Homemade Battery Packs

[e-beach]

All battery types self-discharge!
Test is to determine rate and depth of self-discharge.
I recommend self bleed down test only to eliminate the obviously bad cells.

I agree with you on these statements, but I still think a bleed down test is a waist of time until one has identified the potential cells for usage.

My, presently, favorite developed best-fastest cell testing method.

Stage 1
Charge all cells equally to a voltage above preferred use voltage.
I charge 40p using modded 5V MeanWell
Keep eye or finger on cells, remove any that start getting warm, 40p 2600mAh = 104Ah so 30A Meanwell will not create heat while charging unless cells are bad.

Sounds like .288C or something. .288C should not warm them up much.

Stage 2
Separate and allow cells to set and self discharge - the longer the better
Eliminate all with substantial voltage loss - keep only cells that maintain above your preferred use voltage.
I used to charge to 4.20V but have begun charging to 4.05V for certain cells and 4.15V for others.

OK, this is where I feel the bleed down test is a waist of time. Batteries never get better like a fine wine. They all have their individual capacity weather they are new, used or abused. So, the best thing to do is to charge them to as close to full voltage as they will take and then discharge them to a per-determined terminal voltage through a watt meter....something like 4.20 to 2.65v. The watt meter will tell you if they have capacity or not. Putting them on the shelf and waiting is a waist of time. Once a cell is determined to be in good enough condition for future use, then and only then should it be fully charged, the date and voltage noted and be put on the shelf while other cells are tested and readied for usage.

[DrkAngel]

All battery types self-discharge!
Test is to determine rate and depth of self-discharge.
I recommend self bleed down test only to eliminate the obviously bad cells.

I agree with you on these statements, but I still think a bleed down test is a waist of time until one has identified the potential cells for usage.

Bleed down is of more primary importance, IMO.
Any cell with noticeable self-discharge will continually unbalance the entire pack.

If you constantly balance charge ... you might be OK for a while.
Balance charging typically involves the painfully slow process of bleeding down any bank that is charged higher than the others. With one cell of excessive bleed down, it's entire bank will bleed down, forcing a balancing by bleeding down all other banks, via balance charger or BMS.

And, self-discharge seems to get progressively worse ... so, I prefer to get rid of these "pack spoilers" right at the get go.

In fact, my latest method of cell testing has produced packs of such "balance" and reliability that I do not need to balance charge or use any BMS. I merely bulk charge with a CC\CV power supply ... with excellently balanced "full" and "empty" ... equal voltages between all banks!
Charging-discharging does not actively equalize the pack ... it just does not unequalize it ...
I do monitor bank voltages and "fine tune" as deemed advisable.

As for discharging "to 2.65V" ... I would classify that as needlessly and wastefully damaging!
LiCo cells, (18650 & LiPo), have minimal useable energy-capacity below ~3.6-3.7V.
(Varies by specific formulation)

I thought it might be illuminating to gauge the capacity of my lithium-ion (Cobalt) Lipo pack.
Method -
Begin with cells at 3.5V (my recommended minimum voltage)
Precisely charge to 3.6V - measure Ah needed
Repeat at .1V intervals until 4.2V (my recommended maximum voltage)

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)
----------------------------------------
Total. .................... 18.37Ah
Ah capacity previously confirmed with -
iMax B8 full charge ..... 18.4Ah

I was both disturbed and inspired at the lack of capacity below 3.7V

With these cells ... discharging below 3.7V is needlessly damaging.
Almost 90% of the usable Ahs is between 3.7V and 4.1V.

See threads about mapping battery capacity ... for determining optimal charges and discharges.

Capacity Profile
Capacity Map
Capacity Mapping
Lithiums - mAh/100th V - Discharge Tests
Determining Optimal Charge Voltage

[kje]

If you constantly balance charge ... you might be OK for a while.
Balance charging typically involves the painfully slow process of bleeding down any bank that is charged higher than the others. With one cell of excessive bleed down, it's entire bank will bleed down, forcing a balancing by bleeding down all other banks, via balance charger or BMS.

