It's a perfectly reasonable strategy as long as your parallel groups are of equal capacity.
How many cells of each type do you have? What sort of pack configuration do you have in mind?
18650 cell question
- Thread starter billym1967
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How many cells of each type do you have? What sort of pack configuration do you have in mind?
Whatever way you hook up mismatched cells into strings and then those strings into a battery (10s for 36v in your case ) I understand the underlying two rule to be this
1. Prob best not to, but
2. If you do expect your whole pack to be as good as the weakest cell. First it will pull down that string and then the pack.
At best you’ll get poor performance , voltage sag and a much shortened battery life
At worst , see you tube
Personally I’d keep cell strings to one type. In your case I’d then assume the whole pack to be built out of 5.2a 2600mah and load it as if it were. If course the 2900 string or strings will have capacity to spare when the lvc kicks in due to the 2600 being fully discharged.
The cell strings will be out of balance after every ride of course
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Deleted member 4366
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Logic says that as long as you have the same arrangement of cells in each string, you should be OK, but I have a feeling it's more complicated than that, so best to only use one type and age of cell per battery, but if you don't mind taking a chance on things going wrong, give it a try. Definitely don't put used and new cells in the same battery and don't put different cell-types in different strings. By string, I mean parallel group.
the question was probably more aimed at used cells where the may be mixed types. so i'm guessing that you try and make each string as similar as possible if using used.
but also curiously, at the moment i have 3 sonys left over, and ive got 42 samasungs so will probably end up with 2 left. i'm going to get another 30 or 40 samsungs to make my big battery. of cause i could buy 28 or 38 and if none a faulty, no spare. its just what to do with the sonys.
but also curiously, at the moment i have 3 sonys left over, and ive got 42 samasungs so will probably end up with 2 left. i'm going to get another 30 or 40 samsungs to make my big battery. of cause i could buy 28 or 38 and if none a faulty, no spare. its just what to do with the sonys.
If you've only got a couple of odd Sony cells, you won't be able to do anything with them unless you plan to build a 2S or 3S pack.
Best forget the idea.
Best forget the idea.
yes guessed that unless i buy another 7 off them and 21 samasungs but not worth it on new cells i think
so my new imax came today and ive been having a play. first thing who ever said it only discharges at 1A was correct. so it quite slow lol.
decided to have a mess with a new Samsung 2600mAh cell. first run at 1A discharge was 1500mah. so its running a second time at 0.5A and is at about 750 now.
i also got a couple of scrap batterys to play with. both the same with 35 cells. i stripped the first one and tested all the cells and they all read about 3.53v. the on my charger now getting a charge. now i now my new Samsung cells was from 3.5v puting about 2100mAh of charge in. so first thing is to see what the get up to. once that's done i will discharge some to compare results.
now the second one is stranger and dont 100% understand. once stripped i checked the cells and all 35 only had 1.3v. but i have a couple of new but knacked sonys with 1.3v and when i put them in the charger they wont charge. i tried one of these 1.3v ones and its charging. will have to wait and see hoiw far it goes. so finding that a bit strange.
i love playing lol
decided to have a mess with a new Samsung 2600mAh cell. first run at 1A discharge was 1500mah. so its running a second time at 0.5A and is at about 750 now.
i also got a couple of scrap batterys to play with. both the same with 35 cells. i stripped the first one and tested all the cells and they all read about 3.53v. the on my charger now getting a charge. now i now my new Samsung cells was from 3.5v puting about 2100mAh of charge in. so first thing is to see what the get up to. once that's done i will discharge some to compare results.
now the second one is stranger and dont 100% understand. once stripped i checked the cells and all 35 only had 1.3v. but i have a couple of new but knacked sonys with 1.3v and when i put them in the charger they wont charge. i tried one of these 1.3v ones and its charging. will have to wait and see hoiw far it goes. so finding that a bit strange.
i love playing lol
so Samsung is finished, well i could have done a 3rd run but i only wanted a bench mark. 1 run a 1A and 1 At 0.5A 2497mah i did watch a utube where they ran again at 0.3A but not gonna bother.
the other batterys, the 3.53 ones are now a 4v and heading towards a 1000mAh
the strange 1.3v ones are now at 3.6v and at 400mAh not sure what that means yet lol
i also got another used battery today, a 50cell one. described as a blown BMS board. never though to check it first and just stripped it down to the 50 cells. just checked the V and its reading 41.3v right across.
