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biker 01-04-14 07:43 AM

All li ion cells die someday.

I have some A123m1 cells recycled from 2006 Dewalt packs that are still going strong and might out live me. :)

Li ion cells get little shorts in them over time.

Enough of these little shorts will kill off the cell.

Quality name brand li ion cells are designed to die in a non fantastic way, not short out quickly when they die.

Cells designed to die in a non fantastic way are the only cells that should be used with a bms.

All rc lipo battery makers say to always charge rc lipo with chargers made for rc lipo batteries and to always attend the rc lipo batteries being charged.

Rc lipo can get large shorts inside the cell and cause the cell to die in a fantastic way.

A bms is designed to kill a pack if needed but the way they kill a pack was not designed for killing rc lipo cells that were not designed to die in a non fantastic way.

Rc lipo was designed for rc racing and max power, lowest weight.

Rc lipo was not designed to last very long or die in a non fantastic way.

Good for ebike racers that have money to burn I guess. :)

DrkAngel 01-05-14 01:38 PM

Interesting, I have noticed ...

In many years and with many many builds, 18650 laptop cells seem extremely ... reliable-consistent.
In series + parallel they never seem to fail ... they just fade away.
Of course, I, typically, build packs using same brand-rating cells.
But it is amazing how evenly and predicatively cells head towards "end of life usable."
An initial bank capacity equal build usually retains acceptable high and low "equalization" for many many cycles (100's?).
Even when cells in same bank vary in capacity!

Of course you must avoid overly low or high, (damaging), discharges-charges!

biker 01-16-14 11:00 AM

Using good name brand high quality li ion cells to build an ebike battery is nice.

Not everyone lives near a big city where laptop packs are plentiful like I do though.

Buying the packs on eBay is very hit or miss. Found that out.

I like to ebike way out in the woods, far away from where a car could save me if I broke down.

So for travels way out in the woods I need a setup that is very reliable.

Quiet ebike sneaks up on wildlife so I can take pictures. :)

And a setup that won't catch the woods on fire.

Currie brushed motor with a small A123 power pack backed up with a laptop pack will go all day.

We live in South Florida and test this stuff out all year, on road and off road, almost every day, on an ebike or etrike.

DrkAngel 01-25-14 08:16 AM

33.3V 31.2Ah eZip RMB Pack Build
Well, I keep claiming that I have squeezed the maximum number of 18650s into the oem eZip pack.
7s12p .. 8s12p ...
Finally ... this might be true.

Next build was going to be a "hybrid" 18650 & flat Lipo project ...
but I got tired of all the old Sanyo 18650s laying around.
So I gathered them all up and selected all that measured a retained voltage higher than 4.10V.
(After being equally charged to 4.20V+ 8+ month ago)

9s12p (33.3V 31.2Ah) eZip Rebuild = 1kWh!!!
By staggering the cells I am able to fit the cells in 9 wide.
Case will stack 12 1/2 cells high if I remove center screw and use only a 3/16" Masonite bottom support-protection "shelf".
I chose the 90 best retained voltage cells and stacked so as to have "equal" capacity per stack.
Now, 9 x 12 is more than 90 cells ... and sorting solely by retained voltage is a poor measure of capacity! ... ?
But ...

Bulk Building
I rated and sorted "build" cells solely by "bleed down" - "retained voltage", and will assemble and test as a 9s10p pack.
After initial discharge-recharge cycles, I will "equalize" pack using precisely capacity rated Sanyo cells pulled from my last batch of recycled Lenovo packs.
By adding them as the final 9s2p.
Pack will be used on my Snow Beast and as a testbed for a future build using "new" (NOS) cells.
I have 2 eZips that run nicely on 33.3V batteries.
These Sanyo cells are 3.6V and after learning my lesson by damaging with 4.20V charging, I will be charging at 4.0-4.05V, for increased life.
I will add 1/2 cell height (9mm) "blanks" as additional support for the alternate "banks".

Well ... this leaves a couple hundred "lesser" condition-capacity old Sanyo 18650 cells laying around.
Leftovers and re-recycled from 6 years of multiple builds.

