Total vs Available power?

[OBLIVIONLORD]

http://www.overclockers.com.au/wiki/Images/f/fa/AntecNeoHe430w.png

What is the difference from Available power and Total power on a PSU? You can get the Max combined 12v amps using the figures on the label in the above link by dividing 384w into 12v which equates to 32a, but what does the 'Total Power' consist of?

Second question... Are the 5v and 3.3v driven by their own independent power source which is the reason why the chart shows each rail separately? Perhaps the 3.3v and 5v are powered by the same source that powers the 12v and just allows the PSU to distribute it accordingly?

Thanks

[Neuromancer]

Well somehow your math is right although your formula is wrong. AMps time volts is wattage.. you can not divide wattage into voltsage and get teh amperage. you dividw wattage by the voltage...

Semantics maybe, but as human beings, semantics is all we have.

As for "total power" it should say right on the side of your PSU. If you have a good PSU than you can rely on that. (price paid is not = to quality nor is brand name)

If you bought your PSU used.. you can pretty much throw it outhe windows as well.

Never EVER buy a PSU used. I still do it, cuz money is tight, and I have NEVER bought a PSU that read the rails right EVER when I bought used.

But apart from all that...

It really depends on your usage.. .most PSUs have problems with crossloading, newer PSUs are geared towards modern systems (IE a high 12v rating) older PSU had high 3 and 5 volt ratings which is a simple way to boost Wattage rating of the PSU without actually being beneficial in anyway.

(sorry 40Amp 5v rail on a 500W toughpower psu... when was that EVER necessary??)

Argh.


total amps should be listed on your PSU.. if not, post your model. OW or someone will come along and break it down for you. (I am far too lazy, I can give you keywords for searching for yourself though :) )

www.jonnyguru.com search there for your PSU, if that does not work, google your model number and OEM find out who makes it, look for other models that are the same and look at JG for that unit :)

pretty simple really :)

EDIT: looking tat the pic, is that a n antec true power unit?

[burebista]

Available power is maximum ratings for each rail. Total power is what your PSU can deliver.
So let's say that you need maximum fom +12V (384W) so available for other rails remain 46W. If you need more watts then OCP kicks in and PSU should shut down nicely.

Second question depends on PSU design. Those are group regulated (all rails are powered from +12V) or independent regulated (+12V has his own circuit and +3.3 and +5V are on separate circuit). Group regulated PSU's hate crossload (ie heavy load on +12V and light load on other rails or vice versa) and indy regulated PSU's are immune to crossload.

[MARCI]

Your 650 Watt PSU (for example) has a TOTAL load rating of 650W

It may have 2 12v rails listed that are each rated for 30A, which would be 360W.

You cannot run that load on both rails simultaneously, because that would exceed the TOTAL rating, but one rail can handle up to a 30A draw.


These numbers are made up, I don't know what PSU you're looking at, it's ratings, nor it's ability to actually MEET those ratings. YMMV

Some very well designed PSUs are actually UNDERRATED.. IE they say the can supply 350w, when they can really handle 400 or more, but that's not recommended usage, there's no promise it will do it, or supply clean power, or won't spew fire from the back, etc.


I am not a PSU tester, guarantor, Quality Control agent, or insurer, and make no claims as to the suitability or availability of any individual unit. This advice is given as a public service, and construes no relationship between the individual giving the advice and any person reading the advice. There is no warranty stated or implied in any communication originating from this individual. If you are still reading you should move on the next post, nothing informational will follow in this post. Why are you still reading this, I told you to move along. Seriously this is getting creepy. What more do you want???? I gave my best information. Okay. If you want any more information regarding power supplys check www.jonnyguru.com (www.jonnyguru.com)

[Neuromancer]

Nice breakdown both you guys, OCF has so many member way more eloquent than I.

(And more importantly way less ramblin')

[OBLIVIONLORD]

The reason why i used my formula is because every time its used, it produces the correct outcome.

http://www.overclockers.com.au/wiki/Power_Supply_Unit

That site says...
"the 12V combined rating is 384w, or 32A (384/12=32 - amps is watts / voltage and the voltage is 12V in this case".

Here is another PSU review that uses the same formula for a PSU it tested...

http://www.pcper.com/article.php?aid=187&type=expert&pid=3

"The maximum combined load for the +12V1, +12V2 and +12V3 outputs is 38A."

It shows 456w as the combined 12v load which results in 38a from an equation of 456/12=38

Since wattage is given, you can deduce the result into an ohms law equivalent such as I=P/E.

I = Amp
P = Watt
E = Volt

This wheel even shows that this formula is valid...
http://diyaudioprojects.com/Technical/Ohms-Law/Ohms-Law-Formula-Wheel.png

Even this website uses the same formula...
http://www.simetric.co.uk/si_watts.htm

"by dividing both sides by volts you get - Watts / Volts = Amps"

Which again is showing I=P/E

Here is PSU where E=P/I is applied...
http://www.newegg.com/Product/ShowImage.aspx?CurImage=17-139-005-10.jpg&Image=17-139-005-12.jpg%2c17-139-005-14.jpg%2c17-139-005-13.jpg%2c17-139-005-10.jpg%2c17-139-005-05.jpg%2c17-139-005-06.jpg%2c17-139-005-04.jpg%2c17-139-005-03.jpg%2c17-139-005-02.jpg&S7ImageFlag=0&WaterMark=1&Item=N82E16817139005&Depa=0&Description=CORSAIR%20CMPSU-650TX%20650W%20Compatible%20with%20Core%20i7%20Pow er%20Supply

This PSU has 1 single 12v rail and on that 12v rail it states 52a as the max amperage for that rail as well as 624w for that rail.

Taking both figures you can deduce that E=P/I .. since 624/52=12

[OBLIVIONLORD]

Available power is maximum ratings for each rail. Total power is what your PSU can deliver.
So let's say that you need maximum fom +12V (384W) so available for other rails remain 46W. If you need more watts then OCP kicks in and PSU should shut down nicely.

Second question depends on PSU design. Those are group regulated (all rails are powered from +12V) or independent regulated (+12V has his own circuit and +3.3 and +5V are on separate circuit). Group regulated PSU's hate crossload (ie heavy load on +12V and light load on other rails or vice versa) and indy regulated PSU's are immune to crossload.

http://www.overclockers.com.au/wiki/Image:AntecNeoHe430w.png

If I follow you correctly then you're saying that if the max wattage for the 5v is being used which is 70w then subtracting that from the total of 430w gets you 360w would be the residual for whatever rails need it?

Same would apply to the 3.3v being 72.6w for its max wattage and take that from the total 430 gets you 357.4w.

This is of course a controlled scenario where we stress strictly 1 rail to come up with these results.

Are there only soo many capacitors or type of quality capacitors that would allow a PSU to obtain max wattage for each rail all at the same time instead of just having a total wattage rating? Such as 526.6w which equals the max wattage of 3.3v + 5v + 12v.