# Thread: My idea for powering carpc off wall at home (cheaply!)

1. Okok I know this thread has been dead for a while but.....

I finally had some time this weekend, so I took 3 ATX power supplies and wired them up in series. After some tinkering, I managed to get the output voltage stable at 14.36 volts (which is within 0.02 volts of what my alternator outputs) and able to deliver up to 20 amps. Now I have a simple question on how the cigarette lighter on cars are wired up.

Suppose I wanted to power my car's electrical system at home (such as running the carpc). Then could I simply take my DIY power supply and just plug it into my car's cigarette lighter (with the car keys turned to ACC)? Then would the entire car electrical system then be running off my power supply and not be draining from the battery? This would be much easier than to pop up the hood and wire it in parallel with the battery each time I wanted to use it. My cigarette lighter is fused at 25 amps, and I will add a 20 amp fuse to the power supply. Are there any other considerations I should take?

I am guessing this would work because Ive seen those commercials with the battery boosters which you can charge your dead battery simply by plugging it into the cigarette lighter.

2. Originally Posted by nobb
Okok I know this thread has been dead for a while but.....

I finally had some time this weekend, so I took 3 ATX power supplies and wired them up in series. After some tinkering, I managed to get the output voltage stable at 14.36 volts (which is within 0.02 volts of what my alternator outputs) and able to deliver up to 20 amps. Now I have a simple question on how the cigarette lighter on cars are wired up.

Suppose I wanted to power my car's electrical system at home (such as running the carpc). Then could I simply take my DIY power supply and just plug it into my car's cigarette lighter (with the car keys turned to ACC)? Then would the entire car electrical system then be running off my power supply and not be draining from the battery? This would be much easier than to pop up the hood and wire it in parallel with the battery each time I wanted to use it. My cigarette lighter is fused at 25 amps, and I will add a 20 amp fuse to the power supply. Are there any other considerations I should take?

I am guessing this would work because Ive seen those commercials with the battery boosters which you can charge your dead battery simply by plugging it into the cigarette lighter.
goodnight brother!!! Why not just get a removable (usb hdd) and keep it simple?
Why are you going through all this?
You could cause some serious damage to your electrical system and car computer too!!

3. Originally Posted by techeros
goodnight brother!!! Why not just get a removable (usb hdd) and keep it simple?
Why are you going through all this?
You could cause some serious damage to your electrical system and car computer too!!
I dont really see how it could be causing "serious damage" to my electrical system. The voltage is what my alternator puts out (my alternator actually puts out 0.02 volts more), and it is able to do it at up to 20 amps. I think it is more damaging to be running down my battery and letting sulfation occur. I have done much reading, and 14.36 volts seems to be good to keep the battery topped up, as long as I dont plan on keeping it connected for days at a time.

I am pretty sure it isnt damaging to hook up a power supply which produces the right voltage in parallel to the the car's electrical system since it would just be like adding a second battery (except this battery is infinite). I am just wondering if hooking it up in parallel through the cigarette lighter may be a bad idea. If so, does anyone have any exact reaons why?

Also, I figure I can just leave the power supply in the garage, so if my parents' cars (or mine) ever have a dead battery, they can simply use it as a charger.

4. Originally Posted by 2k1Toaster
I think one of those battery chargers with a "maintainer" circuit should do the trick as long as you aren't drawing too much current.
I fried two wall wart type transformers building files on my via/mtx/lilliput on my desktop.

I figured that a 12V power supply rated at 2 amps would be enough. No way. After they quit working (and were about 130F on contact temperature), I pulled my benchtop digital power supply (rated at 50 amps) upstairs.

And I discovered that Via EN15000+HDD+CDROM+Lilliput 7" draws a combined of about 3.6 amps at 12.5 volts.

So make sure that you buy a transformer that puts out enough juice, so you don't fry the transformer.

5. ## foolish I think

you know, I guess if I had the extra money, I had an extra junk vehicle, and the curiosity enough to make something work, I would be deturmined to make something like this work no matter what someone says.

PLEASE UNDERSTAND THIS- HEAR ME OUT!! JUST MY OPINION -
I would NEVER want to discourage someone from being creative and comming up with something cool.

HOWEVER, if this is your "primary"mode of transportation, and you don't mind if you smoke your electrical system or possibly catching fire to your vehicle I say go for it.

Otherwise this is foolish! There are SEVERAL cheeper ways of accomplishing the same task and easier ways by far.

I don't think I personally would do this.

6. Why make things so complicated? Hack an ATX power supply for 12v and attach whatever power wire setup you use on your case. Easy.

7. When I want to spend time configuring my CarPC I attach a battery charger to the car battery and plug in the charger. Then I grab my cat5 cable that is coiled at the battery and extend it to my house port (mounted outside my house at my phone box). I plug that in and then put my CarPC dash switch into always-on mode instead of car-switched mode. I can then use PC-anywhere (same function as remote desktop) from inside the house.

Powering your battery with a battery charger causes no harm to your car battery and likely tops-off the battery while its there. That system works for me.

The logical extension would be to mount that battery charger into the vehicle and save a couple of hookups when I want to do this. That way I could just plug the 120V extension cord into the vehicle somewhere and the battery charger would be on.

8. Lol...ok so regardless of your guy's advice (sorry techeros), I hooked up my DIY powersupply in parallel with my car yesterday because I really thought I knew what I was doing. I had the carputer powered for about 5 hours doing some computer related maintenance. I also put on some music as I was cleaning out my car. So far...no problems, battery was not drained, and my power supply worked exactly as if it were a second infinite battery =)

I did not blindly go about connecting everything. There were precautions that I took. I made sure to fuse my powersupply, as well as adding a diode to prevent current from going the opposite way (like in a solar battery charger).

But I have to admit...it would probably have sucked if something did go wrong...

EricE: Just curious. Could you tell me if your battery charger is constant voltage, or is it "intelligent." If it is constant voltage, how much voltage exactly does it put out? And at what maximum current? I am trying to accomplish what you are doing, except I will be using wifi instead of cat5.

9. Originally Posted by nobb
EricE: Just curious. Could you tell me if your battery charger is constant voltage, or is it "intelligent." If it is constant voltage, how much voltage exactly does it put out? And at what maximum current? I am trying to accomplish what you are doing, except I will be using wifi instead of cat5.
I don't know much about chargers. It is just a standard charger for car batteries (not a trickle/maintenance charger). It puts out either 2 or 6 amps (switch selectable). Within that it varies by how many amps under the selected amps it will put out based on how much the battery needs. No doubt it does that by constant voltage? Long term it seems the computer needs 4 amps to run so I always use the 6 amp selection. So running at 6 amps with the computer eating up 4 means the battery is only getting 2 amps of that. 2 amps charging is very gentle on a car battery.

(irrelevent but I use an Optima red top)

10. I did this: http://www.wikihow.com/Convert-a-Com...b-Power-Supply and made up power connectors that matched. I used a 9 pin female connector that i'd picked up at a surplus store and that went to my M2ATX. THen I had a male one attached to the power, ground, and acc wires in the car, and a seperate male connector wired the same way to the power supply that i'd converted so i could just unplug it from the car, take it in, and plug it into the power supply

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