Homemade Battery Packs

Batteries, Chargers, and Battery Management Systems.
SamTexas
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Re: Li-ion vs SLA

Post by SamTexas » Dec 19, 2012 11:54 am

DrkAngel wrote: SLA (10Ah) - expended in 1 hour = 6.14Ah *
This SLA would not last past 50 cycles if used this way. Should have stopped and recharged at 4Ah max.

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Re: Homemade Battery Packs - Rebuild!

Post by DrkAngel » Dec 30, 2012 3:36 am

I decided to rebuild all my 2008 era "homemade" 18650 packs.
Most have been sitting a couple years.
I noticed a bad "balance" on my 37V 20.8Ah build.
So I have decided to rebuild my 3 - 37V 20.8Ah and 2 - 25.9V 31.2Ah packs, a total of 408 18650 cells.
I still have another 100+, unused cells.

1. Disassembly of hundreds of solder connections

2. Charge all cells to 4.2V
After I disassemble all packs, I will gang together 1s40p cells and charge with my modded MeanWell S-150-5 @ 4.2V 30A. (Note: recycled Lipo cells will be tested at a modest 4.1V per cell, but monitored for self-discharge for a considerably longer time period, several days, a week?)

3. Test all cells
a. After fully charging, separate, let set ~24 hours, any noticeable self-discharging cells will be eliminated. (Degree, and depth, of self-discharge has proven to be a reasonably reliable "yardstick" of cell condition!)
b. Apply a .5C, timed, drain to each cell, low ending voltages will be eliminated.

4. Build packs
I intend on a modular construction.
3s8P 11.1V (12.6 fully charged) 20.8Ah modules
(I plan on using 25.2V*, 37.8V*, 50.4V* builds)
I will install balance plugs, but after thorough testing I intend on bulk charging ... with scheduled balance charges.

5. The builds (eZip pack capable)
a. 22.2V - 6s16p 96 cells 22.2V 41.6Ah 923.5mAh
b. 33.3V - 9s8p 72 cells 33.3V 20.8AH 692.64mAh +9s1p 5700mah RC Lipo 5.7AH 189.81MaH = 26.5AH 882.45MaH total - Hybrid Pack
c. 44.4V - 12s8p 96 cells 44.4V 20.8Ah 923.5mAh

6. I intend to streamline pack build using flat tinned 9-10ga copper braid, replacing 10ga insulated stranded copper. 22ga tinned copper wire for balancing.

* Fully charged

Any cells not rated as grade A, but reasonably good, will probably be allocated to other applications such as:
Lanterns - florescent, LED etc.
Power inverter - pulled 36Ah SLA out of a 200watt pack, could pack in 11.1V ... 100Ah Li-ion?
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Re: Homemade Battery Packs

Post by spuzzete » Dec 31, 2012 4:16 pm

Hi guys,

here a discharge test on a laptop battery (Panasonic), 1s2p, 3.6v 4.4Ah nominal. The battery used is the same, recharged after each test.

The tests have been done with a CBA 4 battery analyzer.

A picture is worth more than a 1000 words!
LiCo_Various_C-001.jpg
LiCo Cell Discharge
LiCo_Various_C-001.jpg (109.6 KiB) Viewed 142 times
Legend:

1C Green
2C Blue
0.2C Red

SamTexas
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Re: Homemade Battery Packs

Post by SamTexas » Dec 31, 2012 5:07 pm

Good discharge graph spuzzete.

Questions:
- What is the model of those two Panasonic cells? CRG18650CA?
- Are they brand new or recycled?
- Does the CBA 4 actually maintain a true constant current throughout the discharge?
- What is the meaning/relevance of the vertical dashed green line at around 3.3Ah?

Comment: I would not classify the 2C discharge as "fail". Laptop cells are not meant to be discharged continuously at 2C.

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Re: Homemade Battery Packs

Post by spuzzete » Dec 31, 2012 5:48 pm

Hi SamTexas,

The cells are Panasonic CGR18650CG

They are recycled from a laptop battery.

The green vertical line represent 75% of the nominal charge, I use this limit when discharging laptop cells at 1C, as most of them give around 77-78% of their nominal capacity.

"Fail" means only that they have not reached the 75% mark..if I lowered the cut off voltage they would have probably made it at 2C, but maybe the cells would have been damaged?

Anyway the CBA 4 is a good instrument, the current set is constant, and it's really easy to use. So far I am very pleased with it :D

8)

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Re: Homemade Battery Packs

Post by SamTexas » Dec 31, 2012 6:02 pm

That's very good for recycled battery.

