Using Donor LIPO Cells with Individual Integrated BMS Per Cell for a DIY Pack?

LanM

10 mW
Joined
Oct 25, 2019
Messages
29
Hello fellas, I'm new to the forum. Long time Lurker, first post. I'm in the beginning stages of putting together a diy project.
Pics below.
EDIT** Added photos of the cell tear down now that I have them in hand.

Going with a standard 26 inch hub motor kit and planning on upgrading the controller.

The specs for the cells I'll use for this project are:
part: Eg20-1s10400-t1t2.
3.8 volts.
10,400mah (2 5200mah cells in a 1S2P setup with a board attached), 8 wire connector.
Made by TCL hyperpower.
I purchased these from a manufacturer liquidation auction, and have over 250 of them so I'll be using them however I can.

Can anyone tell me if that pcb looks like a built in BMS for each cell, and if I should keep it or try to remove them. Will use for ebike project, for my kayak trolling motor, and wherever I can find a use.

I appreciate any advice.
Thanks!
Lan
 

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Get a CC dummy load and data logger, and test each cell for mAh actual capacity.

Then set up a short-term high C-rate load at your target voltage (that determines how many in serial) and see how the pack handles it, measuring voltage sag and temperature rise to determine its realistic max discharge current profile.

This together with your range desired, will determine how many in parallel required to get to the pack Ah you need.

 
Good score- how many did you get? I’m powering a bike with new old stock Panasonic toughbook batteries with great results. Key thing to recognise is that these are cells that are meant for lower current, high capacity use; so voltage will sag under high current. To get around this have as many in parallel as you can; rule of thumb is that continuous draw should not exceed 1x or 2x capacity rate (1C) however it seems unlikely you would get 10A out of one of those for too long without voltage sag and heating. Also you need a sturdy box in case you crash or the bike falls over- the short circuit current will be high enough to start a fire if it’s not physically secure.
 
John, Thank you for the info. When you suggest to make a test pack to determine voltage sag and temp,
does that mean to make a pack of 1 single bank in a series (so for a 52v pack I'd make a test battery from 14 packs in a series and 0 in parallel)? Thanks for the help so far.

electric_nz : The toughbook battery sounds interesting, I'll take a look to see if you have a build thread.

I bought about 350 batteries. I haven't picked them up yet, but based on the boxes I have at least 40 of these, and likely 120-160 of them.
When you refer to the limitations of the amperage on these and the largest parallel arrangement--does that mean that a lower amp larger capacity battery is all I should be going for? In regards to the amperage, will I have the ability to make a pack powerful enough to propel my heavy self to reasonable speeds (20-25mph is fine). I'll have more than enough donor packs hopefully. Thanks for the tip on the box. I figured I'd make a kevlar enclosure for the battery since I have about 7 yards of 50 inch kevlar 429 that's been sitting unused for years.

Thanks for the help so far.
 
LanM said:
John, Thank you for the info. When you suggest to make a test pack to determine voltage sag and temp, does that mean to make a pack of 1 single bank in a series (so for a 52v pack I'd make a test battery from 14 packs in a series and 0 in parallel)?
Well 1P is implied.

Actually doesn't matter much what voltage xS count you use, depends on the hardware you have available for testing, charging etc.

The ideal is whatever voltage you want to end up with, so as the packs age you have commissioning-time benchmarks to compare.

Actually one suggestion to help keep gear costs down by using stock COTS hobby chargers, 7S packs are much easier to deal with for testing / balancing / charging with 8/10 series gear, then put those subpacks in series to discharge at 14S.

But 1S initial testing is fine too if you have an adjustable charger, dummy load etc that do decent amps in that voltage range.

But 7S (21-30V) is easier to deal with


 
Thanks for the info.

I'll look to begin with a 7s structure for the pack. I'm assuming that means I'll have a pack approximating 52v connecting 2 together then determine my P from there. like 2x7S then around 9p would give me 1.3kw of power roughly by the looks of things which would be a bit more than the long range triangle batteries if I'm not really screwing the concept up (likely right in the ballpark of the number of cells I'll have)

I am a little confused about the utility of these cells from an amp draw perspective. It was stated that these don't like high amp draws, (1C), so does that mean I will be limited to a 10 amp draw on the battery? I'm assuming a 20 ish amp draw seems to be what I should be going for. Would that mean that if I were to use these I would be limited to a low power state/slow speed application?