So, a "true" bulk build!
I have a couple "antique" 200w inverter packs.
2 - 18Ah SLA outputting 200w continuous through a GFCI 110V AC outlet.
Well I'll pull the 12V 36Ah Lead Acid and pile in all the 18650 cells that will fit.
3s66p might fit = 171Ah
(Check bank voltages after 1st discharge, add cells to any low bank - re-cycle - repeat.)
But, probably be lucky to get 72Ah actual capacity out of these ... rejects.
Still, that is 200% the oem capacity at 1/2 the weight.
Most importantly!
I have those old cells safely stored and not laying around.
And, of course, a nice supply of emergency-portable power.
It also has a 12V "cigarette lighter" outlet for a more powerful inverter or 12V.

Will add pictures ...

DrkAngel 01-27-14 09:43 AM


After draining my 33.3V 26Ah (9s10p) to 33.2V, ~3.7V per bank, I marked resultant voltages and added complementary 2s to each bank as deemed advisable.
Lowest bank got the best cells - best got the worst.
Lowest bank (3.65V) got 4500mAh, highest (3.71V) got 4100mAh, the remainder apportioned in between.
Since I will discharge to not below 3.8V, where cells were within 2/100th of each other and "good" ... now they are just "more good".

At 3.8V - 4.05V capacity is still >20Ah ...
I will measure Ah capacity after next deep discharge ... though I typically recharge immediately after any use and weather is too cold for any extended rides, so, full capacity test might wait till near Spring.

Last 2 banks were pulled from a different batch that had oddball tabs ... sorry, wanted it to look prettier!

I will monitor 1st few discharges ... mainly to check for bad-poor solder connections.
After that I will rely on bulk charging with the occasional balance check.

Edit - I did add 4 - 9mm, 1/2 cell height, blanks as support for the alternate banks.
And re-covered all cells with a wrap of boxing tape.
Both ends of cells were covered with closed cell polystyrene, (foam sheet, as is used for durable padding), to secure-stabilize cells tightly in pack.

DrkAngel 07-22-14 05:58 AM

22.2V 30.24Ah Battery Build

Originally Posted by DrkAngel
I believe I will attempt to build another 22.2V pack.
Previous 22.2V pack consisted of 40Ah+ of old re-re-recycled Sanyo cells and I rated as ... lack-luster - too wimpy! in performance.

Proposed build will consist of the same type Lipo cells used in 25.9v 22mph pack.
Instead of using the 12 side cells as an additional 7th bank they will add 2 cells to each of the 6s "bricks".
Same total capacity
7s12p = 25.9V 25.92Ah = .671 kWh
will become
6s14p = 22.2V 30.24Ah = .671 kWh
22.2V pack should be an enforced economical and "legal" alternative for my 2008 Trailz w/16T mod and my 2013 Trailz LS w/13T mod.

22.2V Lipo should outperform, or at least compare favorably with, 24V SLA.
SLA 24V controller w/~21V LVC should be perfect for the 22.2V Lipo.
Balance charge with cheap iMax B6 or equivalent ~$20
6A CC/CV charging with MeanWell S-150-24 ~$20 + shipping
And should provide 600% the range of the oem SLAbatts! ... at 1/2 the weight!!!

Oh ... and ...
5x the range of the $400 Currie Lithium alternative (6.14Ah)
3x the range of the $600 Currie Lithium alternative (9.6Ah)

22.2V 30.24Ah NOS Laptop Lipo ... ""100701" = 2010 July 01 dated cells.
I know, I know ... I said 22.2V was too wimpy!

But, I tried my latest 25.9V 25.92Ah battery build on my latest ...
2013 eZip Trailz LS w/13T motor sprocket ... cruised at 22-23mph.
Couple problems:
Exceeds "legal" - 20mph.
Running at +22mph strains the battery well past my recommended .5C.

Running the numbers ... 22.2V looks to cure both problems.
Took the 7th"s" and split it up between the remaining 6s.
Dropped top cruising requirement by 100w.

1st build using the newer black eZip "RMB" pack.
I had to chisel "ribs" out of pack, to provide proper clearance.
Used Formica as shelves to support cells.
Wedged a wooden block as additional support under lower cells-Formica.