You can safely discharge them to 2.5V and probably gain an additional 0.5%. I don't have any empirical data to say whether that will hurt the cell capacity in the long term. No immediate short term effect from my own experience. In fact 2.50V is when I stop discharging when I do capacity testing. In regular/normal use I stop and recharge at around 3.0V.

http://industrial.panasonic.com/www-dat ... 0CE234.pdf

Edit: Added missing "0." in "additional 5%"
Last edited by SamTexas on Jan 01, 2013 10:24 pm, edited 1 time in total.

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Re: Homemade Battery Packs

Post by spuzzete » Jan 01, 2013 12:30 pm

First of All:

Happy New Year to all of you!

Thank you Sam Texas for the info! I always try not mistreat my cells, it's nice to know that they can go as low as 2.5V! Are your cells recycled or new?

Having a graph makes it really easy to understand if the cells are good or not. Laptop cells don't like to be discharged over 1C, and even at 1C some don't perform well. I am going to run a bunch of tests at 0.5C or lower on laptop cells that didn't pass the tests.
The only negative thing of the CBA is that you need a computer to run the tests..I will probably buy a cheap netbook/laptop only for that purpose.

Anyway, here is a discharge test of the Sony Konion cells, those are LiMn cells, 18650 format 3.7v 1500mAh for each cell. The cells are connected in parallel, so the battery is a 1s2p 3.7v 3000mAh nominal.

Tests are performed at 1C (3A) and 3C (9A):
LiMn_1C_vs_3C_Ah.jpg
LiMn 1C & 3C
(59.17 KiB) Downloaded 8 times
The vertical line represent 75% of the capacity.

Quite a big difference compared to the laptop cells.


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Re: Homemade Battery Packs

Post by cassschr1 » Jan 01, 2013 1:48 pm

Since there 2p I'm assuming these are the V cells. Comments?

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22.2V! ...?

Post by DrkAngel » Jan 01, 2013 2:06 pm

DrkAngel wrote:I decided to rebuild all my 2008 era "homemade" 18650 packs. ...
5. The builds (eZip pack capable)
a. 22.2V - 6s16p 96 cells 22.2V 41.6Ah 923.5mAh

b. 33.3V - 9s8p 72 cells 33.3V 20.8AH 692.64mAh +9s1p 5700mah RC Lipo 5.7AH 189.81MaH = 26.5AH 882.45MaH total - Hybrid Pack
c. 44.4V - 12s8p 96 cells 44.4V 20.8Ah 923.5mAh
22.2V (25.2V full charge) might sound pretty wimpy compared to to oem 24V SLA (26V+ full charge).
But considering the voltage sag from the SLA under use, the minimal sag from the 40Ah Li-ion, and the typical 24V controller LVC of 20.5V, I believe that the 22.2V will outperform the oem SLA in every way ... plus 6.5X the range. (OEM with 15mile range - ~100mile Li-ion range!)

I believe that the 22.2V Li-ion is also a better fit for the typical 24V controller!
A controller LVC of 20.5V leaves a 12V SLA at a dangerously rundown 10.25V.
While a 22.2V Li-ion still retains a 3.4V+.
Now ... 3.4V is below what I consider optimal, but when you figure voltage sag under throttle 3.5-3.6V actual capacity sounds ideal.

Oh! My Trailz with 25.9V & 16T mod cruises at 22mph, 22.2V will drop that to a "legal" ~19mph.

22.2V - 41.6Ah eZip pack rebuild will consist of 2 - 6s8p modules, will install connectors for quick switch to 44.4V - 20.8Ah. - TURBO mode!
Alternately, 2 - 22.2V packs with switches from parallel to serial.

Yes 2 - 41.6Ah packs, ~10lb each, should provide a possible 200 mile range!
A little better than the oem SLA at 15 miles, with a 16lb+ pack!
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Re: Homemade Battery Packs

Post by SamTexas » Jan 01, 2013 4:32 pm

spuzzete wrote: Thank you Sam Texas for the info! I always try not mistreat my cells, it's nice to know that they can go as low as 2.5V! Are your cells recycled or new?

Having a graph makes it really easy to understand if the cells are good or not. Laptop cells don't like to be discharged over 1C, and even at 1C some don't perform well. I am going to run a bunch of tests at 0.5C or lower on laptop cells that didn't pass the tests.
The only negative thing of the CBA is that you need a computer to run the tests..I will probably buy a cheap netbook/laptop only for that purpose.