And, self-discharge seems to get progressively worse ... so, I prefer to get rid of these "pack spoilers" right at the get go.

In fact, my latest method has produced packs of such "balance" and reliability that I do not need to balance charge or use any BMS. I merely bulk charge with a CC\CV power supply ... with excellently balanced "full" and "empty" ... equal voltages between all banks!
Charging-discharging does not actively equalize the pack ... it just does not unequalize itself ...
I do monitor bank voltages and "fine tune" as deemed advisable.

Very good argumentation for the "bleed down" phase. It makes the battery pack safer and more reliable.

I like your accurate knowledge about this DrkAngel. I appreciate your contribution in both knowledge and time on this subject!

[e-beach]

.....
Bleed down is of more primary importance, IMO.
Any cell with noticeable self-discharge will continually unbalance the entire pack. If you constantly balance charge ... you might be OK for a while. Balance charging typically involves the painfully slow process of bleeding down any bank that is charged higher than the others. With one cell of excessive bleed down, it's entire bank will bleed down, forcing a balancing by bleeding down all other banks, via balance charger or BMS. And, self-discharge seems to get progressively worse ... so, I prefer to get rid of these "pack spoilers" right at the get go.

I agree with you mostly except I reiterate that the "Bleed Down" test is a poor way to test cells. Here why: Cells that have reached their useful life don't always bleed down.

Ok, after reading this thread I made an impulse buy of what turned out to be about 325 18650 cells. They cost me $70.00 USA and were mostly from used dell laptop battery packs. I have separated all the cells and I am just finishing the study of potentially usable Samsung cells (just over 100 pink, 2600 mAh cells of various dates and chemistry) and my data show that cells beyond their useful life can be nearly fully charged and won't always loose that charge once put on the shelf. This is regardless of the fact that they won't even last 15 minutes under a .38C discharge. So the question becomes how does one separate the cells that don't bleed down and are good, from the duds that don't bleed down and are no-good.

One could make a guess....and that is what most who use the "Bleed Down Test" are doing, guessing. And one can even get very good at guessing...Or one can just charge the cells in a smart charger then discharge them through a watt meter and skip the time wasted of putting them on the shelf for weeks.

As for discharging "to 2.65V" ... I would classify that as needlessly and wastefully damaging!
LiCo cells, (18650 & LiPo), have minimal useable energy-capacity below ~3.6-3.7V.
(Varies by specific formulation)

I agree with you that a continuous and repeated discharge of lithium cells to a low voltage will shorten their life span. A lot of good science is out there to support that statement. (Never fully charge, Never fully discharge, Never store fully charged, The fastest charge possible without heating the cells because heat is the killer of lithium cells...) I believe, all things you have posted in this thread at some point, but lets look at a real world situation....

I roll around on a 36v front DD hub motor. The LVC on my controller, cuts out at about 31.5v. So if I were to build a 12s pack the LVC would kick in at 2.625v per cell (31.5/12=2.625v) Now, I don't get to LVC often, but it can happen. It has happened to me only once in 18 months when I unexpectedly needed to extend a days ride for business.

So, since LVC happens, used cells need to be tested to their full capacity under controlled conditions to fully understand the characteristics of that cell. So by testing a cell from full charge to deep discharge, through a watt meter, we can see what the full capacity of that cell is.... their-by making it mush easier to group cells for optimum pack balance and keeping the weak or expended cells out of the pack in the first place, no "Bleed-down" guessing needed.

[Jonathan in Hiram]

e-beach,

You seem to be arguing that it doesn't make sense to test bleed-down on a cell that otherwise fails internal resistance or capacity checking, that makes sense looking at it one way but there is more than one perspective.

Bleed down test is one that doesn't involve much effort or time aside from storing the charged cells, testing internal resistance on the other hand is a little more difficult and time consuming and capacity checking is considerably more time consuming on a per cell basis.

