# PSU current draw

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January 30, 2007 2:15:00 AM

Can anyone tell me how much a 430W psu draws from the wall?

I know the output power is lower than the input, ie, to get 700W of power, it draws say 800W from the power point.

As far as i can tell, iv looked on different websites, CoolerMatser, TT, Antec and so on, yet they all say "Input Current 115VAC 10A/230VAC 5A.

This can't be true. All the PSU's ive looked at, wheather 350W, 500W, or 750 all say this.

So is there a way to calculate the power draw?

(I have a cooler master eXtreme Power 430W, Thermaltake Toughpower 750W, and an AOpen 250W PSU)

More about : psu current draw

January 30, 2007 2:43:21 AM

It's a function of the PSU's efficiency rating and the combined DC load at any given time (which varies on the PC's load demand - that varies greatly with the task at hand). So if you give the PCs detailed specifications you can estimate for idle and full 100% component load at best.

If you are calculating for a UPS unit you may want to consider the power factor as well since the reactive component can affect the runtime considerably. Active PFC is your friend in that case :wink:
January 30, 2007 2:47:30 AM

Well i need to know approximately (to the nearest 100) how many watts it draws. I need to calculate it as I have limited power sockets and need to balancee the laod between powerboards/power strips.

The psu I'm trying to work out is a 430W 70% effeciency typical, with no PFC.
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January 30, 2007 2:54:47 AM

Power (Watts) = Current (Amps) x Voltage (Volts) --- P=IxE
110v x 10a = 1100w max power draw from the outlet.
Multiply that by the efficiency rating at the max load and you should get max wattage, give or take some slop. You will only use the amount of wattage that you need to power the given hardware that you have plugged into the PS. Also as you move away from the maximum rating of the PS the efficiency increases so you will draw less from the wall proportionate to the output wattage. I hope that helps.
January 30, 2007 2:58:42 AM

ahh, I see you want to estimate the worst case scenario. Well I will use my specs as an example and we will leave out the power factor...

Quote:
eXtreme PSU calc"]
System Type: Single Processor
Motherboard: Regular - Desktop
CPU: AMD Opteron 170 2000 MHz Denmark 1.35v
CPU Utilization (TDP): 100% TDP

RAM: 2 Sticks DDR SDRAM
Video Card: NVIDIA GeForce 7800 GT 470 MHz
Video Type: Single Card

IDE HDD 7200 rpm: 2 HDDs
SATA HDD: 1 HDD

DVD-ROM Drive: 1 Drive
DVD-RW/DVD+RW Drive: 1 Drive

Sound Blaster - All Models: Yes

Fans
Regular: 2 Fans 80mm; 2 Fans 120mm;

Keyboard and mouse: Yes

PSU Utilization: 100 %

Total: 339 Watts
[/url]

I will probably kill that cooler master 430w PCAR model in a relatively short amount of time

Anyhow, since I am at 340w simply divide by the estimated efficiency of 70% and I get 485w or 4.05A on a 120v circuit. Worst case of course...
January 30, 2007 2:59:39 AM

Wait, have i got this right or am i hallucinating?

230V x 5A =1150W
1150W * 0.7 (70% effeciency) = 805 Watts??????

So my 430W PSU draw 805W from the wall? Wouldn't that means its ~50% efficient then?
January 30, 2007 3:03:30 AM

Hmmm

So 430/0.7 is 614.3W draw. Does it matter whether it is 110 or 240? Here in australia, the power runs at 240V, instead of 220/230 like some other countries or 110/120 in us.
January 30, 2007 3:07:25 AM

yes 240v is half the current, I just plug-n-chug'd for my location. Really you have to calculate for the device demand not the watt rating on the psu itself - then again I guess that's the absolute worst-case :wink:
January 30, 2007 3:13:04 AM

Quote:
Wait, have i got this right or am i hallucinating?

230V x 5A =1150W
1150W * 0.7 (70% effeciency) = 805 Watts??????

So my 430W PSU draw 805W from the wall? Wouldn't that means its ~50% efficient then?

What I was saying is that if you use the rating given by the PS specs and work back that is what you would get. I don't believe that the typical efficiency of the PS is the MAX rated efficiency. I'm no PS expert but at the max rating the efficiency takes a big hit possibly even to 50-60%. More likely they rounded up on the actual max wattage that the PS would draw from the wall. Doolittle has the right idea. Work from the hardware load backwards to the outlet load understanding that the closer that you get to max wattage rating the lower the efficiency. There is a PS load calculator on these forums somewhere mpmilchfamily had a link in his sig
January 30, 2007 3:18:34 AM

When I saw 1100w I just thought you were bragging about your enermax galaxy or something

edit - I embedded the psu calc link in my quote if you want to check it out
January 30, 2007 3:20:42 AM

Quote:
When I saw 1100w I just thought you were bragging about your enermax galaxy or something

Naw, Antec Truepower 430. I'm only running an x850 oc, no need for more power.
January 30, 2007 3:27:04 AM

Quote:
When I saw 1100w I just thought you were bragging about your enermax galaxy or something

edit - I embedded the psu calc link in my quote if you want to check it out

I'm not sure what Technosponge is running. I used the PS draw in his op. With your PS calc Techno can work it out. I'm going to sleep.