Anyway, here is a discharge test of the Sony Konion cells, those are LiMn cells, 18650 format 3.7v 1500mAh for each cell. The cells are connected in parallel, so the battery is a 1s2p 3.7v 3000mAh nominal.
I have a few brand new Panasonic cells I use for reference. The rest (over a thousand) are recycled. My recycled cells have an average of 75% of their original capacity. Any cell with less than 60% are discarded or set aside for lighter duty uses (flash lights, head lights, voltmeters and air pumps.)

I have no problem discharging them at 1C. They get warm (not hot) after 30 mins. 2C continuously is definitely out of the question, 15 minutes is the most I have tried, too warm for my taste. I have discharged them at 4C too for a very short time, just to ascertain that they are capable of doing so momentarily.

I have tried those Konion, Emoli, and Samsung LiMn cells too. I have tested them at 3C and they perform well. But I don't use any of them on my bike. Their low energy density makes them too heavy for me. My ebikes, escooter and etrike all have an average discharge of 0.5C or less (minimum of 2 hours runtime) so I use laptop LiCo for the highest energy density.

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mAh per 100th V

Post by DrkAngel » Jan 01, 2013 8:58 pm

Various LiCo have different "usable" voltage ranges.
The red line (5200mAh) is from Gateway laptops - recycled 18650's. Expending below ~3.6V seems needlessly damaging, but seems to have good capacity right to 4.2V. Anything below 3.5V looks to be a microscopic additional energy!
The yellow line (4320mAh), recycled LiPo, seems to have a broad band of good capacity, but with a lower max usable voltage. 3.7V - 4.05V looks optimal.

Strangely, the green line (5700mAh), RC LiPo, seems to have its best capacity between 3.5V and 3.7V ... where the recycled cells seem nearly "empty"!

Image

I just became concerned with the talk of expending to 2.5V! I tested these different cells to the point of no more usable energy - imo.

Testing was done at a .2C discharge rate, so as to minimize voltage sag-distortion.
Last edited by DrkAngel on Jan 01, 2013 11:43 pm, edited 1 time in total.
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SamTexas
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Re: Homemade Battery Packs

Post by SamTexas » Jan 01, 2013 9:43 pm

DrkAngel wrote: I just became concerned with the talk of expending to 2.5V! I tested these different cells to the point of no more usable energy - imo.
You are forgetting that we tested our cells at a more realistic discharge rate of 1C. I stopped my test at 2.50V. Within 30 seconds the cell voltage jumped back to 3.2 to 3.5V, depending on brand and model. I would never have your patience or time to perform a 0.2C test.

Edit to add: You can also look at the 2nd discharge graph in the link I provided earlier. That's done by Panasonic itself. I have another datasheet for another Panasonic cell in which the discharges are stopped at 2.0V.

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Re: Homemade Battery Packs

Post by DrkAngel » Jan 02, 2013 12:54 am

Personally, as a yardstick, I recommend minimum discharge voltage as 3.0V under load, 3.5V static.
Higher charge voltage and lower discharge voltage both damage capacity and lifespan.
The deeper the discharge the worse the damage, discharging below the useful point seems akin to vandalism, against ones own property!
Deep discharges needlessly damage the cells, for a minimal increase in output!

The LiCo 18650 cells (Pink Line) seem 95%+ expended at 3.6V another 3% till 3.5V then seconds of use till voltage plummets below 3.0V.
If you can accept the supposition that a cell only has a certain number of volts output.
Then discharging from 4.2 to 3.6V (.6V) would be 1 complete cycle, discharging further to 3.0V (.6V) would be another complete cycle ... for a mere 5% more drizzling output. Effectively giving you 1/2 the life cycles.

Of course it is actually worse.
It is widely accepted that discharging only 80% will double the life cycles! That might be discharging to only 3.7V, instead of 3.6V
If reducing discharge by .1V can double life cycles imagine how damaging it must be to increase discharge by an additional .6V?

OR
3.7 to 3.6V = 50% cycles
If that is an accurate then ...
3.5V = 25% cycles
3.4V = 12.5% cycles
etc.

I'm not saying that these are accurate figures ... merely that, logically, they tend towards the reasonable.

So, once again, I highly recommend against deeply discharging!