I did add a balance connector ... had the silicone 22ga balance connector anyhow ...
Just cause I could ... I balanced all banks to precisely 4.186V.
Ooh! Tried bleeding down a bank using jumper wires connected to ends of soldering gun tip. Worked pretty good ...

Speed settled perfectly ... just a fraction under 20mph.

Testing now.
Ran 20 miles at 19mph+ and have all banks still at 3.84V.
Likely another 7-8 miles at 19mph?
Oh ... motor only, no pedal assist.
40miles plus @ 16mph?

Will mod a MeanWell S-150-24 as 25V 6A charger.
The 24V 40mm fans seem a bit fast-loud so I tested with a 2watt 47ohm resister, in series, and resulted in a moderately quit fan with minimal resister heat.
Upgraded charging wire to 14ga for rapid charging ... if I care to try ...

Reread the post...
Sounds like I rebuilt my 25.9V into a 22.2V.
Separate build!
I still have both and need 25.9V for my 16T mod eZips.

DrkAngel 07-22-14 07:41 AM

22.2V 6s LiPo Bulk Charger (24.84V 6A)
Built 24.84V 6A MeanWell charger (S-150-24) ... for 22.2V LiPo pack.
Yes I labeled it.
Don't want to plug into wrong pack!
18ga computer power cord fit through wire hole.
4.14V per bank looks optimal.

MeanWell will be outputting 6A continuously for nearly 5 hours so I felt it advisable to add a 24V fan.
At about 25V it seemed annoyingly loud , so ... I added a 47ohm 2w resistor in series.
Dropped voltage at fan to 21V and quieted to ... acceptable.
Fan placement appears optimal.

DrkAngel 07-23-14 06:06 AM

25.9V 25.92Ah eZip LiPo Build + Rebuild

Originally Posted by DrkAngel
Built a replacement 25.9V 25.92Ah Recycled Lipo pack for my eZip.
7s12p 2160mAh cells, paired, in 3s2p 6 packs.
All new packs-cells, with identical date of manufacturer.
(081209 2008 December 09 ... Yes! ... 5 years old+.)
Charged in 4 bay bulk chargers last summer ... all cells were still 4.09 or 4.08V.
Assembled and ran for 20 miles at between 18 and 22mph.

Resultant cell voltages were either 3.82V or 3.81V ... except the 12cell side cells at 3.80V,
Close inspection found a poor solder joint
Fixed ... and charging now.
Will balance at full charge -4.17V per cell as maximum, typical "full" charge will be ~4.05V ... except for trips.
I anticipate many years and many many thousands of miles.

These 6 packs are ideal for 22.2V, 33.3V, 44.4V builds.
7s is awkward ... but does fit efficiently in the eZip RMB packs.

After initial monitored cycles, I intend on bulk charging only ...
No BMS! ... I view them as band-aids for defective packs.
(Of course I also prefer the tech friendly Windows XP ... so ...)
Additional points:
Removed built in pack fuse, to simplify wiring.
Added in line fuse (40A)
Replaced all internal ≥ 12ga
Except charging wires upgraded with 16ga
Layed sheets of closed cell foam below and above, to stabilize cells in pack.
"Bricks" of cells are supported by "sheets" of Formica.

Old one passed its 3rd year and 7000 miles ... and was built with the rejects, the recycled packs that would not charge properly!
Still 10-12Ah usable ...
Will keep until I need the shell for next build.


Originally Posted by DrkAngel
Broke a LiPo ribbon cable - thin aluminum
One bank low, so I disassembled and traced the problem.
6pack, nearest the back-bottom, broke the pos power ribbon from one cell.
For convenience, I have the top banks setting on the connections.
I better supported the top bank by placing wooden spacers between the bottom banks and the Formica "shelf".
If it does not work for an extended period, I will ...
I will flip upper bank and run longer wiring. (Probably a good idea!)
Ribbon broke at poorly supported bank with brown heatshrink.