To get the most return from your efforts it looks to me like getting rid of all the cells which fail bleed down first is the most efficient way of going about it, then you only test the low-leakers for the IR and Ah.

If you need cells quickly to get a working pack just because your transportation situation requires something ASAP and ACAP (as cheap as possible) on the other hand your method would make more sense.

Remember; fast, cheap, good, pick any two.

[DrkAngel]

e-beach ... rather than bickering about whether a bleed down test should be the 1st or last step in determining cell condition ...
I recommend that you post up your entire cell testing methodology ... as I have done ...

My, presently, favorite developed best-fastest cell testing method.

Stage 1
Charge all cells equally to a voltage above preferred use voltage.
I charge 40p using modded 5V MeanWell (combine cells when of nearly equal voltage )
Keep eye or finger on cells, remove any that start getting warm, 40p 2600mAh = 104Ah so 30A Meanwell will not create heat while charging unless cells are bad.

Stage 2
Separate and allow cells to set and self discharge - the longer the better. (Minimum of several days )
Eliminate all with substantial voltage loss - keep only cells that maintain above your preferred use voltage.
I used to charge to 4.20V but have begun charging to 4.05V for certain cells and 4.15V for others.
(Different variations in formulation produce different optimal charged voltages)

Stage 3
With all cells at equal voltage, discharge at a measured rate.
I began using 28s2p, discharging with 2 - 60w light bulbs (~120V DC discharging 120w = 1A=1000mA per hour)
2x2600mAh cells = 5200mAh, 1000mA discharge = ~.2C
Monitor each cell voltage, remove any that fall below 3.5V (voltage will drop suddenly at this voltage, so monitor carefully) and mark time, 1000mAh capacity for each hour
Discharging for 2.5 hours(50%+ oem rated capacity), 3 hours(60%+ oem rated capacity), or, if very good cells, 4 hours(80%+ oem rated capacity). Then rating cells by residual voltage, works nicely.
If cells don't last 2.5 hours, less than 50% capacity, probably not worth building into pack? (unless large bulk pack?)
Mark rated capacity on cells-pairs. (eg "3H 3.82V" or "3000mAh + 3.82V")
Method provides a fairly accurate comparative capacity ... 56 cells capacity tested in 3 hours.

Stage 4
Recharge all cells to equal voltage.
Build banks of equal capacity.
Line up all cells, best to worst. Shuffle into banks.
6s = 123456654321123456654321 etc
Should provide reasonably well balanced capacity banks.

Stage 5
Test full pack discharge, if not perfectly balanced at deep discharge, reshuffle cells to equalize, or add cell-cells to any weak bank.

Quick and easy and reasonably accurate method to test cells - build pack with equal bank capacities.

[e-beach]

e-beach ... rather than bickering about whether a bleed down test should be the 1st or last step in determining cell condition ...
I recommend that you post up your entire cell testing methodology ... as I have done ...

Yep, I knew that challenging the Status-quo would get everyone all "fluffed-up", it always does.....

As for posting my methodology, thank you for the recommendation, I will when I am finished with the 325 cells I have for this test. I still have 80 or so cells to charge and discharge. As a side bar, I fully intended to post my findings in the first place. I just got caught up in responding to a question on your thread.

@ Jonathan in Hiram....Tell me again how charging a bunch of batteries and putting them on the shelf for a month or more is fast?

[Jonathan in Hiram]

@ Jonathan in Hiram....Tell me again how charging a bunch of batteries and putting them on the shelf for a month or more is fast?

I didn't say it was fast, I said it's more efficient of your actual working time, two rather different things.

If you are going to test bleed down to a strict level of tolerance the cells are going to have to sit for a while, the longer they sit the more sensitive the resulting test.

[kje]

Bulk charging:
Confirmed 16 cells at roughly 3.5V
I found a 14awg wire and stripped off the insulation. Soldered all the cells in parallel and my Imax charge them now with 4A.