Of course optimal discharge limit varies by formulation.
The yellow line LiPo looks good at 3.7V while the green line RC LiPo looks good down to near 3.4V.
Last edited by DrkAngel on Jan 03, 2013 9:05 am, edited 1 time in total.
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SamTexas
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Re: Homemade Battery Packs

Post by SamTexas » Jan 02, 2013 8:14 am

Yes the common wisdom has always been longer life for shallower discharge. But it's one of those things that we choose to accept without verification. I certainly don't have the time, money and patience to spend a few dedicated years to prove or disprove that wisdom.

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DOD Drama

Post by DrkAngel » Jan 02, 2013 9:33 am

SamTexas wrote:Yes the common wisdom has always been longer life for shallower discharge. But it's one of those things that we choose to accept without verification. I certainly don't have the time, money and patience to spend a few dedicated years to prove or disprove that wisdom.
I have many used notebook battery packs.
I will choose one that has been setting for 4 years and has 8 cell, 4 mated pairs, that has retained the closest equalized voltage amongst all cells.

To further equalize I can take 2 mated pairs, separate individual cells and re-twin with its new brother cell.
This should effectively create 2 "identical twins" (T1) or a close equivalent, and a second pair of identical twins (T2) from the remaining cells.

All new pairs will then be discharged to 3.7V then individually recharged to 4.2V using an iMax B6, using the same iMax and recording watts and time required. This will be the base, or control, measurement.

I will then engage in a daily charge - discharge cycle, separate discharge depths for each twin.
T1a - 3.7V
T2a - 3.6V
T1b - 3.5V
T2b - 3.4V

Weekly measured recharges should demonstrate the minimal capacity added by the lower discharge depth and a map of deterioration for each voltage.
This will be a long term project, there might be a report on discharge monitoring procedure, then many weeks before initial results will be posted. As this process progresses I will give it its own thread and post location.

I would invite another to perform the same, similar?, test.
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Re: Homemade Battery Packs

Post by SamTexas » Jan 02, 2013 9:44 am

I admire your dedication. Your plan sounds good and scientific to me. The results should be relevant and meaningful.

As for the invitation, I'm afraid I have to decline. I just don't want to spend my time that way. Hopefully someone else will join you in your long term effort. How many cycles are you projecting before you can draw a meaningful conclusion? 100, 200 or 300 cycles?

Anyway I look forward to seeing the results should you decide to go ahead with this project.

Edit to add: You might also want to investigate the effect of the upper voltage limit as well. i.e. 4.10 versus 4.15 versus 4.20V

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Re: Homemade Battery Packs

Post by DrkAngel » Jan 02, 2013 10:11 am

SamTexas wrote: You might also want to investigate the effect of the upper voltage limit as well. i.e. 4.10 versus 4.15 versus 4.20V
Since these particular cells show good capacity at a full 4.2V (pink line) I don't foresee any point.
I believe that damage, reduced capacity, is caused by needlessly draining where there is minimal energy stored.

On the other hand testing the LiPo (yellow line) in this manner would be very telling.
4.2V - 4.15V - 4.10V - 4.05V

I'm predicting 4.05 as being optimal.

Image

My next LiPo (yellow line) builds are scheduled for a 4.08V max charge and 3.7V DOD, leaving a fair bit of "limp home - reserve". (I use precisely adjustable bulk chargers ... 1/100th V per pack)

I also picked up a few kWh of Sony Lipo (recycled), I must keep them separate as they have a much different discharge profile.

Image
Tho ... mixing the 2 would add substantial low voltage "beefiness" while maintaining the same 4.08V to 3.7V charge - discharge profile! Hmmm ... possibly 3.6V DOD?
Last edited by DrkAngel on Jan 02, 2013 11:03 am, edited 3 times in total.
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Re: Homemade Battery Packs

Post by SamTexas » Jan 02, 2013 10:28 am

DrkAngel wrote: Since these particular cells show good capacity at a full 4.2V (pink line) I don't foresee any point.
I believe that damage, reduced capacity, is caused by needlessly draining where there is minimal energy stored.
That's another problem with these wisdoms. We tend to choose to accept only what we want to hear, what best fits our needs.

Just as shallower discharge is beneficial to longer life, so is lower max voltage, according to the wisdoms. I have verified that none of my laptops (Dell, HP and Toshiba) exceeds 4.12V. I have also verified that none of my cellphone (Samsung and AT&T) exceeds 4.10V.

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Re: Homemade Battery Packs

Post by DrkAngel » Jan 02, 2013 11:13 am

As noted in previous post, by words and graphs, LiPo would definitely benefit from an upper voltage test, as they do demonstrate a marked decline in capacity at near 4.2V.
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Re: Homemade Battery Packs

Post by SamTexas » Jan 02, 2013 12:08 pm

Capacity is not the question here. Longevity is. The pink LiCo 18650 is the one that needs to be investigated most. How much longer would it last if some of the upper capacity is sacrificed.