650+ miles
4th metered recharge 3.70V - 4.182V = 24.42Ah (Black iMax B8)

1st metered recharge 3.82V to 4.16V = 18Ah.(Blue iMax B8)
2nd metered recharge 3.695V - 4.170V = 24.264Ah (Blue iMax B8)
3nd metered recharge 3.666V - 4.185V = 27.647Ah (Black iMax B8)
4th metered recharge 3.70V - 4.182V = 24.42Ah (Black iMax B8)

Sadly my "repair" with added support etc. failed miserably!
2 banks showing additional damage, after a few cycles.
So, rather than another "repair" I pulled the 6 major banks and replaced with new 2010 cells.
I did position to prevent further damage!

I have run a few cycles and then a deep discharge for capacity check.
Discharged to 25.66V.
All cells were equal within 2/1000th V at 3.666V!
This shows excellent matched capacity!
Beyond any reasonable expectation.
The quality control and durability built into these 4 year old cells is astounding!!!

Did a metered recharge using iMax B8 (Blue).
3.666 - 4.156V = 25.376Ah

#1 Laptop LiPo Build
2011 - 24.0Ah (25.9 to 29.4V)
2012 - 20.8Ah (25.9 to 29.4V)
2013 - 15.8Ah (25.9 to 28.7V) 6500+ miles
2014 - 13Ah+ (25.9V to 29.2) 7000+ miles

#2 Laptop LiPo Build
1st metered recharge 3.82V to 4.16V = 18Ah.(Blue iMax B8)
2nd metered recharge 3.695V - 4.170V = 24.264Ah (Blue iMax B8)
3nd metered recharge 3.666V - 4.185V = 27.647Ah (Black iMax B8)
4th metered recharge 3.70V - 4.182V = 24.42Ah (Black iMax B8)

#3 Laptop LiPo Build - Rebuilt 25.9V 25.92Ah 2010 Laptop LiPo (Dell)
1st metered recharge 3.666V to 4.156V = 25.376Ah.(Blue iMax B8)

cat0020 08-13-14 04:53 AM

New to ebike, just ordered a 48V 1000w 26" rear wheel to use on my old hardtail MTB.$_12.JPG

Can i can some suggestion where to souce RC or laptop LiPo batteries?

I plan to commute between Manhattan, Brooklyn and Queens, distance between chrarge will likely be under 20-25 miles.

DrkAngel 10-03-14 08:09 AM

Previously, I have documented a wide variety of mods for the MeanWell S-150-24.

Spotted a cheap Volt amp meter that inspired me to one further mod.
<$5 100V 10A dual color meter

MW 15-29V 0-10A PS-Charger

I lucked into a supply of Genuine MeanWell S-150-24's with the switch and shroud that made this build extra nice.

Using my documentation on values for different mods ...

Originally Posted by DrkAngel

Wider Amp adjustment:
Disconnect, or remove R33 & R38.
Replace with adjustable" pot"
Working with 12.6V LiPo pack through inverter

Amps ...... Ohms
1A ... from ... 70 ohms
2A ... from ... 175 ohms
3A ... from ... 287 ohms
4A ... from ... 392 ohms
5A ... from ... 500 ohms
6A ... from ... 610 ohms
7A ... from ... 715 ohms
8A ... from ... 855 ohms
9A ... from ... 920 ohms
10A .. from .. 1050 ohms = 1.05 k
11A .. from .. 1140 ohms
12A .. from .. 1293 ohms
13A .. from .. 1357 ohms
14A .. from .. ? ohms
15A .. from .. ? ohms
16A .. from .. ? ohms
17A .. from .. ? ohms
18A .. from .. ? ohms
19A .. from .. ? ohms
20A .. from .. ? ohms

I disabled R33 and R38 and ran wires to a 1K large turn pot.
This gave me an amp adjustment from .17A to 10A.
Surprisingly, the amp graduations are fairly equidistant!

I wanted a minimum 15V capability and could have used a 2K pot to acquire the capability, but I preferred more precision.
So, instead of removing the SVR1 pot I cut the "sweep" leg and ran wires to the leg and to the circuit, then added the 1K large turn pot in series.
The result?
19-29V adjustment from the top mounted pot, with the optional adjustment of the on board pot shifting the top mounted pot to as low as 14.5-19.3V.

I wanted 15V capability for a full 10A @ 15V.

Since I intend this as a fairly universal power supply, I used a Deans T-Plug for mounting various output connections.

