question on by pass diodes.

Discussion in 'General Electronics Chat' started by toffee_pie, Dec 8, 2011.

  1. toffee_pie

    Thread Starter Active Member

    Oct 31, 2009
    162
    7
    hi all,

    I am wondering about a scenario on by pass diodes.

    these can be placed across cells to stop reverse charging (battery depletion) and also prevent cells from damage.


    I have a situation where I have 4 cells and 4 by pass diodes.

    If i replaced the 4 individual diodes with 1 single diode across all cells would this protect all the cells.?

    Ie the same protection but less real estate.

    I am looking at a 36 cell battery stack also and its not really feasible to have that many byp ass diodes (4S 9P)

    I am unsure on placing just 1 diode across a string of cells.?

    thanks.
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,415
    3,354
    Please post a circuit drawing.
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,977
    3,221
    You need one diode across each cell (cathode to positive side) if you want to protect each cell from reverse charging. One diode will just prevent the whole battery from being reverse charged, not each cell.

    Schottky diodes work best for this since they have a lower forward voltage drop.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, I worked up this circuit for them before... and didn't hear anything more about it.

    See the attached.

    Lacking any information on the batteries aside from they are some variation of lithium chemistry, I simply threw together a schematic and simulation. The only thing really relevant about the simulation is that it shows the diode changes Vf over temperature.
     
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