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New vs Used Cells
#1
Hello everyone, 
This is my first post. I apologize if it is not on the correct board or if someone has asked these questions before. 

     I am planning on building 14s100p bank in the next year or two when I build my tiny house on wheels. I am trying to gather enough knowledge to do it right, and hopefully on the first try. I've noticed that most, if not all, of the powerwalls I've seen were made using recycled cells from laptops and other products. It seems to me that it would be much easier to buy new cells, assuming one could find a good bulk deal. That got me thinking and I came up with a couple of questions:

  1.  Has anybody built a large (10kWh+) battery bank from new 18650 cells? 
  2. Would a bank of  new cells not have a longer lifer than that of one made from recycled cells?
  3. If you buy new, high capacity cells like the Samsung 30Q INR or LG Hg2, each cell could handle 15A or 20A, respectively. I see most people use 2A-5A fuses going from cell to busbar. Could I safely use a 10A or 15A fuse on a 15A or 20A cell? Is it likely that I will ever actually take advantage of that increased draw capability or is it a case of bigger isn't always better?
  4. Is it bad to use the full 70% of your cells' capacity? Regularly? 
  5. If you buy new, would you still need to check every cell's mAh before building, or can you test just a sample?
  6.  Would the benefits of buying new cells outweigh the increase in cost?

Thanks, Zane
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#2
Welcome!

1) Yes, though I don't remember who it was. I think daromer has one made of LiFePO4 cells
2) Yes they would, drastically more life; especially the way most of us use the cells
3) You "could", but the fuse is to protect the cell from the pack if it fails due to an internal short. If you are building a 100p pack, you would need to draw over 100A from the string to get anywhere near what those cells could handle
4) It's not "bad" to use the full 70%. It's just that it prolongs the life cycles of the cell. By using 4.1V - 3.2V, you can add 1000's of cycles to the cell life expectancy.
5) You wouldn't need to test every cell for capacity, no. But would recommend doing random sample testing, though. Like test 1 cell from each "batch" of cells that are bundled together
6) This one is kind of a loaded question. It all depends on "you're" budget and time. If you don't have a lot of free time to test used cells, then new cells are worth it. Plus, new cells have a higher guarantee of success. So, with new cells and higher costs, you have a more reliable, faster, uniform packs and easier to maintain
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Proceed with caution. Knowledge is Power! Literally! Cool 
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#3
I am one of those with new cells...  Smile
No regrets at all... more expensive, yes ... but way less work and time to invest.
I agree on all 6 points of Korishan, just not happy he has forgotten me.... Tongue


You can read it here: https://secondlifestorage.com/t-Instant-powerwall
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18x 300Wp solar off grid and 10x 180Wp solar tracker grid-tie
10KW 3phase hybrid inverter. 40Kwh 18650 storage (for now)
My setup: https://secondlifestorage.com/t-Instant-powerwall
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#4
1. No wasnt me.
2. Of course longer. Several factors and some are: 1. All cells are new. 2. On 2nd hand cells they are used. 3. You dont know how used they are on 2nd hand.
3. I wouldnt fuse a new cell pack at all. the fusing in my eyes are since its mixed 2nd hand cells. With new cells there is a different scenario. As long as they god CID´s. With that said if you want to add that extra layer of safety do it.
4. Bad is a definition. You will drop of the lifespan alot compare to using 50% instead.You need to calculate how much total energy you get out of it cycling lets say 70% untill you got 60% total capacity left lets say 1000 cycles compare to cycling 50% and 2000 cycles instead. Which one gives you the most kWh of energy in the end?
5. I would never test new cells. You buy them new because you want to have a fully uniform system! In the end though you can test the packs but thats different.
6. Totally depends on how you build, how long it will last and how you plan to use it.
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#5
(06-12-2018, 01:48 AM)Korishan Wrote: Welcome!

1) Yes, though I don't remember who it was. I think daromer has one made of LiPO4 cells
2) Yes they would, drastically more life; especially the way most of us use the cells
3) You "could", but the fuse is to protect the cell from the pack if it fails due to an internal short. If you are building a 100p pack, you would need to draw over 100A from the string to get anywhere near what those cells could handle
4) It's not "bad" to use the full 70%. It's just that it prolongs the life cycles of the cell. By using 4.1V - 3.2V, you can add 1000's of cycles to the cell life expectancy.
5) You wouldn't need to test every cell for capacity, no. But would recommend doing random sample testing, though. Like test 1 cell from each "batch" of cells that are bundled together
6) This one is kind of a loaded question. It all depends on "you're" budget and time. If you don't have a lot of free time to test used cells, then new cells are worth it. Plus, new cells have a higher guarantee of success. So, with new cells and higher costs, you have a more reliable, faster, uniform packs and easier to maintain

   OK, great, thats what I was hoping. I think I will proceed with new cells. That means a lot less work for me. Thanks for the info.

