Power laptop from headunit?

LordSnow · 04-06-2005, 10:58 AM

Would it be ok to just chop off the lighter plug adapter for my laptop car adapter and wire it directly to the power going into my headunit? I'm not the most electronically inclined and wasn't sure if the headunit+laptop be would be too much on that particular line. The laptop draws 3.6A @ 16v. Are there better options? I'm trying to avoid running a line directly from the battery if at all possible and would like to have power going to the laptop only when the car is running or when the key is turned. I chose the headunit power line just because I know where it is and would have easy access to to it. Any help would be appreciated...

kiltjim · 04-06-2005, 12:09 PM

When you say the laptop takes 16V @ 3.6 amps, you're talking about the utput of the charger right? You are going to have some sort of regulation in between the laptop and the lighter plug right? Like a 12V-ish -> 16V regulated charger, right?

If you don't have any regulation, between the laptop and the car's electrics, you are going to be in the market for a new laptop very soon. This is of course, unless the laptop has built in regulation, but I seriously doubt it.

trimpy · 04-06-2005, 12:15 PM

Id look around for a DC/DC converter to get that 12v up to 16v. They make things specifically for laptops to be used in cars/boats/etc...
http://www.powerstream.com/dc-3318.htm

Bobby Digital · 04-06-2005, 12:28 PM

I think you guys are confused, isn't the cigarette lighter adaptor thing (which he mentioned that he was using) already doing the 12V -> 16V conversion? Otherwise what is the point of the adaptor...

What joshthepilot meant was to find out where the actual adapting takes place on this device, is it in the part that actually plugs into the cigarette lighter (the head)? Because if so then you would essentially be cutting off the adaptor and having a straight wire to your laptop. You have to make sure there is some type of "box" on the line that is doing the actual 12V -> 16V conversion and regulation.

Anyway, I don't like the idea of tying it in to the headunit's power line. Depending on the headunit's power consumption you might overload that line. But you can try it if you want, I think it'll just blow a fuse if you draw too much current.

kiltjim · 04-06-2005, 12:41 PM

Usually the laptop is expecting a very nice clean 16V or whatever the voltage coming out of the adapter that comes with it is (mine is 19V). If he were to get rid of that adapter (which I thought he was saying) his laptop would be trying to adapt 13.x volts to 12v and 5 volts, and maybe the 3.3v. The circuitry in there would not be getting the 16v that it needs.

If it is a simple passive filter (say a binch of resistors and some caps) to just filter out any of the noise from the stock adapter, his laptop wouldn't be getting a full 12v/5v after the filtering. It might burn out something simply because it doesn't have the voltage required. This would mean more amperage requirements, and possible smoke leakage.

The same goes for if it has some sort of active filtering (probably more likely). If it doesn't see the full 16V it wants, it'll pull more amperage, to compensate, and thus leak smoke.

And I agree with BobbyDigital on this. You should probably add a second wire to the battery. Just to be on the safe side.

LordSnow · 04-07-2005, 12:49 PM

Just to clear the air a bit on this subject, when I say I'm cutting the end off of the car adapter I mean just the lighter plug portion so I can hardwire it to the accessory line or headunit voltage or whatever while keeping the power "brick" in the equation, which to my knowledge is doing the job of regulating the power. How well of a job it does is another question...

I went with a 3rd party for the charger just because I've heard that they are generally more reliable (mine's a Kensington), but just a couple days ago it stopped getting power (LED on the brick no longer lit, laptop not charging). This was just while using it plugged into the cigarette lighter but the charger works when plugged in with the AC adapter. So I started troubleshooting a bit and found the problem. On the cigarette lighter adapter end there is a small component between the brick and the lighter plug(see pic, same thing but closer to the lighter plug), which I've cut off and rewired the rest back together. It works now without it but I'm afraid to use the charger in case it was something important. Any ideas?

LordSnow · 04-07-2005, 07:24 PM

And no, that's not an actual picture of my actual adapter cord. It was just the first pic I could find with component I am referring to (circled). I've checked inside the lighter plug connector itself and there aren't any components inside, just the physical connections. I've tried to get inside the cylinder thing to find out what's inside but it's made with a thick metal casing covered in plastic sheath. So my question is....does that component that I've removed do any kind of regulation or something else important? Any help would be appreciated.

Scouse Monkey · 04-07-2005, 07:32 PM

the component is a ferrite core to abosrb electrical noise. Have you not seen them on the VGA cable for your PC or on some other cables?

It is a noise suppressor and has nothing to do with power regualtion

LordSnow · 04-07-2005, 07:44 PM

Sure I've seen them, just never knew what they were exactly. If that's the case, should I attribute it to poor construction that caused that to fail? Will I be ok without it?

Scouse Monkey · 04-07-2005, 07:46 PM

Quote: Originally Posted by LordSnow

Sure I've seen them, just never knew what they were exactly. If that's the case, should I attribute it to poor construction that caused that to fail? Will I be ok without it?

how did it fail? you can jsut remove them but if you get noise problems you might want to put a new one on. Depends how clean your input is as to whether it is needed.

LordSnow · 04-07-2005, 08:41 PM

I'm not sure how or why it failed. I had been using it in the car for about a week just to test things out and it worked fine then one day I noticed the laptop wasn't being charged when it should and the power LED on the brick of the charger was not lit. And I'm not talking about heavy use, just the 15 minutes or so to each trip to and from work. Temperatures have been around 60 degrees (F) so that shouldn't be a factor.

toadster123 · 04-07-2005, 08:59 PM

loose connection?? maybe voltage difference in car... is the voltage always the same in your car? (each time u used it)

LordSnow · 04-07-2005, 09:25 PM

Do you mean a loose connection within the ferrite core? Because I've isolated the problem to that single piece and I wouldn't think there's much to move around in there.

What exactly do you mean by voltage changes? I know it's not a constant 12v, that it ranges like most cars but the car charger is rated to take 11.75-16v so I would hope that all of the components of the charger could handle that range.