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12v and 24v battery box

  1. Jun 6, 2010 #1
    I have built these before, but have forgotten how I did it. I am making a battery box with four 12v batteries (7.5 Ah each). I will have only one pair of output terminals, one + and one -. Inside will be a switch to toggle between 12 and 24v. I do remember that in the 12v position all batteries could be charged (all parallel). I thought I used a dbl.pole, dbl. throw, ctr. off switch. I can't see how to do it now. Maybe it was a 4 pole switch. I know this seems simple, but I am drawing a blank right now.
    Anyone have an answer??? Thanks in advance. Stuts
  2. jcsd
  3. Jun 6, 2010 #2


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    You would need to do this:

    [PLAIN]http://dl.dropbox.com/u/4222062/12%20V%20-%2024%20V.PNG [Broken]

    The batteries are arranged in two parallel banks permanently wired together.

    Note that the two switches are linked together and they need to be a non-shorting type so that the top batteries cannot be shortcircuited, even briefly, while switching.
    Last edited by a moderator: May 4, 2017
  4. Jun 6, 2010 #3
    Dear vk6kro- Thank you. I could not find where the negative 'out' would be, unless it was any point along the ground leg. Also, the 'second' leg of the switch connected to the negative terminal of the lower batteries goes to an empty terminal for the 12v position. It seems to still work that way. I was convinced that I needed another pole to make this work. Thank you so much. R.
  5. Jun 7, 2010 #4


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    Yes, that is right, anywhere that is shown as a ground connection can be taken as the negative output.
    I have modified the diagram above to show this.

    The right hand switch really only needs to be a single throw, but the other switch is double throw. So, the switch that goes nowhere is OK.
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