Building my first pack, need some help.

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pankajdas

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Sep 24, 2021
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Hello, I am planning to build my first 18650 7s battery pack for my small home which uses roughly 2kWh per day. Currently im running on two 150Watts solar panels in series and two 40Ah Lead acid batteries with a 24v Inverter which has solar charge controller built in. Im not running the house off-grid but I want to if I can with these 18650s

I have collected 47 dead laptop batteries and from these I got 183 18650 cells which had 2.9-3.6 volts in them. currently im charging them all with 10 TP4056 all of them are beign powered with a 5V 5Amp power supply and capacity testing them with 2 Keiweisi usb testers with 1Amp load on them. I cant use opus and liitokala chargers as banggood dont ships them to my address also I dont have much money for fancy battery charger and testers. I will be expanding my pack as a found more laptop batteries.

My Questions are

1. Some of my 18650 cells doesnt charge up to 4.20V, they only go to like 4.08-4.16. Are these bad cells? or I can use them in my pack.
2. How much voltage drop is acceptable in 2 weeks. Like if I charge them to 4.20V and store them for 2 weeks then test their voltages and I get 4.15V can I use them?
3. Can Sanyo heaters be fixed? I have searched for the thread but seems like it has been deleted.
4. Can I use my pack without a BMS? Because the Daly BMS on banggood which will ship to me will take almost 2 months to reach and is a bit high on price for me. So, im thinking of building and using the pack until I save the money for the Daly BMS. I will be monitoring the voltages everyday.
5. Is self discharging an issue as I will charge them and discharge them everyday.

If Im doing something wrong please guide me through the steps to cells harvesting and pack building.
Thank You.
 

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Oberfail

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Jun 22, 2021
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1. Some of my 18650 cells doesnt charge up to 4.20V, they only go to like 4.08-4.16. Are these bad cells? or I can use them in my pack.
The TP4056 stops to charge, when the battery is only taking 55mA of charge at 4.2v. Meaning the lower the cell voltage after charging, the lower the capacity of the cell overall.

2. How much voltage drop is acceptable in 2 weeks. Like if I charge them to 4.20V and store them for 2 weeks then test their voltages and I get 4.15V can I use them?
Depending on the capacity, I'll go down to 4.1v in 30 days.

3. Can Sanyo heaters be fixed? I have searched for the thread but seems like it has been deleted.
Heaters can often be fixed, however i dont know if its permanently or temporary, by charging them until they get warm, letting them sit for 3 days, charging them again and repeat that cycle until they aren't heating up anymore. They pretty much always start to heat up at and above 4.0v.

4. Can I use my pack without a BMS? Because the Daly BMS on banggood which will ship to me will take almost 2 months to reach and is a bit high on price for me. So, im thinking of building and using the pack until I save the money for the Daly BMS. I will be monitoring the voltages everyday.
Yes you can, but you would need to pay close attention to your batteries voltage all the time, to make sure they aren't being overdischarged or overcharged.

5. Is self discharging an issue as I will charge them and discharge them everyday.
If cells discharge themself a lot, yes thats an issue. Don't use cells with a low % of their capacity as you'd need to replace them quickly and don't use cells, that drop their voltage quickly.

You also want to look up, how to properly treat Li-Ion cells. The higher you charge them, the faster they will loose their ability to store energy over time.:

Some fancy tools:

Try to look on some scrap places for dead batteries, maybe there you can get more of them & cheaper.
 

pankajdas

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Sep 24, 2021
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The TP4056 stops to charge, when the battery is only taking 55mA of charge at 4.2v. Meaning the lower the cell voltage after charging, the lower the capacity of the cell overall.


Depending on the capacity, I'll go down to 4.1v in 30 days.


Heaters can often be fixed, however i dont know if its permanently or temporary, by charging them until they get warm, letting them sit for 3 days, charging them again and repeat that cycle until they aren't heating up anymore. They pretty much always start to heat up at and above 4.0v.


Yes you can, but you would need to pay close attention to your batteries voltage all the time, to make sure they aren't being overdischarged or overcharged.


If cells discharge themself a lot, yes thats an issue. Don't use cells with a low % of their capacity as you'd need to replace them quickly and don't use cells, that drop their voltage quickly.

You also want to look up, how to properly treat Li-Ion cells. The higher you charge them, the faster they will loose their ability to store energy over time.:

Some fancy tools:

Try to look on some scrap places for dead batteries, maybe there you can get more of them & cheaper.
Thank you for all the answers and the links, I appreciate it. I will cycle the heaters and try to fix them. I have a 7s cell voltage monitor which beeps if a cell gets below the set voltage but doesn't do anything if a cell gets higher than normal voltage so I will be watching the voltages every day Again thank you for your help.
 

Wolf

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2. How much voltage drop is acceptable in 2 weeks. Like if I charge them to 4.20V and store them for 2 weeks then test their voltages and I get 4.15V can I use them?
I consider anything >0.045v too much of a voltage drop after 30 days. That being said be sure to measure the voltage of the cell right after you finish your C/D/C cycle. Not all cells will measure the same especially if you use more than 1 charger. You cannot assume that all your cells are at exactly 4.2V when exiting the charger. they may be 4.185V or 4.156V so your SD numbers need to be matched with the exit voltage not the presumed 4.2V.