the other batterys, the 3.53 ones are now a 4v and heading towards a 1000mAh
the strange 1.3v ones are now at 3.6v and at 400mAh not sure what that means yet lol
i also got another used battery today, a 50cell one. described as a blown BMS board. never though to check it first and just stripped it down to the 50 cells. just checked the V and its reading 41.3v right across.
hears another question for you wizards lol
so i got some cells, when first tested many had a vaultage of under 1v, so i stuck them in my XTAR and they started charging. they put about 300mAh in up to 3.5v (took a long time), so had to switch the charger of last night. put it back on this morning and its now up to 4v and 1700mAh.
so my question is why and how does a battery get that low, and a second question would be as there charging does that mean the saved and ok.
so i got some cells, when first tested many had a vaultage of under 1v, so i stuck them in my XTAR and they started charging. they put about 300mAh in up to 3.5v (took a long time), so had to switch the charger of last night. put it back on this morning and its now up to 4v and 1700mAh.
so my question is why and how does a battery get that low, and a second question would be as there charging does that mean the saved and ok.
<1v means they are toast and will eventually bleed back down if left for some time, under load they will crash. Poor voltage cells like that are only fit for recycling.
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So is there any other possible reason to cause it. Also can you do anything to test that. If I charged them and left them standing for some time to see if the vault age drops. Or is there any way I can put single cells under heavy load
So and me being maybe numb. If you have a bank of 4 cells and one dies. Won't that fetch the other 3 down even if there ok. The reason I ask that is I noticed if one cell in a bank reads low they all do
High IR will cause a cells voltage to collapse under load, though a healthy cell be discharged by a faulty bms.
Or a poor quality built cell or fake .
So if I can't put one cell under heavy load. If I charge them fully and leave them for 3 months any goosed should discharge. My broken battery the other month was a BMS fault and they went really low
Yes.
A poor cell will bring good cells down stressing them and eventually they will show signs in loss of capacity and voltage drop.
If a bms bleeds them low then they may well be recoverable as the bleed load is small measured in milliamps.
A high output torch could be used to see how good a cell is, time a known good cell against a known defective cell and then measure their voltages at said given time intervals ( leave the torch on and measure voltage every half hr over a 3 or 4 hr period). Unprotected cells will drain till there spent.
There are cell testers that can put cells under load to check for performance.
A high output torch could be used to see how good a cell is, time a known good cell against a known defective cell and then measure their voltages at said given time intervals ( leave the torch on and measure voltage every half hr over a 3 or 4 hr period). Unprotected cells will drain till there spent.
There are cell testers that can put cells under load to check for performance.
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D
Deleted member 4366
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There are so many reasons how a cell becomes faulty and lots of different ways they behave when faulty. Some go weak, some self-discharge, some lose capacity, some get high resistance, etc. That's why it's not a good idea to use used cells. You have no idea what they're like unless you test for all those things, which will take forever, and most will fail one of the tests. Voltage and capacity measurements are not enough on their own. You have to do load tests, self-discharge tests and measure internal resistance.
Obviously, if one cell is self-discharging, it will drag the whole string down.
There is virtually no charge in a cell between 1v and 3v, so within a few seconds of charging a 1v cell, it will spring back to life. It works the other way too, which is how they get to 1v. Somebody runs them down to 3v, then doesn't charge them. the smallest amount of self-discharge, which many cells do, sends them down to 1v. You wouldn't notice self discharge when the cells are properly charged because it takes a comparably massive amount of discharge to go from 4.1v to 4.0v.
Cells that have been down to 1v will never behave like new cells, and are not suitable for ebike batteries, so keep them for lights and power banks.
You will soon learn that all this messing about with used cells is a complete waste of time, like we told you in the beginning. I guess that you're already starting to figure that out from the experiments and tests that you've already done.
The only time it's worthwhile is if you can get hold of relatively new, but faulty ebike batteries. I got one recently that had 50 cells, but one string was down to zero volts. I hoiked them out and reconfigured it to a 40 cell battery with a new BMS, which should give years of service. I put a new BMS in because the most likely cause of the string going down was a stuck open bleed resistor.
Obviously, if one cell is self-discharging, it will drag the whole string down.
