Power Supply Section in A+ Book

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Not in the book (or, probably, the exam) but in the real world it is useful to remember that hard drives take a high current when starting to spin up the drive. After that the current drops as it merely has to maintain the rotation. This was much worse in the old days of 5 1/4" drives as the intertia was huge on those!

SCSI has the ability to 'spin-up' drives on command, so a large array of drives doesn't all come on at once and fry the PSU.

Again in the real world, as well as the overall wattage of the supply I tend to look at the possible currents on the two important voltage lines - 5V and 12V. It is possible for a PSU to apparantly have enough overall power, but not enough 12V capacity.

I'll restate my first comment - all this is probably beyond what A+ needs, but is needed in real life.

Harry.

 

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Taken from page 304 [yeah, finally picking up some steam ]:

"Although it's tempting to recommend that you get the most powerful power supply you can afford, such a recommendation misses crucial points. The more a power supply can produce, the more AC it draws and the more heat it produces. Thus, you need a more powerful exhaust fan or fans, which generate more noise. Having a pc sound like a helicopter perhaps doesn't bother the gamer in real life in the heat of flying a fighter plane, but such a noise level is unacceptable in a box that's part of a home entertainment center. Plus, putting a monster power supply in a pc that will do nothing but surf the internet and do email is a phenomenal waste of money and electricity."

 

so MM is saying that when you buy a PSU, base it on your circumstances, e.g. no point in having a 400w psu if your only web browsing or just surfing the net, but if your a hardcore gamer, then you'll need one...

 

well put, from reading all of this I still don't know which overall wattage to get for a new pc. I understand about looking for the different features in a PSU and about calculating the wattage requirements of each "major" component but how do you account for all of the smaller stuff? Meaning, I jot down the wattage requirement for HD, CD-ROM, DVD e.t.c and add them all up, let's say all of these bigger components add up to 300watts so then should I get a 400, 500 or 600 to cover the rest of the smaller stuff and to have extra power for future add-ons/upgrades?

 

i think as long as you have worked out all of your major juice munching devices then thats the main part done, obviously we dont know what devices we will be getting next year to upgrade on our computers, but the main upgrades are generally more usbs, harddrives or little devices, unless of course you upgrade your gfx card each year, if you dont then i think an extra 100-150w plus what you have already calcuated should be ok, thats my opionon,

for me since building my comp in 2004? i have only upgraded my gfx card (free), got a front firewire/usb slot thing (floppy drive size) and a harddrive (120gb)... thats it...

 

what do you guys think about this?

http://extreme.outervision.com/psucalculator.jsp

 

That seems to be a good link - but i cant tell you whether the calculation at the end is correct, but im sure there is someone here that could...

 

IMHO you shouldn't try and be too 'acurate' on this. These days the PSU is usualy 300W for ordinary machines and 400W or so for gamers machines. You only need to get serious if you start using extreme hardware.

Big servers are, of course, a different matter.

Harry.

 

I've used that before when I was looking to get a more powerful graphics card. It calculated that I should just about be able to manage it on my 300W PSU and I haven't had any problems since getting the graphics card.

So either the calculation is spot on, or it's a little over in its estimates - either way it means you wont be under-powered

Something to look out for when buying a PSU is its efficency. Some cheap ones have a low efficiency so a 500W PSU at 80% efficiency will only supply 400W. But I don't think you need to know that for the A+

 

My point was, it's no good buying a PSU that is only borderlne adequate for your needs. My PSU is only 350w and I have upgraded my PC beyond recognition, even installing a graphics card that requires a 400w PSU, and I have no power related issues at all but for all I know, one more device added to the system may tilt the balance.
I still disagree with what MM says about needing increased cooling for a bigger PSU. Any PSU must have adequate cooling built into it or it would be a danger. Also, you can get some very quiet (even fanless I think) PSUs these days.

 

I think it would be great if we could draw up a simple graphic showing the movement of electricity, eg. I picture a guy standing in front of a regular outlet in the wall with a screwdriver into one of the slots of the outlet, there will be a pic of the 3 wires in the outlet, this way we can show the effects of grounding and eveything related to simple electricity, something which I personally think every Tech should know both for his/her own safety and the safety of the pc. I have come across many tech's who don't know anything about grounding equipment in particular and I sure as hell don't want to be one of those [no offense meant to anyone].

I realize that we don't need this for the A+ but guys, really, what would happen if you come across someone else's pc that has an electrical short or noise or some other electrical problem, wouldn't it be very embarassing to turn and tell that person that you don't know how to fix the problem or that you will have to consult with someone else?

What I am proposing here is something that will not take much time and effort and this is something we could all do together so when we are finished with the project we will ALL understand the basics of electricity that will help us.

Ok, so I propose we draw the graphic first then all of you more experienced guys here who understands this stuff can map out the flow of the electricity for us and give brief explanations then whichever of us has questions we can ask those questions relating to the graphic so it will be easier for everyone to follow, any volunteers on this project please? I will create a new thread for this.

 

There are loads of online calculators to help you calculate your power requirements. Good for theoretical situations as well as looking at what you may need if you are going to upgrade later and want to get a PSU thats going to give you a bit headroom

http://extreme.outervision.com/psucalculator.jsp for example.

As Baba O'Riley says, the PSU will draw as much current as it needs, up to it's rating, so overheating shouldn't be an issue. The better PSU's will also have either a manual adjustment a built in sensor for the fan speed so heat shouldn't be an issue.

Lord Deckard.