Parallel connections of battery banks and DC breaking problems

Discussion in 'General Electronics Chat' started by Santosh Baratam, Jan 5, 2015.

  1. Santosh Baratam

    Thread Starter New Member

    Jan 5, 2015
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    Hi all,

    I need a help in one of my project.
    I want to connect two battery banks each of capacity 240V, 1000Ah in parallel and want use as master n slave operation and system always connected to inverter to run the load. Now I am having a doubt that if master battery bank is discharged totally then I need to connect slave Battery bank. I want to connect the slave battery bank which is charged in parallel and then disconnect the master battery bank which is discharged.
    Is it the right way to operate?? What will be the standard practice and Problems with DC braking??

    Thanks Guys.
    Santosh
     
  2. profbuxton

    Member

    Feb 21, 2014
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    One method would be to use 2 double pole isolators to isolate each bank from the load as required. Also use four suitable diodes. Two to isolate the batteries from the charger and two to isolate the batteries from each other.
    One diode in positive side from charging system to slave and one to master will allow charging both batteries from one charger. Another diode in each battery positive to the load (via suitable fused double pole isolator) will isolate the batteries from each other. This arrangement will prevent backfeeding a discharged battery from charged one although if charger is always on batteries should be able to stay charged(depending on load and charger rating). Switching from one battery to another should be no problem.
     
  3. Santosh Baratam

    Thread Starter New Member

    Jan 5, 2015
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    0
    Thanks Prof.Buxton.

    A continuous load is connected to inverter which is driven by any of these battery banks. I don't want to isolate the load at anytime. If you are willing to keep a diode in series with each bank means, diode with very high current rating is required and it has to withstand with voltages that occurs during transients. is there any standard practice to choose diode for this applications??

    Thanks
    Santosh
     
  4. profbuxton

    Member

    Feb 21, 2014
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    You are correct in saying that diodes with suitable rating need to be used, as mentioned in my earlier reply. Sorry I can't specify a particular part for you. I don't know what sort of transients you are expecting. I guess you may need protection from transients from the load. You could connect some sort of VARISTOR across the input to the inverter.
    It would need to suitably rated and would absorb any excess transients, although actually the battery itself acts very well to absorb transients from the load.
     
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    the need to have the load powered during switchovers, will mean you must use diodes to isolate the banks. when one bank is low and a switch is made without diodes you must have both banks connected if only for a fraction of a second. the high voltage and amp hour capacity will cause very very large currents to flow during this time. think blindingly bright arcs and molten copper from switch contacts flying through the air. not a joke sir.
     
  6. profbuxton

    Member

    Feb 21, 2014
    233
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    Kermit2, I agree that diode isolation is a MUST for this application. The real issue is finding suitable diodes(current rating). If both batteries are connected to a charging system(via diodes) then there should be minimum difference in charge state and no drama when switching banks. Overload protection is also vital.
    A better solution would be to have two converters separately fed from each battery bank and inverters synchronised to each other in master /slave setup. This is very commonly used in inverter systems for railway control systems where reliable supply is vital.
     
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