DrkAngel 10-23-14 04:24 AM

Bulk Cell Testing
All battery types self-discharge!
Test is to determine rate and depth of self-discharge ... to eliminate dangerous cells by diagnosing abnormal self discharge.
I recommend self bleed down test only to eliminate the obviously bad cells.

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.

DrkAngel 11-21-14 09:49 PM

Testing up my latest 12 x 3s4p batteries in bulk.
(2 batches of 6 x 3s4p)
1. Removed from packs
2. Used imax B8 to balance charge to LiPo voltage 4.17V per every cell.
(with 1 exception, all cells in each pack began within 1/100thV )
3 Ganged cells in parallel 3s24p to precisely equalize to 1/1000V
4. Re arranged in series, 18s4p
5. Connected 90V 20A V-A-W-Ah meter and 100w light bulb and 150w heater which supplied a 1.35A discharge.
6. Monitored voltage until 1st cell dipped to 3.65V

1st batch (Sony) metered at 8.43Ah with all 72 cells within 2/1000th V of median.
3.658 - 3.661
This demonstrates an excellent degree of quality control in manufacture!!!
And a very modest 4.17V to 3.66V metered discharge showed 81% of rated capacity.
Probably 90%+ if I pushed voltages to what most consider usable.

Next up, 2nd batch, (Sanyo) using same procedure.

DrkAngel 12-01-14 08:54 AM

1 Attachment(s)
Got 108 excellently capacity matched cells ready for my 33.3V 31.2Ah, (1kWh), eZip pack build.
33.3V x 31.2Ah = 1038.96Wh (1kWh+)
Compared to the OEM
24V x 10Ah 240Wh/2(SLA) = 120Wh
So 800% the usable capacity ... at about 70% the weight!

Will be using 6 12pks of Sony and 3 12pks of Sanyo

Recharging cells now and should have pack built this weekend.

Looking to prolong life as long as possible, so will, typically, be charging to 4.05V per cell, possibly lower.
Charging to 4.10V instead of 4.20V is reputed to double cycle life, 4.05 likely to triple it!
Will determine optimal voltages after capacity mapping Sony cells.

Not built as a replacement for my re-re-recycled 33.3V 31.2Ah eZip pack.
Now at less than 50% of original capacity ...
But all cells have diminished at a nearly identical rate and banks are still remarkably equal in capacity.
(These cells have been built and rebuilt into multiple of my pack builds)
I will retire old pack to Winter duty ... don't want to take any extended trips in the cold and snow ...
Pushing 60 and the cold reminds me of every ol' "poor decision" I've ever made.

DrkAngel 03-16-15 07:41 AM

Laptop Cells vs RC Lipo
Laptop cells are designed to be the safest possible.
RC Lipo are designed as the most volatile - capable of the most dramatic discharge-danger!

If built with optimal quality control and treated with proper handling-care, RC Lipo can be reasonably safe.
If you wish to build a RC Lipo pack ... I recommend you use my testing methods to
1st - eliminate self-discharging cells
2nd - build banks of equal capacity and similar IR (Internal Resistance)

and further
3rd - use in a protective case
4th - continually monitor cell-bank level voltages
5th - Limit charge and discharge levels to more central-safer voltages
6th - Limit charge-discharge rates to much lower-safer than rated

Following these simple guidelines greatly increases the safety, durability and usable lifespan of Lipo.

BoxTurtle 03-17-15 02:32 PM

Hi Folks,

While I'm waiting on my first (next week!), I'm learning about DIY battery packs. The Falco assist on my bike has a five-year warranty if the Falco battery is used. Not wanting to void the warranty, I'm wondering if I can use a DIY battery pack to recharge the Falco battery? On the other hand, is this even a worthwhile consideration? Perhaps the Falco battery will have sufficient "legs" to get me home every day. Anyway, if anybody has thoughts on this idea I'd like to hear them.

Thank you.

Take care, Tom

DrkAngel 03-21-15 07:24 PM


Originally Posted by DrkAngel (Post 17634319)
Laptop cells are designed to be the safest possible.
RC Lipo are designed as the most volatile - capable of the most dramatic discharge-danger!

