I'm multi-talented but very weak on electrical/electronic issues. I hope these are simple questions for you. I want to switch a 12VDC automotive "fog" light (or similar, about 5amp draw) on and off at my gate from my house 150 feet distant from the gate. At the gate I have a 12v deep cycle battery that runs my newly installed gate opener. The battery is charged by hardwire to a transformer at the house (18VAC, came with opener). At the house I have an available SPST household switch. Between the switch and gate I have 18/2 direct bury wire. The distance between the gate battery and light is 10feet. Since the 18ga wire cannot carry the load of the light from the battery to house and back to light I think what I need is a simple relay switch at the gate. My questions are: 1) Is the 18ga wire adequate and safe for the relay switching? 2) What kind of draw is on the 150 ft 18ga switch wire when the switch (light) is off? 18ga current when on? 3) What type of relay should I get? Please be very specific, I'm a newbee. 4) How should I wire the relay to the switch and light and battery? A diagram would be helpful. Thank you.
This is a little tricky because there are a few details left out. However I can attempt to guide you in the right direction. First off you would not need to worry about any current draw when the switch was off. regardless you are correct in having a concern about the 150ft run. If the fog light is only 5 amps that is not really that much current but for safety reasons I would still use a relay. the coil of the relay which will be all that is being drawn off the switch as well as the 18ga wire when the switch is on is 150ma (or .15 amps), which is fine. Now the wiring of the relay depends on several factors. I will give the most likly scenerio. we are dealing with 12volt DC so use a standard 12volt automotive SPDT relay. If you have 12v + at the switch connect that to one side. connect the other side to the 18ga wire that goes to the gate. Connect the other end to terminal 86. connect 85 to 12v -, the relay will only be drawing current when the switch is on, and very little at that. Now connect 30 to 12v +, then connect 87 to one of the fog light wires. connect the other foglight wire to - and it will work fine. Make sure to fuse the wire at terminal 30 as that is the main power, we don't need any smoke shows. Use a fuse with a rating slightly higher then the draw of the fog light and that will be sufficient. good luck.
-------------
Thank you. This was just the information I needed.
You are welcome, let me know how the project turns out..unless of course theres a fire. Kidding, the 25 cent fuse will protect from that. I remember years ago when I finally grasped the concept of how a relay works. Being in this business basically for every $1.50 relay I install I can charge from 30 dollars and up. In addition I can make a relay do virtually anything I want without needing a diagram. I would advise anyone who enjoys tinkering with electronics or as a career to learn relays. best of luck.
-------------