Zorg
January 30, 2007 3:29:15 AM

Quote:
For \$30 you can find out exactly what any item in your house pulls from the wall.

There you are. If you would, check over what I said to make sure I didn't give misinformation.

Good Night

Zorg
a b ) Power supply
January 30, 2007 3:35:59 AM

Quote:
Well i need to know approximately (to the nearest 100) how many watts it draws. I need to calculate it as I have limited power sockets and need to balancee the laod between powerboards/power strips.

The psu I'm trying to work out is a 430W 70% effeciency typical, with no PFC.

well @ 120 volts you are talking about 560 watts(so about 130 watts lost in the conversion......mmmmm heat)

so for the 240 world you need half the current

Does this help any....

There are lots of 80+ efficiency PSU's out there....
a b ) Power supply
January 30, 2007 4:07:10 AM

I am not trying to contradict....

Why??

Transformers run most efficiently @ around 110% (i learned this when i was 5   what can i say i like to work with electronics)

In a PSU the transformers are run closed to 180-200% of there rating thanks the addition of the fan/cooing... You can over rate ANY transformer with cooling by a fan or heatsink(when you buy one the rating is for no fan or cooling...)

So power supplies @ half load are in most cases most efficient....

OCZ 700 watt....

ATX guide line

This is not meant to be a disrespectful post....just trying to clear things up a bit....

EDIT....

Thus the reason why i want a 620ish(maybe 700) watt PSU....for the efficiency/low heat....
January 30, 2007 4:22:07 AM

Quote:
A US houldhold can support allot of wattage on a single dreaker. Voltage here is at 120VAC on a 15A breaker. So you have abour 1800W to work with before you trip the breaker. Ussualy there is a breaker per room. At least in newer houses.

Having done electrical system mods in many homes, both new and old, I would never assume that breakers are organized one to a room. It totally depends on the builder and/or if the original configuration has been modded. For example, in the house I live in now, the master bedroom has 5 outlets. One of them is connected to outlets in the master bath as well as the laundry room one floor below and to the sump pump down in the basement. Two of the other outlets are also connected to outlets in the kitchen, which is one floor below. Etc., etc. I know this because I have a device that allows you to easily determine which outlets are connected to any given breaker. You can pick up one of these devices at hardware stores, electrical supply stores, Home Depot, etc.

It's good to know how your home's electrical is routed but the best thing to do for any kind of "important" electrical equipment is to run a separate circuit or two - where nothing else is on those breakers except the stuff you want on it. I'd just finished a complete mod job on our last house the year before we moved out. In this house, I'm setting up separate breakers for the home entertainment center, the server, main office PC, etc. It's a bummer when you're doing something important one one device only to have a vacuum cleaner or other load trip the breaker and shut you down.
January 30, 2007 5:34:24 AM

Quote:
I am not trying to contradict....

Why??

Transformers run most efficiently @ around 110% (i learned this when i was 5   what can i say i like to work with electronics)

In a PSU the transformers are run closed to 180-200% of there rating thanks the addition of the fan/cooing... You can over rate ANY transformer with cooling by a fan or heatsink(when you buy one the rating is for no fan or cooling...)

So power supplies @ half load are in most cases most efficient....

OCZ 700 watt....

ATX guide line

This is not meant to be a disrespectful post....just trying to clear things up a bit....

EDIT....

Thus the reason why i want a 620ish(maybe 700) watt PSU....for the efficiency/low heat....

I'm not exactly sure what you're saying, but every test I've ever seen shows that PSUs run most efficiently at or near their rated output...and by rated output, I mean the output listed in spec sheets, which on quality PSUs (not necessarilly expensive) are generally the number on the box.

So, for example, 400w PSU will hit it's peak efficiency somewhere between 350 and 400 watts....as I understand it if efficiency starts going down, it generally means it's overrated (no pun intended).

There are plenty of examples on silentpcreview.com that show these results.

What i'm not sure is if what I've seen contradicts what you're saying or not.
January 30, 2007 5:40:09 AM

FYI, in australia, we work on 240V @ 10A per socket. So a powerpoint/wall sockt/whatever the terminology in your country is, can handle 20A total.

Also, here, its not 1 Breaker per socket. Houses have power zones ie

Zone 1 - living room, kitchen sockets
Zone 2 - bedroom 1, bedroom 2, hallway sockets
Zone 3 - toilet, bathroom, laundry sockets
Zone 4 - Air conditioning
Zone 5 - Garage sockets and lights
Zone 6 - Living room, kitchen lights
Zone 7 - bed 1, 2, hallway lights
Zone 8 - toilet bathroom n laundry lights.

Each power socket zone will have a 20/30/40A breaker, depending on sockets available. Lights are usually on 10A, and AC's on 15A
January 30, 2007 5:42:53 AM

Or i could use my \$45 Digital Auto-ranging Multimeter
Albeit with a higher risk.

