Choosing PSU for Laptop

**speakers_86** · 04-10-2009, 11:10 PM

Ive done the research, but I'm still not clear. Can someone tell me if I got it right?

Inverter-Bad, because its inefficient (understandable)

DC/DC adapter-goes from cigarette lighter directly to laptop. My understanding is that this is not regulated, and could result in a ground loop. Also, gives no power to the screen (although I read in another post the screen can be powered via usb, I have a sneaking suspicion that is wrong). Also requires start up controller. Screen would have to be powered by other means, which means ground loop is probable.

Intelligent DC/DC-Wired to the battery. Regulated. Powers screen without ground loop. Also acts as a startup controller (shutdown can be handled in windows). A little more expensive. No ground loops with this method.

My laptop is a compaq V2000 running XP Pro.

I read here that a good PSU for a laptop is Carnetix P1900. I looked at the manual and the word laptop does not appear at all. Is this the best bet? Also, can someone describe to me how the unit is connected to the laptop? Is it a barrel plug that plugs into the laptop? Or is there some splicing involved?

**Bugbyte** · 04-10-2009, 11:15 PM

P1900 outputs up to 19 volts, which is why it is desirable for a laptop. Some use higher voltage than 12v. However, cigarette adaptor will also work. With either solution, the issue is still that you must signal the laptop to start up. You will have to come up with some way to do this, whether DC-DC or inverter or P1900.

**speakers_86** · 04-10-2009, 11:53 PM

Starting the laptop shouldn't be a problem using webmaster's controller.

So I see 3 reasons that make the P1900 better than a DC/DC
No ground loops
Powers the screen
Regulated

Does that sound right?

**DarquePervert** · 04-11-2009, 08:48 AM

Originally Posted by speakers_86

Starting the laptop shouldn't be a problem using webmaster's controller.

So I see 3 reasons that make the P1900 better than a DC/DC
No ground loops
Powers the screen
Regulated

Does that sound right?

The only reason that is valid is that the P1900 has the ability to power the screen with the extra 12v output.

The auto power adapter for your laptop will provide regulated power to the laptop.
Ground loop issues are a possibility with ANY power supply, since it is usually a wiring problem.

The P1900 has a startup/shotdown controller built into the unit, so you wouldn't need WebMaster's controller. However, you'd need to crack the laptop open and wire something to the power switch. That may no be the easiest task in the world.

**speakers_86** · 04-11-2009, 04:22 PM

Thank you. I understand now. The only thing that makes intelligent dc/dc better than dc/dc (for a laptop) is that it supplies regulated power to the screen (and is also a startup controller).

The P1900 is not what I imagined based on what I read, but since it powers the screen with regulated voltage, it still sounds like the best answer.

**Thefdog** · 04-28-2009, 08:46 PM

I used a relay wired to my ignition to turn power on and off to a Kensington power supply for my IBM laptop install. I have the power switch in my dock wired to a push button on the dash.

The other benefit of the Carnetix is that it can also provide a constant 5V with 3 amps which is critical if you run a USB hub with a number of powered devices, which is often likely with a laptop install, especially if you use an external sound card.

Of course, you will have to choose between 5V and 12V on the secondary output, but my touchscreen monitor does not seem to require a regulated 12V input.

As for a ground loop problem, this occurs when a power differential occurs between grounds which causes noise and interference that often responds to the engine speed, i.e. it gets louder or higher pitched when the engine revs up. The easiest way (ha) to fix this is to ensure that all of your computer and stereo equipment is grounded with the shortest possible wire to the SAME LOCATION. Ensure that this point is properly prepared (a substantial piece of metal attached to the car frame that has been sanded to bare metal to ensure proper contact) and located in the optimal spot for all of your equipment. These are notoriously hard to fix for some setups.

Cheers

**Jitters333** · 04-28-2009, 09:07 PM

Originally Posted by DarquePervert

However, you'd need to crack the laptop open and wire something to the power switch. That may no be the easiest task in the world.

And Compaq's are a ****** to open up

**speakers_86** · 04-28-2009, 10:59 PM

Originally Posted by Jitters333

And Compaq's are a ****** to open up

Figures, doesn't it?

**Jitters333** · 04-29-2009, 01:27 AM

i would go with an inverter Much cheaper, easier.. and nothing thats soldered in your comp, so if you wanna grab it and mob to a starbucks.. well there you go

http://www.newegg.com/Product/Produc...82E16882021115