Using Low mAh Cells

chris330

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I have searched but I am struggling to find the answer to this question, I have alot of cells that I gotfor next to nothing but the only downside is they are coming back from my testing between 1200mA and 1600m.

Now I know generally people use cells that are over 2000mA minimum usually if and if people can get hold of them they prefer over 3000mA but my question is what is the negatives of using these low capacity cells? Is it purely because of the low Amp hours? Personally I wont be running tons of my stuff and looking at starting with a 12v shed
 
chris330 said:
I have searched but I am struggling to find the answer to this question, I have alot of cells that I gotfor next to nothing but the only downside is they are coming back from my testing between 1200mA and 1600m.

Now I know generally people use cells that are over 2000mA minimum usually if and if people can get hold of them they prefer over 3000mA but my question is what is the negatives of using these low capacity cells? Is it purely because of the low Amp hours? Personally I wont be running tons of my stuff and looking at starting with a 12v shed

Many advantages to using low capacity cells ... I use 500mA and above ...

A powerwallis a stationary application , so why not use them ..... for an ebike you need a light battery, so must use the best cells ....

You have already done most of the work already, bought and transported the laptop batteries , torn them open , tested them ... So why trash a 500mA cell which has the same energy density of a new lead acid battery, and probably more cycles left than a new lead acid ...

Also the more cells ofany capacity in your wall means that all cells run at a lower current, the lower the current the more efficient the wall is and it perlongs their life , also you can run at a lower top voltage which also prolongs life of all the other cells too ....

I understand some believe these low cells are close to death ... this is not clear ... If you have gone to the trouble of testing capacity you may want to put low cells 1000-500 mA in separate parallel blocks , perhaps spot welded without the black cell holders ... these low capacity cells reallydon't hold the energy of a new cell, so are even less likely to 'blow up' so there is even less case for fusing them.
 
While you have enough space and the cell doesn't self discharge, are Wh that you add to the powerwall, personally I don't use cells below 1000 mAh, usually low capacity cells are the same that self discharges, and if not they are at the end of his life, so adding to the powerwall to start getting problems with these cells in one year, I prefere not to include them.

Maybe a different serie of packs for these is an option. So you can easly take them apart and test them to renew the bad ones.

Regards
 
I wish there was a market for cells in the 1400 to 1600 range
About 50% of my laptop cells are testing in this range and I have hundreds.

I think there is a distinction between drill cells that have only lost 10-% vs a laptop battery that has lost 40%. Most of these are samsung from 50 different batteries. My conclusion is these have some manufacturing flaw as there is no way these all have been through sever life cycles
 
Thanks for the replies guys maybe I should of worded it a little better, although they are low capacity sells they are all close to what they are meant to be on the spec sheet. Most of the 1300mAh are testing around 1100-1290 and the 1600mAh are testing around 1500mAh rather than 2200mAh cells testing in those ranges. The cells are good think I;ve had one bad one so far just wasn't sure why tons of people don't use the smaller cells? I'm assuming its more the space thing and double the amount of cells required to reach the same as the 3000mAh ones
 
Using lower capacity cells doesn't make a huge difference as long as your packs across the string (serial connections) are as close as possible.

If the cells you are using are close to spec, then why not use them? That shows they are probably low on the cycle count and weren't abused much.

Just remember though that you will need more cells in parallel to achieve the same Ah capacity. But if you have enough cells, you could just make two strings of the smaller packs and then parallel the strings together.
 
Korishan said:
Using lower capacity cells doesn't make a huge difference as long as your packs across the string (serial connections) are as close as possible.

If the cells you are using are close to spec, then why not use them? That shows they are probably low on the cycle count and weren't abused much.

Just remember though that you will need more cells in parallel to achieve the same Ah capacity. But if you have enough cells, you could just make two strings of the smaller packs and then parallel the strings together.

Thanks everyone thats what I've been looking for making sure there was nothing I missed that would make these sells unusable, most of them are out of Dyson hoovers :D

I'll continue making my packs
 
Chablis_m said:
I wish there was a market for cells in the 1400 to 1600 range
About 50% of my laptop cells are testing in this range and I have hundreds.

I think there is a distinction between drill cells that have only lost 10-% vs a laptop battery that has lost 40%. Most of these are samsung from 50 different batteries. My conclusion is these have some manufacturing flaw as there is no way these all have been through sever life cycles

There's something very peculiar about how cells fail ...

