Batteries, Chargers, and Battery Management Systems.
spinningmagnets   100 GW

Posts: 11141
Joined: Dec 21 2007 10:27pm
Location: Ft Riley, NE Kansas

If you have an 80A battery pack, and it is 8P, then each cell series connection must carry 10A from one group to a cell in the next group. Once you get to the end of the series groups, those 8 cells in the last row must be able to conduct that amount of current into one wire.

If you can visualize a pack with no parallel connections, that might make it clearer.

Spongeworthy   10 mW

Posts: 32
Joined: May 15 2016 8:33pm

spinningmagnets wrote:If you have an 80A battery pack, and it is 8P, then each cell series connection must carry 10A from one group to a cell in the next group. Once you get to the end of the series groups, those 8 cells in the last row must be able to conduct that amount of current into one wire.

If you can visualize a pack with no parallel connections, that might make it clearer.
Not sure if I'm misunderstanding your post, but why's it carrying 10 A from one series group to the next? Like I said earlier, doesn't the whole 80A run through each series connection?

DrkAngel   100 GW

Posts: 5117
Joined: Dec 15 2010 11:14am
Location: Upstate-Western-Southern Tier NY. USA

Spongeworthy wrote:
DrkAngel wrote: Ideally with a reasonably heavy (large gauge) "rail" to provide good equal discharge from each series of cells.
Why is it more important for the ends of the pack to have more conductive mass than say in between each parallel group? Doesn't the same amount of current run through both? I'm just a bit confused since I see some packs that don't do this at all and just solder leads directly onto the + and - ends of the pack, and other packs with thick copper bus bars at the end.
In normal use, there is no throughput in the leads connecting parallel cells, except for the end cells in series.
The large end rails allow a fairly equal draw from each series >> cell, meaning that there is no voltage differential between parallel cells, thus, no voltage-amperage throughput on the parallels!
Parallels are to confirm voltage equalization (balance), buffer minute capacity variances and insure against a single series destruction in the event of a single cell failure. - Will 90% buffer voltage deviance in 10 parallel battery.
Spongeworthy wrote: Not sure if I'm misunderstanding your post, but why's it carrying 10 A from one series group to the next? Like I said earlier, doesn't the whole 80A run through each series connection?

Attachments
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Last edited by DrkAngel on Apr 04 2018 3:08am, edited 3 times in total.
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And drinking largely, sobers us again.

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

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Animalector   10 kW

Posts: 844
Joined: Mar 17 2012 4:50pm
Location: Mareeba - Queensland

My take on this is that the interconnects are very short therefore they do not have to be as large. For the main battery cable it usually has to run 1m plus. Therefore you choose more square mm to handle the current. This means there is a physical challenge to connect this large cable to the end cells... Running it all the way along the end cells makes sense, is stronger and balances the draw from the last cells in the series.

Anyway. That's why I do it.

Spongeworthy   10 mW

Posts: 32
Joined: May 15 2016 8:33pm

I think I understand now, reading a bit more I didn't realize that some cells in a parallel group draw more or less current depending on where the series connection to the parallel group is hence the need for a thick bus across all cells. There's usually multiple series connection between parallel groups so that's why it's not an issue for those connections I suppose, thanks for the help guys.

DrkAngel   100 GW

Posts: 5117
Joined: Dec 15 2010 11:14am
Location: Upstate-Western-Southern Tier NY. USA

.
...
Power Rail Connection Points

Serial-Parallel connection point does matter!
As illustrated, with the bottom left of the negative rail as the fixed connection point, various points of connection on the positive rail produce variances in the series drain-throughput.
Pwr rail.jpg (171.71 KiB) Viewed 3403 times
With both power contacts at the bottom, power drain might be 4Amps from the closest (bottom) series but 2Amps at the furthest (top) series.

With Positive contact point at top series and negative contact point at bottom series, electrical conductive paths are equal with a resulting equal 3Amp drain from each series, resulting in equal wear and tear with an expected long and stable lifespan.

Positive rail at center point might alter drain to 4Amp equally from bottom half declining to 2.5Amps at top series
Moving both contact points to the center of the rails might equalize this disparity somewhat, possibly 3.5Amps at center declining towards 2.75Amps at each periphery.

Varied discharge rates produce varied deterioration. For maximum life, equal treatment of all cells should be "mapped". Simple measure and equalization of electrical path is a good plan.

Most of my builds have connected both neg & pos at the bottom points, as a convenience factor.
However, to mitigate this disparity, relatively massive rails are used!
Possibly 8-6ga tinned copper braid for a 15-30Amp draw. ... line drop and the resultant deviance of Amp draw should be negligible.

