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Thread: Series Parallel

              
   
   
  1. #11
    Member Nicman's Avatar
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    Quote Originally Posted by Spoonman View Post
    WOW!

    Dude I'm very glad you came on here, and I hope you've done so before you attempted anything like what you've drawn.
    I reckon some serious 'book time' would be a very wise investment before you do too much more tinkering as, and I don't mean any offence here, I'm genuinely concerned that you might wind up doing yourself some serious damage.
    What you've drawn here in itself isn't actually very likely to lead to injury but it does highlight that the fundamental comprehension of the systems you're working with simply isn't there.

    To address your questions:
    Parallel means more charge at the same voltage - yes.
    Series mean more voltage at the same charge level - yes.

    But
    Parallel involves having multiple cells connected positive to positive, and negative to negative - ie: BOTH poles are connected between adjacent cells
    Series involves multiple cells connected positive to negative at ONE pole only.

    and
    Parallel cells MUST be of equal voltage.
    Series cells MUST be of equal charge.

    Hence
    YOU CANNOT MIX AND MATCH BETWEEN THESE TWO ARRANGEMENTS!
    The stack voltage in your left hand drawing will wind up being 0V - you've basically stacked pairs of modules in opposition with each other. This isn't actually dangerous unless you attempt to charge them, at which point you'd be in for a VERY bad day!
    The image on the right however will lead to the failure of the lower 2/3rds of the arrangement if you attempt to charge or discharge to the full extent of the capacity in the parallel bank on top - how dramatic the failure would depend on a number of external factors, but failure *is* assured.

    There are only two combined arrangement options which will result in a pack configuration which is both safe to operate and will last past one charge-discharge cycle:

    You can have an arrangement of 7 (arbitrary number) banks connected in series, where each bank is comprised of 20 (arbitrary number) cells in parallel.
    or
    You can have an arrangement of 20 parallel strings or 7 individual cells in series.

    Either of these arrangements requires a total of 140 identical cells, and have the same voltage and charge.
    The former requires voltage monitoring for balance at only 7 locations; whereas the latter requires voltage monitoring at all 140 cells.

    Finally then I feel the need to point out that 8.4V is NOT one cell, it's TWO - they just happen to be in one MODULE, and the voltage at the center tap should be monitored by whatever mechanism you feel is appropriate to observe your pack balance. I will also add that this SHOULD ABSOLUTELY BE A BMS! I understand that this makes for additional expense, and I'm fully aware that it is possible, with the appropriate manual intervention, to operate a pack without one - but I would very STRONGLY advise against it given your apparent knowledge base.


    In close, once again, my intent here is not to offend - I am merely genuinely concerned for you.
    Thank you! Safety is my top priority.

    Sent from my SM-G955U using Tapatalk

  2. #12
    Senior Member Spaceweasel's Avatar
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    I find it helpful to think of each of the Leaf cells as one old-school battery. I was a scout, so we always had flashlights that would take 2 or 3 C cell batteries. You want to stack the batteries end to end (i.e. + to -) until you get a stack that has enough voltage to make your flashlight as bright as you want (i.e. up to the required voltage). In your case, that appears to be 12 leaf cells strung + to -. Then do it again with a second set of 12, also strung + to -. Then you would take the two strings of 12 and run them + to + and - to -, with those becoming your battery leads.

    The two packs you've drawn are identical. Think of it like a string of beads, if you pulled on the ends and straightened them out they would look the same. They also wouldn't flow any energy. To go back to the flashlight analogy, you have some of your C cells in backwards.

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  4. #13
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    Nope dude, you're still arranging cells back-2-back here. Sum voltage will be zero.

    You need, in the parallels, to tie BOTH poles together - in effect creating ONE battery.
    THEN you wire that battery into series.

    See attached.

    12s2p.jpg



    Quote Originally Posted by Nicman View Post
    Attachment 7687

    (Updated Picture)

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  6. #14
    Senior Member Stevo's Avatar
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    ^^^^ ya... like this. Spoonman has the best illustration of what I was trying to say!
    Current rides: '96 Honda Ohlins VFR, '03 Cannondale C440R, '03 Cannondale Cannibal, '06 Yamaha 450 Wolverine 4x4
    Current builds: http://elmoto.net/showthread.php?t=4354

  7. #15
    Empulse R #24 frodus's Avatar
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    Quote Originally Posted by Nicman View Post
    Attachment 7687

    (Updated Picture)
    Your latest drawing (and one before) won't work. NEVER CONNECT in series + to +, or - to -. You show all of your batteries in series. There's no paralleling shown on any of your drawings. Please DO NOT wire it that way.

    I'm not sure you are following us when we're saying paralleling.

    Please refer to figure 6:
    http://batteryuniversity.com/learn/a...configurations

  8. #16
    Member Nicman's Avatar
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    Thanks man! That looks great. I think I'm overthinking (probably underthinking) this.

    I learn visually so that picture makes sense to me


    Cheers

    Quote Originally Posted by Spoonman View Post
    Nope dude, you're still arranging cells back-2-back here. Sum voltage will be zero.

    You need, in the parallels, to tie BOTH poles together - in effect creating ONE battery.
    THEN you wire that battery into series.

    See attached.

