Smart li-ion batteries - how to charge?

Discussion in 'The Projects Forum' started by soravis, Feb 24, 2010.

  1. soravis

    Thread Starter New Member

    Feb 24, 2010
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    Hi!

    I'm in a team, and we're working on a robot project, and of course we need some type of battery. Li-ion is the best alternative, but not so cheap...
    I've read about the charging process, smart battery packs with monitoring circuit, etc... But never found an exact answer on how these smart li-ion packs (eg. laptop batteries) can be charged. Does the protecting circuit do all the voltage and current regulating necessary for the charge process, so I can charge the pack with a simple voltage generator power supply? Or I still need a special li-ion charger?

    Thanks in advance.

    Soravis
     
  2. bertus

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  3. t06afre

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  4. soravis

    Thread Starter New Member

    Feb 24, 2010
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    Thanks for the links.. I've read the li-ion parts on batteryuniversity, but I haven't found an exact answer to my question.

    And the linear charging ic-s are suitable for distinct cells, not battery packs. (At least I think so...)
     
  5. t06afre

    AAC Fanatic!

    May 11, 2009
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    LT have a wide range of chargers also for several Li-ion cells. But also other manufactures have such ICs
     
  6. trader007

    Active Member

    Feb 27, 2010
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    let me take a crack at actually responding properly to op's post.

    Li-ion packs arent some magical type of battery, they dont require some weird pulse charge or anything... they actually charge just like any other lead acid- give it a couple more volts then what your target is, and it will charge.

    the difference is you cannot let the cells dip below a certain voltage, and you can not let them get above a certain voltage. you also cannot let them pump out or draw in too many amps at once- all these things are what the cell protection chips are for.

    you cannot use the protection chips as chargers alone. reason being you cannot trickle charge li-ion batteries. once the current draw drops significantly, the charger itself must detect this and turn off the power because the cell protection chips cannot discern low input current. this is where some chargers are better then others, because some will allow for a monitored trickle that can get more life out of your batteries. this can be either a short timed trickle or actually monitoring the very low current flow (which is why you need the li-ion battery disconnected from the device for it to charge fully)

    they usually make 2 or 4-cell protection chips for battery packs. some put 8 cells on these 4 cell circuit boards, so theyre relying on every pair of cells to be protected as one. which of course increases the chance for hindered performance and failure. in general though, this works because the real key is the charger itself shutting off when its supposed to. you can only add cells in parallel to protection chip, the chips are only designed for pre-determined voltages. generally, do not protect more then 2 cells with one monitor (so, if you have a 4-cell chip protector, you can add up to 8 cells to it, doubling your amp-hours)

    in a lot of cases, you will actually see generic devices charge li-ion batteries without any protection chips at all. this works because of 3 things- the charger itself shouldnt ever supply too much current, the charger itself shuts off when needed, and the device itself should never draw too much current. but as you can imagine, this requires all 3 things to work properly all the time or you will have battery failure. this makes it better to understand what exactly the protection chips are for, and the reason for at least 'semi-smart' chargers (whatever you do, use protection chips and do NOT trickle charge them!)
     
    Last edited: Mar 4, 2010
    soravis likes this.
  7. soravis

    Thread Starter New Member

    Feb 24, 2010
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    Thank you very much!
    That's exactly the information I needed.
     
  8. trader007

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    Feb 27, 2010
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    no prob m8. i actually recently learned all that myself, as i needed to build a 14.8v 8ah li-ion battery pack but i didnt want to spend the $100+ just for one prebuilt.

    i ended up with some cheap-ass pre-made packs off ebay that i will take apart and make into a larger pack, but i get nervous with cheap chinese cells thats why i did some research to make sure i wasnt going to burn myself down in my sleep.
     
  9. Audioguru

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    Dec 20, 2007
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    Make and post a video of the (quote) "cheap-ass Chinese cells" burning down your house.
    Then replace the battery with a safe and reliable name-brand one.
     
  10. retched

    AAC Fanatic!

