Choosing right PSU for my MB

**Heckler** · 09-11-2007, 07:44 PM

Have a few questions for those far more technically minded than I.

Had a search and read around the site, but am a little confused about a few things. I'm not electrically minded at all, it's a blind spot.. can do most other things, but when it comes to working out power needs and circuitry,,, nope, not a clue.

So I am trying to work out the best DC/DC PSU to use for my system, here's the specs so far.

Gigabyte 7VAXP Ultra MB
AMD Athlon XP 2800+ (333FSB)
1GB Crucial Ram (2x512mb)
100GB laptop HD
Radeon 9200 Vid card
Liteon DVDRW

Aside from adding around 3 USB dongles for Wifi/GPS/Card reader and possibly a wireless joypad, that's the system.

I just can't work out the power consumption I require. Using the power calculator and adding everything above and a couple of case fans to aid cooling. It comes in at 219w required, but it also says this

*This calculated Power should be understood to be the Absolute Maximum Worst Case Scenario. In many cases you will be able to divide the calculated power by 2 and achieve a Minimum Continuous Power rating that a power supply must be capable of delivering. Most Power supplies give their ratings in Peak Power or Continuous Power which is not the same as Continuous Power. To be as safe as possible, use the exact numbers given by this calculator to guide you in purchasing a power supply

So can I just go for a 150w one and still be ok, or should I pay twice the price and get the 250w one to safe.

I have tested the cars system, and when cranking the engine voltages drop to around 7-8v.

Money is also an issue as I still have a screen to source as well as the startup/shutdown controller and PSU. I'm also in the UK which makes things harder to source (unless anyone has tips on UK sellers for this stuff).

Want to get it right first time, before I start installing and building the boot enclosure for this and the amps/sub.

Thanks

**DarquePervert** · 09-12-2007, 07:26 AM

The CPU you're running has a power draw of nearly 70w. That's CPU ONLY, and doesn't include anything else drawing from the 12v rail (motherboard, full-size HDD, video card, full-sized optical drive, LCD possibly).
The Opus 150w supplies only 60w on the 12v rail. You will be overloading it and the 150w Opus will not work with your setup.

If you're going to be dropping cash on a PSU, I recommend the DSATX with the brainstem (an additional $10). It is far more customizable than any of the Opus offerings and the developer is an active member of these forums, providing top-notch support.
I'm not slamming any of the OPus products. They are certainly quality pieces. However, for the money, I think the DSATX is a better value, even if the output rating is a bit lower.

Also, if you purchase an Opus PSU or the DSATX, you don't need a seperate startup/shutdown controller. These PSUs have the SSDC built-in.

Wanting to get it right the first time is always a good idea.

**Heckler** · 09-12-2007, 09:38 AM

Thanks for the input. I had overlooked that I need the correct w to each rail, have read a little about it and trying to absorb and understand it.

From my limited understanding, a PSU has something like 4 rails, a 12v, 5v and some others. The CPU will draw power from the 12v rail, and as you pointed out the 2800+ CPU has a max draw of upto 74w. The 3 USB dongles each have a draw of around 4-5w and use the 5v rail I believe.

Not sure on which rail the AGP card (around 25-35w) is on, although I think 8x AGP uses 1.5v, memory, DVD, HD and case fans I have no idea which rail they would be on at present.

I need to break down my power needs and find the right PSU to meet them... it's not enough to say my max need is 219w and get a 220w PSU if it's not supplying enough to the right rails.

See, I do learn stuff from time to time.

Just spoke to a colleague at work as I was checking the DSATX specs you mentioned, btu was confused by the volts/amps thing. he explained that if I multiply the voltage by the ampage, I get the wattage. So the DSATX has a nominal 12amps Peak 15amps on the 12v rail, giving a range of 144-180w. More than enough to power the CPU... if anything, a little bit of overkill. Using the same sort of calculations for the 5v, 3.3v rails gives me more than enough power.

Does that sound about right?

You mentioned they also have the start up shutdown controller built in, so potentially saving me money buying 2 things when 1 will do, even if it's a little more expensive.

Couple more questions, then back to work this afternoon.

My current head unit can power up the CD changer when it's switched on. Is it possible to do the same thing with a motorised touchscreen, so when I power it up it boots the carpc? I'm assuming I just need to make sure I have a screen with a remote power feed like the Pioneer headunit. I've decided to get rid of the headunit and use amps for sound as I just don't ahve the dash space for both.

**DarquePervert** · 09-12-2007, 11:19 AM

Originally Posted by Heckler

Thanks for the input. I had overlooked that I need the correct w to each rail, have read a little about it and trying to absorb and understand it.

From my limited understanding, a PSU has something like 4 rails, a 12v, 5v and some others. The CPU will draw power from the 12v rail, and as you pointed out the 2800+ CPU has a max draw of upto 74w. The 3 USB dongles each have a draw of around 4-5w and use the 5v rail I believe.

Three rails: 12v, 5v and 3.3v.

Not sure on which rail the AGP card (around 25-35w) is on, although I think 8x AGP uses 1.5v, memory, DVD, HD and case fans I have no idea which rail they would be on at present.

Fans usually draw 12v. Some draw 5v, though.

I need to break down my power needs and find the right PSU to meet them... it's not enough to say my max need is 219w and get a 220w PSU if it's not supplying enough to the right rails.

That's good thinking.
According to your specs, there are some things that you can change out to save some power. I believe you specced a full-size optical drive, whcih would draw both 12v & 5v. A laptop drive will draw only 5v.
Also, the 3D card isn't really needed for the car, so a lower-power video card could be substituted, further reducing power draw. In most cases, onboard video is more than sufficient for in-car use.

