I have finally got all the bits and bobs to setup my carputer...

Just wanting to run my powering up solution pass a few gurus before putting it in place.

First of all the devices:
1) Laptop (16V at 4.5A max) = 72W
2) Screen (12V at 1A max) = 12W

Total of 84W max

I am planning to power this through the cigarette lighter power supply.

I will get 2 DC-DC "regulators" -
A) for the laptop a 12V to 16V car cig lighter power adapter for laptop (by Targus) - capable of supplying 120W max 70W contin.
&
B) for the screen a smaller cig lighter power supply to supply 12V regulated (although I am still looking for this).

I plan to connect these two power sources in parallel from the cigarette lighter power source and put a switch in place of the cigarette lighter so it only powers up when I want it to...

Does this sound like it will work - or will the power supply to the screen suffer inconsistencies because it is from the same wire as the supply to the laptop (even though they are in parallel).

Since the fuse for the cigarette lighter is 15A I figured it can easily handle 84W total (far less then 15Ax12v=180W).

Heath, Tim and all else who care to comment, your opinions would be greatly appreciated!

quick reply, i gotta fly...

Ciggy lighter power is pretty messy usually. Better off rewiring it using proper lines. You can splice into the back of the ciggy lighter if need be but the actual connection into the lighter are usually really poor.

Usually pc power is easy as it is already 12 v. But since it's 16 volt u will need an inverter. My laptop runs fine of an inverter, but you need one powerful enough to run it. So do ur research and bigger is better.

Good luck

Tim

Wow that was quick - thanks!

So do I need to power it up from the battery and get a relay from the accessory line to turn it on (so that when I turn the car off the power to the screen and laptop is cut?) or can I just power it off the accessory line?

Just another question - does the power line to the car stereo have regulated 12V or unregulated?

Actually no, your first idea of using the DC-DC converter will do, an inverter is not required if you are going to follow that route.

The power to the car stereo is unregulated, however the DC-DC converter should already incoporate some sort of regulation circuit.

Also, you should never power devices off the accessory connection, that should only be used for switching purposes, so you'll need to wire up a relay to switch constant +V current.

I concur with one of the above posts. 84W will be around 5.8Amps @14.4v or 7Amps with the car turned off. One would assume the cigarette lighter circuit is not designed with a 100% duty cycle in mind and as a subsequence i too would recommend you run a new feed (fused) directly to your battery and wired via a relay for turning it on/off.

As for regulators... Usually regulators require at least 1.7volt more than it's output voltage so with the car turned off you may have a problem at 12volts. Obviously no problem with the car running. Also a regulator which can handle around 10amps at 12volts reliably isn't going to be small.

Had a quick look at the circuit diagrams, and the cig lighter is actually switched by the Accessories line, normally I wouldn't connect Auxillery circuits directly to a acc 12v line, but in this case it seems to be isolated from other circuits. The cig lighter is rated for 180w, so there shouldn't be any problems using it, the wiring is capable to running 180w as specified in the handbook, otherwise they wouldn't have fitted a 15A fuse in the first place for lack of safety.

The bigger concern I have would be noise, but any good power supply should have some sort of noise supression anyway.


If the regulator circuit is designed properly, then it should be able to compensate for the loss of high voltage when the ignition is off.

I would use something like a Maxim MAX724 (http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1269)

Obviously you'd want to keep it cool, so a heatsink is mandatory, possibly also a fan but I won't know until doing the maths and experimenting.


Anyway boys and girls, I won't be building power supplies for you, I'd already gone through enough drama building mine just so I didn't have to pay $300 for a professionally built power supply :D

Thank you again TecoDan, 410 and Tim!

Do you have a copy of the wiring diagram that you could post please?

have you thought of just usinga small PC rather than a laptop

you can get micro PC motherboards wich include a built-in processor for about 200-300 bucks. all you will need is a bit of ram (not much maybe 150, depends how much you think you need). these motherboards are quite small and inside a small custom box will easily fit under a seat. all you need now is a 12V - 12V regulated power supply (see mp3car.com) and swap your VGA screen for a VGA touch screen (350 - 500 for a good one).

A friend and i have looked into this a fair bit, i have even seen several of these motherboards housed in old amp cases.

either way you decide to go, are you aware that you can easily add navigation to the system. i think GPS usb dongles are quite cheap and then you need to find some software wich wont be hard.

An update - I decided to power the laptop and screen off the cigarette lighter with a cigarette lighter switch/ extension lead ($10 drom Dick Smith's) and I found 2 DC-DC regulators.

A larger one for the laptop - Targus car adapter - being shipped from US (bought for $50 on ebay).

The smaller one a simple kit (than I am yet to make) from Dick Smith's for $10.

And ofcourse VGA extension cable, USB extension cable (for the touch screen component), wires etc...

All up pretty fun...it's working with the screen running straight off the cigarette lighter/battery at the moment (unregulated) and the laptop on batteries.

Waiting for the car laptop power adapter to arrive and to make the Dick Smith's kit...and then to hack the tray under the front seat to mount the laptop.

Will post pictures when done.

Thanks to all for their advice and thank you to Bain for the great pics on the how to take apart your console (and still live to tell the tale) - I had it on my laptop by me while I did it yesterday!

P.S. As I was fiddling about yesterday - I noticed when I connect the sound output from the computerto the cable which is meant to go to the external amplifier (marked front right, front left) on my Clarion, the sound goes directly to the front speakers and (on top of whatever is playing) - which is cool cos I don't want to switch to auxillary to listen to the GPS guidance... However I chickened out for the moment and I have just connected the output from the computer to the Aux in of the headunit - will connecting the output from the computer to what should be the preamp from the headunit damage the headunit?!

hey mate. good thread. i have a mini ITX board in my car too.. and now a laptop as of last night. i still dont have power to the mini ITX yet because i am lazy. but it will be done.

make sure you get wifi too.. then you can have net in your car. a lot of peoples wifi connections are unsecured and you can hook in to it and use their net. :D


what sort of monitor is it you are using and what size?

In dash motorized 7" VGA touchscreen called K301 - do a search on the internet for it - also sold as MTSVO or something at MP3car; also sold with some german name at CarTFT...

Bought it from Shenzhen electronics in China - pain in the ass but was worth it!

Yeah I got wireless too lol