Hello all,

I'm looking for some help on a simple LED project. Please bear with me, to say I am novice at this would be flattering and I'm confident that this is FAR below what most people here are capable of. I've searched all over the web but can't quite find what I'm looking for...or maybe I'm not recognizing it when I see it. I've recently built out a trailer for my business that I am adding LED strips to for lighting since winter is making it dark early here. The trailer is parked at customer locations 99% of the time so I am adding a male AC plug to the exterior so I can plug the trailer in on location for 120v AC receptacles. I am splitting off a 12v transformer for the lighting. Here is where I'm getting caught up; my aim is to have the LED strips I am adding work off the AC powered transformer AND the factory wired power that comes from the harness that plugs into my truck during transport. At no time will both sources (AC or 12v truck) be on together. Someone has mentioned to me that I will need to add a relay to safely do this. So first off I want to verify that is correct and, if so, that's fine. The real problem lies in the fact that I can not wrap my head around how to wire such a configuration up. I can read about it until I am blue in the face but if I cant look at a diagram I'm basically useless. Any chance anyone would take a stab at drawing a simple detail of which wires go where on a relay? I would be endlessly grateful. Again, I am looking to wire an LED light strip powered by 2 separate 12v powers sources that will never be supplying power at the same time, one OR the other will provide the power. Thanks so much, be gentle with your responses.

 

If you rectify the output of the 12 volts transformer to get 12 volts DC (Or buy a 12 volt DC power supply rather than just a transformer.) then all you need is two diodes. The negative of the two supplies would be connected together. The positve of the LED lighting would be connected to the positive of each power supply via a silicon diode. The diodes would need to be rated for the current taken by the LED lights. The diodes would create a small drop in voltage of about 0.7 volts but you would probably not notice the slight reduction in brightness. If you want a schematic drawn then post the schematic of the existing wiring so we know how the switching is done.

Les.

 

Welcome to AAC!

Use diodes to OR the two power sources. If both are ever available at the same time, the higher voltage source will power the LEDs.


It would be easier to read your posts if you used paragraphs to organize your thoughts. If your "wall of text" had been any longer, I might not have bothered to read it...

 

+1 on both of the answers above. The key is making sure you've got 12V DC (not AC) in both cases, then a pair of diodes gets the job done easily.