Homemade Battery Packs

Batteries, Chargers, and Battery Management Systems.
ASK1
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Re: Homemade Battery Packs

Post by ASK1 » May 09, 2015 11:04 pm

DrkAngel wrote:Current equalization is helped by providing extra heavy wire on the end "rails".
See = Cell interconnections for cans - ES Wiki

Alternate method for true equalization...
P1.jpg
What exactly do you mean by end rails? I'm not familiar with the terminology. It's basically the 2 parallel rails on the end that actually lead directly to the positive and negative terminals? Can you explain why having more conductor there would help, my (probably wrong) intuition would be that any smaller rail in the pack would act as a bottle-neck.

As far my parallel rail conductors: I'm using fairly heavy wire on the whole pack - tinned copper braid similar to what I see in your pack here:

Image

Does using a high-enough capacity conductor (like this copper braid) basically eliminate the electrical path length concerns?

I could wire it as you suggest, but my hope is to keep all the major connections on one side (which would be the top side of the pack) for housekeeping & various other reasons[/quote]

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DrkAngel
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Re: Homemade Battery Packs

Post by DrkAngel » May 10, 2015 5:55 am

It appears you are building parallels first, then running in series using a single connection. ... ?

I, personally prefer to build in series first, so there would be 8 low current series connections, evenly distributed current.
Then I run parallels, creating redundancy and equalization functions ... lighter gauge wires required.
Full current is then combined and collected into the high capacity, heavier gauge, "end" power rails. (Of gauge substantial enough and short enough to minimize voltage drop as a factor )
UL rating is:
14ga = 15A
12ga = 20A
10ga = 30A
8ga = 50A
I tend to double the UL rating for maximum surge-brief throughput and consider line drop as a negligible factor.
14ga = 30A
12ga = 40A
10ga = 60A
8ga = 100A

7s10p 18650 diagrammed - 25.9V 26Ah (w/2600mAh cells)
Image
The tinned copper braid I use weighs more than 3 strands of 12ga copper and should be good for 100A, so is overkill on my 40A fused pack.
Oh yeah! Don't forget to add a fuse to your pack! Could save you a whole lot of heart ache!!!

You could easily up your equalization factor with dual series connections ... ? Or attach in center of parallel ... ?
Output connections will be 13s apart!
P8.jpg
P8.jpg (29 KiB) Viewed 3775 times
My typical method would have 8 series connections.
As mention in the Wiki article, I tend to build in parallel 1st for large bulk packs only and would use multiple series leads ... providing redundancy, equalization and the necessity for lighter gauge, easier to work and safer to solder to cells, wire.
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Re: Homemade Battery Packs

Post by ASK1 » May 10, 2015 4:01 pm

I can't really change the circuit configuration, I already have a 13S BMS and the design of the 8P group prevents them from having connections besides the end-connections at cells 1 and 8.

I will try to do it as you have suggested. Thanks for the advice.

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Re: Homemade Battery Packs

Post by Skalabala » May 15, 2015 9:12 am

Could this be of any help to test cells with?
http://alienpowersystem.com/shop/electr ... ontroller/
Image
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Re: Homemade Battery Packs

Post by jaunty » May 15, 2015 12:30 pm

maybe a silly question here but...

I need a 48V battery. I want to build in series, but not one entire string of 13S. maybe one 6S pack and 1 7S pack.

if 48V requires 13S..how many in series is required for 24 systems? certainly not 6.5S (unless youre a badass).

I'd like to segment the pack into two 24V packs.. then wire those in series. But what problems does that pose for BMS?

Thanks

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Re: Homemade Battery Packs

Post by riba2233 » May 15, 2015 2:43 pm

Actually 14S is better match for 48V, and 7S is great for 24V. There should be no problems for two bms in series.

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Re: Homemade Battery Packs

Post by jaunty » May 15, 2015 7:18 pm

i have a lot of sanyo 18650 (red ones from lenovo thinkpad) and im finding that most of them only charge to about 3.9-4.1 volts. most in the 3.95 range.

either thats their max voltage, or im not leaving them on the charger long enough. Basically because im paranoid and i dont want to overcharge them.

anyone have input on this?

