How to get specification of an unknown rechargeable battery?

Discussion in 'General Electronics Chat' started by cardiology, Feb 8, 2009.

  1. cardiology

    Thread Starter Member

    Feb 8, 2009
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    Hi, I am new to this forum.
    Yesterday, I bought a 220V rechargeable emergency LED tourch.
    While charging the tourch using 220V from the powerpoint, I heard some popping/bubbling sound coming from the unit. I therefore opened it up.
    I noticed that there are 4 black rechargeable batteries connected in parallel to the circuit board. The bubbling sound is actually coming out from each one of these batteries while they are charging! Is it normal??

    I want to replace these rechargeable batteries as I am afraid that they are not working properly. However, I could not find any specifications on each of these batteries. I tried to check the combined voltage with my digital meter and it is 2.46V, when I tired to meausre the mV, I could not get anything, when I swtiched to Amp measurement, I come up as 14A, and then the wires overheat and smoke came out! I stopped immediately and everything seem fine.

    Are there anyway to check the specification of these batteries without seeing any labelling on their surface? Is the bubbling sound/fine clicking/ popping sound while charging normal??
    Please see the attached photo for details.

    Thanks in advance.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    You never want to measure current across the terminals of batteries, because you will very likely damage the batteries, blow the fuse in your multimeter or destroy the multimeter.

    I've never had batteries that made noise when charging - unless they were being overcharged.

    Can you return the unit under warranty? Or can you obtain an owner's manual from the company that made it?
     
  3. cardiology

    Thread Starter Member

    Feb 8, 2009
    12
    0
    Thanks for the comment.

    I also belief that there is something wrong with the batteries, that is why I want to replace them.
    But as the LED tourch is made in China, as usual, there is no manual or warrenty. I have tried to contact the supplier in China but no reply yet.

    Are there anyway that one can get the approximate V and mAh of a rechargable battery? Those in the torch has no marking or lables on it!

    Could I remove the 4 batteries and measure the charging output from the circuit board?

    Thanks
     
  4. studiot

    AAC Fanatic!

    Nov 9, 2007
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    From the picture your batteries look like standard 1.5 volt sealed lead acid cells.

    This would make 6 volts total, which is about right for a torch. 2.5 volts is not enough for an LED light.

    These cells are sealed so you can use them any way up. However they are delicate, relative to standard cells. They have an emergency vent button, to prevent explosions if you charge them too hard or they fail for other reasons.

    I would guess that at least one has died, hence the excess current and the boiling.
     
  5. cardiology

    Thread Starter Member

    Feb 8, 2009
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    Thanks. But the LEDs (40 of them) works fine when switched on.

    Should I take out each of the SLA batteries and check the V of each of them to see whether one of them is dead?

    Should I also check the charging voltage and current from the circuit board after I disconnect all the 4 batteries?

    If I am going to replace the batteries, what SLA batteries should I buy?
    4 x 1.5V ??mAh batteries
    or
    1x 6V ??mAh battery?
     
  6. NavjeetSingh

    New Member

    Feb 8, 2009
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    Please explain to me why measuring current across the battery will damage the batteries or multimeter?

    I would be thankful for explanation.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Because maximum current would flow through the multimeter.
    The only limiting factors would be the internal resistance of the battery, the resistance of the current shunt inside the meter (usually a rod made of brass) and the meter leads.
    Since I=E/R (Current = Voltage/Resistance), when R is nearly zero, nearly infinite current will flow.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    I agree with StudioT's assessment.
    Try measuring the voltage across each battery when the LEDs are turned on.

    The charging circuit needs some kind of a load. You won't get a good picture with nothing attached. Perhaps a large capacitor in series with a 5 Ohm power resistor would give you a better idea.

    We don't know enough yet; you haven't even given us the physical dimensions of a single battery.

    There's another possibility too - the LED powering circuit could be a boost or flyback circuit. Hard to say without at least having some really good photos of the circuit board, with the part numbers documented.
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    No.
    A lead-acid battery cell is 2.1V. An alkaline or carbon-zinc cell is 1.5V.
    a lead-acid cell is charge up to 2.3V. This torch has it overcharged to 2.46 which makes them gass and produce bubbles.

