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What kind of switch do i need?

Discussion in 'General Electronics Discussion' started by Garywoo, Apr 22, 2012.

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  1. Garywoo

    Garywoo

    10
    1
    Apr 22, 2012
    I have 3 batteries and want to connect them separately to one output.

    So basically 3 inputs and one output, each input and the output has to have 2 terminals for +ve and -ve.
    I select one battery to use, then switch to another battery when that one is empty. I will also need to charge the batteries again seperately, selecting which one to charge. The switch should be rated to at least 3.5amps.

    Here's an image to help visualize the layout.
    [​IMG]

    I'm assuming i need a rotary switch for this, but what kind. A link to one i can buy would also be helpful.
    Any help would be great!
     
  2. GonzoEngineer

    GonzoEngineer

    321
    0
    Dec 2, 2011
    First of all, you can go ahead and connect all the negative terminals from the batteries to the negative output.

    You only need to switch the positive sources.

    This means you nead a 3 Pole, 1 Terminal switch.

    Commonly called a 3P1T switch.

    You can get a 3P rotary switch, or a 3P slide switch, or a 3P toggle switch.

    Try googling 3 Pole switches.:D

    That just compensates for your problem of switching the sources to one uouput.

    If you also want to switch them to a charging circuit, then you need a different schematic showing the charge circuit.

    Then you will need 3 pole, 2 terminal switches.

    Still available in rotary, slide or toggle format.:D
     
    Last edited: Apr 22, 2012
  3. Garywoo

    Garywoo

    10
    1
    Apr 22, 2012
    There is a battery charge indicator in the unit i am supplying power to that was only intended for one battery, will this still function correctly if the negative terminals are connected together?
    Also will charging in this layout also be okay? They are 12v sealed lead acid batteries.
     
  4. GonzoEngineer

    GonzoEngineer

    321
    0
    Dec 2, 2011
    Yes, as long as the indicator is on the common side of the switch.
     
  5. Garywoo

    Garywoo

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    1
    Apr 22, 2012
    Okay, great. Thanks!
     
  6. Garywoo

    Garywoo

    10
    1
    Apr 22, 2012
  7. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    If I understand correctly you want to at any given time switch to one of the three batteries?

    If so I believe a 1P3T is the correct configuration, or did I miss interpret?

    I agree with Gonzo on connecting the negatives all together, but not on the switch configuration, as the 3P1T would switch all batteries on/off at the same time not individual...
     
  8. Garywoo

    Garywoo

    10
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    Apr 22, 2012
    That's correct, i have chosen this switch http://www.maplin.co.uk/rotary-switches-2417 (Rotary SW 3 P 4 Way) adjusted to 3 stops.
    I hope it's correct this time.
     
  9. duke37

    duke37

    5,297
    739
    Jan 9, 2011
    You will only need 1 pole, 3 way. The Maplin switch is 3 pole and the 3 poles should be connected in parallel to get the current capability that you are after.

    A 4 pole 3 way would be even better so that the curent is divided 4 ways.
     
  10. Garywoo

    Garywoo

    10
    1
    Apr 22, 2012
    Oh okay i think i understand now. What if i just get the 1 P 12 Way switch and adjust it to 3 stops instead of connecting terminals in parallel? The switch is rated at 5A max.
     
  11. duke37

    duke37

    5,297
    739
    Jan 9, 2011
    The more poles you have, the more the current can be shared. I did not see the 5A rating, it seems a bit much to me for this type of switch.
    If you go for the 12 way, nine of the contacts will never be used.

    When you come to try it, I suggest that you connect battery A and see if it switches to the output and that there is no voltage at battery B or battery C terminals. Repeat with B battery connected etc. Then you can connect all three batteries.
     
  12. Garywoo

    Garywoo

    10
    1
    Apr 22, 2012
    I went for the 1 pole 12 way, here are my findings.
    [​IMG]

    As you can see (accidentally reversed, fixed after this photo was taken) I connected the +ve through the switch and tested voltage from the -ve on the battery to the next pin up. It read zero. The device is a portable amplifier and speaker, so I turned the volume to max to check max current and it still stayed at zero. I added the second battery, connected the -ve's together and connected the +ve to the pin I tested, then checked pin 3 next to it. Still zero.
    I'm assuming it's safe to go from here and connect the 3rd battery and solder it all up.

    Thanks so so much for all your help guys!
     
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