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18650 battery pack 5A charger

Discussion in 'Power Electronics' started by BlinkingLeds, May 27, 2013.

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  1. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    Hi got 4 18650 batteries (4.5Ah) and i want to connect them in series to make a flashlight with a 10w led. The problem is how to charge them.
    I don't trust those "quick chargers" that one can buy from ebay because they reduce the life expectancy of batteries.
    That's why i want to make my own among other reasons. I need to charge them at 5A. I've been going through the datasheets on digikey for bat charger ICs and the most i could find is 3A for a linear charger. I have found some switch mode charger chips but i'm not sure if the circuit in the datasheet is correct.

    http://cds.linear.com/docs/en/datasheet/1510fc.pdf

    http://cds.linear.com/docs/en/datasheet/4006fa.pdf

    http://www.ti.com/lit/ds/symlink/ucc3956.pdf


    Thanks
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    The two Linear Technology devices are limited to 1.5A and 4A charging current respectively. The Texas Instruments device has an external MOSFET so you should be able to go higher, though the sample circuit only charges at 1.2A.

    The Panasonic 18650 is specified at only 2.5 Ah. Which brand claims 4.5 Ah? Have you confirmed this capacity? The rechargeable battery market is very competitive and many companies are... creative with their specifications.

    Are you sure you "need" to charge the cells at 5A?

    Why are you not sure about the circuits in the data sheets?
     
  3. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    They say "The internal switch is capable of delivering 1.5A" isn't that a hint that i can add an external one?
    I got the batteries from china on ebay :) so definitely not 4,5Ah?
    Well i don't need to charge them at 5A i just want 1C or more

    Another time i tried a schematic from a datasheet it did not work. Later i discovered that some components were missing from the schematic.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Chinese batteries? AND from eBay? You'll be lucky if you even get 2.5 Ah!

    Stick with the reputable brands to avoid imaginative specifications, and buy from reputable companies to avoid counterfeits of the reputable brands!

    It's not just the capacity that will be a lie. Do you care about the number of charge/recharge cycles you will get? Or about the battery's basic safety? The knock-offs are cheaper but this is often more than offset by the problems they bring.

    Data sheets do sometimes have errors, especially in the application schematics (in my experience), but I wouldn't assume any particular data sheet does.

    In my experience, Linear Technology products are very well-designed for ease of application. On that basis I was going to suggest you try the LTC4006, but it won't charge a single cell at a time. There are other manufacturers though. Look through the charge controllers available from Digikey or Mouser. They carry a huge number of semiconductor manufacturers so you'll get a good idea of what's available.
     
  5. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    The problem is i don't have an idea which one to choose from those 3000 or so components listed on digikey or mouser. I only know that switching type chargers are better but i don't know how to use them.

    So if use LTC4006 should i connect it as the application circuit on the first page?
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Yes, but it doesn't charge cells singly. I'll have a look and see what I can suggest.
     
  7. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    i have 4 cells in series why should it need to charge 1?
     
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I assumed you wanted to charge them separately for best performance. Also 4-cell chargers are less common than 1-cell and 2-cell chargers.
     
  9. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    By best performance you mean that they will last more charge cycles?
     
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Yes. I'm not very familiar with Li-Ion chemistry so you should do some research, but generally, when cells are connected in series, as the individual cells age, their characteristics deviate further from each other, which leads to some cells being overcharged and some being incompletely charged when they're charged in series. This happens with other chemistries, but as I said, do some research, because it may not be a problem with Li-Ion.

    Digikey don't distinguish linear and switching chargers. So you need to go to the manufacturers' web sites and use their filters. Select options that meet your requirements for charger type (switching, not linear), battery chemistry, number of cells, and charge current, and eliminate anything that requires a microcontroller and anything that has a BGA or no-lead package (package name contains BGA or ends with the letter N). (Unless you plan on getting a PCB made and soldered professionally.)

    These are the manufacturers listed in the Digikey selection results.
    Analog Devices http://www.analog.com
    Linear Technology http://www.linear.com
    Maxim http://www.maxim-ic.com
    Micrel http://www.micrel.com
    Microchip http://www.microchip.com
    Microsemi http://www.microsemi.com
    STMicroelectronics http://www.st.com
    Texas Instruments http://www.ti.com

    When you look at the data sheet or summary page for a device, look for the application circuit. See what external components and signals are needed. For example, all of the small-package devices need at least one external MOSFET; some need an external microcontroller to tell the device what to do (not appropriate for your application); most will need some kind of temperature feedback from the cell or pack, and so on.

    If you can come up with a list of links to devices you think might be suitable, I (or someone else) can check them out.
     
  11. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    well i think that LT3651 for single cell or ltc4006/7 for multiple is the simplest way to do it
    i prefer LT3651
     
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Yes, the LT3651 looks nice if you're going to charge the cells separately. It has an on-board MOSFET which is a big advantage for simplicity and ease of use. It's not standard stock at Digikey or Mouser though. Do you have another supplier in mind?
     
  13. BlinkingLeds

    BlinkingLeds

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    Feb 23, 2013
    i could buy it directly form LT but i think i may have to choose the LT3651-8.4 2cells charger which will only cost half :)
     
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