First pack build

M

mynameisjoe

New member
Joined
Jan 3, 2024
Messages
4
I have been given a large amount of salvaged 18650 cells and am going through them slowly using the spec sheets I found in here, then testing/charging. The ones with the best hit rates are Samsung ICR18650-26D and Panasonic CGR18650EA. I have enough of these two types to make what I wanted, 7s8p. Problem is they have different stated capacities and charge/discharge rates. To keep things simple for my brain I was thinking of making two 7s4p packs, so 28 cells of each, and then putting the two packs in paralell. Can anyone see a problem with this? Is there a better way of doing it? I also have around 400 Sanyo R1122 of various top cap colours, 70% of which are the Teal ones in red wrap. But most of these are showing high IR compared to the Pana and Samsung. Plus I read that the Sanyo aren't quite as good a cell and have a higher failure rate. This pack is not going to be stretched, it's main use will be for charging my drone batteries in the fiels, and for powering LED lights in the house when we have power cuts. I will be adding a BMS when I come to do the build and using a 7S charger when the time comes. Any thoughts or advice would be most welcome

​

 
Hi there, welcome to the forum.

It's ok to make two 7s4p packs and put them in parallel. The best case is when both packs are exactly the same capacity, same IR. But using second hand cells you'll have to be carefull in distributing the cells in such a way to have the two packes as similar as possible.

I have packs with IR ranging from 40 to 70mohm, I distributed the cells to make packs as similar as possible one to the other. Otherwise, with the Sanyo cells you could make a separate battery.
 
Aaahhh ok that makes sense, thank you. The two different cell types are originally rated at 2550 and 2600. So I was going to make one 7S4P out of one type and another out of the other. But best to mix the cells up, regardless of type, into what they actually measure so that both packs are as close as possible.
 
Hi everyone and sorry if I ramble a little here.

So I have now collected 100's of cells from the old laptop batteries and over the last wee while have been sorting them out into groups. Anything with physical damage or below 2 volts were recycled. The cell type I have the most of are Sanyo R1122, around 300, so it made sense to use these first as they're all the same type, same chemistry, same charge/discharge etc. I have tested each for voltage and sorted into piles of 2.5-3v, 3-3.5v and 3.6-4.2v. Fortunately I have enough of the 3.6-4.2v cells to build the pack. So I have now charged a little over 100 of them, monitored for heat and further discarded any that were abnormal, and then checked their internal resistance. All are 4.12 to 4.18 volts so shouldn't cause any problems as there is less than 0.1v difference. IR is between 45 and 70mOhm. All I can find on these cells so far is IR should be below 100mOhm. My plan was to group them by IR, but now I read it is better to group by capacity. OK, I can do that as my charger/IR tester can also test for capacity. The problem is it can take 5 hours or so to test 4 cells, and I will not charge/discharge cells unatended or overnight so it is going to be a lengthy process. While I am thinking on this I have these cells stored in holders, and will check for self discharge in another 3 or 4 days. The plan is to build a 7S12P pack. I was going to go for 4S10P, but the voltage did't really quite work out (I want 12v) so decided on 7S with a 24-12 regulator. The 12P is purely because that is how many I can fit in the available space. Now the batteries for the drones I have are 3500 mAh 40.42 Wh (3S) and 2250 mAh 17.32 Wh (2S). Their respective car chargers will handle the charging so I don't need to worry about the different voltages, never more than two being charged at a time. Plus I'll be fitting some panel mount PD and QC outlets that can take the voltage down from 26v so I can charge things like phones and tablets if needed. There will also be an XT60 connector to take charge in from a 7S balance charger, and yes I will be fitting an appropriate BMS. Does all of this sound reasonable so far?
As for grouping the cells, do I REALLY need to do a capacity test on a minimum 84 cells for this type of build? I would have thought that IR is a decent indicator of battery health? I'm not fussed about getting the full (almost) 700watts out of it, I'd be happy with somewhere between 400 and 500.

Do any of you experienced members have input or can highlight any failings? Things I should definitely do/not do.
Thanks in advance for any input or thoughts
 
A lot to unpack.

First, I'd suggest you step back and work on a test process - you should test each cell and put them in 100mah capacity groups by cell model number (e.g. Samsung or Sony or X).

Basic Test Process...
- Measure IR - if bad then toss.
- Charge, then Discharge (to get capacity and write it on the cell), then Charge and put the cell in a bucket or on a shelf or X by cell model and 100mah grouping. For example, group all the 2500mah cells in 1 bucket, the 2400mah cells in another, the 2300mah cells in another and so on.
- As the final Charge occurs and especially near the max charge, touch the cell with a finger and anything hot should be tossed. A little warm is OK.

Once you have enough cells for the entire battery - e.g. 7s12p would be 7 x 12 = 84cells + a few extra.....
- Wait at least 2 weeks (or up to 3 months) and check the voltage on each cell. Anything <4.10v is too much of a self-discharger and I'd toss it.

Next, assemble you're packs by evenly distributing the 84 cells among the 7 packs by type and 100mah grouping - so that each pack (pretty much) has the same mix of cells + same capacity. If 84 cells doesn't quite get you the capacity you want then do 7 x 13 or 7 x 15 etc.

Safety.... I've not found any issues with safety doing testing with brand name chargers.

Time... Yes, it can take weeks and months and years. I've processed ~15,000cells over 5+years. I did mine 12-16 cells (3-4 chargers) at a time but some folks setup a charging station with as many chargers as you can afford and do 20 or 40 or 60 or 100 cells at a time - there's no limit except $.

Here's a 12 cell setup using 3 x OPUSs that @Wolf used early on and this is what I've used the whole time - https://www.amazon.com/Battery-Charger-Tester-Analyzer-Adapter/dp/B09FRFPNXY/ref=sr_1_3 or on ebay - https://www.ebay.com/itm/233191785125 or cheaper (rawer) alternative such as in this recent thread - https://secondlifestorage.com/index.php?threads/new-tester-from-ali-any-good.12400/#post-90667
1709187888927.png


@Wolf upped his testing to a 64 cell charging setup using 4 x MegaCell Chargers - https://www.megacellmonitor.com/MegaCellcharger
1709187973471.png



Whether you do 4 cells at a time or 64 cells at a time...... or do 18650 or LifePo4 XXXah cells/bricks or pouches or whole batteries or whatever....
***there's no other way to get good results than to test each cell or battery pack ***
If you don't test, then you will likely be unhappy with the results.
I don't say this to 'judge', just sharing what we've all learned the hard way :)
 
Last edited:
Thanks for your reply, much appreciated.
I have tested everything you have mentioned above, apart from actual capacity. I guess I'm just going to have to accept the fact that it will take time to capacity test all of the cells I have. I just didn't think it would be that citical to group by capacity, at least not for my needs. I'm only wanting to be able to charge a few drone batteries when out and about.
 
You must log in or register to reply here.
Back
Top