Analog Based Battery Balancing System

Discussion in 'The Projects Forum' started by CircuitRust, Aug 29, 2016.

  1. CircuitRust

    Thread Starter New Member

    Aug 29, 2016
    1
    0
    Hi,

    I'm trying to build a purely analog based battery balancing system. So far, I'm having a hard time building a circuit that would just be analog based since most system out there rely on some kind of microprocessor that monitors voltage.

    Here's a my thought process so far

    Two Battery Cells > Compares two voltage w/ voltage comparator > Switch (Need to be analog) > Add voltage through capacitor/inductor > Repeat

    So far, In order to detect the voltage of the cell battery, i chose to go with a voltage comparator. I've been digging around and can we use transistors as a management to switch between the capacitor/inductor back to the cell?

    Any feedback is welcome! Just looking at what kind of components I can use to make this happen!

    Cheers
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,518
    1,247
    Are you talking about load balancing or charge balancing? Very different animals. Also, you don't "add voltage" to a battery. You add charge by connecting the battery to a voltage source or current source.

    Don't know your background, so just to make sure... By "voltage source" and "current source" I mean two different types of power supply circuits.

    ak
     
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  3. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    Keep us informed on any progress. I would like to actively balance 24s.

    If you have any interest in shunt balancing, I'll send you a 12s pcb. Could use some input.

    Might try dissecting a <$10 7s balancer.

    What rate are you shooting for?
     
  4. Kjeldgaard

    Member

    Apr 7, 2016
    71
    16
  5. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,282
    1,234
    I'm not sure exactly what you want to do but I think I do. :D
    Several years ago I built a switched capacitor balancer for my golf cart. Basically what it did is this: It would switch a large capacitor across the first battery and allow a little time for it to charge. Then it would switch that capacitor across the next battery in the string. If the first battery was at a higher voltage the cap would discharge into the second battery or vice versa. There was no change to the original charger so it managed the total voltage/current as it did before. I left it on all the time as it drew very little current. I probably still have a schematic somewhere if this is what you are looking for.
     
  6. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    For some years now, I've been using TL431 based shunt regulators on single lithium cells for an e-cigarette.

    There are some applications in consideration that require multiple cells, the TL 431 could work, but they need a resistor divider that will leak a small current even when the battery is not in use.

    My idea so far; is to switch in the shunt regulators with a multi pole relay energised by the charger - when the charger is off or unplugged, the relay drops out and isolates the shunt regulators.

    The TL431 can handle 100mA, for moderate current it can be boosted by a PNP power transistor in a hybrid Szicklai arrangement. More current can be accommodated if the TL431 current develops a voltage across a small resistor to drive an common emitter PNP signal transistor - that in turn drives the gate of a logic level power N-channel MOSFET that carries pretty much all of the shunt load.
     
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