20140323_233842.jpg (246.08 KiB) Viewed 2856 times

20140324_000341.jpg (234.47 KiB) Viewed 2856 times

[e-beach]

e-beach,

You seem to be arguing that it doesn't make sense to test bleed-down on a cell that otherwise fails internal resistance or capacity checking, that makes sense looking at it one way but there is more than one perspective.

I am not arguing perspective. I am stating that through thorough research I have found that not all bad cells bleed down much. So, if not all bad cells bleed down, the bleed down test becomes a guessing game. I am glad it doesn't involve much effort because it is a wholly inaccurate way to determine cell health.

[DrkAngel]

e-beach,

You seem to be arguing that it doesn't make sense to test bleed-down on a cell that otherwise fails internal resistance or capacity checking, that makes sense looking at it one way but there is more than one perspective.

I am not arguing perspective. I am stating that through thorough research I have found that not all bad cells bleed down much. So, if not all bad cells bleed down, the bleed down test becomes a guessing game. I am glad it doesn't involve much effort because it is a wholly inaccurate way to determine cell health.

? ...

Bleed down test is not being promoted as a singular test for determining cell health ...

It is a simple, minimal effort, method for eliminating one type of "defective" cell, the most dangerous kind.
(Excessive self-discharge indicates some form of internal short = heat = progressive heat? = !!!)
Preferably performed before expending-wasting the time and effort of capacity testing.

At minimum, running this test will eliminate the cells that cause the pack to unbalance itself!

[e-beach]

? ...

Bleed down test is not being promoted as a singular test for determining cell health ...

It is a simple, minimal effort, method for eliminating one type of "defective" cell, the most dangerous kind.
(Excessive self-discharge indicates some form of internal short = heat = progressive heat? = !!!)
Preferably performed before expending-wasting the time and effort of capacity testing.

At minimum, running this test will eliminate the cells that cause the pack to unbalance itself!

A bleed down test might work for the most egregiously defective cells, but it will also miss a great number of the kind of cells that would need to be eliminated later.

Below is a sampling of the pink Samsung 2600 mAh cells that I tested for capacity. With this set I was classifying them at 3.25v or above upon arrival to me. I charged them on my smart charger, let them rest for a bleed down test and then discharged them. They represent about 28% of total number of Samsung pinks cells from this battery buy.

As you can see many of the cells didn't "Bleed down" much, and some didn't "Bleed down" at all, even after as much as 30 days (note SA-44, 45 and 46.) Yet all these cells failed a simple .38C discharge test. If any of these cells were put into a pack they would have to be replaced later. A "Bleed down" test would not have caught many of these defective cells.

(Note: click on the picture if you need to enlarge it.)

[DrkAngel]

? ...

Bleed down test is not being promoted as a singular test for determining cell health ...

It is a simple, minimal effort, method for eliminating one type of "defective" cell, the most dangerous kind.
(Excessive self-discharge indicates some form of internal short = heat = progressive heat? = !!!)
Preferably performed before expending-wasting the time and effort of capacity testing.

At minimum, running this test will eliminate the cells that cause the pack to unbalance itself!

As you can see many of the cells didn't "Bleed down" much, and some didn't "Bleed down" at all, even after as much as 30 days (note SA-44, 45 and 46.) Yet all these cells failed a simple .38C discharge test. If any of these cells were put into a pack they would have to be replaced later. A "Bleed down" test would not have caught many of these defective cells.

Can you really be that dense?
For the 5th+ time ...

Bleed down test is not designed as a single determining test of cell condition!!!

Merely as a preliminary test ... before running capacity-discharge test.

[e-beach]

The bleed down test is a useless time waster and should be abandoned. Go straight to charge then discharge through watt meter. It is faster and more accurate.