    No and no.
    The op says and the pic shows the cells connected in parallel.
    There are 40 LEDs and LEDs should not be connected in parallel so the complex circuit board probably boosts the 2.1V to make a much higher voltage.
     
  10. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Guru, you are correct about the voltages and the implications. I apologise.

    The torch circuitry is overcharging the batteries, if they are indeed in parallel.

    On the photograph I can only see twin red wires to each battery, but cannot determine if one is used a negative. It definitely goes to a different place on the circuit board. I cannot see the actual connections to the batteries to see if the wires alternately cross over or are indeed in parallel.

    This question would be worth confirming.
     
  11. Audioguru

    New Member

    Dec 20, 2007
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    The torch manufacturer over-charges the battery so that it quickly fails and forces you to buy another torch.
    The battery is no-name and is a custom size so you cannot replace it, then you are forced to buy another torch.

    I was given a electric model airplane for father's day. The el-cheapo charger overcharged the Ni-MH battery so hard that the charger and battery got extremely hot.
    I made my own charger to replace the el-cheapo one.
     
    Last edited by a moderator: Feb 9, 2009
  12. mik3

    Senior Member

    Feb 4, 2008
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    These batteries seems to be 6V (or 12V) lead acid batteries about 750mAh.
     
  13. Søren

    Senior Member

    Sep 2, 2006
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    Hi,

    Nope, they are single cell SLAs as allready mentioned and they sure seems to be parallel connected which is a bit lunatic.
     
  14. NavjeetSingh

    New Member

    Feb 8, 2009
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    Thanks for the explanation. Now I got it. I knew the relation but it never clicked my mind.
     
  15. cardiology

    Thread Starter Member

    Feb 8, 2009
    12
    0
    Update:
    Battery size: 5.5x3.5x2 cm x 4 in parallel

    When not charging on the 220V main, voltage across battery terminal 4.28-4.32V. When 60 LEDs (sorry it is 60 LEDs) all on, voltage around 4.1V

    I disconnect one battery and measure the voltage is the same at 4.28V for one battery. Even with on 3 batteries in parallel, all LEDs still work and are bright.

    Attached are the photos of the LED back panel and the circuit board. On the lower side of the board is the swtich to turn on the LEDs to low or Hi power + the charging LED indicator, on the top of the board is the 220V supply plug. The switch on the middle is for switching on and off of the LED tourch.

    Any comment guys??

    Thanks
     
  16. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    If they were crossed, confirmation would be a blast... Quite literally ;)

    In a serial string, one wire would return from the leftmost cell directly to the PCB.
     
  17. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    Ahh, they are dual cell batteries - sneaky :p but that explains a lot.
    Even with one battery it will work, just not for the same time of course.
    If charged fully and then left off for about 8 hours without charging or discharging, the terminal voltage should be close to 4.2V and the slightly higher voltage is probably due to slightly over-charging it.

    All LED's seems to be in parallel - the person "designing" that piece of crap is a moron, whether you pardon my French or not - and it appears to be the 1 Ohm resistor (plus wire/contact resistance) that is keeping it from blowing them all in a semi-second.

    The LED's are wildly over-driven, possibly to be able to give good light with lesser LED's.

    I would completely rewire the thing, because if one LED dies it will be a short which will soon rip up traces or worse.
     
  18. cardiology

    Thread Starter Member

    Feb 8, 2009
    12
    0
    Dear Soren, could you suggest to me how I am going to rewire the thing?
    Should I buy some new rechargeable batteries? What are dual cell SLA? Any specifications?

    Thanks
     
  19. Audioguru

    New Member

    Dec 20, 2007
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    Before the battery voltage was 2.46V.
    Now it is 4.3V.
    Which voltage is correct?

    The torch was designed by a moron.
     
  20. cardiology

    Thread Starter Member

    Feb 8, 2009
    12
    0
    My apologies. The charging voltage is actually 4.72V. Unplugged voltage and individual voltage of each battery is about 4.23V.
     
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