Power Inverter for Laptop Question

Make sure to get an inverter with auto shutoff if the battery is low on power.
You need to use a ground loop isolator on the output of the laptop being fed into the head unit through a FM modulator, or whatever.
To use the isolator you need a miniStereo male adapter to RCA 2 output.

You can replace the inverter and power supply with a DC-DC transformer if the voltage the laptop uses is less than the battery voltage.

ie. Battery 12V Laptop 10V -- DC-DC
ie. Battery 12V Laptop 18V -- AC

yup, the link above has some DC-DC power supplies. If the voltage required by the laptop is above 12V then these units are simply an inverter and a power supply in the same package.

Check out this site: http://www.mp3car.com/vbulletin/forumdisplay.php?f=24

They have hella stuff on software, power supplies, whatever.

edit: I've designed a setup I want to put in the corolla when I go get the xrs later this year... not sure if it's really helpful to you.

Parts List

1 Xantrex X Power Plus 400W Inverter $40
1 POS Windows Laptop
1 Ground Loop Isolator $10
1 FM Modulator or AUX input
1 mini-Stereo to RCA jacks cable
1 Xenarc 700TS 7” Touch Screen LCD
1 USB hub (optional)
1 Travroute Copilot 2003 with USB GPS $360
1 Mono audio cable 15ft. low power
1 cheap small microphone
1 USB external DVD-Rom (optional)
1 DVD Player software (Intervideo, PowerDVD, etc.)
1 Rocker Switch
1 Wireless keyboard mouse combo. (optional)
1 cheap USB PC video camera (optional)
1 Pivot Pro Software (maybe)

Powering the PC
There are two methods to powering your laptop. You can either use an AC inverter and your existing power cube, or you can buy a DC-to-DC converter. The only advantage of the DC-to-DC converter is efficiency and electrical losses. The difference in efficiency is usually less than 5%. I’m planning to use an AC inverter and use the existing power cube included with my laptop. The max power required for my laptop comes up to 180 Watts. You can figure this out by looking at your power cube. Here is a handy formula. P = IV meaning Power = Current (Amps) * Voltage

I picked a 400W inverter instead of a 200W inverter because it gives some extra power for other mods later. This also doesn’t put a heavy load on the inverter. The next important consideration is wiring. The wires that go between the battery and inverter must be especially heavy to handle the amount of power needed. According to the draw of 400W max, the wires need to be able to handle around 35 Amps. Here is a table of the distance of wiring versus the current handling. I would need 10 gauge to handle 40 Amps for a 10 foot span.

Distance - Feet
10 15 20 25 30 40 50
Amps Wire Gauge
5 18 16 14 12 12 10 10
10 14 12 10 10 10 8 6
15 12 10 10 8 8 6 6
20 10 10 8 6 6 6 4
25 10 8 6 6 6 4 4
30 10 8 6 6 4 4 2
40 8 6 6 4 4 2 2
50 6 6 4 4 2 2 1
60 6 4 4 2 2 1 0

Make sure the inverter’s heat sink has air around it. If not, the inverter would most likely overheat and your car would become non-existent. A power switch needs to be placed up front to turn the navigation system on and off. On my laptop this is a momentary push button that I will hardwire into the power control board inside the laptop. This involves board level soldering. Then the computer will fall to sleep on the internal battery for up to a week.

Sound System
My plan is to send the computer’s sound output back to the head unit and send it over the factory sound system. To do this you need a ground loop isolator and an FM Modulator/AUX input box. On the computer the sound output should be from the “Line Out” jack if available. If not, you can use the headphones output and turn the volume up all the way. The output of the computer is connected to the ground loop isolator through a mini-Stereo to RCA jack connector. The output of the isolator should then go to the FM modulator. The software I’m using (discussed later) allows voice input. For this, an audio cable is run to the front of the car and a microphone is attached to this.

Display
The display consists of a USB touch screen mounted up front in the car. The display I picked is the Xenarc 700TS 7” Touch Screen LCD. This is powered by 12VDC and draws 1 Amp. The touch piece requires a USB input, while the screen requires a VGA input. The VGA can be run with a long cable from the trunk. Make sure the cable has magnetic field isolators on both ends. (Doughnuts) For the USB part, I’m planning to run a cable to the front, and then place a USB hub up front. This will allow extra devices later. I may add a slim USB DVD-Rom up front near the display for quick loading of movies. I’m not sure if this screen will fit yet, I need to take measurements first. If the screen is mounted vertical instead of horizontal, you can use Pivot Pro to adjust the display of windows and rotate the VGA signal to match the screen orientation.

Software & GPS
For the navigation part I plan to use Travroute Copilot 2003 made by ALK. This offers voice recognition, spoken directions, etc. It is also one of the easiest to use with touch screens. The only downside is the price of the software. It’s $360 for the software and a USB GPS receiver. For playing DVD’s I’ll probably use Intervideo WinDVD.

Because Windows is a pain to use with a small touch screen there are several software packages that work with car computers. Most are free. There is MediaCar, CarBox, and Media Engine. These create a front-end launcher similar to what you would see on an OEM system.

I’m planning to mount the GPS receiver in the back window of the car.

Input / Output
I’m planning to mount a USB DVD-Rom up front with the screen so you don’t have to walk all the way to the trunk to put in a DVD movie. I’m also planning to have the system equipped with a wireless (RF not IR) keyboard mouse combo.

Other
As an add-on, you could add a second non-touch screen for the rear passengers. This would allow your friends in the back seat to watch the movie or the GPS screen. They could also use the wireless keyboard to type up something in MS Word etc. You could also add a rear view pc camera for backing the vehicle.

The inverter is at GiJoes, http://www.gijoes.com
(It's a sports store, they sell some auto parts)
I don't know if you have those stores or not where you live?

The only thing I can think of is a relay with a secondary switch.
Example of relays: http://www.power-io.com/products/hda.htm
This one only takes .02 mA to turn on, which is nothing.
Battery
+ -------- Relay ------------- Inverter
- -------- Same Relay-------Same Inverter
...............| |
...............============= Switch

The switch should probably still handle a couple of amps
This should work just fine: http://www.radioshack.com/product.asp?catalog_name=CTLG&product_id=275-731

holy shit! 850W is 70 amps! You're going to need 4 gauge wire for even a 3 foot section. That's almost what an alternator can put out. Extra battery = must if you are drawing that much power.

An inverter works by taking an RMS DC voltage of 12V and chopping it into sections. It will chop at the rate of 60 Hz and make half of the wave positive and half negative. This then runs through a transformer and is upped to 120V. This generates a square wave power output. Some high end inverters actually have inductors and caps to filter this to a real sine wave. But, if it's going back to DC that doesn't matter.

edit:must have posted right before me...
The 75W and 90W inverters may be enough to charge the laptop when it's off, or run the laptop, but run and charge at the same time


It depends how many watts your laptop uses.

This is my power cube. You can see that it is rated at 100-240V @ 1.5Amps (top left)

So since power in the US averages 120V and Power = Current * Voltage
1.5A * 120V = 180 Watts

This would mean I want an inverter between 180 - 300 watts. Just read the fine print on some of the inverters. Some can only operate at max power for a very short time, and then must scale back to 80% of max. That's why I would just get 50 - 100 watts extra.

If you want I'll calculate it for you if you post a picture or info from your power cube.

yup, supposedly if you are drawing over 15A then you need to have it connected directly to the battery. So, that's about anything 180W or greater.