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    Is there a need for bms?

    My experience with second use cells is they do not fail catastrophically , but when dyingself discharge at a rate depending on the voltage ... if you have a 3.7 V pack with one cell self discharging at 1A it will slowly drain that whole pack , the other packs will go high and the BMS will burn...
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    Is there a need for bms?

    You don't specify what size of pack you are talking about ..... For power-wall I have never used a BMS ... the vast number of cells involved mean each 3.7V block making up the wall will have around the same capacity so they will stay very close voltage wise ... I have a small voltmeter on each...
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    Advice needed

    The big problem with Li-ion is they have such a large voltage drop during discharge 4.2 to 3.5 .... 5s would give 21 to 17.5 luckly that is fairly good for 19v , but still the variation is too much to use directly for a lap top Lifepo4 6s does come out as 19.2 so could be used without...
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    18650 Battery Holders

    This sounds a crazy (high) price for used particulary Auto since they will have been hammered ... I can buy New LiFePO4 cells in small or large quantities (price is the same) from my local online store , delivered to my door for $125US/Kwhr ... If you don't keep up with the fact that cell...
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    Bulk Nissan Leaf Batteries for sale

    These are very popular where I am (Thailand)... new Li Fe PO4 ... Online store here will deliver to your door for just under $2US each they are bigger than 18650's ...advertised as 6 AHr ... when I tested the 8 I bought they were all slightly over 5Ahr ... Nominal voltage 3.2 = 16 Whrs each...
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    Falling Battery Prices ....

    I clicked on your link and got this page ....https://www.aliexpress.com/item/4000001219462.html?spm=a2g0s.8937460.0.0.e2b22e0eR6f4Dl $1998 for 16 ... and another $11 off , discount vouchers ...and free shipping ... I do live in Thailand ... Your recent price jump is probably due to US taxes...
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    Falling Battery Prices ....

    That's still a good price ... they are a different chemistry ...they have life of3,000 cycles at 80% DOD (depth of discharge ) Li -ion would only give about 1,000cycles at 80% DOD ... to get 3,000 cycles you would have to go to 70% DOD ( to be accurate , only use 70% of rated capacity , charge...
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    Falling Battery Prices ....

    This chart is not for bulk (million cell) buying .... The tests done on Queen batteries by a member here give a price of $200/Kw on purchases of around a 100 cells delivered to your door , and that's what the graph shows $200 in 2019 ... At this price reusing is not sensible.... No reason to...
  9. O

    Falling Battery Prices ....

    That seems a high price for used , you need to pressure your supplier for a reduction... New cells can be bought for less.... For comparison a fairly high capacity NEW18650 holds 10Whrs ... 100 would hold 1KW ...$2 each gives a price of $200/KwHr on the chart ... We are reaching the point...
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    Falling Battery Prices ....

    Here's an interesting chart I stumbled upon !! Solar panels also show a similar curve!
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    Results of Capacity Testing 18650s for 1,600+ Cycles

    This test is all about measuring reduction in capacity over cell life , measuring the % drop , so using opuswill not effect things too much , particularly at low discharge currents.... My instinct tells me the material the contacts are made from will not have a significant effect ... Lets do...
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    Results of Capacity Testing 18650s for 1,600+ Cycles

    I tend to agree , but this is a comparative test .. As long as same procedure was used throughout these are accurate results ... Contact resistance due to cell not being held firmly won't effect capacity readings significantly , only internal resistance measurements . We can see results are...
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    Samsung 26J (26JM) 2600mAh low price cell's capacity test

    I don't know if an old production date is typical for most new cells... Where have these cells been for over two years?? I would think manufacturers want a quick turn around and would normally sell within a month of production. But it doesn't seem to have reduced capacity!
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    Samsung 26J (26JM) 2600mAh low price cell's capacity test

    Wow ... that's rather a short life .... " 300 cycles capacity 70% original " Works out at around 5Whrs/$ great value for a 18650.. Cycle life , normally around 400 (charged to 4.2 V) ... this means 400 cycles before below 80% original capacity , for some reason this manufacturer has given...
  15. O

    18650 in use 24/7 outside, how to prevent overheating?

    You give lots of irrelevant information and omit the most important thing .... LOCATION Are you in Norway or Saudi Arabia where air temperature can reach over 50C ... Temperature is not an issue unless you are somewhere very hot and drawing large currents.
  16. O

    Powerwall using 50 AH cells

    On your first point , see Geek's post On limiting depth of discharge for Fe , there is no great advantage , we must remember if you discharge to 50% you have only processed half the WHRs ... so you would expect to get double the cycles , It's all about how many WHrs are processed over the life...
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    Powerwall using 50 AH cells

    Yes ... this is a very sensible idea ... main differences between li-Fe and li-ion is that Fe weigh about twice as much for the same storage ... not an issue for static applications .... Also Fe life cycles are not influenced by how high you charge ... with Li-ion it's paramount to keep top...
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    Nickel sheets

    eBay is always the best for small amounts ....Pure nickel may be a bit floppy , I have worked with Stainless Steel 0.1 and 0.15 , very strong and ridged in thin sheets , can be cut with scissors , spot welds well ... it does have fairly high resistance but this is not aproblem when in sheet form...
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    Queen Battery QB10440 300mAh - a 3.7V AAA-size Li-ion battery

    As usual another very professional review from thunderheart . I've no idea what people do with these cells , obviously cannot be put in domestic products which take alkaline AAA ... Compact size comes with a penalty theyhave exactly half the WHrs/gm that 18650s have... For small devices...
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    Results of Capacity Testing 18650s for 1,600+ Cycles

    Brilliant work Dallski ... this fills in a big gap in our knowledge .... just what sort of life can we expect from generic cells ??? It would seem from your early results that they hold up well , perhaps just as good as recognized brands ... this sounds logical , it's basically the same...
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