18650 battery's float voltage setting

DConlyGuyDConlyGuy Registered Users Posts: 80 ✭✭
i am making 2 4p4s 16 volt battery's using the 18650 cells they are the 3.7 volt variety. my charge controller will charge at 16 plus volts and
it can limit how much amps it can put out too. im know full charge on the battery would be 16.8, but thinking of making it 16.4 or maybe even 16 volts . i can set the bulk and absorb to those voltages, but i know these cells dont like floated or trickled charged, so i was wandering on the float voltage to set is low so it never comes on might work? another thing is amp setting, these cells are averaging 2k mah so what amps setting on controller should i use to safely charge them ? 
600 watts of solar panels,Epever 30 mppt , 2 PWHR12500W4FR battery's in 24 volt setup

Comments

  • mvasmvas Registered Users Posts: 298 ✭✭✭
    edited December 2016 #2
    RE: Charge Amps
    The "Bulk Charge Amps" is usually between 0.5C to 1.0C.
    Follow the mfr specs.

    RE: Float
    Correct, it is better to not float at 16.8v
    Let the voltage drop and the trigger a recharge

    RE: Max Voltage
    Yes, lowering the max voltage will significantly increase total cycles, with slightly lower capacity ...
    16.4 Volts vs 16.8 Volts could produce twice the cycles @ ~92% capacity
    16.2 Volts vs 16.8 Volts could produce triple the cycles @  ~86% capacity
    16.0 Volts vs 16.8 Volts could produce quadruple the cycles @ ~75% capacity

    RE: Recharge Modes
    Mode 1: Bulk Charge to 16.8v, then STOP. Wait for voltage to drop 
    Mode 2: Bulk Charge to 16.8v, then Absorb Charge until Amps < 3% then STOP. Wait for voltage to drop

    http://http//batteryuniversity.com/learn/article/charging_lithium_ion_batteries
    http://dolgin.net/Charging%20Lithium-Ion%20Batteries.html

    Do not over-charge.
    Do not under-charge
    Follow mfr specs.
  • DConlyGuyDConlyGuy Registered Users Posts: 80 ✭✭
    thanks for the info so far, but here where i dont understand the math, ill have 32 cells total to start with and they will hopefully avg 2k mah each (dont have them yet) this is where i dont under stand how many amps to charge them all at at same time
    600 watts of solar panels,Epever 30 mppt , 2 PWHR12500W4FR battery's in 24 volt setup
  • mike95490mike95490 Solar Expert Posts: 7,249 ✭✭✭✭
    edited December 2016 #4
    invest in a smoke alarm and keep exit routes clear. 
    String a whole bunch of batteries together, no BMS, no Binning of Cells to match them up, you will have trouble.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators Posts: 26,768 admin
    Just a generic warning about any small lithium rechargeable battery:



    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    edited December 2016 #6
    DConlyGuy - thank you for identifying your cells as the 3.7v lithiums, which are far different from 3.2v nominal LiFeP04.

    The catch-22 about doing lithium based projects, is that if you have to ask, you are unsafe.  And with the limited info provided, you definitely are already in unsafe territory by thinking you just have to tack these things together, and set your charge controller voltage and be done with it.

    So here are some more questions you need to know before you get started:

    1) How are you going to handle temperature-compensation?  (trick question)
    2) What is your method of proving the all the cells have nearly identical capacity and internal resistance before assembly?  How good are you at spotting fakes, or do you have a known good supplier?
    3) Are you aware that these cells only have 300-500 cycles, and that a far safer but mech less energy-dense chemistry, like lead-acid AGM has similar cycle life?
    4) Does your application actually demand this kind of energy-density? What voltage is your application actually going to use?
    5) How much current does your application pull? - are you going to use "protected" or UNprotected cells?
    6) What are your plans for over-charge and over-discharge?  Similarly, what are you going to be doing in regards to balance?
    7) What is your method of paralleling these 2K cells together?  Soldering iron?  Tack welds?  Loose-fitting holders?
    8) Have you give thought to switching lithium chemistry to LiFeP04, which is 3.2v nominal, and cutting your cell count down by only using 4 or 5 cells, like Headway's?  Easier to charge with solar too by switching to the lower-voltage LFP chemistry.

