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12v Batteries - Series & Parallel

  • 04-02-2009 10:29am
    #1
    Turbury
    Closed Accounts Posts: 144 ✭✭


    Hello, I have a battery bank consisting of 4 x 12v batteries, wired in parallel at the moment. Is it possible, by using a change over switch, to also connect the batteries in series (for use with a 48v inverter)?

    Batteries are being charged by a 12v turbine.


Comments

  • #2
    KoolKid
    Moderators, Home & Garden Moderators, Technology & Internet Moderators Posts: 24,789 Mod ✭✭✭✭KoolKid


    Yes its possible. Ensuring the switching never shorts the batteries.
    What current are you planning on drawing?


  • #3
    Turbury
    Closed Accounts Posts: 144 ✭✭Turbury


    koolkid wrote: »
    Yes its possible. Ensuring the switching never shorts the batteries.
    What current are you planning on drawing?

    I have a 48v 1kw inverter and only feeding metal halide lights - so I'd say max. current about 10A.


  • #4
    DublinDilbert
    Registered Users, Registered Users 2 Posts: 5,401 ✭✭✭DublinDilbert


    As cool kid has said you have to be really careful not to short the batteries. You may even have to look at the order you switch the relays in. Also what happens if a relay fails... I've attached the most basic configuration i can think of...

    Its very difficult to charge batteries in parallel, you would be better off charging them as a 48V series pack and avoiding the change over altogether.

    What is performing the charging? I'm guessing its a automotive alternator ( hence the 12Vs). It might be possible to modify the regulator to give out 56V, provided you don't need max current from it. You'll need about 56V to correctly charge a 48V pack. Just an idea....


  • #5
    Turbury
    Closed Accounts Posts: 144 ✭✭Turbury


    DublinDilbert wrote: »
    As cool kid has said you have to be really careful not to short the batteries. You may even have to look at the order you switch the relays in. Also what happens if a relay fails... I've attached the most basic configuration i can think of...

    Its very difficult to charge batteries in parallel, you would be better off charging them as a 48V series pack and avoiding the change over altogether.

    What is performing the charging? I'm guessing its a automotive alternator ( hence the 12Vs). It might be possible to modify the regulator to give out 56V, provided you don't need max current from it. You'll need about 56V to correctly charge a 48V pack. Just an idea....

    Thanks for that - I'm using a proper Rutland wind charger so cant really mess with the 12v output. Was thinking of another possible option but not sure if it would work, a second bank of batteries connected in series to each other but this bank 2, connected in parallel to bank 1.
    I think even if this did work some of the batteries in bank 2 would not charge.


  • #6
    DublinDilbert
    Registered Users, Registered Users 2 Posts: 5,401 ✭✭✭DublinDilbert


    Turbury wrote: »
    Thanks for that - I'm using a proper Rutland wind charger so cant really mess with the 12v output. Was thinking of another possible option but not sure if it would work, a second bank of batteries connected in series to each other but this bank 2, connected in parallel to bank 1.
    I think even if this did work some of the batteries in bank 2 would not charge.

    Ahhhh ok... Another option would be to have one 12V battery, then have a step-up chopper to the 48V battery pack.

    I'm not sure what's available off the shelf to act as a step up chopper, as i've built these from scratch before in the past and never bought one.

    An advantage to this method that when your windmill is turning, generating power, you can run the inverter also. So you can run off the battery pack + generator at the same time, giving you extra run-time....


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  • #7
    Stoner
    Registered Users, Registered Users 2 Posts: 10,952 ✭✭✭✭Stoner


    DublinDilbert wrote: »
    , as i've built these from scratch before in the past and never bought one.

    ....

    any chance of seeing the ccts behind what you actually built and used ?


  • #8
    DublinDilbert
    Registered Users, Registered Users 2 Posts: 5,401 ✭✭✭DublinDilbert


    Stoner wrote: »
    any chance of seeing the ccts behind what you actually built and used ?

    I've attached a basic schematic of a step up chopper. The key is in the duty cycle control. The duty cycle on the FET will change based on output voltage and output current. This can be done with fairly basic analogue electronics, ramp generator & comparator.

    The theory of operation is given here :-
    http://en.wikipedia.org/wiki/Boost_converter


  • #9
    Stoner
    Registered Users, Registered Users 2 Posts: 10,952 ✭✭✭✭Stoner


    thanks for that, I remember the theory alright boost and buck and buck boost and the maths behind it etc. good to see someone actually building one and using it, there is huge difference between drawing something out and using one you built yourself. Recently my I found one of my old circuits we used to mess around with PWM, funny that this thread should come up.


  • #10
    DublinDilbert
    Registered Users, Registered Users 2 Posts: 5,401 ✭✭✭DublinDilbert


    Stoner wrote: »
    thanks for that, I remember the theory alright boost and buck and buck boost and the maths behind it etc. good to see someone actually building one and using it, there is huge difference between drawing something out and using one you built yourself. Recently my I found one of my old circuits we used to mess around with PWM, funny that this thread should come up.

    I think it would be an elegant solution in this case, as it would allow the generator to keep running an pumping out 12V, while the inverter for lighting runs off the 48V supply. Rather than switching between the 2 systems and wasting all that power.

    Boost circuits are also very common now at the front end of mains power supplies, to correct the power factor, and ensure that current is taken in phase with the voltage.


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