But ... next pack builds will include equalized electrical pathways!
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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DrkAngel   100 GW

Posts: 5117
Joined: Dec 15 2010 11:14am
Location: Upstate-Western-Southern Tier NY. USA

Next project:
2 - 25.9V 26.4Ah eZip RMB Lithium upgrades using new recycled Samsung ICR18650-22P 2200mAh cells at 7s12p.
Purchased 29 x 36V 4400mAh hoverboard batteries.

All charged, I am now:
separating,
will precisely equalize,
monitor for any self discharge (internal short)
discharge a precise equal amount (30s2p in series through 2x 60w (120V 120w) light bulbs = 1Ah/hour 3hr = 3000mAh
monitor voltage sag during discharge (comparative IR)
compare residual voltage (comparative capacity)
Sort cells of stable self-discharge,and good IR by capacity
Arrange banks of equal capacity

Cells are rated for 10A continuous 20A surge discharge for a pack capability of 120-240Amp, but will only be tasked at 25-35Amp maximum.
Previous similar builds used 2600mAh cells,, but laptop cells of minimal discharge capabilities!
I anticipate greatly enhanced low end and hill performance with, probable, cold weather performance enhancement!

Saving several 36V 4.4Ah packs for 36V projects (each has it's own BMS)

Used:
2 packs for 2x 5s2p 18.5V 4400mAh B&D tool packs & 2x 11.1V 4400mAh B&D tool packs w/spares
9 packs for 2x 7s12p 25.9V 26.4Ah
3 packs tested in eZip RMB pack for 36V 13.2Ah testbed.

15 packs for next projects:
5s2p Ryobi Lithium rebuilds
7s2p B&D Firestorm 24 >> 25.9V upgrades
More 5s2p 18.5V 4400mAh B&D tool packs
etc.
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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x.l.r.8   100 W

Posts: 117
Joined: Jul 30 2017 12:13pm
Location: Toronto and Cambridge

Pack check please. I have been reading the 100 ways to skin a cat thread for a while and I have done 3 u-turns. It’s the first 12s of a 13s 7p pack. I used pre tinned bus bar from solar panels 5mm x0.2 mm and doubled up on the parallel connections. Pre tinned the cells (original nickel strips folded over).
There the lg mf1 cells from the 36v hover board packs and it’s replacing a 48v 12Ah SLA arrangement. It’s the pre run before I attempt the 20s15p pack. The bms is a 20Amp continuous affair. I just want the practiced eyes to look it over before I seal it up and charge it. All the cells were pre balanced to 3.85v so I can do some quick calculating using 2 smartmeter connections so I can plug one in to check a 7s and a 6s periodically to see how each group is doing.
Intelligence is distributed nearly evenly, with only the occasional concentration in one person. The total quantity of Intelligence is a constant: as more people come into being, fewer and fewer get a sufficient amount for themselves.
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DrkAngel   100 GW

Posts: 5117
Joined: Dec 15 2010 11:14am
Location: Upstate-Western-Southern Tier NY. USA

12s7p right?
I would be very concerned about the odd brand cells in the bottom left bank.
The entire pack will be dragged down to the capacity-performance of the weakest bank.
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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Buk___   10 kW

Posts: 750
Joined: Jul 28 2017 5:59pm

DrkAngel wrote:I would be very concerned about the odd brand cells in the bottom left bank.
I noticed that. There is also an odd one far right (and 5th column from left, 2nd row down); but looking closely, I think it may just be different colored insulator stick-ons.

x.l.r.8   100 W

Posts: 117
Joined: Jul 30 2017 12:13pm
Location: Toronto and Cambridge

There all lg mf1 cells, different color wrap.
If you go to alarmhookup you will see the new lg packs are a Dark purple as opposed to the light violet. They went into this pack because I’m just seeing how easy it is. I had concerns but seeing as they are the same spec cells I’m pretty confident they will perform the same. It’s for my emmo urban so it’s not the performance monster. I’m more concerned about the connections.
And yes, I have a pack of red insulators but the green ones I salvaged from the originals
Intelligence is distributed nearly evenly, with only the occasional concentration in one person. The total quantity of Intelligence is a constant: as more people come into being, fewer and fewer get a sufficient amount for themselves.
Some say this has already reached homeopathic levels.

DrkAngel   100 GW

Posts: 5117
Joined: Dec 15 2010 11:14am
Location: Upstate-Western-Southern Tier NY. USA

OK
Took a better look.
3 weak points.
1. Serial connections are 7 tabs, except ... between 6s and 7s, bottom center, all current bottlenecks through a single tab-strip. Recommend heavy overlay strip or additional bridge strips.
2 & 3. Pos and neg connections are at thin connection strip, multiple contact-connection points recommended.