There is virtually no charge in a cell between 1v and 3v, so within a few seconds of charging a 1v cell, it will spring back to life. It works the other way too, which is how they get to 1v. Somebody runs them down to 3v, then doesn't charge them. the smallest amount of self-discharge, which many cells do, sends them down to 1v. You wouldn't notice self discharge when the cells are properly charged because it takes a comparably massive amount of discharge to go from 4.1v to 4.0v.
Cells that have been down to 1v will never behave like new cells, and are not suitable for ebike batteries, so keep them for lights and power banks.
You will soon learn that all this messing about with used cells is a complete waste of time, like we told you in the beginning. I guess that you're already starting to figure that out from the experiments and tests that you've already done.
The only time it's worthwhile is if you can get hold of relatively new, but faulty ebike batteries. I got one recently that had 50 cells, but one string was down to zero volts. I hoiked them out and reconfigured it to a 40 cell battery with a new BMS, which should give years of service. I put a new BMS in because the most likely cause of the string going down was a stuck open bleed resistor.
yes experimenting and learning. but i have figured out how to test load a small number of cells. it sort of worked then went wrong. 12v 50w halagion bulb will draw power at 4A so depending on how many cells you use will determine how hard you tax the batter. 2 cells only 8v will draw heavy and a poor battery should wipe out quickly. 3 cells and less draw should do better. but again if there's a knacked cell it should last long.
so i tried it and it work apart from 10 minutes in it melted my cheep cell holders lol batterys got quite hot. so i need to work away round that. spoke to an electric guy. his opinion is if the cells can with stand that, then charge them put them to 1 side for a month and check for vaultage leakage and is minimum and they withstand both tests then you should have a decent battery.
next step is to build a cell holder that can cope with the heat, runt the test with 3 new cells to get a bench mark and then try it.
like what been siad on here even though the cells may hold 2000mAh, you need to find out weather the cells are dead due to a faulty BMS or a faulty cell. drawing 4A from 3 cells should let you know this. then standing for a month should tell you the full answer.
problem is some used cells are advertised with a faulty BMS board (you dont know if that's true) others dont tell you the reason. i need to build a strong cell holder now with decent wire to test the theory.
so i tried it and it work apart from 10 minutes in it melted my cheep cell holders lol batterys got quite hot. so i need to work away round that. spoke to an electric guy. his opinion is if the cells can with stand that, then charge them put them to 1 side for a month and check for vaultage leakage and is minimum and they withstand both tests then you should have a decent battery.
next step is to build a cell holder that can cope with the heat, runt the test with 3 new cells to get a bench mark and then try it.
like what been siad on here even though the cells may hold 2000mAh, you need to find out weather the cells are dead due to a faulty BMS or a faulty cell. drawing 4A from 3 cells should let you know this. then standing for a month should tell you the full answer.
problem is some used cells are advertised with a faulty BMS board (you dont know if that's true) others dont tell you the reason. i need to build a strong cell holder now with decent wire to test the theory.
D
Deleted member 4366
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so test 2 lol didn't go well either lol, home made battery holder. 3 new Samsung cells . ran the bulb for 30 minutes. took the cells out and check the vaultage 2 were down to 37v and there 3rd was dead. burried it as it was gone. so not a good test.
spoke to the guy again told him what happened and we had a long chat. he says heat has killed the battery.
so we discussed it again. run one cell for 10 to 15 minutes. runing that cell on a 12v 50w bulb will put it under heavy load without over heating it. i good cell will drop in vaults and a poor one will probably die. even if it doesn't. check what vaults a good cell drops in 15 minutes (do a couple or few cells to get a bench mark) so even if a poor cell doesn't die the vaults will drop a lot more. so if a new cell drops from 4.2 to say 3.9 your looking for around that from old cells. and you should notice the difference. recharge any that pass, put them on a shelf and check in a week and check the vaults drop and you know if there any good.
on another note my vautameter has a A check on it.
spoke to the guy again told him what happened and we had a long chat. he says heat has killed the battery.
so we discussed it again. run one cell for 10 to 15 minutes. runing that cell on a 12v 50w bulb will put it under heavy load without over heating it. i good cell will drop in vaults and a poor one will probably die. even if it doesn't. check what vaults a good cell drops in 15 minutes (do a couple or few cells to get a bench mark) so even if a poor cell doesn't die the vaults will drop a lot more. so if a new cell drops from 4.2 to say 3.9 your looking for around that from old cells. and you should notice the difference. recharge any that pass, put them on a shelf and check in a week and check the vaults drop and you know if there any good.
on another note my vautameter has a A check on it.