Power Supply / Ciruit Noob help!

[CSutton]

I apologize in advance is this is a stupid quesiton. I am a beginner when it comes to electronics and this idea may be completely off base.

I am trying to setup LED lights in a garage. These will be 12v DC powered light strips, and I would like to have them come on via a normal wall switch OR when the garage door is opened. I will be hacking the garage opener to use 120v that normally goes to the light on the opener. I also have a wall socket that I can just plug into for the wall switch.

My question is, if I hook up two 12v power supplies and attach them in paralell, would they fry the LEDs if both were turned on? Is there some kind of switch before the LEDs that would only allow one input at a time?

The ideal solution would be to actually have a single power supply that would accept 2 120v inputs w/ a single 12v output. I have searched and I am not sure which direction would be best / safest / cheapest / even possible. Any guidance would be appreciated. Thanks!

 

[KrisBlueNZ]

Edit: Welcome to Electronics Point

Your simplest solution would be to use a relay with a 120V AC coil, with its coil connected to the 120V AC from the garage door opener, and its contacts connected across the contacts of the wall switch.

When the garage door opener is active, and sends 120V AC through to its light bulb socket, that voltage would activate the relay. The relay contacts would close, and create a path across the wall switch, connecting the 120V AC from the wall socket through to the power supply.

Turning on the wall switch would also connect the 120V AC from the wall socket through to the power supply.

You would need a relay with a 120V AC coil and a "SPNO" (single pole, normally open) contact. This relay would have two pins for the coil, and two for the contact. Many relays have extra connections for contacts, and these relays are suitable if you connect to the right two pins. The contacts should be rated for 5A or more.

Relays are available in several styles. You want one that will mount directly to a flat surface, or that will fit into a socket that will mount to a flat surface. Here is a suitable panel-mount relay from Digi-Key: http://www.digikey.com/product-detail/en/K10P-11AT5-120/PB322-ND/254539 but you can probably find something similar at a local store.

You need to consider safety. Have you done this kind of thing before? The relay needs to be mounted properly such that it can't move and short onto anything. Connections should be insulated. All wiring must comply with your local safety standards.

 

[Harald Kapp]

Even more simple could be a multiway switch arrangement. Replace the light bulb in the schematics by a power supply 120V/12V. Power the LEDs from the 12V side. The power supply will be powered by mains if either switch (manual or from the door) is activated.

Drawback of this solution: If you turn on the light e.g. manually and then open the door, the lights will turn off. Or vice versa.