Closer inspection confirms bottom "rail" as doubled, dependent on expected amp throughput, additional might be advisable. ... ?
Best determined by temperature rise at vulnerable points during test discharge.
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Last edited by DrkAngel on Oct 27 2017 6:04pm, edited 1 time in total.
A little learning is a dangerous thing;
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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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x.l.r.8   100 W

Posts: 117
Joined: Jul 30 2017 12:13pm
Location: Toronto and Cambridge

Thank you for looking, the positive I’m going to put a solid link over the top of the doubled strip and from the center of that link my power wire. The negative will be going to the 13s that will sit on the side and again the negative side will be doubled up like all the parallel connections are, a solid bar across that and the negative wire will come from the center of that bar. I will loop from 3-4 points across p7-p7 to share the load like you suggested.
Intelligence is distributed nearly evenly, with only the occasional concentration in one person. The total quantity of Intelligence is a constant: as more people come into being, fewer and fewer get a sufficient amount for themselves.
Some say this has already reached homeopathic levels.

markz   100 GW

Posts: 7313
Joined: Jan 09 2014 11:38pm

You need to put another strip on the parallels for sure! Lets call them the "E"

x.l.r.8   100 W

Posts: 117
Joined: Jul 30 2017 12:13pm
Location: Toronto and Cambridge

There all double stripped already, I took a lot of care to make sure they were on top of each other to ensure maximum contact between the 2 layers, if you look at the ends you can see they are folded over not cut.
Intelligence is distributed nearly evenly, with only the occasional concentration in one person. The total quantity of Intelligence is a constant: as more people come into being, fewer and fewer get a sufficient amount for themselves.
Some say this has already reached homeopathic levels.

markz   100 GW

Posts: 7313
Joined: Jan 09 2014 11:38pm

neon green is good.jpg (39.9 KiB) Viewed 2779 times

x.l.r.8   100 W

Posts: 117
Joined: Jul 30 2017 12:13pm
Location: Toronto and Cambridge

Got it, I looked at that but somewhere in this thread said that was not necessary that's why I doubled up the other parallel connectors. I shall go back and do the other side of that series bridge and make that additional connection. Thank you for clarifying with pre-tinned strip it makes an easy to change stuff like that.
Intelligence is distributed nearly evenly, with only the occasional concentration in one person. The total quantity of Intelligence is a constant: as more people come into being, fewer and fewer get a sufficient amount for themselves.
Some say this has already reached homeopathic levels.

DrkAngel   100 GW

Posts: 5117
Joined: Dec 15 2010 11:14am
Location: Upstate-Western-Southern Tier NY. USA

I don't see any "need" for additional parallels, on the series tabbed banks, except for cosmetic purposes.
Parallels, typically have minimal current throughput! (except 6s >> 7s and end rails, as noted in example)
With identical cells of identical condition, there is no parallel current transfer.
"Similar cells" have negligible parallel transfer, balance function is typically only a fraction of an amp through any parallel.
Might make it look pretty?
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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DrkAngel   100 GW

Posts: 5117
Joined: Dec 15 2010 11:14am
Location: Upstate-Western-Southern Tier NY. USA

### 7s12p 25.9V 26.4Ah (2017 Build)

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...
Battery Day

Lousy and wet outside, decided to post pictures to help dedicate my energies to finish some of my long delayed battery builds.

2 x 25.9V 26.4Ah (7s12p) with new Samsung ICR18650-22p 2200mAh cells
Dedicated for use with 1 eZip OEM LiFePO4 with 20A controller
+
eZip with 28A replacement controller
BMS units rated at 25A continuous and 50A cutoff, so hopefully adequate.
Selling 2 old eZips, with new battery builds. Will instruct new owners on battery care but adding the protection modules cause some people are ... seem, belligerently ignorant! (My own brother has been running his Lithium powered phone, tablet and laptop till cutoff, thinking it helps something)
I have been reluctant to build eBike batteries for others, only 1 so far, lives 2 blocks away, so adding, what I consider to be, a security blanket, to these builds.
33.3V 32Ah (9s12p) is for me, for use on Snow Beast, long trips (1kWh+) and 25mph cruising.

1 x 33.3V 32Ah with new Sanyo + Sony 2600mAh cells
Might replace red Sanyo with Samsung, with a loss of capacity but an increase in surge capability ... ? Will decide as I build the 25.9V batts.

25.9C 4.4Ah with 20A continuous >> 40A surge replacing 24V 1.4Ah NiCd
No room for BMS but will install balance leads-connector!
171105 B&D.jpg (136.87 KiB) Viewed 3047 times
Got plenty of raw materials + 10 more 10s2p bricks
171105 spares.jpg (148.05 KiB) Viewed 3047 times
Well, too work now ...
Attachments
171105eZip.jpg (222.64 KiB) Viewed 2770 times
Last edited by DrkAngel on Nov 05 2017 8:59pm, edited 1 time in total.
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.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - February 2019

EBike Toolbox - Bargains! \$

Endless Sphere Wiki - Lost?

