Cigarette Socket Power Questions

**jfeinman** · 02-24-2008, 11:47 PM

Ok, so I'm a little new to the electrical system of cars, so these will probably come across as dumb questions that have been answered somewhere in these forums before:

I have an 2005 Impreza Rs. My plan is to use my laptop as a car computer, as it has an IR sensor on the front which allows me to turn on the computer from a completely off state with its included remote (i'll just use an IR repeater).

My only hitches are with how the 12v power system works in a car. Is the Cigarette Socket wired directly to the battery, or is there regulation in between? I'm not at all concerned about how it's switched, only with how the current works. In other words, if I had something that had a cigarette lighter male plug on the end of it, could I just cut it off and wire it directly to the battery? Or, would there be any problem with just splicing it into the circuit that feeds the cigarette socket? I've already done this to install a second socket in my center console to gain extra power to power my USB hard drive thats connected to my Pionwer DEH-6900UB headunit

I'm trying to avoid purchasing a regulated power supply. The laptop is going to be powered with a Auto/Air adapter (I work for Circuit City, so I can get that kind of stuff dirt cheap).

I'm inclined to just wire everything to the cigarette lighter circuit with a distribution block, but something in the back of my head says that having a liliput touchscreen and a laptop wired to that circuit may not be the best idea.

I could use some enlightenment, if anyone can provide it....

**Arrow** · 02-25-2008, 12:24 AM

The cigarette lighter socket is not regulated. It just goes through a fuse then to the battery. The lilliput is made to handle the voltage fluctuations in a car, so you can wire it directly. The laptop power adapter has a built in regulator, so you can wire that directly to the car as well.

**FusionFanatic** · 02-25-2008, 09:03 AM

you're going to wire a distribution block to your cig lighter wires? no, the is definitely not the best idea. I would recommend you run a clean/fused power line from the battery for your carputer power.

the monitor doesn't draw much current, so you can wire that up to the cig lighter wires, but you're already powering a HDD, cellphone charger, etc off that circuit as well. adding a 5a auto charger might overload that circuit.

you don't need to buy a regulated power supply, your current plans will work fine, but don't wire everything to your cig lighter wires. do you have an amplifer/subwoofers? if yes, the you could power it off that power line.

**cMags** · 02-25-2008, 10:52 AM

I've got basically the same car, so I can attest that the cig. lighter plug is not regulated, and is connected to the ACC circuit, which powers for the '05 Impreza:

Compass mirror
Front accessory power supply socket
Body integrated unit (I think this is part of the ECU)
TCM (transmission control module- for the automatic)
Rear 12V accessory relay
Remote control mirror switch
Intercooler water spray switch (N/A - the RS doesn't have this)
Intercooler water spray timer (N/A)

So there's a couple things on that circuit you wouldn't want to be caught without if you blow that fuse. If you do, its 20A and located under the dash (behind the left change holder cup) in slot number 4 as pictured here:

It would definitely be best to run a dedicated line from the battery. There's a grommeted hole through the firewall above the brake pedal inside, and just below the master cylinder in the engine bay. For all your accessories, I'd make my own accessory circuit by running a 20A fused line from the battery, through a relay, to your own distribution block. You can then control the relay from the ACC circuit (tap off the back of the lighter plug or the fusebox at #4). You could also throw in a switch so you could power your ACC circuit from constant 12V if you choose to w/o the car being on.

PM me if you have any Impreza-specific questions since I've been thru most of the electrical system (especially the ACC circuit) a dozen times and have the diagrams to refer to.

Oh yea, and welcome to the boards! Now fill out your profile!

**jfeinman** · 02-25-2008, 11:54 AM

I guess there's some confusion as to my plan: I don't think its a good idea to run everything off the cigarette lighter circuit. The distribution block idea was going to be from the line I run from my battery into my car for my mono block, not the cigarette circuit. I'm also not going to be powering a cell phone charger, or my portable hard drive, since it can run solely off usb (its a seagate that has the dual usb plugs because it runs needs about .75amps, and the USB 2.0 standard is .5 with anything extra being luxury).

But yeah, even so I'm still not going to power it all off the cigarrete lighter.

And that 20 amp fuse? I know all about it

. I've already blown it once, when I was wiring up my second 12v socket in my center console and the ground and power wires accidently touched.

Thank you all for the advice, I really appreciate it.....

**FusionFanatic** · 02-25-2008, 10:09 PM

Originally Posted by jfeinman

if I had something that had a cigarette lighter male plug on the end of it, could I just cut it off and wire it directly to the battery? Or, would there be any problem with just splicing it into the circuit that feeds the cigarette socket?

in most cases, this would work fine. but make sure the cig lighter plug has no circuitry in it first. sometimes there are circuits (like regulation circuits, etc) inside the plug housing. if you are going to use your cig lighter socket wiring then the easiest way to deal with it is to wire a couple of extra sockets to it, so you don't have to modify any of the cig lighter plugs or worry about frying something because you bypassed an important circuit.

in my car, I bought a standard "Y" adapter, cut the main plug off, and wires the outlets to the factory wiring. this allowed me to plug in two devices without modifying the plugs. also, it kept everything hidden under my center console panel

**jfeinman** · 02-26-2008, 01:15 AM

Probably not a bad idea, that way I can easily change something out without having to cut wires or splices if something changed in the setup. I have one of those Y adaptors sitting around, but I think I'd still want to give it its own circuit off the battery.

**HiJackZX1** · 02-26-2008, 03:59 AM

Originally Posted by ComputerGeek

you're going to wire a distribution block to your cig lighter wires? no, the is definitely not the best idea. I would recommend you run a clean/fused power line from the battery for your carputer power.

the monitor doesn't draw much current, so you can wire that up to the cig lighter wires, but you're already powering a HDD, cellphone charger, etc off that circuit as well. adding a 5a auto charger might overload that circuit.

you don't need to buy a regulated power supply, your current plans will work fine, but don't wire everything to your cig lighter wires. do you have an amplifer/subwoofers? if yes, the you could power it off that power line.

**FusionFanatic** · 02-26-2008, 08:40 AM

Originally Posted by jfeinman

Probably not a bad idea, that way I can easily change something out without having to cut wires or splices if something changed in the setup. I have one of those Y adaptors sitting around, but I think I'd still want to give it its own circuit off the battery.

yes, it's always better to run a new power line from the battery. you can use the same "Y" adapter idea, just wire it to your new power line instead of the cig lighter socket wires