# Need some guidance on picking a DC switch

#### ThirtyWest

Joined Jul 15, 2017
150
Hello,

I need some help picking a switch for a project.

I have a single consumer that needs to be powered by one of two available sources (both sources are 3V dc wires).

So:
position1 = source 1 to load
position 2 = off;
position 3 = source 2 to load

Is it acceptable to take a normal DPDT switch and put the DC sources on the "end" pins and the consumer in the middle (which is essentially backwards from the examples shown) since we're just talking about directing current?

The goal is to have a small project box power the consumer by the USB power source, but if that should be unavailable, then the 2xAA would be the backup.

Thank you for taking a moment to read and apologies if the simple answer is staring me in the face.

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#### ThirtyWest

Joined Jul 15, 2017
150
Hi, and thanks. I suppose I got confused since the common explanations of those switches use a single power source and two loads (or reversing a motor) as an example.

#### k1ng 1337

Joined Sep 11, 2020
584
Hi, and thanks. I suppose I got confused since the common explanations of those switches use a single power source and two loads (or reversing a motor) as an example.
Don't forget about the power rating of the switch.

An alternative is to use 2 diodes or similar arrangement when you have 2 power sources to avoid having to switch manually. Note this application comes with additional considerations.

#### ThirtyWest

Joined Jul 15, 2017
150
Hi. Yes the rating shouldn’t be a problem.

max would he 3V and 40mA

diodes would be slick but a simple switch is all I’d need for now.

I’m fighting the urge to think outside of the simple needs now.

#### ErnieM

Joined Apr 24, 2011
8,315
This type of switch is called an "ON-OFF-ON" type to denote the center off position.

My favorite switch is called an "ON-ON-ON" type. It needs to be a double pole type (four pole also exist). The 3 positions can be wired so the control can be pos 1 off, pos 2, power 1, pos 3 power 2.

#### crutschow

Joined Mar 14, 2008
30,109
. I suppose I got confused since the common explanations of those switches use a single power source and two loads (or reversing a motor) as an example.
The switch doesn't care (or know) which direction the current is going.