DrkAngel   100 GW

Posts: 5117
Joined: Dec 15 2010 11:14am
Location: Upstate-Western-Southern Tier NY. USA

### Re: 7s12p 25.9V 26.4Ah (2017 Build)

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...
25.9V 26.4Ah #1 finished

7s12p Samsung cells are capable of 120A continuous 240A surge but controllers are <30A and installed 40A fuse (trying new 58V fuses & holder)
Just finished 1, had to test drive it ... rain stopped for awhile.
No BMS installed! Turned out were only 20A continuous.
Mostly worried about parasitic draw when customers let set for the Winter.

10s2p Bricks disassembled into 8s2p + 2s2p and I was oh so tempted to build as 8s12p ... but needed for 24V bikes and I already have the 7s chargers.

25.9V 26.4Ah #2 nearly complete
Just need to run the parallels and power rails and install fuse.
Attachments
Last edited by DrkAngel on Dec 01 2017 8:01am, edited 1 time in total.
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.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - February 2019

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petrun   100 µW

Posts: 7
Joined: Feb 13 2016 8:48am
Location: Romania/Sweden

Hello, this is my first post here but reading this forum for ~2 years.
I just bought a spot welder (sunkko 709ad+) and made a 12p10s battery using panasonic pf cells.
Now i dont know if i should put on a cheap bms from ali or should i use one from hilti tool packs. They are 36v and at least 30a continuous and i think they can do more but my controller its only 30a so i cant test it.
Curently i am using hilti batery packs, they are 36v/6a using samsung 20Q cells(30 cells in one pack). First i used them 1 by 1 and a few months ago from 2 packs i made one connecting it in parallel with one bms.
Now i checked the pack if its balanced and its ok , same voltage on all groups and i would use a bms from theyr packs. I made 3 double packs for me and my friends and had no problems with those batterys.
What do you think? Thanks

Later edit, they use a nickel strip on negative with 50A label.
Attachments
IMG_20171104_212624~01~01.jpg (158.44 KiB) Viewed 2978 times
IMG_20171107_180622~01.jpg (222.71 KiB) Viewed 1775 times
IMG_20171107_180505~01.jpg (174.71 KiB) Viewed 2780 times
IMG_20171107_181111~01.jpg (201.12 KiB) Viewed 2780 times

DVDRW   100 W

Posts: 211
Joined: Sep 10 2012 10:57am
Location: Tallinn, Estonia, EU
Contact:

Check voltages every 5th charging or so at first. If they get out of balance then add BMS.
My panasonic 18650PF packs 22S18P 14S12P using every day over a year without BMS and still perfectly in balance.
Checking voltages every three months now.

DrkAngel   100 GW

Posts: 5117
Joined: Dec 15 2010 11:14am
Location: Upstate-Western-Southern Tier NY. USA

petrun wrote:Hello, this is my first post here but reading this forum for ~2 years.

What do you think? Thanks
Nice tight build ... ... welcome to the mad scientist club!

3.2-3.3V looks to be maximum static discharged point.
4.10-3.30V working, (charged/discharged), voltages for optimal performance-lifespan?
NCR-18650PF
.
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.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - February 2019

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Allex   1 GW

Posts: 3201
Joined: Dec 05 2011 8:46am
Location: Stockholm, Sweden

x.l.r.8 wrote:Got it, I looked at that but somewhere in this thread said that was not necessary that's why I doubled up the other parallel connectors. I shall go back and do the other side of that series bridge and make that additional connection. Thank you for clarifying with pre-tinned strip it makes an easy to change stuff like that.
https://endless-sphere.com/forums/viewt ... 14&t=84412

DrkAngel   100 GW

Posts: 5117
Joined: Dec 15 2010 11:14am
Location: Upstate-Western-Southern Tier NY. USA

### Re: 7s12p 25.9V 26.4Ah (2017 Build)

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...
25.9V 26.4Ah #2 finished

Not enough matched 7s2p premade strings. Used 4s2p plus 3x 1s2p pairs.
Made preliminary run and bank voltages were very similar, indicating cells of like condition ... age, batch etc.
Will double rails and retest before declaring acceptable.

#1 pack appears immaculate!
Discharged to 3.566-3.567V, all banks within 1/1000th V.
Recharged to 4.166-4.168V, within 2/1000th V.
.
Attachments
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.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - February 2019

EBike Toolbox - Bargains! \$

Endless Sphere Wiki - Lost?