[Tench]

DrkAngel, I understand where you are coming from, your method of spending time wisely to arrive at a heap of cells arranged to build the best pack possible from what you have makes sense to me. Some good methods in there to concentrate your efforts on the good cells and eliminate wasting time on the duffers.

[DrkAngel]

The bleed down test is a useless time waster and should be abandoned. Go straight to charge then discharge through watt meter. It is faster and more accurate.

So ... your method processed 34 cells taking, (Nov 23 - Feb 9), 77 days ...

I processed. allotting a 7 day bleed down period, 500+ 18650 cells, taking about 2 weeks ... in my spare time.

All cells 1st confirmed of no noticeable self-discharge - bleed down test (failures removed).
Then, every remaining cell deeply discharge tested and marked with an accurate comparative capacity rating.

Later ...
Refining my method and working with "6 packs" of recycled LiPo ...
I accurately processed 300+ Lipo cells taking about 10 days, 3 days of simple soldering and leisurely monitoring, plus an allotted 7 day bleed down period in the middle.

[e-beach]

The bleed down test is a useless time waster and should be abandoned. Go straight to charge then discharge through watt meter. It is faster and more accurate.

So ... your method processed 34 cells taking, (Nov 23 - Feb 9), 77 days ...

Nope....as I said, that is a portion of my experiment.

I processed. allotting a 7 day bleed down period, 500+ 18650 cells, taking about 2 weeks ... in my spare time.

Everything I have done is in my spare time also, and watt meter accurate. No dud cells will have to be removed from my pack.

[DrkAngel]

They all have their individual capacity weather they are new, used or abused. So, the best thing to do is to charge them to as close to full voltage as they will take and then discharge them to a per-determined terminal voltage through a watt meter....something like 4.20 to 2.65v.

Nope....as I said, that is a portion of my experiment.

Well ... be sure and check with me after the portion of your experiment where you discharge all your cells to 2.65V, ...

2.65V LiCo-Lipo Discharge.jpg (56.34 KiB) Viewed 2869 times

... there will be another step that you had better perform!

[e-beach]

........... there is another step that you had better perform!

[diggler]

hi im just getting into this and I my opinion It makes no difference which test you do first. because a bad battery (meaning no capacity) apparently can sit for a month or so showing no sings of bleed down or internal short ill call it. But a battery that has a hi capacity % can still have an internal short....So I agree with both of you but more so drkangle cause either way the bleed down test will have to be done sooner or later. you can do the capacity test first it doesn't matter but then your just going to have to turn around and do a bleed test after that or vicea virca tell me if im wrong like I said im a week into this stuff and just reading about it but I do need to know cause I got 336 cell coming and only a imax b6 with parallel board and balance leads. so charging is going to be a pain! I like your way of rapid/balance charging with a bulk charger in parallel with a balance charger that has a diode. Genius! I never would have thought of that! So you put the diode on the bulk charger right? then set the volts a little bit lower than the final topping charge right? again please tell me if im wrong I have 0 experience with this but I did take automotive tech. so I have a basic understanding of it. I plan on doing the whole light bulb thing to capacity test but I think im going to get a watt meter also cause I will need it to measure how much capacity I have left on a bike ride anyway. I have many more questions and ideas but ill wait a bit.

[DrkAngel]

Just finished an updated ... better(?), procedure for cell testing.

Step by step used cell testing and capacity rating.
Also provides multiple methods for greatly reducing required time for individually discharge testing to selected DOD - capacity testing.

See - Bulk Capacity-Discharge Testing

Updated ES Wiki page - Soldering and Soldering Irons

Will update Index - Homemade Battery Packs - very soon ... in progress ...

[kje]

Great job DrkAngel. We are carefully following your thread.
I'm almost finished capacity and IR testing all my 150 cells with my Imax B6. Then I maybe need some help/tips on how to distribute the cells together...