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Re: Homemade Battery Packs

Post by DrkAngel » Jan 02, 2013 12:56 pm

SamTexas wrote:Capacity is not the question here. Longevity is. The pink LiCo 18650 is the one that needs to be investigated most. How much longer would it last if some of the upper capacity is sacrificed.
Capacity is the measure of longevity.

All ratings, that I have seen, or recall anyhow, measure longevity by the number of cycles until full charge reduced to 80% rated capacity.

My whole point, is solely that, deeply discharging below the point of reasonable capacity is needlessly damaging.

There is the separate point that charging beyond the point of reasonable retained capacity is also needlessly damaging.

I have not, directly, addressed your, presumed, point that lowering peak charge, even though reasonable capacity is sacrificed, is greatly beneficial to longevity. My plate is too full with more basic-essential considerations.

But ... Of course, lowering peak charge and raising the DOD will prolong cell life. Measuring that for every type of cell would be hopeless.

On the other hand, showing benefit by retaining discharge deeper into the predetermined, densest capacity region of a cell and comparing to outside those voltages, can yield results applicable to many cell types.
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There, shallow draughts intoxicate the brain,
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I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Homemade Battery Packs

Post by spuzzete » Jan 02, 2013 10:26 pm

@ DrkAngel

On my test on the Panasonic CGR18650CG (4.4Ah) @ 0.2C 3.6v is way too safe as LVC. in the test under load the cells give less than half the nominal capacity @3.6v (about 2.0 Ah), the lowest "useful" point is about 3.35v (3.9Ah), after that there is very little capacity/energy left in the cell.
Other cells (Panasonic CGR18650D) show similar behaviour, with useful capacity up to 3.4-3.35v (But test @ 0.5 C this time).

8)

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Re: Homemade Battery Packs

Post by DrkAngel » Jan 02, 2013 11:03 pm

spuzzete wrote:@ DrkAngel

On my test on the Panasonic CGR18650CG (4.4Ah) @ 0.2C 3.6v is way too safe as LVC. in the test under load the cells give less than half the nominal capacity @3.6v (about 2.0 Ah), the lowest "useful" point is about 3.35v (3.9Ah), after that there is very little capacity/energy left in the cell.
Other cells (Panasonic CGR18650D) show similar behaviour, with useful capacity up to 3.4-3.35v (But test @ 0.5 C this time).

8)
Never intended to recommend 3.6V as LVC.
3.6V was recommended as bottom static voltage after drain removed.
To attain this, discharge to 3.6V after load removed, apply typical load, check voltage - this should be your LVC setting.

Please note!
3.6V was my recommended DOD for the 2600mAh cells that I tested. All cells consist of different formulations, 3 that I graphed demonstrated a variance of from 3.7V to near 3.4V as optimal DOD. Typically, this is in the range of 3.6-3.7V.
While erring towards a higher voltage will reduce capacity some, it will prolong your packs useful lifespan-survivability.
Please! Determine your own DOD.
Last edited by DrkAngel on Jan 03, 2013 9:32 am, edited 1 time in total.
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And drinking largely, sobers us again.

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Re: Homemade Battery Packs

Post by etriker » Jan 02, 2013 11:06 pm

spuzzete wrote:@ DrkAngel

On my test on the Panasonic CGR18650CG (4.4Ah) @ 0.2C 3.6v is way too safe as LVC. in the test under load the cells give less than half the nominal capacity @3.6v (about 2.0 Ah), the lowest "useful" point is about 3.35v (3.9Ah), after that there is very little capacity/energy left in the cell.
Other cells (Panasonic CGR18650D) show similar behaviour, with useful capacity up to 3.4-3.35v (But test @ 0.5 C this time).

8)
If you look at the laptop pack it will say 10.8v or 11.1v ?

Some cells are rated at 3.6v and some are 3.7v and do not discharge the same. The 3.6v cells fall off the cliff at a lower voltage.

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spuzzete
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Re: Homemade Battery Packs

Post by spuzzete » Jan 02, 2013 11:43 pm

@ DrkAngel

Thank you for your explanation, it makes perfect sense. :)

@Etriker

The datasheet says 3.6v nominal and 4.2v fully charged. I believe that the final voltage after recharge has influence on the discharging curve too.

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