See, I do learn stuff from time to time.

It's always a good day when you learn something new.

Just spoke to a colleague at work as I was checking the DSATX specs you mentioned, btu was confused by the volts/amps thing. he explained that if I multiply the voltage by the ampage, I get the wattage. So the DSATX has a nominal 12amps Peak 15amps on the 12v rail, giving a range of 144-180w. More than enough to power the CPU... if anything, a little bit of overkill. Using the same sort of calculations for the 5v, 3.3v rails gives me more than enough power.

Does that sound about right?

Yup.

You mentioned they also have the start up shutdown controller built in, so potentially saving me money buying 2 things when 1 will do, even if it's a little more expensive.

That, plus it's all contained on a single circuit board, which makes for a cleaner install, in my opinion.

My current head unit can power up the CD changer when it's switched on. Is it possible to do the same thing with a motorised touchscreen, so when I power it up it boots the carpc? I'm assuming I just need to make sure I have a screen with a remote power feed like the Pioneer headunit. I've decided to get rid of the headunit and use amps for sound as I just don't ahve the dash space for both.

That's the whole purpose of a SSDC (startup/shutdown controller). It senses when the ignition is on and initiates booting the PC. When you turn the key off, it will trigger shutdown of the PC (or hibernation or standby, depending on how your power settings).

**Heckler** · 09-12-2007, 02:40 PM

OK, that's starting to make more sense now. Not really an option to start buying new components as what I'm using is what I have spare. With the cost of buying the motorised screen and PSU, along with the other wiring and cables... budget is maxed out.

**BiG K** · 09-12-2007, 03:46 PM

I was just about to post up with buying a new mobo + ram + cpu might be a good idea. Anyway you can scrounge another £100??

CPU: AMD Athlon X2 BE-2300 45w Socket AM2 1.9GHz Energy Efficient 1MB L2 Cache (~3800+)

Processor you picked is most likely uses 65w of power, whilst the energy effiecient version I have picked uses 45w.

Motherboard: ECS AMD690GM-M2 V1.0A Socket AM2 AMD 690G

Tip: The chipset is derived in part from a laptops chipset. What this means, it uses less power!! Also has an ATi X1250 graphics chip onboard!!

Ram: 1Gb should be more than plenty!

Graphics card: NONE! Yup that is correct. NONE. Why you ask? Well the radeon 9600 is a low end graphics card that appeared two generations ago. These days you can get MUCH better onboard graphics, which is useful when trying to achieve a setup which uses less power and less space.

The motherboard I have picked already has a kickass graphics embedded into it. Sure, it shares the RAM from the computer, but trust me, you won't know ;-) I used to game on a AMD XP 2200+ with a onboard geforce4.........what you might not know about me, I am a hardcore gamer!! This was with only 512mb of ram with 128mb going to the onboard graphics.....I was using this until a year ago!!

Also as a bonus, if and when you want to upgrade the graphics card later on, you are free to, as it has a full PCI-e 16x slot.

Oh and one more thing, the onboard graphics card has full video acceleration features, i.e Avivo. (Enhances video playback and takes the stress off the CPU leaving it to do other things such as GPS etc)
The radeon 9600 features no such thing, its simply too old!!

All the above can be purchased from www.ebuyer.com

If you can't get the extra £100, how about just getting a better CPU?? Go on ebay and lookout for a Mobile Athlon XP.

The processor is usually found in motherboards, but plugs straight into a desktop motherboard! You get the added advangtage that it usually uses around half of the power a regular desktop chip uses!

p.s go with the most powerful PSU you can, ATX motherboards need alot of juice but roughly speaking 250w should be fine. I ran a XP 2200+, MSI K7N2G-ILSR motherboard with onboard geforce 4 graphics, 80gb 3.5" hard drive, 1 dvd rom drive, 1 cd rw drive, couple of case fans and modem on a cheapo no-name 300w PSU which held out ok!

**DarquePervert** · 09-12-2007, 03:52 PM

Hey BIG K....
While your recommendations are certainly sound.. Did you just miss the part where he said that purchasing new hardware is out of the question due to budget limitations?

**Heckler** · 09-12-2007, 04:06 PM

Thanks for the suggestions Big K, but I am limited right now by what spare parts I have lying around. I have components that will do the job for now, still got the PSU and Screen to purchase before even considering anything else.

I've got a Sempron 2400 spare, but I believe that's a 400FSB part and this MB doesn't support it, max is 333.

**2k1Toaster** · 09-12-2007, 04:26 PM

What I usually suggest and what I think would be best, is to get new stuff. Not to just throw away the old stuff, but exchange.

Reason being a mobile chip on ebay usually goes for the same price as a desktop chip.

Mobile $25USD: http://cgi.ebay.com/Intel-Mobile-Pen...QQcmdZViewItem

Desktop $20 (Some for $1 with better specs but not BIN): http://cgi.ebay.com/HP-Pentium-4-Pro...QQcmdZViewItem

So sell the cpu get a better one that is mobile. You will be out shipping but if you play your cards right you may be out on top.

Sell the mobo and get the mobile mobo. Usually desktop chip mobos are not compatable with mobile chip mobos. But they may, or maybe just need a pin adapter. Again similar pricing if you look around.

So that is how you get the best of both worlds. Low power, and out no money.

**Heckler** · 09-12-2007, 05:54 PM

I do watch ebay and am keeping my eye on a couple of shuttle systems.. if the price is right, I might grab one and sell on the 2 MB's and CPU's I have knocking around. Would be nice to wrap it all up in a nice little package like that... But the budget is, what the budget is... and that will ultimately dictate the end product.