150W PSU - P4/AMD XP Cabable?

[TJ69]

I am attempting car computer project with mp3/cd/dvd/divx/mpeg/nav/tv features.

I found this dc-dc psu specifically designed for car applications, but it only offers 150W. There are a few 250W 12V Input PSU out there, but they do not offer the load protection or auto shutdown features with ignition off like this product.

The system will probably be around a P4 2.4 Ghz+. I will either go with a sis 655 or 845PE chipset MB. I will most likely use an Audigy 2 or better soundcard. It will have one 20-40GB 7200RPM IDE harddrive and 256-512 mb ddr ram (fastest supported). A dvd drive (maybe w/ burner) will be the only other drive (no floppy). And possible a few firewire/usb/ethernet peripherals. Will I be able to power this with a measly 150W PSU? Has anybody attempted it here?

What will happen if the PSU can't supply enough power or the computer draws too much?

 

[AtomicDude512]

No way. Both of those CPU's like at least 300w, if you try to use that powersupply you may burn out your hardware because of it's not getting enough juice.

 

[tranceport]

Speaking of which. I need a new ps. When my processor runs prime95 my tornado fan slows down.

 

[TJ69]

I know what the cpus like. I know what cpu mfr recommend. I want to know how low I can go.

After some research, I found that AMD XPs and P4s use around 60W of power. Lower or higher depeding on speed and voltage applied.
A maxtor data sheet says their fireball HD uses less than 20W.
A DVD drive is also around 20W.
These are conservative estimates.

So far I have less than a 100W, and that takes care of the moving parts and the power hungry cpu. I still have at least 50W to spare.

So what else using so much juice that I need 3-400W PS?

 

[mastay]

Here is a good guide about powersupplies
http://firingsquad.gamers.com/guides/power_supply/page2.asp
But for the record, a P4 consumes more like 80-90W rather than 60. HD and DVD are more like 25Watt. Then, take into account your mobo, which is something like 10-15W, then video card is something like 10-30W. The Audigy also likely takes something like 10-15W. Ram also eats up somewhere about 7 to 10 W per 128meg. Little things add up and I doubt 150W is enough.

Also, I looked at the specs for that PSU. Note, you need about 8AMPS on the 12V for a P4. That thing only gives you 5. Right there, you are sunk.

Besides, do you have enough at each rail? Overloading the 3.3V but have 5.0V extra doesn't do you any good. You are right, most computers really don't need 300W overall. Howeevr, in most cases, one rail hits the limit and the other 2 rails is sitting there idly humming. Plus, power ratings are goofie in general. Some alleged 400W PSU act like 250W ones, and PSU efficiency decrease with heat. Bad PSU, when overdrawn, also tend to damage your system, although not a spetacular fire more people like to imagine.

If you want to build a low power system, consider tuning down you system. Go with a PIII or a duron in the under 1Ghz range to budget that output to >35W. If you aren't playing games, you don't need that much power. Maybe even grab a mobile PSU Also, go with a SDR system over DDR, again for power reasons. Grab a 5400RPM or ideally a laptop HD to reduce power consumption there. Even after all that, you probably still need something like
12V->10AMP
5V->15AMP
3.3V->20AMP.

 

[Cerb]

For a 150w or so, why not get one that the shuttle XPCs use? Sure, you still need an inverter...

 

[TJ69]

Mastay:
Thanks for the great link.

I think you're right, 150W will be underpowered. I can only hope that the specs are underrated for this PS.

I gave them a call today and recieved some more specs via email. They claim it does support P4 systems. So, I bit the bullet and ordered it.

I'll prime it with my power hungry Amd 1.4 Tbird oced to 1.6, plextor burner, dvd, maxtor 7200 dual 40GB raid stripe, 20GB 7200 maxtor, G4 Ti, and a few other power hungry addons, which probably will draw more power under load than my new system. I have 30days to convince myself it wont work. But it really is the best car ATX PS out there. I only wish it had more power.

Cerb:
Inverter are very innefficient for this application. Also, it will not react very well when your trying to start your car. And, when there is no auto shutdown. Instead, its like a power outage everytime you turn off your car, which cant be good.