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simple current question

Discussion in 'General Electronics Discussion' started by userqq, Oct 4, 2012.

  1. userqq

    userqq

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    Oct 4, 2012
    Hi, If I put 3 (three)1.2 volt, 600 mah li ion batteries in series will I have 3.6v 1800mah or 3.6v 600 mah?
    thanks in advance
     
  2. BobK

    BobK

    7,599
    1,641
    Jan 5, 2010
    You have 3.6V at 600maH.

    Except that Li ion batteries are 3.7V.
    Bob
     
  3. userqq

    userqq

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    Oct 4, 2012
    Thanks for the answer Bob and yes you are right I had not checked the actual voltages I just needed to know the physics of it and I thank you for that info:)
    So now I have another question. Lets say that I take 3 (three) 3.7 v 600mah batteries and connect them in parallel will I then have 3.7 v 1800 mah?

    I need to build up a small (protected) battery pack for a portable device which an exact replacement battery is not available. Its requirements are 3.7v 1800mah.

    Thanks again!
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
    2,690
    Jan 21, 2010
    Yes :)
     
  5. donkey

    donkey

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    Feb 26, 2011
    batteries in parrallel increase amp hours and batteries in series increase voltage.
    as for not finding an exact replacementt depending on the circumstance you could use plugpacks, wallwarts, etc. the big thing to me though is the 1800mah rating may not be required. some projects I do have a single AA battery inside them. by upgrading the unit to let me have 2 or 3 in parrallel I get 2-3 times the run time. I also sometimes use a lower amphour battery on some projects they run for less time.
     
  6. userqq

    userqq

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    Oct 4, 2012
    Thanks guys, I am about to order the batteries from manafont.

    My choices are 3 individually protected batteries (easier, guaranteed fit)
    or
    3 unprotected batteries (same specs) in parallel all connected to ONE PCM (pictured below)
    PCM1.JPG
    Note:as you can see below the original battery (NG) was one (i think there are 3 cells in there because there are creases in the metal at 1/3 1nd 2/3 from each side) with a single PCM on right (burned out, I checked it)

    My concern is overcharge and discharge protection maybe being uneven with the individually protected batteries. Does it even matter?
    m40 battery.jpg

    Note to donkey, thanks and I see what you're saying but I should add that this device is safety equipment so I feel that I must stick to the original specs as close as possible.
     
  7. donkey

    donkey

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    Feb 26, 2011
    may I be so bold as to ask what sort of safety equipment?
     
  8. userqq

    userqq

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    Oct 4, 2012
    sure, gas detector.
    still unsure about any difference in charging single protected batteries and 'a bank' of 2 or 3 protected by one circuit.
    I hate being uncertain like this.The parts will take a long time to get here from HK so I need to make a decision soon.
    Im starting to think that it doesnt matter.
    anyone?
     
    Last edited: Oct 10, 2012
  9. CocaCola

    CocaCola

    3,635
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    Apr 7, 2012
    What are the dimensions of the battery compartment? You can almost certainly find an over the counter [email protected] cell phone battery that will fit... I have replaced several different internal device batteries with the old style iPhone 2g replacement batteries (they are cheap and have wired leads)... Matching the mAh perfectly is not all that critical as it will only effect run times slightly if you are only off by a little bit, possibly not at all since the ratings can be all over the place and rarely translate to real run times...
     
  10. userqq

    userqq

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    Oct 4, 2012
    sorry guys, I did not mention that I am sick and its now a bad time. I'll have to get back to this hopefully sometime next week.
     
  11. userqq

    userqq

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    Oct 4, 2012
    OK ins co finally paid for my meds! so im back.
    CocaCola the dimensions are kind of hard since the space is trapazoidal but basically I have 3.2 X 5 cm, Im looking at 3 unprotected 10440s with this
    http://www.ebay.com/itm/350608175291?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 PCM that I already ordered. I never got any opinions about the seperate vs 'banked' charging protection so Im going with 'banked'.because that was the original design.
    I DO see your point about finding a batt that fits and yeah I had also considered that but since this has turned into such a PITA due to the original manufacturers greed making the battery 'non replaceable' (they WILL sell you an entire plasic 'back' of the unit with an embedded battery for $185.00 but will not simply sell the replacement battery) I have decided that the batteries will be a user replaceable bank of 3 'off the shelf' li ions and what fits with a bunch of custom work is 3 3.7v 10440s.

    Imagine a car that the starter is not replaceable and when it breaks you must buy a complete new engine.
    well im preaching to the choir here because im sure many of you have seen the same before. anyways ill put up an update when its done and I want to say thanks to everyone here and hope to interact more with you guys in the future. :D
    Of course all input appreciated, I have not done much of this since I was a kid and thats been awhile:)
     
  12. userqq

    userqq

    10
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    Oct 4, 2012
    PCM Connection

    Hi, As you know I had to replace the li-ion battery in a portable device. I have the unprotected battery and proper PCM (protection circuit module).
    The PCM wiring is pretty straightforward as you can see by the pics. I have Battery + and - and power (load)+ and - but there is one more terminal on the PCM and it is labeled 'T'. I dont know what this is or if I even need it for this application. The original PCM (bad) and battery only had batt in and power (load).
    The PCM is for Hauwei HB5F1, The battery is 3,6v 1800mah and the device is a rechargeable gas detector.
    Question: Does anyone know what the terminal 'T" is and if I even need it.
    (maybe it is for test?)
    Thanks!
     

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