[DrkAngel]

2014 Homemade Battery Packs - projects and plans

18650 - recycled laptop cells
My massive quantities of old re-re-recycled Sanyo cells will be retired to portable power inverter use. Except for latest 33.3V 31.2Ah build, will lower to storage voltage and store in cool basement for use as dedicated Winter pack. (still +50% of rated capacity w/reduced (4.05V) charge voltage)

Have 84 NOS matched Sanyo 2600mAh and 72 NOS matched Sony 2600 for, as yet, undefined projects.
Will keep my eyes open for more cells

Also have a good assortment of unmatched but very good Panasonic, Sony, Sanyo , LG cells for smaller projects.
Cordless power tool rebuilds (some have excellent IR rating=good surge capability!)
12V packs for lighting, small air pumps, etc.
Axillary packs

laptop LiPo - Re-tasked NOS (New Old Stock)

I will build multiple eZip 25.9V 25.92Ah battery packs. These are ideal for eZips and iZips that use the RMB removable battery "cartridge". Improves range ±500%, in combination with the 16T mod, upgrades oem speed to the "legal" 20mph. (Compared to oem, new, Slabatts)

Special request for a 12s10p - 44.4V 21.6Ah (.96kWh) build - fits perfectly in a 6 pack cooler (±12lb)

12s14p 44.4V 30.24Ah (1.35kWh) Saddle bag pack
(Should allow 30mph, motor only or light pedal, cruising for eZips-iZips.)
(Gearing and cooling ... to be determined.)
(Lowered seating and small fairing ... in the works.)

RC LiPo
I know, I know ... "these are the most dangerous type of lithium for pack builds!"
While I have never heard of a single recycled laptop build "fire-explosion", on the forum ... seems like almost daily, there is another LiPo fire.
But, rather than just building packs of packs ...
I intend to treat RC LiPo the same as I treat recycled laptop cells.

Every individual cell will be tested for :
1. self discharge
2. comparative IR
3. and discharge-capacity tested
4. all banks will be capacity matched and monitored

No BMS! I've come to view them as bandaids for defective packs!

So, rather than relying on some, lowest cost, mass production factory, I will perform the QC, (quality Control), and testing that they don't seem to care about.

Preliminary RC Lipo builds will be as auxiliary or hybrid packs, RC LiPo "buffering" for large capacity, but low surge capable, laptop rebuilds.
9s8p 33.3V 17.2Ah Laptop LiPo buffered with 9s2p 33.3V 4Ah RC LiPo = 33.3V 21.2Ah w/good surge capability! (Fits in eZip RMB battery case.)

[TheBeastie]

If you got a lot of low C rate batteries have you ever considered hooking them up to some ultra caps to boost their performance for ebikes and extend their life via using the ultracaps to store regen energy?
Thought this video was cool to demonstrate the stored energy http://www.youtube.com/watch?v=5hUxCYixoE4
This guy is using them to start his car http://www.youtube.com/watch?v=z3x_kYq3mHM
http://www.youtube.com/watch?v=8miq6sDy ... -hot-vrecs
This guy got a nice little ride on his electric scooter http://www.youtube.com/watch?v=exwd-tswyzA
Ready to go 48v version http://www.maxwell.com/products/ultraca ... 8v-modules

[DrkAngel]

If you got a lot of low C rate batteries have you ever considered hooking them up to some ultra caps to boost their performance for ebikes and extend their life via using the ultracaps to store regen energy?
Thought this video was cool to demonstrate the stored energy http://www.youtube.com/watch?v=5hUxCYixoE4
This guy is using them to start his car http://www.youtube.com/watch?v=z3x_kYq3mHM
http://www.youtube.com/watch?v=8miq6sDy ... -hot-vrecs
This guy got a nice little ride on his electric scooter http://www.youtube.com/watch?v=exwd-tswyzA
Ready to go 48v version http://www.maxwell.com/products/ultraca ... 8v-modules

Limited pack size.
Super low budget builds.
30Amp controller, so 17Ah Laptop cells at ~1C and 4Ah LiPo at <5C is plenty ... with no strain on any cells.