Or can that only be determined by testing

thanks again
 
Well testing is the only reliable predictor,

Once you know if going to your desired C-rate is not going to be too stressful on a give P-count,

reconfigure the cells so all the paralleling is down at the lowest level.

So first e.g 9P groups, each acts as if a single big cell,

then make two strings of 7S each for balance charging, then those 2 sub packs get serialed to create 14S for use.
 
What would the solution be if the test pack did not function as needed at the 20+ amp draw level?

Would that mean that the pack could only be used at the 10amp level due to the low draw nature, and would that mean that it would be limited in speed or is amps more of a torque/acceleration limit
 
Looking at the connectors and wiring, I would guess they are rated for a low ish draw. Maybe have a look at the published power draw and battery life of the intended device to see if you can get some numbers. Laptops often have 3-4 cells in series and 2-3 parallel.

If you’re running a 1000W motor at 52V nominal (14 cells in series), you need a pack which will handle 20A continuous. So if each cell is rated say 5A continuous, you need 14S and 4P, for a total of 56 cells.if the batteries can’t provide the 20A it will sag hard and get warm- but easy fix just add more in parallel. The more in parallel the better - but size and weight gets to be impractical.

Suggest a BMS and controller that are rated a bit higher so they can handle peaks- a 40A or more BMS and a 20A controller with higher peak handling
 
LanM said:
What would the solution be if the test pack did not function as needed at the 20+ amp draw level?

Would that mean that the pack could only be used at the 10amp level due to the low draw nature, and would that mean that it would be limited in speed or is amps more of a torque/acceleration limit
Getting a higher current as an absolute number, e.g. 20A continuous, or

20A for up to 30sec bursts

is no problem, up to space/weight limitations.

Just keep adding Ah capabity, if 9P is not enough go to 12P

this brings the C-rate down to less stressful levels.



 
Thanks John and electric_nz,

I believe 9p may end up being near my limit as I think I will have under 140 cells. Ill know when I pick them up.

7s packs x2 to get 52v pack
14 x 9p = 126 cells right?
I couldn't imagine someone actually purchasing this particular type of battery retail to use on a project like this since the price would be sky high.
 
For a high-power use case, one good battery pack can easily cost as much as the rest of the build put together.

Not to mention it's as much a consumable as brake pads, costs a lot more up-front to build one that will last more than a couple years.

That's why so many try to get by with salvaging scrapped cells.
 
A couple of good spor welders out as soldering is trouble and add a gasket on the pos. end. DrAngle has a lot of good threads for you. High parallel groups
 
john61ct said:
For a high-power use case, one good battery pack can easily cost as much as the rest of the build put together.

Not to mention it's as much a consumable as brake pads, costs a lot more up-front to build one that will last more than a couple years.

That's why so many try to get by with salvaging scrapped cells.

That's understandable, and I've seen quite a few videos on balancing 18650's and similar since I originally intended to use those, but came across these. I'm hoping these are a high quality cell. They're made by TCL, have the ROHS stamping on the boxes and were used in the production of a $600 tablet with a 2 year warranty so I'm assuming they're not bargain basement quality.

I'll have to weigh them when I pick up but I may be delusional about being bale to use them weight wise. I'm assuming 126 of these will be a lot bigger than a pack of 120 18650 cells.They look to be about the size of a hershey bar.


Zip, I read your mention of a spot welder, is it not possible just to buy harnesses to plug into the packs as is? Or should I expect to be cutting/splicing wires. I figured buying the matching 7 pin connectors would give me the ability to replace cells and break down the pack without issues.
 
/ i think we are missing something with these cells ?
The pack has a 8 pin connector , 3 black, 3 red , 1 white , 1 yellow,. Suggesting a 3p assembly for that 10,400mAh capacity. (39.5Wh).
Are you actually talking of using these 10.4 Ah “packs” as-is or breaking them down into individual 3.5Ah cells. ?
Decent Lipo weighs approx 200Wh/kg, so each of these 36.5 Wh “packs” should weigh approx 200g
I do not understand why you feel the need for a 9p (93 Ah, 4.8kWh) pack construction with 126 of these packs, ??...
That is going to weigh around 25 kg ! :shock:
Even if you are only intending to Use 126 indivual cells, that would still be a 30+Ah, 1.6kWh pack weighing around 8 kg
Even 8 kg is a lot of weight on a bike.
 