3. Can Sanyo heaters be fixed? I have searched for the thread but seems like it has been deleted.
Once a heater always a heater. The chemistry of the cell has been damaged and there is no magic procedure to revert it back to a good cell.
You can fool the chemistry only so long till it reverts back to its original damaged state. Besides why go through all the hassle of building a battery pack just to have to disassemble it once the heaters rear their ugly head. Also heaters can be totally avoided by a simple IR check. With the proper equipment of course.
Here is the tread

Wolf
 

Wolf

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Sep 25, 2018
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Have you ever done any proper testing for that claim?
Good point but no I haven't as the IR of these cells (Sanyo) is always greater than my cutoff which is ≈60mΩ, the max being the UR18650FJ at 76mΩ and only a 2100mAh cell so in my case I wouldn't use it anyway. Also with the higher IR the SOH of these cells will be lower than 80% so I would have no need to test them. All this info can be gleaned from my database of +6200 tested cells. https://docs.google.com/spreadsheet...ouid=105132588382800520118&rtpof=true&sd=true
Wolf
 

floydR

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Aug 23, 2017
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4. Can I use my pack without a BMS? Because the Daly BMS on banggood which will ship to me will take almost 2 months to reach and is a bit high on price for me. So, im thinking of building and using the pack until I save the money for the Daly BMS. I will be monitoring the voltages everyday.
It is not recommended to use a any powerwall without a BMS. But it has been done.
Monitoring the voltage: would need to check Total battery pack voltage and the cell voltages. Several times a day.
There are other BMS's besides Daly perhaps one of the other BMS would work and many are less expensive then the Daly.

Later floyd
 

pankajdas

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Sep 24, 2021
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I consider anything >0.045v too much of a voltage drop after 30 days. That being said be sure to measure the voltage of the cell right after you finish your C/D/C cycle. Not all cells will measure the same especially if you use more than 1 charger. You cannot assume that all your cells are at exactly 4.2V when exiting the charger. they may be 4.185V or 4.156V so your SD numbers need to be matched with the exit voltage not the presumed 4.2V.


Once a heater always a heater. The chemistry of the cell has been damaged and there is no magic procedure to revert it back to a good cell.
You can fool the chemistry only so long till it reverts back to its original damaged state. Besides why go through all the hassle of building a battery pack just to have to disassemble it once the heaters rear their ugly head. Also heaters can be totally avoided by a simple IR check. With the proper equipment of course.
Here is the tread

WI dont have an IR tester so I dont have any other way than charging the cell and checking them.
 

pankajdas

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Sep 24, 2021
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Have you ever done any proper testing for that claim? So far I've never seen you trying to fix them and do a long term test on how they hold up.
i cycled 4 of the heaters now 3 of them doesnt heat up while charging. I will cycle them 3-4 times more to see if the problem reoccurs if it doesnt I will use them in my pack.
 

pankajdas

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Sep 24, 2021
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It is not recommended to use a any powerwall without a BMS. But it has been done.
Monitoring the voltage: would need to check Total battery pack voltage and the cell voltages. Several times a day.
There are other BMS's besides Daly perhaps one of the other BMS would work and many are less expensive then the Daly.

Later floyd
can you name one for me? I dont have much information about bms and bms makers.
 

Wolf

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i cycled 4 of the heaters now 3 of them doesnt heat up while charging. I will cycle them 3-4 times more to see if the problem reoccurs if it doesnt I will use them in my pack.
Are you cycling them at 1A? If not you should be.
Also what is the cell part number? What is the mAh result you are getting and what is the IR of the cell. Before you commit any cell to a pack know all theses numbers. You are really playing with unknown factors otherwise.
Wolf
 

pankajdas

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Are you cycling them at 1A? If not you should be.
Also what is the cell part number? What is the mAh result you are getting and what is the IR of the cell. Before you commit any cell to a pack know all theses numbers. You are really playing with unknown factors otherwise.
Wolf
The part numbers are UR18650A, UR18650E and some of them have nothing written on them. The lowest mAh is 937 & the highest is 1709. Dont know about IR because I dont have any IR tester.
 

cak

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Mar 14, 2021
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The part numbers are UR18650A, UR18650E and some of them have nothing written on them. The lowest mAh is 937 & the highest is 1709. Dont know about IR because I dont have any IR tester.
Check out the Cell Database tool here on the forum and see the new specs for those cells. Based on that you got these cells from laptops and from looing up one of those part numbers you almost certainly have standard capacity/discharge cells which means that getting a 1709mAh is pretty low and means the cell has seen significant use and degradation. In my sorting procedure I recycle all cells testing below 1000mAh and anything under 1800mAh is separated as B grade cells for low intensity/importance uses since I expect them to be unreliable/low performing. The only exception for the B grading is High discharge cells like the ones found in power tools so if those test above 1000mAh and close to new capacity(which can sometimes be as low as 1200mAh) then they are good to use with similar capacity cells only. Sorry to be the barer of bad news but from my experience trying to use lower Grade B cells on some of my early practice packs they are disappointing and problematic and you defiantly won't be able to power a house off it. You could probably get away with making smaller packs as long as you don't overload them too much but 300w of panels is not enough to run your house anyways so I say play around with what you have and you will learn loads that will help you be efficient as you build up to a whole home power system. I have included my testing flow chart for your preference but I know there are many other shared on this form as well so not a golden standard or anything.
 

