Car Computer

[dreamproject]

Hi all,

I am fixing up a computer for my car . The following are its specs:


I am using a Gigabyte Motherboard hosting a AMD 2400+ processor , the board's SMPS is powered by a 400w off-the-shelf inverter (1.3 A max.)(running on the car battery) . The Computer's VGA output is fed to a VGA-AV converter and then to a 8" LCD-TFT monitor (NecVox)(Accepts only AV input). The monitor is driven directly by the battery . All ports present in a normal desktop are available (USB , Parallel , Serial , Etc..) . My doubts are:


1. A warning on the inverter says " The output is not purely sinusoidal " . Is this cause for worry ?

2. When I start my car with the computer running , will it restart due to the voltage drop that occurs during a start ?

3. I have noticed waves on the monitor display , Is this due to the inverter being on the same line as the monitor or due to the inconsistencies in the refresh rates of the PC , VGA-AV converter and the Monitor ? . The waves become more prominent when the car is running.


Thanks

 

[zachtheterrible]

2. When I start my car with the computer running , will it restart due to the voltage drop that occurs during a start ?

With a big enough capacitor it wouldn't :lol:

 

[MARINE1142]

What kind of plans do you have for a onboard pc in your car> Why cant you just put a laptop in there and call it a day?

 

[tansis]

The output of the inverter should not be a worry,
what is cause for concern is why you are using it in the first place?

For this application a DC/DC converter would be more efficient
in terms of both electrical losses and space as it replaces the computers SMPS

http://www.mpegbox.net/products.html

 

[Oznog]

1. A warning on the inverter says " The output is not purely sinusoidal " . Is this cause for worry ?

2. When I start my car with the computer running , will it restart due to the voltage drop that occurs during a start ?

3. I have noticed waves on the monitor display , Is this due to the inverter being on the same line as the monitor or due to the inconsistencies in the refresh rates of the PC , VGA-AV converter and the Monitor ? . The waves become more prominent when the car is running.


Thanks

1. Don't think so. The SMPS rectifies it out anyways. The rectifier won't charge to the same peak voltage but I think it's ok.
2. Yeah, and a cap won't help here because it will instantly drain into the starter. You need a second battery and battery isolator to keep current from flowing backwards out of it. Or a UPS. The thing to watch out for is charge current. If you run a small secondary battery down and start the vehicle, it might put out a 50 amp-100 amp charge current to it.
3. Probably ignition noise or maybe the alternator's AC peaks are coming through.

Be aware your big issue here is vibration and shocks. This is very harmful to desktop drives. Much less so to laptops. It may also present problems for card connections, etc.

 

[dreamproject]

points

Hi all ,

Thanks for taking the time to discuss this issue . I could have gone in for a laptop but I considered these points:

1. A laptop would have looked like an after-market fitment.

2. I already had a 8" LCD-TFT screen in the car , Connecting the computer to this made it look really cool the primary purposes being music and movies.

3. All that is visible is the DVD-ROM drive in the dashboard , a couple of USB ports and a RJ-11 Ethernet jack for data transfer.

4. A cordless trackball completes the setup for total wirless use .


5. The total cost of the setup was less than 60$ , but a comparable laptop would have cost more (2.4Ghz , 80 Gb , 512 Mb)

6. A Laptop screen's hinges would definitely be damaged during vehicle movement.

7. A DC-DC converter is possible but using an inverter simplifies things and avoids messing with power wires inside the CPU. we have to contend with four voltage levels (+12v,-12v,+5v,-5v)

Thanks

 

[Someone Electro]

Yea an 400W PSU from scratch wod be prety complicated.

btw: You forgot the +3.3V rail That rail is probobly the most inportant since it powers the CPU (The modern CPUs went to 3.3V to reduce the heat produced and so making the cooling problem well... less a problem)

 

[Jay.slovak]

You forgot the +3.3V rail That rail is probobly the most inportant since it powers the CPU (The modern CPUs went to 3.3V to reduce the heat produced and so making the cooling problem well... less a problem)

Well most modern CPUs have even lower voltage (I think 486 had +3.3V Core), for example my AthlonXP has Vcore of 1.65V. Motherboards use step-down converters to lower +3.3V to Vcore of procesor that is installed.