If built with optimal quality control and treated with proper handling-care, RC Lipo can be reasonably safe.
If you wish to build a RC Lipo pack ... I recommend you use my testing methods to
1st - eliminate self-discharging cells
2nd - build banks of equal capacity and similar IR (Internal Resistance)

and further
3rd - use in a protective case
4th - continually monitor cell-bank level voltages
5th - Limit charge and discharge levels to more central-safer voltages
6th - Limit charge-discharge rates to much lower-safer than rated

Following these simple guidelines greatly increases the safety, durability and usable lifespan of Lipo.

"New" cells does not guarantee them being of good condition!

Especially with budget priced cells, quality control-consistent quality is often lacking.
Test thoroughly and if possible, demand replacements for any packs with poor-bad cells.

DrkAngel 05-17-15 09:41 AM

To BMS or To Not BMS?
With properly tested, matched and monitored cells ...
A BMS becomes more an expensive security blanket than a necessity.

Test cells

1. Eliminate self discharging cells!
Charge cells to rated or anticipated charge voltage
Let set idle for several days and monitor for and eliminate all with a notable self discharge
(I bulk charge large numbers in parallel, then separate to diagnose self discharge)

2. Test IR (Internal Resistance)

An IR meter is rather expensive ...
So I run a comparative IR test
With cells still of equal voltage, apply a measured drain to each cell or pair of cells etc.
Monitor voltage sag with the specific discharge amperage for a specific time
EG .5C for 1 minute ... ?
Label each cell or pair with the sag voltage for use as it's comparative IR (-.12V)
Cells with excessive IR should be eliminated, or separated for alternate use-project.

3. Test Capacity

Cells can be capacity tested individually

a. But I prefer to do a time and effort saving bulk capacity test
(Self discharge and IR tests will eliminate most low capacity cells)
I rig 28-30 cells, (typically paired cells = 56-60), in series for a 117.6-126VDC .
120V DC can be very dangerous - electrocution hazard!
Then I attach 2 - 60w (120w) light bulbs for a 1Amp discharge. (1 - 60w for .5A discharge etc.)
(Quick check for any "bad" IR cells I might have missed)
Check-monitor voltages of every cell at specific intervals, 15min = .25Ah, 6min = .1Ah etc.
Monitor very closely as cells near 3.60V, as voltage will drop suddenly near that voltage!
You can end test when first cell hits 3.50V and label each cell with time expired (2 hours = 2000mAh) and residual voltage after discharge removed.
This will give you a reasonably accurate comparative capacity.
You can further, more accurately, test capacity by continuing test with matched cells for subsequent batches of cells.

b. I combine 20 cells (or cell pairs = 40 etc.) in series and discharge through a cheap 90V V-A-W-Ah meter - $12 (requires external battery connected for maintaining mAh reading when cells removed)
Add electrical discharge devices till desired discharge rate attained (2-3 bulb light fixture, various wattages - 50-100-150w 3-way bulb?)
As cells hit discharge voltage ( 3.50V?) remove cells and mark with mAh when cells removed from series.
(For ease, I, now, connect cells in series with small 8mm neodymium magnets, steel wire on end of strings to fold into shorter stings)

(Recharge all cells to identical voltage)

Match cells

Build banks of equal capacity.
If IR varies noticeably and short of spare cells, distribute a similar sampling of differing IR cells to each bank.
Connect cells in series and parallel and perform a monitored discharge at near anticipated use.
Monitor banks for any sags or low final voltage.
If banks of equal voltages during deep discharge (3.50V?) and after discharge removed, pack is of equal capacity and IR.
Banks of equal voltage after deep discharge (~3.70V?) indicates banks of equal capacity.
If unequal, rated cells can be swapped to equalize.
If' when drain removed, bank voltages diverge, then IR can be adjusted by replacing individual cells with ones of higher or lower comparative IR.

Building banks of equal capacity and IR is more important than individual cells!

It may seem like a lot of effort!
But after many, many builds and 10s of thousands of eBike miles ...
Building it right to begin with saves much time and effort!!!

Banks of equal capacity and IR will discharge and recharge nicely to nearly identical voltages!
Bulk charging recommended with the occasional or scheduled balance charge.
Do monitor charged and discharged voltages for any problem or to determine balance charge desirable.