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pankajdas

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Sep 24, 2021
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Check out the Cell Database tool here on the forum and see the new specs for those cells. Based on that you got these cells from laptops and from looing up one of those part numbers you almost certainly have standard capacity/discharge cells which means that getting a 1709mAh is pretty low and means the cell has seen significant use and degradation. In my sorting procedure I recycle all cells testing below 1000mAh and anything under 1800mAh is separated as B grade cells for low intensity/importance uses since I expect them to be unreliable/low performing. The only exception for the B grading is High discharge cells like the ones found in power tools so if those test above 1000mAh and close to new capacity(which can sometimes be as low as 1200mAh) then they are good to use with similar capacity cells only. Sorry to be the barer of bad news but from my experience trying to use lower Grade B cells on some of my early practice packs they are disappointing and problematic and you defiantly won't be able to power a house off it. You could probably get away with making smaller packs as long as you don't overload them too much but 300w of panels is not enough to run your house anyways so I say play around with what you have and you will learn loads that will help you be efficient as you build up to a whole home power system. I have included my testing flow chart for your preference but I know there are many other shared on this form as well so not a golden standard or anything.
Yeah you are right, but my house barely uses 300 watts at once. so the load on these batteries will be low. I'm planning to use the cell which has 70% or more of their rated capacity.
 

pankajdas

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Sep 24, 2021
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hey @Oberfail @Wolf @floydR I just bought an used Liitokala Lii 500 from a guy. I want to ask what current rate should I use to test my 18650s in Normal testing mode? I used 700mA but they are getting pretty hot and the charger is also getting very hot, and after finishing discharging they arent charging up to 4.20 not even over 4.00v two of them got to 3.56v & 3.45v and the IR rating is changing every time. Am I doing something wrong or this charger is faulty?

Edit - The IR im getting from these cells are 27,43,52 and the cells are from 1680 to 2869 and one NCR18650A got 3045 but the cell is rated at 3000mAh.
 
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Dr. Dickie

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Sep 23, 2020
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hey @Oberfail @Wolf @floydR I just bought an used Liitokala Lii 500 from a guy. I want to ask what current rate should I use to test my 18650s in Normal testing mode? I used 700mA but they are getting pretty hot and the charger is also getting very hot, and after finishing discharging they arent charging up to 4.20 not even over 4.00v two of them got to 3.56v & 3.45v and the IR rating is changing every time. Am I doing something wrong or this charger is faulty?

Edit - The IR im getting from these cells are 27,43,52 and the cells are from 1680 to 2869 and one NCR18650A got 3045 but the cell is rated at 3000mAh.
Many use 1 amp, I prefer 0.2 C (which is what most manufactures use).
Yeah, the Litokala gets hot (I think this is one of the reasons why it tends to over estimate the capacity--but that is just my belief). Mine seemed to discharge the heat though the the area where the cells were--heating them up.
It looks like someone previously used that for LiFePO4 cells, there should be a way to change the charging voltage to what you want. I haven't used my Littokala for a long time, so I forget how to change that, but as I remember it was pretty easy to figure out (clicking the buttons).
The folks you listed will know a lot better that I, but I was just sitting and killing time, so I figured I would reply.
 

pankajdas

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Many use 1 amp, I prefer 0.2 C (which is what most manufactures use).
Yeah, the Litokala gets hot (I think this is one of the reasons why it tends to over estimate the capacity--but that is just my belief). Mine seemed to discharge the heat though the the area where the cells were--heating them up.
It looks like someone previously used that for LiFePO4 cells, there should be a way to change the charging voltage to what you want. I haven't used my Littokala for a long time, so I forget how to change that, but as I remember it was pretty easy to figure out (clicking the buttons).
The folks you listed will know a lot better that I, but I was just sitting and killing time, so I figured I would reply.
Thank you for your reply. I am new here so don't know whom to ask. they had helped me on my first post which is this one that is why I mentioned them. I think mine is also discharging the heat where the cells are which is heating them up too. Cells are in good condition and they have most of their capacity and the IR ratings are also good according to the charger but still, they are getting very hot.
 

Dr. Dickie

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Sep 23, 2020
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Thank you for your reply. I am new here so don't know whom to ask. they had helped me on my first post which is this one that is why I mentioned them. I think mine is also discharging the heat where the cells are which is heating them up too. Cells are in good condition and they have most of their capacity and the IR ratings are also good according to the charger but still, they are getting very hot.
You picked the right folks to ask.
I am a newb still learning.
They will come along and offer some real help.
Hang in there, there are a lot of great folks here that will help you with what you need to undestand--then again, I am just a learning new stuff geek.
 
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