(06-12-2018, 10:33 AM)wim Wrote: I am one of those with new cells...  Smile
No regrets at all... more expensive, yes ... but way less work and time to invest.
I agree on all 6 points of Korishan, just not happy he has forgotten me.... Tongue


You can read it here: https://secondlifestorage.com/t-Instant-powerwall

Cool, thanks. You've got a nice setup. I'm thinking thats the way to go. So much time saved

(06-12-2018, 10:39 AM)daromer Wrote: 1. No wasnt me.
2. Of course longer.  Several factors and some are: 1. All cells are new. 2. On 2nd hand cells they are used. 3. You dont know how used they are on 2nd hand.
3. I wouldnt fuse a new cell pack at all. the fusing in my eyes are since its mixed 2nd hand cells. With new cells there is a different scenario. As long as they god CID´s. With that said if you want to add that extra layer of safety do it.
4. Bad is a definition. You will drop of the lifespan alot compare to using 50% instead.You need to calculate how much total energy you get out of it cycling lets say 70% untill you got 60% total capacity left lets say 1000 cycles compare to cycling 50% and 2000 cycles instead. Which one gives you the most kWh of energy in the end?
5. I would never test new cells. You buy them new because you want to have a fully uniform system!  In the end though you can test the packs but thats different.
6. Totally depends on how you build, how long it will last and how you plan to use it.

Thanks for the info. After 3 months, Im starting to get a basic understanding of all this. 

Learning Everyday
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#6
I used Samsung 30Q new cells on my build
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#7
In relation to new vs used cells it is either preference or economics that will drive your decision.
For economics read my post on how much you should pay ..https://secondlifestorage.com/t-How-much-should-you-pay-for-batteries

New will not always be longer because it depends on the cells you aquire as you can buy some nice high capacity cells new which will only last 500 cycles on 100% discharge (yes I know 80%, 70%, etc). High capacity does not necessarily mean a long cycle life.

4. Think of your battery pack like a car engine, drive it around at 7000rpm and it will not last very long but you can drive it like that IF you need to, while being conservative an 2000prm will make it last a long, long while.
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#8
Those who want to use new cells might just as well buy large packs already built , many manufacturers produce every size and voltage imaginable made from 18650 , and the price is about the same cost you would pay for the individual cells themselves ...

If using new cells I certainly wouldn't solder them ...a big cloud hangs over soldering , some believe it damages the cells internally to hold the high temperature for the time it takes to solder ...

For the same price you can make a powerwall with about 7 times the capacity by using second life cells compared with new ... this extra size allows you to cycle in mid range 3.93 -3.6 V and at lower current ... getting much more efficiency and much longer life.

But this game is for people who enjoy tinkering around and building things , if it's a chore , just buy a big , already made powerpack.

EDIT...have just checked out the latest prices ... buying 100 samsung 3000 mAhr cells (aliexpress) is $440 including delivery ...

For used laptop batteries I pay $3.5/Kg ..... 20 cells per Kg .... I use 70% of cells , average capacity 1650 mAh = 23.1 mAhr /Kg

So new cell price = $1.47 / 1000mAh .............................. second life cells $0.15/1000mAh

So for the same expenditure you get 10 times the capacity .... but second life won't last so long ... a big unknown , perhaps half the useful life compared with new cells ....

But whatever cells you use, the really important thing is not to charge above 3.93V ... by doing this cells will have 5 times more life, compared to going to 4.2V
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#9
(06-15-2018, 01:19 AM)ozz93666 Wrote: But this game is for people who enjoy tinkering around and building things

Exactly! Big Grin Helps keep our minds sharp, and our finger cut from sharp minds Tongue
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Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
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#10
Well after making my rounds of suppliers for used batteries again this week ...one big factor is can you in fact buy used batteries at a reasonable price? I can testify that presently within a 150 mile radius of my location you cannot.  The prices for used now compete with what you pay for new ....considering the time and labor you have to put into the used cells.
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