lifepo battery pack design

Discussion in 'The Projects Forum' started by Georgec5, Nov 19, 2013.

  1. Georgec5

    Thread Starter New Member

    Nov 19, 2013
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    Over the past two weeks I've read everything I can find about Lifepo batteries. They seem to be the answer to powering and extending the range of my electric kayak. The motor is a Minn-kota 35 lb thrust. It has the latest design controller and draws 28 amps at full throttle. I am dissatisfied with the range afforded by the 93ah deep cycle lead acid battery I am currently using. Based on what I have read it appears that I can afford to construct a pack using 3.2 10ah cells. For the sake of economy can I safely use these cells 3 in parallel and four of these in series to provide 12.8 volts and 120ah? The next question I have arises from my inability to find any literature/diagrams/schematics which illustrate a method of balancing paralleled cells. Do I wire each cell to a balance plug or are the 3 parallels treated as one cell? It appears to me that if it's each cell then I would need a BMS between the pack and a charger, if treated a 3 as 1 then I can use a Thunder AC 6 type charger and skip the BMS. In either case I intend to install a Watt meter on the 'yak to prevent over-discharge on the water. Thank you all in advance for any help. I've tried hard to read up and not have to come to this. G
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
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    The ones in parallel will balance themselves. You just need to worry about the series string.
     
  3. Georgec5

    Thread Starter New Member

    Nov 19, 2013
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    Thanks for the quick response!
     
  4. bertz

    Member

    Nov 11, 2013
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    Make sure you use a charger specifically designed for LiFe batteries or you will destroy them
     
  5. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Safety is always relative..... as Tesla owners are finding out, Li batteries burn when things go wrong. The problem with paralleling is it only goes well if the batteries are healthy and well matched. Laptop makers routinely make battery packs with parallel cells but they get them from a single maker and they are well matched.

    And do not over discharge them or over charge them.
     
  6. Georgec5

    Thread Starter New Member

    Nov 19, 2013
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    Thanks BH, every thing I've read stresses your point. I just found a build on this forum where the parallels are set up to be individually charged by means of a 8 wire harness combined down to two wires which are then plugged into an adjustable smart charger thus eliminating any need for a PCB/BMS. One less thing to go wrong? What' your view?
     
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Not sure, I haven't seen that. I do know the electric car guys out here would build Li Fe PO4 batteries with many cells and each one had a sensing line and balancing device so that the CPU could monitor each cell.
     
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