v4x

Hi, I'm trying to build a carPc out of an eeepc. For my project i need to be able to have the pc stay on while cranking without its battery.
I have those power requirements:
- 9-10v with 2A max to power eeepc and lcd
- 5v with 2.5-3.5A to power hard drive, combo drive and peripherals (bt, gps etc..).

It sums up at less than 40w total power consumption.

I assessed various options but my best bet at the moment seems to be the M1-atx, stripped of its atx connector and with it's 12 volt line soldered directly to one of those cheap eeepc 9v car chargers off ebay, and its 5v line attached to cd and hd and an usb hub.

But i still have some doubts, as i don't know if this set up will really work, so i need your advice on this.
Plus i'm really cheap so i feel that a 90w power supply is a bit overkill for what i have and i would prefer another solution if you have one, even a custom built one, i have a fair experience with soldering or building circuits, i just don't have a clue of how to design them.

FusionFanatic

using the M1 should work fine as a startup/shutdown controller, but I don't think it has enough power on the +12v rail to power the EeePC and a monitor. the total wattage of the PSU doesn't matter, each power rail has it's own maximum output (power cannot be shifted from rail to rail).

the M1-ATX can only provide 2A MAX on the +12v rail. the eeePC's AC home charger outputs 9.5v@2.3A. most small LCD monitors use around 10w (12v@~.8A). that brings your 12v power draw to roughly 3.1A which is too much for the M1.

the M2-ATX can provide 7A on the 12v rail, so that should be able to handle everything no problem. otherwise you can power the EeePC's car charger from an external 12vdc source (car battery, cig lighter socket, etc) and use the M1 as a 5v power supply and a system startup/shutdown controller.

another option is to buy a separate startup/shutdown controller and a separate 5v point-of-load (POL) power supply. you can power the computer and monitor from the car's 12v, and the HDD and USB hub from a POL.

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current carPC setup
previous carPC setup

v4x

I think i'm going with the M3, it's smaller, produces less heat and has 6A on the 12v rail and costs pretty much the same as the M1, at least here in italy...
Anyway i'm using the eeepc's own lcd with a touch panel, so 2.3A are actually more than what i will use as it will have no battery to recharge, and the lcd is already included in that current absorbtion...
Your third option is actually what i though of first, building my own startup/shutdown controller is not a problem (i've seen many useful diagrams here in the forums), but my eee won't have any protection against cranking downvoltages and will restart every time i start the car up...

2k1Toaster

If you are powering it through a car charger, the charger has a regulator built in. So no need to even worry about the 12v. And then you can get a power supply that outputs only 5v with a SDC. use the 5v output to trip a relay that gives constant power to the PC. That will also give the 5v stuff time to be on before post.

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FusionFanatic

why don't you want to use the EeePC's own battery?


If you keep the battery connected then it will be able to easily survive engine cranking (the EeePC will be powered by it's own battery while the the engine starts)


If you can build a startup/shutdown controller then that may be your best/cheapest option but you may need to keep your EeePC battery hooked up to survive engine cranking unless you can somehow delay the "turn-on" pulse until after the car has been started.

you can also buy a pre-built standalone startup/shutdown controller like the MP3car uSDC20D
. (if the MP3car store is out of stock then you can get the same unit at mo-co-so or on ebay)

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current carPC setup
previous carPC setup