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Re: Homemade Battery Packs

Post by parabellum » May 15, 2015 10:16 pm

riba2233 wrote:Actually 14S is better match for 48V, and 7S is great for 24V. There should be no problems for two bms in series.
There can be a problem actually.
1) If they have separate charge/discharge leads (describe the processes )
2)If charge/discharge are together, what happens when charged one shuts down first (repeatedly)

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Re: Homemade Battery Packs

Post by parabellum » May 15, 2015 10:20 pm

jaunty wrote:i have a lot of sanyo 18650 (red ones from lenovo thinkpad) and im finding that most of them only charge to about 3.9-4.1 volts. most in the 3.95 range.

either thats their max voltage, or im not leaving them on the charger long enough. Basically because im paranoid and i dont want to overcharge them.

anyone have input on this?
Yes, charge to 4.2V whatever it takes attended, use cc cv method and come back. :)

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Re: Homemade Battery Packs

Post by riba2233 » May 16, 2015 3:12 am

parabellum wrote:
riba2233 wrote:Actually 14S is better match for 48V, and 7S is great for 24V. There should be no problems for two bms in series.
There can be a problem actually.
1) If they have separate charge/discharge leads (describe the processes )
2)If charge/discharge are together, what happens when charged one shuts down first (repeatedly)
I don't get it, just wire bms for each half of pack, and then wire packs in series?

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Re: Homemade Battery Packs

Post by DrkAngel » May 16, 2015 6:38 am

Build 2 identical 7s packs each with it's own BMS. (Confirm controller compatibility? 58.8V)
Rig the 2 packs in series for use.

Confirm electrical isolation between chargers - if 2 separate chargers used, (1 to each pack), still in series, at same time.

Single full voltage charger through 2 BMS'ed packs in series ... of unknown recommendability. (Dependent on BMS functions - quality)
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Re: Homemade Battery Packs

Post by jaunty » May 16, 2015 3:13 pm

Image

I bought some of these...

Anybody have any bad information about these? all but one contained the sanyo 2600 mah. red ones. I think they're pretty crappy so far considering i paid a buck a piece.

They dont reach 4.1.. they heat up at 4V, then those ones that heated up end up resting at 3.85'ish.

hmmm.

Image
picture uploading

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Allex
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Re: Homemade Battery Packs

Post by Allex » May 16, 2015 3:17 pm

I would not even use those for my flashlight :)
Not to mention high current ebikes

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Re: Homemade Battery Packs

Post by tomjasz » May 16, 2015 3:57 pm

jaunty wrote:[img=http://s5.postimg.org/n76xm7igj/lenovo.jpg]

I bought some of these...

Anybody have any bad information about these? all but one contained the sanyo 2600 mah. red ones. I think they're pretty crappy so far considering i paid a buck a piece.

They dont reach 4.1.. they heat up at 4V, then those ones that heated up end up resting at 3.85'ish.

hmmm.
I made some packs for my 24V scooter with them but if you're getting heat and they're all mismatched...well, not good. Group them by output if you must. It's a fun project just be mindful of the heat and have low expectations. It is fun... I ran mine through all sorts of charging and discharging cycles and used what was left for solder practice. It's a lot of work to build a pack and get shutdown by a couple of crap cells. But again, it's a good learning platform for the day you can build with a decent set of batteries.
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

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Re: Homemade Battery Packs

Post by jaunty » May 16, 2015 4:00 pm

[/quote]I made some packs for my 24V scooter with them but if you're getting heat and they're all mismatched...well, not good. Group them by output if you must. It's a fun project just be mindful of the heat and have low expectations. It is fun... I ran mine through all sorts of charging and discharging cycles and used what was left for solder practice. It's a lot of work to build a pack and get shutdown by a couple of crap cells. But again, it's a good learning platform for the day you can build with a decent set of batteries.[/quote]

yeah im just here for fun really. the learning experience. I'm looking for a good pack to buy, then i can continue collecting cells for a build. The prices for parts for building just seems really high. Those ebay guys think their shit is worth gold!

