a little confused, why a relay

I read through it and at the risk of being called a moron, I have to ask, why do you need relays instead of just a manual spst switch?......I have always just used a 10 or 12 gauge posative wire and branched off of it with multiple wires and switches to the item I want powered, so I am a little confused on why a relay would need to be used. For instance, I ran a 12 gauge wire from the stereo (always on) wire back to my 4 switches and then off to the DVD, Headrest Monitors and headphone amp. It all seems to work fine with the switches, why would I need a relay?

Relays would be used for a variety of reasons in this case.  If you wanted the equipment to turn on without the use of a physical switch then a relay would be needed.  Also, if the switch amp rating is too small to safely carry the load of all the equipment you have hooked up to it, you'd need a relay.

no wires are getting toasty so I should be good. So a relay would hook the battery to a component and then use anouter swiotched wire (say the acc on the ignition) to turn it on and off? is it like the remote wire on the stereo?

Relays allow you to switch high current loads from low current sources.  In a car this allows you to use low current switches (say 3A) to switch loads up to 30-40A (even higher with multiple relays in parallel).  The "best" part of this is that the lower current switches are prettier and much smaller then the high current switches.

You could also use a relay like you mentioned - to turn something on and off when the car is turned on and off.  By hooking to a low current ignition source (like a 10A switched cigarette lighter) you can turn a high current inverter on and off with the car

-------------
Kevin Pierson

Thank you, I guess I better check the rating on my 12 volt illuminated switches and the current being drawn from the accessories. (headrest monitors, dvd player and a smallheadphone amp)

megaman wrote:

---

Relays would be used for a variety of reasons in this case.  If you wanted the equipment to turn on without the use of a physical switch then a relay would be needed.  Also, if the switch amp rating is too small to safely carry the load of all the equipment you have hooked up to it, you'd need a relay.

---

I am not questioning you in any way, but in the case you stated,,,, instead of a relay why wouldn't someone just wire it to an existing wire that only has power when the key is on? that would do the trick, maybe I am missing something.....I just want to make sure that what I have done (although it works fine) is not going to create some long term issue............

KPierson wrote:

---

You could also use a relay like you mentioned - to turn something on and off when the car is turned on and off.  By hooking to a low current ignition source (like a 10A switched cigarette lighter) you can turn a high current inverter on and off with the car

---

Most of my stuff. (DVD, Monitors, etc) are low current I am assuming, I have no inverter but I do understand what your saying about that.

04nata wrote:

---

I am not questioning you in any way, but in the case you stated,,,, instead of a relay why wouldn't someone just wire it to an existing wire that only has power when the key is on? that would do the trick, maybe I am missing something.....I just want to make sure that what I have done (although it works fine) is not going to create some long term issue............

---

So what wire are you going to tap into?  What is already connected to that wire in the vehicle?  The problem with tapping into existing wiring is that you will most likely increase the safe current draw for that particular circuit and either pop the fuse, or damage the oem equipment it's tied to.  A relay will completely isolate the circuit so nothing happens.