DC battery switch

Discussion in 'General Electronics Chat' started by aac9876, Jan 15, 2010.

  1. aac9876

    Thread Starter Active Member

    Dec 9, 2006
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    You might have seen those big red DC battery switches that have 1,2,1+2,Off
    They work with battery/inverter set ups. Does it matter which cable..neg/pos is
    switched.? One cable goes to the 1 post and the other goes to the common post.
    Can it be either one..???
     
  2. whatsthatsmell

    Active Member

    Oct 9, 2009
    102
    4
    I'm very hesitant to answer that without having a lot more info on what you intend to do with it.

    While "it's only 12 volts", the amperage involved here can do a lot of damage.

    Please post more info (and schematics are always nice).
     
  3. aac9876

    Thread Starter Active Member

    Dec 9, 2006
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    I got it... break the pos but either will work. The common is for the jumper to the inverter.
    no break in the other cable.
     
  4. whatsthatsmell

    Active Member

    Oct 9, 2009
    102
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    Any reason you don't want to run the batteries in parallel to the inverter?
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Sounds like he wants the capability to run both in parallel to the inverter, but have the option to charge one while using the other one.
     
  6. whatsthatsmell

    Active Member

    Oct 9, 2009
    102
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    I thought of that too, but then I thought if you have the power to run a battery charger, why would you need an inverter? And if it was in a vehicle, why the first question?

    It's so hard to read people's minds sometimes! :D
     
  7. aac9876

    Thread Starter Active Member

    Dec 9, 2006
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    its 1 battery 12v used for short power outages , charged by a cheap AC battery charger.
    The switch can do a lot more but I am not using its capabilities...
    but...since you mentioned it... if I had 2 batts wired to it and I hit 1+2 I guess your saying
    it would deliver 12v in parallel, not 24v ,correct??? this would just increase the amps..
    what if they were 2 different 12v batts that had different voltages slightly..??
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    If they had different voltages and you selected 1+2, you would have a large flow of current between the two batteries. This would not be a good thing.
     
  9. aac9876

    Thread Starter Active Member

    Dec 9, 2006
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    why is that?? and so what is the point of the 1+2..... no 2 batts are going to be
    exactly the same.....
     
  10. whatsthatsmell

    Active Member

    Oct 9, 2009
    102
    4
    The batteries are going to try to equalize. If one is at 12.85 and the other is at 12.65, the effect on your inverter is minimal.

    If, however, one battery has a bad or weak cell and is at 10.5v, it will virtually suck the energy out of the good battery and leave little for your inverter, and shut it down in a very short time.

    Have you bought your battery(s) yet? If not, you may want to consider golf cart batteries. They are 6v so you would have to wire two in series to get a 12v output, but they are designed for deep-cycle service at the amperage draw you will be using.
     
  11. Duane P Wetick

    Active Member

    Apr 23, 2009
    408
    19
    I've used these cutout switches to disconnect batteries in an emergency or for safety reasons, but you should be aware of the potential problems.
    First, it is common to switch the positive battery connections, keeping the negative side connected to all circuits at all times. When the switch is used to connect two batteries together (parallel connection), a Battery Isolator should be used to allow both batteries to send power to a load, but preventing one from discharging into the other. NEVER switch batteries when they are being charged, as the rectifier diodes in the charger will be damaged. Some (not all) of these switches have an auxillary alternator field disconnect that allows an engine alternator's field to be turned off when batteries are switched.

    Having a battery switch is a good idea however, because you are working with a high energy un-interruptable power source that can easily start a fire.

    Cheers, DPW [ Everyone's knowledge is in-complete...Albert Einstein]
     
  12. aac9876

    Thread Starter Active Member

    Dec 9, 2006
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    I know about 1 bad cell sucking the other..it sounded like you were saying somrthing more dire....
    I will buy later a couple of L16 6v when they are cheaper...
     
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