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Switching between charge and load of lipo batteries in series.

Discussion in 'Power Electronics' started by Kenneth Tan, May 27, 2015.

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  1. Kenneth Tan

    Kenneth Tan

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    6
    May 22, 2015
    I would appreciate some pointers to get me started.

    I have build a led light for my photography.
    It uses a 2P4S lipo battery setup.

    I also have pcb's to charge lipo's controlled.

    I would like to build an electronic switch so I could change between load and charging these battery pairs.

    It can be done with a multi pole mechanical switch, but I'm looking if there's an electronic solution to switch between these two circuits.

    I'll post a schematic of the setup later today. Can't do this on my phone.

    Any help will be greatly appreciated.
     
  2. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Hi Kenneth
    First thought is a RF or IR transmitter, but what range would you require? You will also need to consider what you will be powering this electronic switch from.
    Thanks
    Adam
     
  3. Kenneth Tan

    Kenneth Tan

    58
    6
    May 22, 2015
    I'm sorry. Probably wasn't clear enough.
    I would like to build an electronic switch.
    I have 4 pairs of 18650 in series. And I need to charge the individual pairs.
    I don't want to use an external balance charger but 4 lipo charge pcb's I have.
    These pcb's charge a single lipo @1A safe in multuple stages so it gets charges properly. It also protects against undervoltage and overcurrent while in load.
    http://www.ebay.nl/itm/2PCS-5V-Micr...535?pt=LH_DefaultDomain_0&hash=item3ceaceab27


    I can think of using a sort of physical slider switch to toggle between the two circuits (load &charge) , but I would like to do it electronically. Maybe by clever use of mosfets. I can't find a schematic that addresses this challenge.
     
  4. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Ah you want to automatically switch between charging of the different cells. And you want to switch a different pair in as the previous pair have discharged? Is that correct??
    Adam
     
  5. Kenneth Tan

    Kenneth Tan

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    6
    May 22, 2015
    Almost, automatic is a bonus, but welcome. a digital toggle switch or even a single throw mechanical switch would do.
    There are 4 battery pairs in series and all 4 need to be charged at the same time. I have 4 charger boards. So i need the system to be a 4s2p battery or 4 pairs of batteries being charged with each pair having its own charge pcb.

    I'm gping to try to draw a schematic, but not at a pc to do do so atm.
     
  6. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Like this?
    BATT STACK.PNG
     
  7. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Or this?
    BATT STACK2.PNG
     
  8. Kenneth Tan

    Kenneth Tan

    58
    6
    May 22, 2015
    The last one is my load situation, operational state.
    Now disconnect each pair and connect them to a charger board.
    Then you have the charge state.
    The challenge is to build an electronic switch to toggle between these two states/circuits.
    Automatic would be great. Maybe a sense if 5v is connected to the charge boards input.
     
  9. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Like this? Sorry it's on it's side, it was too small the other way.

    BATT STACK3.PNG
     
  10. Kenneth Tan

    Kenneth Tan

    58
    6
    May 22, 2015
    Yes that is basicly it.
    I've made my own schematic, now that I'm home.

    The danger here is that the charger boards all use common ground on both input and output side. So is the batteries are still connected in series (load scenario) that would create a short over the lipo's (n-1).

    A mechanical switch would also need to have a dead zone. to create a floating state. So an electronic switch should also take this possible short in consideration.

    I hope my schematic (I'm new with this) is readable. The MAX1555 is just a stand in for my TP4055 boards.
    The schematic shows the charge circuit on the left and the load circuit on the right.

    The switch on the right circuit will be a Dave Jones' "Soft latch switch." and not a mechanical one.
    Also in the load circuit is a Constant Current circuit for the leds, but that is part of the load and is working properly already.
     

    Attached Files:

  11. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    I have looked and I can't find a suitable switch. The only other option is to use relays but I don't know of any that can float. Solid state switches might be the only option.
    Thanks
    Adam
     
  12. Kenneth Tan

    Kenneth Tan

    58
    6
    May 22, 2015
    I was hoping that there would be a mosfet solution. Kind of solid state i believe.
     
  13. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Yes as I said solid state might be the only option.
    Adam
     
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