 

[Someone Electro]

I thnink his CPU is 3.3V (mine P4 is too)

 

[dreamproject]

thanks

Hi all,


Thanks for your views

 

[checkmate]

There are many car PC project on the web. A Google search yielded some interesting results. I was particularly intrigued by this.

 

[Optikon]

You forgot the +3.3V rail That rail is probobly the most inportant since it powers the CPU (The modern CPUs went to 3.3V to reduce the heat produced and so making the cooling problem well... less a problem)

Well most modern CPUs have even lower voltage (I think 486 had +3.3V Core), for example my AthlonXP has Vcore of 1.65V. Motherboards use step-down converters to lower +3.3V to Vcore of procesor that is installed.

1.2, 1.3, 1.25, 1.5, 1.8 core voltages are common these days.
3.3V & 2.5 are mainly used for I/O. and in most cases, 5V is out of the question altogether.

 

[Thunderchild]

i think most modern cpus get the power from the 12 v rail that has a switching power supply on the mobo. this is more efficient as less amps have to go thru the power transistors per watt of current needed making less heat and power loss

 

[Someone Electro]

12V are they nuts !?

 

[Thunderchild]

no if u had to convert 100 watts of 3.3v to 1.65v then ud get thinking about using 12 too. whats the deal u use 220 volts to power the pc but it is reduced by the psu. on the motherboard there is another psu that reduces 12v to 1.65v. this would also solve the problem of unstable crapy psu's as te mobo one has probably special attention payed to it to ensure stability and reduce interferance from other parts:
open ur pc case and look at the mobo u will see near the cpu (probably between it and the paralel port) many power transistors and coils that is the onboard power supply for the cpu. intel also use another one on a small board plugged into the mobo as modern intel chips take 100 watts easy

 

[mstechca]

2. When I start my car with the computer running , will it restart due to the voltage drop that occurs during a start ?

With a big enough capacitor it wouldn't :lol:

How long is the voltage drop? that needs to take into account. You can get away with a ridiculously large value capacitor (1F +) in most cases, but if you want to save money, you may want to measure the resistance of your load (computer), and then if you use the simple RC equation, you can roughly determine how long it takes for a capacitor to charge up.

 

[dreamproject]

calc

hi,

how do I calculate the load , R=V/I , Is this right , by measuring current drawn ??

:wink:

 

[audioguru]

That's right. If the computer draws 20A from the 13V battery, then its resistance is only 0.65 Ohms.
The capacitor discharges into the computer and therefore powers it while the engine is cranking and the capacitor will need a diode between it and the battery to prevent the capacitor from also powering the starter motor.

The voltage on the 1F capacitor will drop to only 4.44V in only 0.65 seconds! Ridiculous. :roll:

 

[shamikrudra]

Hi all,

I am fixing up a computer for my car . The following are its specs:


I am using a Gigabyte Motherboard hosting a AMD 2400+ processor , the board's SMPS is powered by a 400w off-the-shelf inverter (1.3 A max.)(running on the car battery) . The Computer's VGA output is fed to a VGA-AV converter and then to a 8" LCD-TFT monitor (NecVox)(Accepts only AV input). The monitor is driven directly by the battery . All ports present in a normal desktop are available (USB , Parallel , Serial , Etc..) . My doubts are:


1. A warning on the inverter says " The output is not purely sinusoidal " . Is this cause for worry ?

2. When I start my car with the computer running , will it restart due to the voltage drop that occurs during a start ?

3. I have noticed waves on the monitor display , Is this due to the inverter being on the same line as the monitor or due to the inconsistencies in the refresh rates of the PC , VGA-AV converter and the Monitor ? . The waves become more prominent when the car is running.


Thanks

Hi
i have gone through your problems

as u want to install a pc in your car and want to use a inverter
my first sagesion will be use a UPS in between PC and Inverter
if output is not purely sinusoidal then then ups will solv your problem of heating of SMPS.
and if u can modify the UPS then there is no need for inverter but there may be a problem when starting your car

 

[dreamproject]

thanks

Hi shamik,

Thanks for your input . I think this is just what I needed. Okay , is a 400 w inverter with a maximum continuous current capability of 1.3A good enough to charge the UPS batteries . Also , Did you notice waves on the display screen (TFT) , I have also connected a CCTV camera in the rear for rear vision . The waves appear even when the diplay is switched to camera mode from the computer mode , thus there can be no inteference from the computer . Could the inverter be causing changes in the Power Factor , causing this ????

Kindly advise.