarms) are < $2 each.

These cells have energy up to 2.5 V, they are different chemistry from lipo and limn you are mostly using. When they are at 0% SOC, their OCV is ~3.2 V. It would be wasteful to limit discharge on 3.4 V, you would miss like 40% of capacity.

User reports nearly immediate rise from 3.16V resting voltage to 3.60V, from minimal charge ...
This looks to confirm minimal energy below 3.60V.

Not true, look at discharge graphs on the lygte or dampfakkus site... These chemistries (NCA and NMC) behave differently.

INR18650-25R
Optimal DOD at 1C discharge rate looks to be ~3.30V.
Likely this relates to a 3.40V+ static voltage.



Recommend testing with a 1C discharge rate and a 3.30V LVC (Low Voltage Cut-off).
(1C = 1 hour and gives time for frequent monitoring)
Please post up resultant static voltage = recovered voltage a few minutes after discharge removed.

25R is high current cell, most likely wont be used at only 1C rate. As a high current cell it has a bit higher voltages than standard NCA cell.

But look at more common curve for NCA cells, like this Panasonic NCR18650B (most other NCA cells will have similar unloaded voltages)

http://lygte-info.dk/info/BatteryChargePercent%20UK.html

You can see that there's around 35-40% of energy under 3.6 V unloaded. In load conditions, it' even more, on high rates it can be even 70 or more percent...

User reports ... INR18650-25R

The 3.16V discharge voltage was static. Meaning, it's after I removed the light-bulb. But get this!! When I plug in my 2Amp charger for about 5-10 minutes, these first four 2Ps, immediately jumped to 3.6V just like the rest of the nine 2P packs

Click to expand...

Which is a static voltage from below 0%, (from your the chart), to 40% (according to you) from a 2A charge into 10Ah of battery (.2C charge rate) for 5 - 10 min = 166mAh - 333 mAh into 10,000mAh battery exhibiting a 40% capacity vs the 1.66% - 3.33% input capacity.

Of course charging voltage inflates observed ...
but a .2C charge into high rate cells should inflate actual (static) voltage only slightly.
Seemingly, his cells exhibit minimal capacity below 3.6V

Your graph is for some horribly different chemistry or construction!
3100mAh cell at 3A discharge <1C shows a nearly immediate sag from 4.2V to 3.7V.
INR18650-25R at 1C discharge rate only sags from 4.2V to ~4.1V! ... ?

INR18650-25R graph does indicate reasonable capacity as low as ~3.40V! - (Static Voltage)

You are looking at manufacturer data, that could be inflated..

Let's see some independent testing:



From this site:

http://lygte-info.dk/review/batteries2012/Samsung%20INR18650-25R%202500mAh%20%28Cyan%29%20UK.html

So, if you look at 3 A curve, you can see that we are on 4.5 Wh on 3.6 V, and total capacity is almost nine. That's close to 1C, like on Samsung graph. On 0.2 A discharge we are on 6 Wh at 3.6 V, which is 66% of capacity. This is almost OCV, pretty low rate discharge.

And there's even more capacity left, since test is only up to 2.8 instead of 2.5 V.

Low discharge rate confirms my estimate of 3.40V as optimal DOD - (static voltage) = 3.30V @ 1C discharge rate.

I believe deep voltage discharges in regions of minimal capacity to be needlessly damaging! ... and potentially dangerous.
I strive to not run my batteries "over the cliff".

Using graph I built a discharge map.
(Based on .2A <.1C discharge rate line)
Scaled in Wh rather than my typical mAh ... sorry.


2.80 = .04
2.85 = .04
2.90 = .04
2.95 = .05
3.00 = .07
3.05 = .07
3.10 = .08
3.15 = .08
3.20 = .07
3.25 = .07
3.30 = <.1
3.35 = .1
3.40 =.1
3.45 = .45
3.50 = .4
3.55 = .4
3.60 = .7
3.65 = .85
3.70 = .6
3.75 = .55
3.80 = .35
3.85 = .5
3.90 = .5
3.95 = .6
4.00 = .35
4.05 = .4
4.10 = 1.0
4.15 = .3
4.20 = <.1wh

Bar graph would be more accurate, actual capacity would be a horizontal line to the lower .05V.




Shows good capacity from 3.40V till initial sag below 4.20V.
Displays similar hills and valleys to various other of my "mapped" LiPo.

IN|R18650-25 Capacity Bar Graph from .2C discharge graph



Between 3.40V and 4.10V appears optimal for best usable capacity with least "wear and tear" ... IMO ...

You make good points, but we need to consider two things:

1. people who buy this particular cell will be using it at higher discharge rate, certainly not 0.2C (they can buy cheaper batteries with higher capacity and lower c rate)

2. these chemistries are really good, they are not "damaged" by 100% DOD cycles. Yeah, they last longer on lower DOD cycles, but have no problems with 100% DOD.

I rated at .2A because that should be extremely close to the static voltages.
Static (at rest) voltage is the reasonable way to map a cells capacity.

Every cycle "damages" the battery.
It's called cycle life or deterioration.
I "map" capacities to determine the best output for the least damage.

It is reasonably accepted that charging to 4.10V, all other factors being equal, doubles the usable number of cycles compared to charging to the rated 4.20V. Charging lower would increase cycle life even more ... but at the sacrifice of a big juicy chunk of capacity (with these cells).
Further, It is marginally considered reasonable that deeper discharges are likewise more damaging, (I tend to subscribe to the reasonability of this possibility>>>probability). Discharging more deeply to use minimal capacity of a pitiful sagging nature doesn't seem worth it - IMO.

Do we have any proof of that it actually shortens life(or cycle life) of we go to 4,2 instead of 4.1.
What I mean is that I understand that it does if we let the cell sit at 4,2 for a period of time. But how does it affect the cells if we charge to 4.2 and then start to discharge it as soon as it hits that voltage?
Is it the time spent on in fully charge state that damage the cell or is it a combination of both time and that we crank it up to 4,2?