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Electronics 5V PCB for li-ion cells?

Discussion in 'Modding' started by quizz_kid, 6 Aug 2014.

  1. quizz_kid

    quizz_kid Squid

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    Hi guys

    I going to make a portable Raspberry Pi device, and Im going to use 4 x 18650 li-ion cells.

    Now, I know there are Power Banks out there which I could use, such as these, but I dont need all those USB ports and such.

    I found this pcb: http://www.ebay.co.uk/itm/LOT-3-7V-to-5V-PCB-Li-ion-Lipo-Battery-step-up-Convert-to-output1000mA-DC-5Volt-/151052762793

    ... and was wondering if I could just hook it up to 4 x 18650 cells in parallel?

    And if, do I buy 18650 cells with integrated protection circuit, or without?

    Thanks
    //Quizz
     
  2. Big Elf

    Big Elf Oh no! Not another f----ing elf!

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    I've been reading up on Lithium cells and in particular 18650 and CR123s. I would say always use protected 18650s for safety and NEVER use an Ultrafire battery from eBay.

    I made the noob mistake of buying 4 Ultrafire 18650s which were supposedly 3000mAh but based on running times (I tested each one) I calculate that they're between 500-1000mAh. Suspiciously the seller refunded as soon as I queried the capacity rating.
     
  3. quizz_kid

    quizz_kid Squid

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    Yeah, heard a lot about those ebay cells... I will get proper ones, and protected I guess.

    Any thoughts about the PCB, think it might work?
     
  4. quizz_kid

    quizz_kid Squid

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    Going to check those Samsung out later, thanks.

    Btw, I looked through the PCB info in the ebay link and couldn't find the charging voltage specified anywhere. Am I missing something?
     
  5. Xlog

    Xlog Minimodder

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    Depending an your needs you could use this . The pcbs you linked on ebay are only stepup dc-dc converters, there are no caharging (or cell monitoring) capabilities. If you want charging, monitoring, etc - get a power bank, it will be the cheapest and most readily available option.
     
  6. quizz_kid

    quizz_kid Squid

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    Youre sure the linked pcb doesnt support charging? Whats the purpose of the charging +/- on the board?

    If possible, would really like a circuit without all those annoying power bank usb ports
     
  7. Xlog

    Xlog Minimodder

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    My bad, it seems it does have charging capability.

    You can charge cells in parallel. It might not be the best practice - there is no real way to detect then one cell in the bank is dying, but all bigger batteries do this (battery banks, laptop batteries, etc). Cells connected in parallel are almost always treated as one big cell, there is really no easy/economical way to do otherwise.
     
  8. Big Elf

    Big Elf Oh no! Not another f----ing elf!

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    One of the things I found when I was researching 18650 batteries was that some flashlights can charge them in parallel (but discharge in series) so I don't think it's insurmountable but would guess it needs a clever circuit design and a more complex battery carrier.
     
  9. quizz_kid

    quizz_kid Squid

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    Maybe not the ideal solution, but worth trying from my view. Charging voltage is 4.2, so might work charging with 5v
     
  10. morris8809

    morris8809 Minimodder

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    Figured I may be able to help out with a bit of info.
    I have some experience with 18650's in flashlight, and rc use. I would look at IMR/Hybrid chemistry batteries as they are safer than the ICR (colbat). The IMR are generally safe to use without protection circuit, but that circuit board you are looking at is a protection circuit in itself so the batteries would not need to be.

    Here are some cells I would look at:
    5 Amp drain or less:
    Panasonic NCR18650B (3400mah)

    10 Amp drain or less:
    Panasonic NCR18650BD (3200mah)
    Panasonic NCR18650PF (2900mah)
    Sony US18650VTC4 (2100mah)
    Sony US18650VTC5 (2600mah)

    You will need a special charger for li ion 18650 (3.7v nominal, 4.2v fully charged) such as:
    XTAR VP2
    XTAR VP1
    XTAR SP1
    Pila IBC
    Nitecore intellicharger I2/I4

    With 4 cells in the pack you will have a total capacity of 4x the original batteries capacity, so 4x NCR18650BD would be 12800mah. Your max charge rate for the NCR18650BD is 1000mah, with 4 in parallel you could charge at 4 amps. Parallel charging is commonly used in the hobby world, and each cell in the pack will be balanced with each other (this would require a hobby charger.)
     
  11. quizz_kid

    quizz_kid Squid

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    Thanks for the info, much appreciated.

    I dont want to use a separate charger though, and the board I linked to has a charging circuit built in.
     
  12. morris8809

    morris8809 Minimodder

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    To me it looks like the circuit board is just a protection circuit to keep the batteries from being over charged/discharged. You should be able to wire up all 4 batteries to the Bat +/- in parallel, your output from the 5v +/- outputs and a charger to hook up to the charge +/- hookups.

    I don't think the board actually has the charge circuit integrated as it only specifies over-charge/under-charge circuitry. Being as the Raspberry Pi will only need 1A max, I would recommend going with the NCR18650B (3400 mah) for max runtime. Here is more info on the charging of li-ions: http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

    One thing to think about. When charging the Li-ions, generally you do not want to exceed 1c in charge rate, to extend the life of the battery most people recommend .25/c or .5/c (1/4 of capacity of the cell or 1/2.) To charge all 4 batteries at the same time would require a charger capable of outputting 3.4 Amps for .25/c, 6.8 Amps for .5/c or 13.6 Amps for 1/C. None of the chargers in the previous post will come close to this (max of 2 Amp.).

    Running on 4x 3400mah cells would = a runtime of around 10.5 Hours Max (probably less to not kill the batteries completely.)
    Here are charge times for the above rates:
    .25/c (3.4 Amps) total pack capacity 13600Mah/13.6Ah: 4.44hrs
    .5/c (6.8 Amps) total pack capacity 13600Mah/13.6Ah: 2.22hrs
    1/c (13.6 Amps) total pack capacity 13600Mah/13.6Ah: 1hr
    (go by manufacturers recommendations for charging current, the NCR18650B specifies a max of 1.6Amp)

    Next issue would be having wiring/pcb to support that kind of current while charging.

    You may need to contact the seller to get more specific info about that PCB, if it is a charger, what kind of input does it need, and at what rate does it charge the battery. If it is a charger, and is below 1Amp of charging current, it will take ages to charge the batteries up. (1Amp = ~13.6Hr charge time.)
     
    Last edited: 9 Aug 2014
  13. quizz_kid

    quizz_kid Squid

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    Last edited: 11 Aug 2014

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