    So what exactly is your application with these cells?  Maybe we can dissuade you from becoming a danger to yourself and others.


  • mvasmvas Registered Users Posts: 298 ✭✭✭
    DConlyGuy said:
    thanks for the info so far, but here where i dont understand the math, ill have 32 cells total to start with and they will hopefully avg 2k mah each (dont have them yet) this is where i dont under stand how many amps to charge them all at at same time
    I gave you the answer here ...
    ================
    RE: Charge Amps
    The "Bulk Charge Amps" is usually between 0.5C to 1.0C.
    Follow the mfr specs.
    ================

    If you do not understand the Li-Ion Charging Profile or the math, then you should not be charging Li-Ion batteries.
    You must follow the manufacturers charging specifications.
    Please provide the URL to the manufacturers charging specifications.

  • DConlyGuyDConlyGuy Registered Users Posts: 80 ✭✭
    mvas on the math i should of said how to figure the amp hours of the 32 battery's in the 4s4p configuration so i could get the right amp setting right 
    600 watts of solar panels,Epever 30 mppt , 2 PWHR12500W4FR battery's in 24 volt setup
  • bill von novakbill von novak Solar Expert Posts: 694 ✭✭✭✭
    DConlyGuy said:
    mvas on the math i should of said how to figure the amp hours of the 32 battery's in the 4s4p configuration so i could get the right amp setting right 
    32 batteries cannot be connected in 4s4p.  That would be 16 batteries.  You do not want to charge any faster than 1C; .5C is a lot safer.

    If you don't even understand what that means, you should NOT be trying to charge li-ion batteries.  If you want to learn there are plenty of courses out there.  Batteryuniversity.com is a good place to start.
  • DConlyGuyDConlyGuy Registered Users Posts: 80 ✭✭
    you are right bill i cant seem to ask the right questions the right way the 32 battery's will be two   4s4p battery's
    600 watts of solar panels,Epever 30 mppt , 2 PWHR12500W4FR battery's in 24 volt setup
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    In addition to Battery U., there is also CPF (Candlepowerforum), BLF (Budgetlightforum), and of course EndlessSphere for the ebike crowd.

    You'll get a similar grilling from them asking you to provide more details, such as what is your actual application, to be safe.

    Lithium battery projects, from a single-cell flashlight, your own unknown 32-cell application, to that of a Tesla, requires a *SYSTEMS* approach, where more than just a single spec is involved to be safe and successful.

    Answering any one of the questions I posed above (in case you missed it), will help identify if you are making an unsafe toy, or have a real interest in a working system.

  • DConlyGuyDConlyGuy Registered Users Posts: 80 ✭✭
    thanks bill von novak on the  Batteryuniversity page half way down the 1st page they showed a picture of how to do ah. it amazing how a picture really does say a thousand words 
    600 watts of solar panels,Epever 30 mppt , 2 PWHR12500W4FR battery's in 24 volt setup
  • mike95490mike95490 Solar Expert Posts: 7,249 ✭✭✭✭
    mike95490 said:
    invest in a smoke alarm and keep exit routes clear. 
    String a whole bunch of batteries together, no BMS, no Binning of Cells to match them up, you will have trouble.
    So this is all I have to write, and it gets me flagged for abuse ?   Flag me for being snarky , but this is not abuse, unless you went to college and had "safe zones" to talk in.
     
    I'm glad I don't live within your blast radius (when it goes up).

    Just trying to get your attention that you are into dangerous stuff, and while you are asking some good questions, you have no concept of the other questions you need to be asking.  And I can't ask them for you, because you don't give straight info about what you are doing or the source of the cells,  but hey, go for it.   Post your pics at the end.


    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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