Thanks for the link though. Thing looks cool
January 30, 2007 5:50:10 AM

Dual phase for electric clothes dryers?
Whoa.. ours run at abt 1800W Max @ 240V so thats about 7.5A. Im assuming a standard dryer, not the industrial type.

All of the sockets in oz are 240V 10A single phase. We never have 2/3 phase, except for ducted aircons/pool heaters and pumps. Even then, most are wired direct to the fuse/switchbox, unless its "portable" or outdoors.
January 30, 2007 6:01:45 AM

Hmmm... interesting.

What types of plugs are in use over there? I've heard a lot of criticism about weak/overrated plugs/sockets being used. I don't know fi thats true.

We have 7.5/10/30/45A plugs. (2 phase is uncommon, if used, is normally direct wiring). 7.5 are for double insulated appliances, 10 have active, neutral and earth, 30/45 have 3x active, 1 neutral, 1 earth.
/ \ / \ *
| * * *
*
The 30A/45A look similar, but have thicker pins. They are these massive 10x10x20cm plugs, bright orange/see through, and have a rubebr sealed locking ring.
January 30, 2007 6:10:28 AM

Quote:
Generally we don't have a breaker higher then about 15A unless it's a dual phase socket like the ones used for electric cloths dryers.

You're talking 120V breakers? Go to Home Depot and look at the selection. It's easy to find 20 and even 30 amp breakers for 120 that are single pole/single width. I wouldn't recommend running them at full load into 14/2 but it's been done. 12/2 is rated at 20 amps. You have to be careful when you start pumping up the juice. Link!
a b ) Power supply
January 30, 2007 6:28:22 AM

I think we are talking of different things....i read on SPCR all the time.....

they show the same trend....when i say efficiency i mean how much AC power is lost(conversion=heat) to make the said DC....

Do you mean tolerance?

Like how some old Ultra PSU will start to have the 12 volt down to 11.2(thats out of the ATX spec) @ load..... thats different.....and it happens when a PSU either does not have components that will handle the current...or the transformer is pushed REAL hard.....

Most PSU's on SPCR have the same trend....around half load they are most efficient. For those who care about there power bill this is a thing to consider.

EDIT
--------------------------------
Lets not start a Electrical fight here....there is every kind of combination for that....i mean your kitchen has to have split plugs(top plug has a dif breaker then the bottom.....but they can share to the top/bottom of another plug in the kitchen....)..thats the code..so lots of breakers in there....but....in most cases...In most houses 15's are common....there are dual breakers....for 240 volts items....dryer, furnace, stove, table saw(yes its 240...not that they all are.....ohhh yeah the air compressor too....)

And there are LOTS of plugs to use......

Either way....lets not make it a fight over that....its all about the PSU
January 30, 2007 6:35:00 AM

US sockets seem overrated compared to australias. Our 30/45A pins are about 1.5times thicker. Couldn;t help noticing on the website, the terminals accepr copper or ALUMINIUM wire????

Thought they phased them out decades ago.

Sorry i cant find pics of our plugs/sockets. The the 30/45/3phase plug images are sooo rare on the net for some unknown reason.
January 30, 2007 1:48:36 PM

Quote:
Or i could use my \$45 Digital Auto-ranging Multimeter

Last year for fathers' day sears had a sale on this Craftsman Professional True RMS AC/DC Clamp Ammeter for \$80 so I grabbed it. Well it looks slightly different it was the previous years model but same function...

It's the most versatile since you can measure / calc the power draw on both sides of the PSU and gather your own effiency calculations for idle / load etc. Definitely worth the upgrade
January 30, 2007 1:53:21 PM

Quote:
It's not a single breaker per socket here. It's the same as you have it there. Just diffrent voltage and larger breakers. Generally we don't have a breaker higher then about 15A unless it's a dual phase socket like the ones used for electric cloths dryers. There are smaller breakers for smaller zones.

I'm pretty sure that the NEC has changed the code so that 20A breakers are the standard now. They also want you to install the receptacle upside down, so that the earth ground pin is up. This is so that something that is conductive can't slide down the wall and make contact with the hot and return blades. Here is a link to a handy tester that can be used to find all of the receptacles on a breaker. You plug the unit into a receptacle and then the receiver beeps when it is placed near any other receptacle on the same branch circuit. I use a similar one when installing telephone systems to ensure that the copier/microwave etc. isn't on the same circuit sending crap into the telephone power. I checked the ideal website and apparently it works on 120/220 voltages.

http://www.mytoolstore.com/ideal/ide05-07.html
January 30, 2007 3:21:52 PM

Quote:
I think we are talking of different things....i read on SPCR all the time.....

they show the same trend....when i say efficiency i mean how much AC power is lost(conversion=heat) to make the said DC....

Do you mean tolerance?
.
.
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Either way....lets not make it a fight over that....its all about the PSU

Nope I meant the same thing, and I was going off of memory. You're clearly correct. Looking at a handful of reviews, it seems that I was grouping an entire range that was at or near the max efficiency.

Bottom line is you're correct and my memory is fading fast :wink:

I relearned something, so all is not lost.
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