Author Topic: switching-PSUs: why can't you usually exceed the 50% of declared power?  (Read 11748 times)

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Online bdunham7

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FWIW, it's a myth that higher efficiency power supplies save you a lot of money on your electric bills. Do the math.


Perhaps some people buy high efficiency PSUs for reasons other than saving a lot of money on their electric bill.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline wraper

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FWIW, it's a myth that higher efficiency power supplies save you a lot of money on your electric bills. Do the math.


Perhaps some people buy high efficiency PSUs for reasons other than saving a lot of money on their electric bill.
The thing is in the end you don't save anything by buying trash power supply. If you don't save, what's the reason to buy trash?
 
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Offline engrguy42

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Why do we have this inrush of 11-year-old* gaming kids spewing 500 posts worth of arrogant bullshit in no time, on such fine engineering forum?

*) Physical or mental, doesn't matter

Is it the new general computing section?

I especially like the ones who crank their GPU's to max while sitting on their butts playing video games for 14 hours a day, blowing away gazillions of kWH in energy costs and waste all year, and then claim to care about a higher efficiency power supply to save $2 a year in energy costs. Or the ones who leave the 4,000 watt central air conditioner on an extra hour or two, thereby erasing much of their yearly cost savings. 
- The best engineers know enough to realize they don't know nuthin'...
- Those who agree with you can do no wrong. Those who disagree can do no right.
- I'm always amazed at how many people "already knew that" after you explain it to them in detail...
 

Offline engrguy42

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FWIW, it's a myth that higher efficiency power supplies save you a lot of money on your electric bills. Do the math.


Perhaps some people buy high efficiency PSUs for reasons other than saving a lot of money on their electric bill.

And those reasons would be?
- The best engineers know enough to realize they don't know nuthin'...
- Those who agree with you can do no wrong. Those who disagree can do no right.
- I'm always amazed at how many people "already knew that" after you explain it to them in detail...
 

Offline wraper

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And those reasons would be?
Not buying junk?
 

Offline 0dbTopic starter

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Offline 0dbTopic starter

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Buy a Corsair power supply.
Even Mr.LTT looks lost.

 

Offline engrguy42

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Love how he caters to the 4 minute experts.

Actually it's kinda sad.
- The best engineers know enough to realize they don't know nuthin'...
- Those who agree with you can do no wrong. Those who disagree can do no right.
- I'm always amazed at how many people "already knew that" after you explain it to them in detail...
 

Offline chriva

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LTT is not the correct place to get that type of information.
Granted, I have a hard time not trusting Corsair since I expect them to do proper research before arranging a deal with OEM's (they don't produce their own supplies)
Many of their supplies are built by SeaSonic and CWT.

If you buy the cheapest shit they have to offer, I do suspect you get what you pay for tho...
I've stuck to their supplies with 5 year warranties and none have failed. Oldest one is 13 years old now and I've only replaced the fan since it started to make some noise but other than that, it's A OK.
Do I trust their supplies that are out of warranty? -_NO_. Should you trust any supply that is that old no matter which brand? _NO_(!)


To the actual point: Don't buy the cheapest shit you can find. It doesn't matter which manufacturer it is.
 

Offline wraper

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Love how he caters to the 4 minute experts.

Actually it's kinda sad.
What's sad? It's video on Corsair youtube channel  :palm:. What did you expect?
 

Offline wraper

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LTT is not the correct place to get that type of information.
It's not LTT. As of information, it's good enough for general public. When Corsair gets mentioned every time, what did you expect in their own video, duh.
 

Offline engrguy42

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Love how he caters to the 4 minute experts.

Actually it's kinda sad.
What's sad? It's video on Corsair youtube channel  :palm:. What did you expect?

I was talking about him and his channel, in general. As well as all the other tech youtubers who have given up and cater to those who have the attention span of a mosquito and only want to be entertained.

But I get it, you're just looking for mud to throw.
- The best engineers know enough to realize they don't know nuthin'...
- Those who agree with you can do no wrong. Those who disagree can do no right.
- I'm always amazed at how many people "already knew that" after you explain it to them in detail...
 

Offline wraper

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But I get it, you're just looking for mud to throw.
You watch infomercial on youtube channel of company that sells PSUs. Then make some dumb comment about it. WTF do you expect from infomercial?
« Last Edit: May 24, 2020, 11:44:47 pm by wraper »
 

Offline engrguy42

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But I get it, you're just looking for mud to throw.
You watch infomercial on youtube channel of company that sells PSUs. Then make some dumb comment about it. WTF do you expect from infomercial?

