Choosing between two power sources first and then turn on the power. (Slide switches)

Discussion in 'General Electronics Chat' started by Fuji, Mar 1, 2015.

  1. Fuji

    Thread Starter Member

    Nov 8, 2014
    100
    1
    I have a 1p2t slide switch (3 pins) and a dpdt switch (6 pins). 1p2t slide switch is to choose between two power sources, and DPDT comes after the middle pin of 1p2t slide switch.

    The problem is, 1p2t slide switch turns the power on before having the DPDT switch to turn on the power instead.

    Is there a way to choose which power to have first by a slide switch (power is still off), and then turn on the power with the dpdt switch after that?
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Just use a center-off 1-pole Form-C toggle switch. Now you have three total positions: A, OFF, B
     
  3. Fuji

    Thread Starter Member

    Nov 8, 2014
    100
    1
    Thanks for the reply. I already had that idea but I felt like it would be neat to have two buttons to power a device. One to choose a power source, and a main button to power the device on. I've seen this in some device but I cant remember what it was called.
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,392
    1,605
    The more switches and positions you have the larger the chance for someone to get confused or make a mistake and put something in the wrong position.

    The problem with having two switches is there is no way to choose which power to have first by a slide switch (power is still off), and then turn on the power with the dpdt switch after that.
     
    Fuji likes this.
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    I dont understand the problem... With your diagram, you have independent control of power 0n-0ff (DPDT) , and selecting power source (1P2T). Isn't that what you just described as being desirable?
     
    Fuji likes this.
  6. Fuji

    Thread Starter Member

    Nov 8, 2014
    100
    1
    Thanks for the reply. That makes sense now.

    In my head im picturing 1p2t to switch between either source to be in off states on both pins. Seems like there is no such thing as an off/off slide switch. When a 1p2t slide switch is on/on state, that means BOTH pins can be used only for on states? I just checked the 1p2t switch I have and its on/on.

    I have another question about this. Say I have P1 (Power 1) and P2 (Power 2). If I switch from P1 to P2 with a 1p2t slide switch, will P1 shut off completely with no power? Or is the power still running on P1?
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Depends on the nature of the switch. For this application you should use one that is break-before-make. One that makes-before-breaks would momentarily short the supplies together.

    You could put the DPDT on-off switch upstream of the slide switch using two poles to open circuit the two supplies. The break-before-make caution still applies.
     
    Fuji likes this.
  8. Fuji

    Thread Starter Member

    Nov 8, 2014
    100
    1
    Thats right. As far as I see, I guess its impossible to do this with two slide switches now. Or maybe it would work but depending on the nature of the slide switch. A 3 position slide switch with 1 off state like you said would be a better answer. Or a rocker switch as well.
     
Loading...