Homemade Battery Packs

Allex said:
18650 are actually 3.6V nominal. You always count the nominal value. 4.2V is at full charge.
Click to expand...
Are all 18650 4.2?
 
tomjasz said:
Allex said:
18650 are actually 3.6V nominal. You always count the nominal value. 4.2V is at full charge.
Click to expand...
Are all 18650 4.2?
Click to expand...
18650 Li-ion (LiCoO₂) are rated as either 3.6V or 3.7V, dependent on specific formulation.
Similarly, they seem rated as a full charged value of 4.10V or 4.20V. ..,. ???

file.php

Red line is specific for older Sanyo 2600mAh cells
Blue line is LiPo pulled from Dell 2nd bay modules
Most every brand model will have a differing capacity profile (Others creating similar profiles use the term "current density")

Note the capacity shift, seemingly a direct result of a differing formulation-chemistry.
3.6V and 3.7V match the empty state of these cells rather precisely! (capacity mapped using charge cycle - discharge cycles should match "empty" rather precisely)
Also note that the differing 4.10V and 4.20V "full" voltages are not at the optimal voltages.
Manufactures tend to push to higher voltages to attain a better "rated capacity" ... which tends to sacrifice longevity.
Every 0.10V reduction in charged voltage, reputedly, will double cycle life!
 
tomjasz said:
I've got some new salvaged 18650 batteries from laptop packs the read 3.7v, 24 of them, the packs say they were 14.4 volts but that doesn't add up. 8X3.7=29.6. Huh? Also I have 18 from a 3M projector that rated the battery pack at 10.85 or 11.1v. They read 3.6v. That math pans out. Please explain. 18650 batts that are 3.6v not 4.2? How do I utilize them? I was hoping for 7s for replacement in my little Schwann scooters for the 24v SLA. How do I charge them? Build them into a 7s6p and use a Tenergy 2a 25.9 smart charger? Can a balance charger be used? Wouldn't that be better since you seem to say these should be charged a lower input? Confused but having fun at collecting the goods. Soon to have a new salvage source that may be very prolific. So I need to figure this charging thing out. Is there a BMS out there that will work? Is there a balance charger that can be used as well?
Click to expand...
4s2p 4 x 3.6V = 14.4V

I would recommend against using 3.6V and 3.7V in the same pack ... unless you use an equal assortment in each bank and limit usable voltage between 3.7V and 4.10V?

Using the iMax B8 (will balance charge 7s) as an example, there are 2 LiCo charge settings.
Lion @ 3.6V for charging to ≤4.10V and Lipo @ 3.7V for charging to ≤4.20V

After removing any cells with self-discharge and capacity matching each bank, balance charging at every cycle becomes unnecessary.
I do recommend the cell level voltage meter-alarm as a pack monitor-safety device. see - eBike Toolbox
 
3.7V should charge to ≤4.20V ... less for longer life, but 4.20V for testing purposes, bleed down, capacity etc.
See thread on Bulk Capacity Testing

8s12p pack
Balance leads connected to ends of parallels, 4 more parallels under pack.
All cells left in pairs from laptop packs.

file.php


Accucel-8150 looks fine.
 
I used a cheap 18650 charger on the 3.7 lot and after an overnight charge they read 4.3. :shock:

Thanks, clear as mud. I'm reviewing the picture and formulating to clear my thoughts.

EDIT I expanded the photo. That cleared the water.

Now where to get the balance lead for best price/quality?
 
4.30V is needlessly damaging but good, as long as already there, for bleed down test.

file.php


Mark voltage of each cell (100th V) and monitor for voltage loss -"bleed down".
Important for building reliable pack!
 
Well thats where you original advise about using a cheap charger doesn't work. I have a lot to learn, but couldn't a balance charger be used to set up one of the 4 cell holder to charge to a given level so they don't get overcharged. Sorry thats a dumb question but the build hasn't come on in the brain yet. I need to find a battery geek or RC guy around here to bounce stuff off.

Thanks for the input..
 
I need pictures and arrows. I still haven't quite grasped the last one. I'm going to set up my drafting program to do a battery layout. Finally a good use for MacDraft since I don't design landscapes anymore...
 
Please Note" Methods and procedures have progressed over the years of this thread. Later posts tend to reflect advanced-better procedures and methods.
Check out Index - #1 post, link in my signature.

I tend to charge all cells by combining in parallel.
After insuring cells to be of similar voltage. (Charge lowest voltage cells and add higher as voltages coincide)
I began by soldering all cells together with thin wires.
Lately, I use small neodymium discs and thin steel wires, cell to cell lengths for most reliable contact.
Balance chargers have a 1s setting.
 
Got it, no more charging until balance charger get here. :oops:
 
This should make things clear.

7s10p Diagrammed

Li SP.jpg

7s Balance connector - link is to 10X quantity , extensions not necessary but best price on known good quality item.

7s5p might be 10Ah+, but laptop cells don't have the surge output of LiPo or LiFe.
Would recommend for ≤10A output. Might be OK for 250w eBike?

INR is Samsung-manufacturer
Capacity and formulation is designated by letters and numbers after "18650".
INR 18650 -***
 
After balance charging and resting a few weeks my 3s50p batterypack is unbalanced without any discharging. My three banks are: 4.20V, 4.20V, 4.14V.

What should I do?
Add more cells to the weaker 4.14V bank?
 
No, find the cell that drains down the parallel row
Remove it and replace by a good one.
Because even if you add one more extra it will still go down, just a little bit slower.


50p? shit, good luck!!!
 
And that's why I don't like spot-welding them in place. I use compression clips so I can easily remove any cell.
 
kje said:
After balance charging and resting a few weeks my 3s50p batterypack is unbalanced without any discharging. My three banks are: 4.20V, 4.20V, 4.14V.

What should I do?
Add more cells to the weaker 4.14V bank?
Click to expand...
You failed to eliminate the self discharging cell(s) before assembling pack. ? (don't believe dumun, self-discharging cells must be eliminated!!!)
Confirm with multi-meter(meter-alarms vary in accuracy.)
Charge weak bank to 4.20V.
Let set, to confirm discharging.
IR meter might confirm slightly warmer cell as the culprit?

You can remove both leads on that bank and bad cell(s) will soon show as lower voltage.
 
If confirm that this bank has weak cells inside and you would not want to separate all 50 cells in that bank, I would suggest:
Charge that bank again and then split that 50P bank to five 10P banks (need to make four cuts). Let it set.
after few days (or week) measure all five banks - bank(s) with reduced voltage you need to split again (ex. to two 5P banks) etc. until you find weak cell(s)
 
We found some solderless parts for building 18650 batts. There may be a new way. Sadly it came just as China goes on vacation.
 
tomjasz said:
We found some solderless parts for building 18650 batts. There may be a new way. Sadly it came just as China goes on vacation.
Click to expand...

do tell more.

id love to find a solution for this.

was it something like this?-
http://akbattery.en.alibaba.com/product/1544781642-220504362/72V_60Ah_High_Capacity_Electric_Motorcycle_Lithium_Battery_Pack.html
 
3s60p?

file.php

Recharge bad bank to 4.20V
Separate offending bank
separate into 1/3rds
Allow to set several days ... till bad segment indicated
Separate bad segment further 1/2? 1/4? etc
Allow to set several days ... till bad segment indicated
Repeat, til offending cell-cells identified
replace self-discharging cells ... with cells tested against self discharge
re-assemble pack
 
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