Remove self discharging cells
Build banks of equal capacity and IR
Never over charge or discharge
Monitor bank voltages

Never need or want a BMS ... !

I have come to view a BMS as a band-aid for a defective pack!

See - Bulk Capacity Testing

Designed tests for recycled cells ... but
Test new cells too!
If nothing else ... test for self discharge! and demand replacements for these defective-dangerous cells!!!

Scook116 06-09-15 10:33 PM

Sorry if i'm hijacking the thread from OP's.
I'm making my first multi-cell (6s) lipo/li-ion pack for a large octocopter and would like your guys' opinion.Based on your experience.
Do you think that the flat-pack cells could safely be sandwiched together (shrink wrap) without damaging them?
Using the scavenged li-ion cells from battery packs were you able to accurately charge each individual cell while maintaining a balance?
I just need to approach the feasibility of making a homemade 6s for my requirements. Specifically; capacity, balance, output > 16,000mAh .

DrkAngel 06-14-15 06:30 PM

I'd have to recommend high output RC Lipo only, for any copter.
Laptop LiPo - Li-ion are designed for larger capacity, which sacrifices maximum amp output.
Check out for LiPo and search for RC forums for most relevant advice.

DrkAngel 09-20-15 08:49 AM

1000 Laptop Cell Recycle Job
Half way into the process of evaluating a large batch of LiPo cells ... the deal for my chosen motorcycle, for electric conversion ... fell through.
So, might have some tested and rated cells available ... ?

Self-discharge testing about 1000 2.16Ah cells.
(3.7V x 2.16Ah x 1000 = 7.992 kWh)

All cells in each stack precisely equalized to within 2/1000th V.
Wove tinned copper braid in parallel of closely voltaged cells ... to precisely equalize
Discharged 1st batch as 30s2p using 2 60w light bulbs for a 1 Ah per hour capacity test.
120V DC electricity can be very dangerous - use extreme care!
Nearly 1000 cells running self-discharge test
Finally started evaluating the Dell packs that used the Sony cells

Will eliminate any self-discharging cells;
test all cells for a comparative IR;
confirm all banks in each pack of same IR;
run 30s discharge evaluations (discharge capacity test).

DBrown9383 09-20-15 09:20 AM

Forgive me for not reading every post but you guys still building NiMH packs do you have any issues with individual cells venting?.. I used to build 10 cell packs for high discharge RC airplane motor. I would push 200 amps for short bursts (3-6 sec.) and some of the high capacity cells couldn't take it and would puke their guts ruining the pack, there was never the fire danger that there is with LiPo but it still got expensive. With todays low resistance Lipo cells I can push 200+ amps from a 3 cell pack with confidence however there is always the fire danger if I crash or have an unbalanced or physically damaged pack

DrkAngel 09-20-15 02:19 PM

Comparative IR as Capacity Estimate
Using Comparative IR as Capacity Estimate

With the large quantity of cells that I am testing, it seems proven out that ...

With cells of same manufacture, (age, batch etc.), and same starting voltage, the degree of voltage sag under a specific load-discharge indicates a reasonable comparative estimate of capacity.

With the large quantity of cells in my project I was able to separate cells by "Ver: #" and when indicated, group by actual date of manufacture.
(several dozen more 6 packs not in picture)

After self-discharge test, and removal of defective packs ...
Next test will be a 1 minute discharge using a 12V 3.33A 3D printer heating element, in cup of water.
(4.32Ah battery with 3.33A discharge = .77C discharge rate)
At a timed 1 minute, I will meter and mark pack by voltage sag, EG. .58V.
Then I will quickly confirm individual banks of nearly identical sag. (any notable divergence will be segregated for cell level testing and use.)

Capacity test banks of 30s2p will be grouped by similar Comparative IR and starting voltage.
Most stacks were charged precisely within a couple thousandths of 4.100V/cell.
With 4320mAh (2p), I will likely discharge for 3 hours = 3000mAh, then label with resultant voltage for direct battery capacity comparison.
Might meter samples further for more accurate capacity rating - (3.75V -3.6V = 850mAh + 3000mAh for 3850mAh capacity )
Will use my capacity map of these cells to estimate full capacity:

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