Well just the rider is over 300lb, I was not assuming an ordinary light-frame bike here.
 
LanM said:
I'll have to weigh them when I pick up but I may be delusional about being bale to use them weight wise
Energy density will be good if they are in healthy condition at rated capacity, spec'd for a tablet.

Your wiring, protective casing, BMS etc will all add weight of course.

Longevity likely good as well.

You are correct to be concerned about C-rate, power density will be the issue, require you to cart around a lot more Ah than most using packs designed for EV / ebikes.

But silver lining is a higher range comes with that.

Definitely would be nice to find the matching connectors OTS, but crimping / soldering wiring a custom set of harnesses is definitely in your future, all part of the pack building skillset, so you may well prefer to just cut the wires to go to your own preferred butt connector system.

I encourage you to find a way to allow easy breakdown of the pack for cell / module testing / replacement / reconfiguration as needed.

 
John,
Do you mean I'll have to cut open the silver bags and separate the individual cells?

Hill,
I knew the pack I was considering would be large, however 50lbs is definitely too heavy.

8kg is tolerable for me. For the type of cell I'm using, I've been informed it has to be larger than normal due to them being low draw tablet batteries.
 
LanM said:
John,
Do you mean I'll have to cut open the silver bags and separate the individual cells?
I wouldn't, and you shouldn't need to, depends on the current those cell-level wires / connectors are designed to carry, maybe 2-3A?


 
Yes the silver bags are the cells - don’t open them unless you want smoke!! From the picture, looks like each pack is made 4 individual silver cells of about 2500mah, with + and - wires for each brought out to the connector. That’s very good news and means You can draw 1C or 10A from a single pack and reuse the wiring that’s there.

You can think of each pack like 4 separate 18650s taped together in a flat format. This means a 14S 8P setup of capable of 1000W reliably for an hour will only require 28 packs.
 
electric_nz said:
...
From the picture, looks like each pack is made 4 individual silver cells of about 2500mah, with + and - wires for each brought out to the connector. .....
Whilst 4 x 2600mah cells would make sense for a 10,400mAh pack, ...... i can only see 3 black and 3 red wires at the connector ??
And i cannot imagine a Tablet battery ever being designed to provide anything neat 10amps even at burst rate , let alone continuous !
Most of those types of packs for laptops etc have thermal, and overload fuses built in for safety.
 
what kind of power do you actually want from that battery? volts and amps?

these batteries are for tablets and stuff. so incredibly dense. but that also means they cant handle high currents, think in the range of sub 5A peak to keep it from killing itself. so you need a LOT of them. but that also means you are going to get a beefy battery with massive range.
 
flippy said:
what kind of power do you actually want from that battery? volts and amps?

these batteries are for tablets and stuff. so incredibly dense. but that also means they cant handle high currents, think in the range of sub 5A peak to keep it from killing itself. so you need a LOT of them. but that also means you are going to get a beefy battery with massive range.

I'm shooting for 52v with the 1000w hub motor kits I've been eyeballing to use.

What implications does 5A peak mean in regards to overall amp draw?
 
LanM said:
.

What implications does 5A peak mean in regards to overall amp draw?
Basicly it means you would need at a MINIMUM , 4 of those 10.4 Ah packs in parallel (X 14 in series) in order to intermittently supply 1000W to the motor.
If you want that 1000W (20A) for more than a few seconds , or continuously, then you would need many more in parallel..possibly as much as double , (8p or 83 Ah total pack). Practically back to that 25 kg pack size !
You really need to do as John said earlier and test one of those packs to determine exactly what they can do, discharge wise, without getting hot, cutting off, or worse !
Initially run a continuous 5.0 A discharge ( say 4.1v down to 3.6v ) and carefully monitor temperature etc...then repeat at 10A and see if there is any noticeable increase in temperature.
.. stop the test if the pack starts to get hot (50C+) at any time.
 
Will do.
I'm sure there's a significant amount of info on here regarding equipment options for testing/charging these. Is there anything specific to these cells that I should know about/take into consideration when looking into equipment?
 
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