    12s2p.jpg
    Sent from my SM-G955U using Tapatalk

  9. #17
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    Quote Originally Posted by Nicman View Post
    I learn visually so that picture makes sense to me
    No bother dude - I'm just still a little concerned that you're going to learn visually just how badly things can go wrong when you're dealing with high power batteries.
    You've got to remember that these are effectively infinitely low impedance power sources which CANNOT BE TURNED OFF. When you are working on them you will be working on a live high power electrical circuit with no safety measures.
    They will turn aluminium to putty if they short circuit and they'll go thermal from there.

    DO NOT MESS ABOUT UNTIL YOU KNOW **PRECISELY** WHAT YOU ARE DOING!

    I cannot stress enough, just how quickly things can go bad when you're dealing with high power Lithium packs - all it takes is for the strap of a watch to cross poles, or for you to drop a spanner, a nut, a bolt... in the wrong place.

    So PLEASE start off testing anything you're intending to do, at model scale using AA's or whatever.
    Get to understand the principles and the practical aspects of their implementation before you go mucking about.

  10. #18
    Member Nicman's Avatar
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    Spoonman, I think I understand what you're saying. Below is a jumbled mess of ideas that came flying into my mind and are in no particular order....probably a confusing order

    Your input answers my question really well!

    When making a series parallel connection, one must decide on how many parallel batteries will be used, then make a single connected pack of parallel. Lets say 4 batteries in parallel.

    Then, one must make an identical pack (4 batteries in parallel) and connect the two parallel packs into a series connection.

    Just like with two individual batteries, going from positive on one battery, to negative on the next battery, to increase the voltage, one MUST make 'parallel modules' equivalent in AH and voltage numbers in parallel while making a series parallel connection. ie 4.2v on each cell and 50ah on each cell.

    Using four (4) 4.2v batteries and one (1) 3.0v battery in series would either over-charge the ones at 4.2v or undercharge the one at 3.0v, causing failures (unless a BMS is used and the 3.0v battery has the capacity to be charged to 4.2v)

    2 for 2, 3 for 3, 10 for 10. The amount doesn't matter as much as the consistency of the numbers, and the desired repetition of alternating poles to the desired voltage.

    using the example of 4.2v per cell and 10AH per cell, one could make a pack that has 500AH at only 4.2v by connecting all positive terminals together and all the negative terminals together of 5 batteries to get the desired AH.


    Making the parallel connections first to 'create' the desired amp hour capacity and imagining it as a single battery, then doing that as many times as you need in order to link the paralleled battery 'packs' in series to form the whole module.

    Thanks for all the help guys, I definitely will be reading up on battery university, going back to my old AC/DC workbook, getting in touch with helpful resources (such as this community) in order to safely make a bike that will give me years of enjoyable and guilt-free riding.

  11. #19
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    Quote Originally Posted by Nicman View Post
    Spoonman, I think I understand what you're saying. Below is a jumbled mess of ideas that came flying into my mind and are in no particular order....probably a confusing order

    Your input answers my question really well!

    When making a series parallel connection, one must decide on how many parallel batteries will be used, then make a single connected pack of parallel. Lets say 4 batteries in parallel.

    Then, one must make an identical pack (4 batteries in parallel) and connect the two parallel packs into a series connection.

    Just like with two individual batteries, going from positive on one battery, to negative on the next battery, to increase the voltage, one MUST make 'parallel modules' equivalent in AH and voltage numbers in parallel while making a series parallel connection. ie 4.2v on each cell and 50ah on each cell.
    The last two lines in that confused the hell out of me, but I got what you were saying in the end - yes. (I think )

    Quote Originally Posted by Nicman View Post
    Using four (4) 4.2v batteries and one (1) 3.0v battery in series would either over-charge the ones at 4.2v or undercharge the one at 3.0v, causing failures (unless a BMS is used and the 3.0v battery has the capacity to be charged to 4.2v)
    Actually no, academically at least. In series they'd be absolutely fine as long as they all have identical capacity and charge characteristics.
    You'll want a BMS to monitor balance ie: to see that the 4.2's stay within their permissible operational range, and likewise the 3v, but hypothetically you could bulk charge that arrangement.

    Quote Originally Posted by Nicman View Post
    The amount doesn't matter as much as the consistency of the numbers, and the desired repetition of alternating poles to the desired voltage.
    ...but the above is the heart of it - a good pack is made up of uniform cells, arranged in uniform parallel groups, and then the identical 'modules' arising are connected in series.

    Quote Originally Posted by Nicman View Post
    using the example of 4.2v per cell and 10AH per cell, one could make a pack that has 500AH at only 4.2v by connecting all positive terminals together and all the negative terminals together of 5 batteries to get the desired AH.
    You left out a zero but this is correct yes.

    Quote Originally Posted by Nicman View Post
    Making the parallel connections first to 'create' the desired amp hour capacity and imagining it as a single battery, then doing that as many times as you need in order to link the paralleled battery 'packs' in series to form the whole module.
    Correct.


    Quote Originally Posted by Nicman View Post
    Thanks for all the help guys, I definitely will be reading up on battery university, going back to my old AC/DC workbook, getting in touch with helpful resources (such as this community) in order to safely make a bike that will give me years of enjoyable and guilt-free riding.
    Happy to be able to help - stay safe and have fun!

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  13. #20
    Senior Member Spaceweasel's Avatar
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    Found this on Neil Degrasse Tyson's page. Seemed appropriate. 35475602_1658371497612686_1813982418172903424_n.jpg

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