Cells in the same laptop battery have come off the same production line , use the same batch of electrolyte etc ... they should be identical , yet one in the pack may fail for no apparent reason and the others are perfectly fine when they all have the same usage history .. I can think of no other mass produced item for which this happens ....

It occurred to me that spot welding them , which is done manually by humans may have slight variations , some receiving more heat damage than others , and this may be behind it ... In particular spot welding the base , if by chance the weld is at the exact spot where the negative wire inside the cell is connected , then intense heat is carried deep inside along this negative wire ....

The problem is the battery companies have no incentive to prolong battery lives , they're mission is to sell more batteries.
 
I do use ebike cells and the are nominal 1500mah and i have thousands of them to go into my powerwall. Higher capacity cells are less work to get to certain total capacity but i cant get hold of laptop cells but only ebik. Life could be worse
 
Note that 1300mAh doesnt state if its high or low capacity. You should focus on the capacity left from when its new instead. Thats a bigger factor then the actuall number

You can still find 1300mAh cells that are brand spanking new and you can find 3500mAh cells. Equally as good as the other its just different types.
Example: The cells I use are 1300mAh new and still in good shape.

The drop in capacity from when they where new is what determine how much left they potentially have left. Note that we dont know how they fail or when they fail though. The only thing is that we can guess that cells with lets say 50% capacity left from when they where new potentially have higher risk of failing....

Whats important is that you know what you are doing and know why you mix them. I wouldnt mix new with dead old cells but i would use both if needed...
 
daromer said:
Note that 1300mAh doesnt state if its high or low capacity. You should focus on the capacity left from when its new instead. Thats a bigger factor then the actuall number

You can still find 1300mAh cells that are brand spanking new and you can find 3500mAh cells. Equally as good as the other its just different types.
Example: The cells I use are 1300mAh new and still in good shape.

The drop in capacity from when they where new is what determine how much left they potentially have left. Note that we dont know how they fail or when they fail though. The only thing is that we can guess that cells with lets say 50% capacity left from when they where new potentially have higher risk of failing....

Whats important is that you know what you are doing and know why you mix them. I wouldnt mix new with dead old cells but i would use both if needed...

Thanks for the reply that helps alot

Thats what I was saying earlier maybe I have worded it wrong, I should of probably said low rated cells. Really I was asking the question why more people don't use 1300mAh cells and if there was anything I was missing as I have quite a few of them.The only issue I have with my current Dyson ones are a few of them are unbranded so having a hard time finding the capacity for them. They are pretty much coming back all between 1100-1320mAh

Although good news just opened two packs with Sony batteries in :D

**EDIT**
Just found the unbranded ones are Sony batteries as well from all the other Dyson packs!
Probably have a total of 8 unbranded batteries now
 
Great thread. I'm on a similar situation. Started to recycle laptop batteries and I was dividing them (after testing with OPUS charger) on 2000>, 1400-1999, 1000-1399 and <1000.
Using 2000> for ebike pack, but was thinking of using the rest for powerwall small packs... trying to figure out the best pack size/type for the 1400-1999 and 1000-1399 range cells and if to mix them or not
 
Just mix them up. I do sort them in 100mah steps in boxes after testing and then spread them out of sorting box evenly on 14 packages. Final capacity of 80p i know after testing the one pack with the icharger. For sure, every of the 14 packs has same capacity.

Next set of packs will be with cells less than 1500 mah.

I hope you understand my approach.

Regards
Karl
 
Charly144 said:
Just mix them up. I do sort them in 100mah steps in boxes after testing and then spread them out of sorting box evenly on 14 packages. Final capacity of 80p i know after testing the one pack with the icharger. For sure, every of the 14 packs has same capacity.

Next set of packs will be with cells less than 1500 mah.

I hope you understand my approach.

Regards
Karl

Thanks, got the idea about mixing them but not sure the what the 14 packages or 80p refer to exactly.
 
For 48v you need 14 packs in series... 14s80p. And i hav 80 cells in parallel in every pack.

Best
Karl
 
Thanks for the clarification. Does having 14s40p make any sense? to have somaller packs for easier replacenment?
 
DiegoOoll said:
Thanks for the clarification. Does having 14s40p make any sense? to have somaller packs for easier replacenment?
Well, i am currently building my third 14s80p set... ;-)

Depends on quantity of cells you intend to use in your powerwall... the smaller the packs the more flexibility but the more work and then comes the bms solution question...

Regards
Karl
 
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