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Re: Homemade Battery Packs

Post by tomjasz » May 16, 2015 4:51 pm

By the time you build a pack of the quality you see priced you'll realize that battery packs, that are of high quality, are worth the dollars. At least I've found that. Building a quality pack with a decent BMS and cells is pricey. Period.
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

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44.4V Advantages

Post by DrkAngel » May 17, 2015 8:44 am

You might want to consider a 12s 44.4V pack.
More symmetrical, compatible and much easier! ... ?
Inexpensive 6s chargers and balancers ... 12s BMS's and chargers etc. readily available!
Especially with a 36-48V compatible controller.
(Standard 48V controller might LVC cut-off too high ... but would prolong actual usable lifespan)
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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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To BMS or Not to BMS?

Post by DrkAngel » May 17, 2015 10:14 am

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 1A or .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
(Use self discharge and IR tests will eliminate most low capacity cells 1st)
I rig 28-30 cells, (typically paired cells = 56-60), in series for a 117.6-126VDC .
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.
or
You can further, more accurately, test capacity by continuing test with matched cells from 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 when balance charge desirable.

Summation!
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

Oh!
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!!!
Last edited by DrkAngel on May 18, 2015 7:59 am, edited 2 times in total.
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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 jaunty » May 17, 2015 11:07 am

thanks Drk..

my inclination is that a 48V motor should be operated as close to 48V as possible, in which case the 12S or 13S makes most sense. But i havent performed any tests. What would the drop be (sag?) during riding of a 14s, 13s vs 12s pack?

so i crafted this table up right quick.

Image
windows screenshot

would these numbers also drop by a bit due to load? That would be the only argument i could see for running a 14S pack. Or is some other benefit?

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Re: Homemade Battery Packs

Post by riba2233 » May 17, 2015 1:22 pm

Yeah, you will see big drop with used cells, so go with 14S.

BMS might not be necessary, but it's hard to always take care not to overcharge and over-discharge, so it's good thing to have, and it only costs 20-30 bucks, but it can save whole pack.

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Re: Homemade Battery Packs

Post by jaunty » May 17, 2015 2:00 pm

yeah.. i found a BMS from aliexpress for around $23. So i figure i'll play with that.

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Re: Homemade Battery Packs

Post by DrkAngel » May 17, 2015 2:06 pm

LVC on a 48V controller is typically ~41V.
Which makes 12s seem feasible ... especially if bank 13 and 14 have their cells added to the 12s.
14s10p will sag more volts than 12s12p, ... but not to a lower voltage.
But check your 48V controller for 14s (58.8V) compatibility. Many have a HVC!

With any pack build ... Add a fuse!!!
Can save you from a whole lot of heartache!
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

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

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Re: Homemade Battery Packs

Post by jaunty » May 22, 2015 7:33 pm

Allex wrote:I would not even use those for my flashlight :)
Not to mention high current ebikes
actually, if you dont me asking. Why not?

Inside are the UR18650F sanyo cells. Are those bad news?

Cheers

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Self-discharge

Post by DrkAngel » May 23, 2015 7:57 am

Cells that "heat up" have internal shorts = severe self-discharge.
Unreasonably hazardous to use ... worse when combined!

Best used for "end of life experimentation" ... borrow Ypedal's fire suit?
(They should accept "full" charge, briefly, if extreme current applied = fire-explosion danger! )
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

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

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Index - Homemade Battery Packs - Updated - November 2015

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jaunty
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Re: Homemade Battery Packs

Post by jaunty » May 23, 2015 1:28 pm

Yeah. I mean these particular cells in general.

All the cells that heated up at all I marked and put aside. None of them heated substantially though (could still hold in my hand them easily) But then later i went to charge them and they charged right up without any heat. I'm not sure why that is the case. I believe these are protected cells though, so too high of voltage charge may have caused that.

I finally charged all 60 cells and now time to discharge them all and make plots! I have a nifty rs232 program. I should have bought two of these multimeters so monitor current and voltage simultaneously.

Thanks for all your posts Drk they are very helpful.

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