TTagz

I promise this is TT related in a round about way. It's for my pc I am putting together to go into the TT.

Anyway, a pc uses a power supply that provides 12V, 5V and 3.3V DC. A standard power supply has to convert this from a 110V 60Hz AC source, but since a car already uses a 12 DC source, and all you need is 2 lower voltages, would it be possible to put together a simple circuit to drop to these lower voltages and supply the components in this manner? I asked another engineer friend of mine, and he said it sounded good to him, but electrical was not his discipline. Is there anything I am missing/overlooking here? It seems pretty simple, but there are companies producing DC-DC power supplys for this purpose that cost between $60-$300. Any ideas, theories, opinions, or thoughts?

JustJeff

Classic variable voltage power supply.

<img src="http://woodyjdb.home.comcast.net/images/vreg.jpg">

Problem is, you will need to be aware of the various *current* demands need by the computer.
look at what those voltages draw for wattage and amperage, especially the +5 voltage.

This circuit above is limited to 1.5A, and if you use it, you will nered to heat sink the TO-220 regulator, as it will get HOT.
this circuit is filtered enough for use with a laptop or other computer, but MAY NOT have the current available for your needs.

edrucker

PC's tend to require a fair amount of power. The circuit that was proposed is a linear regulator which will pobably self-destruct with the amount of current you need. You have to drop the 12 volts to 5 and 3.3 (using two differnt regulators). For example, if the 5 volts requires 1 amp, that means the regulator must dissapate 7 volts * 1 amp or 12 watts. I don't know how much current it draws, but I'm sure it is much more than 1 amp. A switching regulator is much more efficient in converting power, but it is not an easy circuit to design and build Leave it to the trained professionals :'). I would recommend buying a commercial supply or why don't you just get a laptop?

msauve

linear regulators are inefficient, would suck lots more juice than necessary (especially important when on battery), and would also run very hot.

Switching regulators aren't typically do it yourself projects.

You should look into a unit designed for what you want, such as this one: http://www.opussolutions.com/modules.php?name=News&amp;file=article&amp;sid=20 , or worst case, try an inverter in front of a standard AC power supply (not very efficient, but should be significantly better than linears).

BTW, a car DOES NOT have a 12V source. "12V," in automotive terms, is usually about 13.4V when the car is running. PCs require much tighter regulation of voltage for proper operation, and you would NOT be able to use a linear regulator to get suitable 12V from a car.

RafaTT

but as said, it is not a easy solution. What I would do, and this depends on how much power (watts) your app will need is to build a power supply using DC-DC converters, called 'bricks'. They take 5-16VDC input and regulate to 5/12/3.3 but again, power is limited to only a couple of amps. Check what is the power requierements for your PC (PC + and all accesories that this supply will plug into) and I'll check what is available. Also, running some app with batteries is not recomended as you'll get a dead batt very quick if forget to shut the PC off.

For mobile apps I recomend using single board computers (a.k.a. SBC - not small block chevy...) as they requiere only one supply (usualy 5V), small footprint (half ISA/PCI) integrated accesories (Video/TV input, audio, serial, USB, kbd/mouse, IDE and so on) and have enough horsepower as to run most apps.

BTW: here is what I'm talking about on bricks, but remember that we are talking $$ for this solution.

Just for the record, I'm NOT seling anything as I design stuff, not sell it (note for moderators)<ul><li><a href="http://www.dcdc.com/PDF/n.pdf">DC-DC supplies</a></li></ul>

TTagz

and a converted desktop will be much easier to integrate into the car. Laptops are also a lot more flaky, and tend to have many more problems than their desktop equivalents. The only components i need to purchase are the lcd touchscreen, a cheap dvd drive and some sort of power supply. If anything in this system goes on the fritz, I can replace it for pocket change. Laptop components are a little more expensive and hard to find.

TTagz

The DC-DC convertors seem like a viable solution depending on them being cost effective. I would need to have around 120-150 watts max I would think. The system is a 500MHz AMD K6-2, 448MB RAM, 40 GB 5400RPM hard drive, then a DVD drive. The only other draw would be from USB devices, but they usually have a low power draw or are self powered.

So in your opinion, would this be a good solution, or should I just go with one of the commercial solutions? Its not a big deal or anything, I was just curious because I didn't know the circuitry involved.

RafaTT

Trying to put a home PC on a vehicle is possible, BUT you have to take care of a couple of things, meaning compromising the following: The The home based PC (i.e AMD KX/ Intel P3/P4)Celeron) motherboards are not energy efficient as needed in a vehicle, this means that as you are saying 130 watts on the power supply is 130 watts from your alternator or battery (when car is off). Also, 130 watts is heat that you will need to dissipate somehow. Also, take into account that the inverters are about 85% effective, so the other 15% is heat (yes, more heat into the equation) so you will end with a ****load on your alternator and battery, besides cooking something when the car is not ventilated. Now, here is the solution for the heat problem: the mobile processors (P3M/P4M,as in the laptops) which in this case will not be used because of cost and that you already have some HW. I suggest go with either a mobile solution or if still want to build it yourself, go with an industrial computer like the SBC mentioned earlier.

I also an thinking about installing a PC in my car, with wireless (802.11b/g) so I can use Hot Spots as internet access from the car, use it as access point for Palm PC's, use it for logging (with VAG-COM), and so on but the solution I have is a mobile SBC with a laptop hard drive (more space/energy efficient) and a single voltage supply (+5V from +12) using only 20W total. If still interested let me know, I can post some pics when done.

miTTchell

<center><img src="http://pictureposter.audiworld.com/62253/audilcd.jpg"></center><p>MediaCar forum pic blurry due to conversion and crop.

This is somthing alot of guys are doing, linking the grid on a touch screen LCD so the buttons work. I dont know all the details, but a search on that forum should cure you.

DC to DC. A friend is doing this in his Infinity (he passed this Audi pic onto me) he found a deal on one at Fry's Electronics. I'm not an Electrical Engineer, but I would be weary of Mcguyvering a solution if your warrenty is still valid. If your solution screws anything up (our cars are finicky on the electrical side of things) your SA would probley question a swiss army knife and tampon duct taped together with 100 wires sticking out of it.

I would spend the cash on the DC to DC, while your spending money, get the Flat Panel touchscreen if nothing else for the convience and coolness factor. USB GPS solution works too.

TTagz

I'm actually an application developer, so I was planning on developing a main control software, if for no other reason, because it would be pretty easy and cool as hell. We'll talk when I become obsessed with it and am on V 7.4

But actually, with all the great responses I received, I decided to go with a commercial solution for the power supply. I wasn't sure what all was involved, so I thought it best to at least ask. I am looking at a 7 inch lcd usb touchscreen, provided it will fit between the aluminum pillars on the console. hopefully, I will be able to make it retractable so it won't be out all the time.

As for uses, I plan on using it for MP3, DVD, internet using my cell phone as a connection, GPS navigation, wifi connection to my home network for syncing files, VAG-COM, usb cam for track events, and the list goes on and on. It should be pretty sweet if i pull it off.