Boy, somebody disagrees with you in some tech discussion and you get all cranky and start hatin' on people  :D

Relax.
- The best engineers know enough to realize they don't know nuthin'...
- Those who agree with you can do no wrong. Those who disagree can do no right.
- I'm always amazed at how many people "already knew that" after you explain it to them in detail...
 

Online bdunham7

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And those reasons would be?

Let me put it another way.  Some people may end up buying high efficiency power supplies because they want a particular power supply for other reasons, such as overall quality or features, and in the process end up with a high efficiency PSU.  I can only speak definitively for myself, so the two times I can remember offhand that I went for a high-efficiency unit, what I was really after was quiet and cool, for HTPC applications.  In one, I used a 600W semi-fanless (no fan until half power) unit with very high efficiency (don't remember the number) in an application that maxes out a bit over 200W.  It also lightens the load a bit on the UPS I suppose, but that's a minor consideration.  I don't care about the power bill.

I think most high-quality units today will also be relatively high efficiency, although perhaps not the other way around.  Can you think of a counter-example, a high-quality low-efficiency PSU?  I can't.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Online bdunham7

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What I cannot understand is why. Which are the technical reasons for this? And what one should look into the circuit to have some enlightenments about the quality of the product concerning its behavior under load?

Thanks

According to many internet teardown reviews, there are a lot of PSUs with shoddy build quality, even name brands.  But that doesn't explain why they blow up, if indeed they do.  I did some GPU BitCoin mining for a few years and of course doing that you need to do it as cheaply as possible.  I had multiple rigs that used about 400W and I started with some cheapo 500W PSUs and they all failed in days or weeks.  I didn't disassemble them, so IDK what killed them, but they didn't catch on fire or fry anything, they just stopped working.  The helpful Microcenter guy suggested some generic 'PC Power and Cooling' 750W units and those worked for years.  I still have one or two.  The only two differences I'm certain of between the two PSU types are that the 500W units didn't have enough hold-up time to reliably allow my UPS to kick in, and that the larger units were significantly more efficient (as measured with a KillaWatt device) although I don't have a number offhand.  It was something like 20 or 30W less at the wall.

My best guess is that cheap no-name brands will have the cheapest, smallest parts and will be optimistically rated.  I suppose most people don't push the limits and if their overall warranty rate isn't too high things are good enough.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Offline 0dbTopic starter

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LTT is not the correct place to get that type of information.

Before buying I checked all the "customers reviews" on Amazon and on websites, including the eBay forum for consumers: 90% incorrect to what I personally measured.

I measured something like 15 units, of which 11 returned to Amazon.

The last three tests of yesterday
  • sharkoon silentstorm coolzero 650 watt (120 euro)
  • seasonic prime gold 750 watt (130 euro)
  • asus rog thor 850 watt (240 euro)

The asus rog thor is really impressive! I will return it just because it's too expensive, but it's a truly great piece of technology  :o
 

Offline 0dbTopic starter

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All tests concern
  • the ripple under load (all rails have resistive loads)
  • the operating voltages range (are ATX ranges respected?)
  • the protection against overcurrent (does it turn off immediately?)

Next weekend, I will go ahead with tests on cheap PSUs in the range 50-60 euro.

I can open the metal frame to have a look, but I am not able to say a word about internal components. I don't have any scientific criteria to test the "visual" quality.

If you show me the pic of a very bad PSU, and the pic of a very good PSU, I am not able to distinguish them without putting them on the testbench, but this kind of "visual" test is very useful when you happen to buy "frameless PSUs", just the naked circuit without any metal, from China.

My next micro-business.
 

Offline engrguy42

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LTT is not the correct place to get that type of information.

Before buying I checked all the "customers reviews" on Amazon and on websites, including the eBay forum for consumers: 90% incorrect to what I personally measured.

I measured something like 15 units, of which 11 returned to Amazon.

The last three tests of yesterday
  • sharkoon silentstorm coolzero 650 watt (120 euro)
  • seasonic prime gold 750 watt (130 euro)
  • asus rog thor 850 watt (240 euro)

The asus rog thor is really impressive! I will return it just because it's too expensive, but it's a truly great piece of technology  :o

So you bought 15 power supplies, ran them thru some tests including overloading them, performing tests on units you admit you don't understand, as well as the ATX specification which you don't understand (and apparently weren't aware of), and when they fail/blow up you return 11 of them?
- The best engineers know enough to realize they don't know nuthin'...
- