Li-ion charging question.

Discussion in 'General Electronics Chat' started by Terry01, Jul 16, 2017.

  1. Terry01

    Terry01

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    I have retrieved 6 Li-ion cells from a think pad I took apart. I've searched them on google and found the same ones Sanyo cells. I've split them into single cells. I've charged them @4.2v 1.7A like the data sheet says. My question is....is it safe to let the A fall away to 0.000A? I've been stopping them @ the 200mA mark.
    Sorry if this seems a silly question but I'd defo rather run it past those that know best.
    Thanks....Terry
     
    Terry01, Jul 16, 2017
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  2. Terry01

    BobK

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    BobK, Jul 16, 2017
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  3. Terry01

    Terry01

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    Cool,thank you. I stopped the charge at 200mA as didn't know. I will read the link then put them on charge again. I'm taking my first TV apart just now so will get to the batteries soon.
     
    Terry01, Jul 16, 2017
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  4. Terry01

    Terry01

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    I read the link you posted,good info for a complete beginner like me. Thanks! I use my bench power supply to charge them so I'll err on the side of caution and stop them around 150mA. I got the cells from an old think pad i stripped,they lay dead for a long time with no charge at all. I'll charge them up then leave them a while and see how they are after a couple weeks.

    I stripped an old TV last night and got some good stuff from it....I think? :)
    I've still got some parts to take from it today so looking forward to that. Hopefully soon I'll have enough bits to start making simple projects to give me a change from eBay DIY kits! :)

    Thanks again for the help!
    Terry
     
    Terry01, Jul 17, 2017
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  5. Terry01

    BobK

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    Salvage is fun, but not really worth the effort except for a few specialty parts.

    What you really need is a large collection of resistors ans capacitors, which can be bought very cheaply on EBay. These will give you several of each common value for less than a penny a piece.

    Bob
     
    BobK, Jul 17, 2017
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  6. Terry01

    Terry01

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    I love having a good look around the stuff before I strip it. Seeing how everything goes together and as I'm learning (all be it slowly) I try to work out why everything is joined up the way it is. I like googling the parts and reading the data sheet and it helps me understand why things are where they are and their exact purpose.
    I realise everything is getting surface mount but most things are the same just smaller. Also...nothing better than speaking with old hands! They know best! :)
     
    Terry01, Jul 17, 2017
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  7. Terry01

    Audioguru

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    It is dangerous to charge a lithium battery cell that has been discharged to a voltage less than 3V. It might catch on fire or explode because instead of having lithium ions some of the ions have turned into the metal lithium that shorts the battery and burns like magnesium ) used in flares).

    A battery charger IC knows about a discharge voltage that is too low and measures the voltage at the beginning of a charge. If the voltage is too low then it tries charging with a low current and if the battery's voltage rises and it does not get hot then it switches to a normal higher charging current. A lithium battery discharged too low is crippled with a much smaller capacity.
     
    Audioguru, Jul 17, 2017
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  8. Terry01

    Terry01

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    I did read that on the data sheet and firstly brought them up to 3v then 3.2v very slowly @ .25A and then left them overnight. I then started the charge again at 4.2v @ 1.7A and I stopped the charge @ 200mA and left them for 2 days. I then charged again @ 4.2v and stopped them @ 130mA,I'll check them periodically over the next couple weeks and see if they are holding their charge. I sat with them all the time they were charging checking if they were heating up or anything like that.
    The data sheet says they should sit around 3.7v so we'll see.
     
    Terry01, Jul 18, 2017
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  9. Terry01

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    They might hold a charge with no load for a long time but the capacity will be reduced since they were discharged too low. The capacity (mAh) is how long it can produce a rated current. If the capacity of a Li-ion cell is 3.4mAh then when fully charged (charged at 4.2V until the charging current drops to about 85mA) then it should produce 1.7A for 2 hours. But since the battery voltage drops from 4.2V to 3.2V when the load should be disconnected then the average discharging voltage is 3.7V.
     
    Audioguru, Jul 18, 2017
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  10. Terry01

    Terry01

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    Its great there's a place where the important information you need is offered freely. This is a great forum!
     
    Terry01, Jul 18, 2017
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