    Dec 5, 2009
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    You should most definitely use a thermal detection/cutoff circuit in you implementation. The cheap cells often have various manufacturing defects that can go unnoticed for a long time. After a few dozen cycles, you can have serious heating issues. The vents in these cheap cells rarely work.. a lot of time they are just scored marks in the case that do not open at all when supposed to. So for safetys sake, use an charge monitoring IC that takes temperature into consideration, or use a thermostatically controlled relay to kill power to the battery packs in event (read: "when") they over heat.
     
  11. trader007

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    Feb 27, 2010
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    thanks for the encouragement:rolleyes: some people just dont like it when others have a little fun. because you care so much, just so you know the batteries are residing in a firesafe box. ill post a video of me having a blast with my new toys- you can post a video of you staring at wall.

    thermal cutoff is something i wanted to add... not sure the best route for that yet but ill find something.
     
  12. Audioguru

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    I removed some name-brand lithium-ion cells from a laptop pc and from a portable DVD player. I don't have the schematic of the protection circuit so I didn't use it. I connected two cells in series and made five 7.4V batteries for my electric RC airplane.
    The batteries have a capacity of 2.2A.

    I charge them in 4 hours with a current-limited LM317 voltage regulator set to 8.4V.
    They get warm when charging then are cold when fully charged.
    In the airplane the current is pretty high and the cells get hot. But the motor gets extremely hot so it must cool for a while before flying again. Then the battery (that was used until the circuit sensed low voltage and disconnected the motor) has recovered and it can fly the airplane again and again.

    "They" say that the cells must be charged with a balancing circuit so that one with a lower capacity will not overcharge. I don't have a balancing circuit and the cells charge the same.

    I haven't burned down my house and my airplane never caught on fire. The name-brand lithium cells or my luck saved them.
     
  13. trader007

    Active Member

    Feb 27, 2010
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    im sorry, i dont mean to be rude at all.. im new here and im sure you have help a many... but that argument is terrible on many fronts.

    just because you removed protection circuits and your house didnt burn down, doesnt mean its becaues you used 'brand name cells'

    furthermore, many 'brand name' cells are just packs with different protection chips on them.

    also, you are charging and discharging your cells about 10x harder then what i will be it sounds like. the charging rate i plan on using is so low that it will take 6 hours to charge and my device might only last 3 hours at best on that charge. my amperage use is so low that the batteries should never even get warm anyway. you are using them in a completely different manner, and also because you are using them for a hobby toy they really dont need protection chips (you are next to them while they charge, and your charger is doing the protecting)

    and another thing, the protection chips i plan on using have resistors built into them to allow auto-balancing of each cell. this is accomplished by charging the whole pack, and then when the charger shuts off the protection chips themselves slightly drain whatever cells need to be so that they all end up the same voltage.

    finally, encased in a fire resistant case, wrapped in fiberglass, with protection chips, and a smart charger... and likely a temp sensor, it is ALMOST impossible to start a house fire. the fires you hear about from lipo packs almost NEVER have protection chips on them (hobby R/C batteries) or the user error was blatant.

    ps- if you look at the hobby forums where most of the fires occur, they use any battery they can find. good brand names blow up and explode just as easy as cheap ones... its all about the safety measures you follow, not the name on the cells.

    and you dont need a datasheet to add a protection cell to a battery pack. just know your cell chemistry and voltage, and buy the appropriate protection pcb.
     
    Last edited by a moderator: Mar 8, 2010
  14. Audioguru

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    I think Sanyo battery company is big enough to have their own manufactuing plant (maybe in China?).
    Energizer is one of two huge battery manufacturers in America and their Ni-MH cells say, "Made in Japan for Energizer" and their 9V Ni-MH battery says, "Made in Germany for Energizer".
     
  15. trader007

    Active Member

    Feb 27, 2010
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    sanyo was bought out by matsushita (panasonic), so combined now they are the larget battery manufacturer in the world, afaik. i would also consider them the best- but like i was saying even their batteries explode too. its all about safety measures.
     
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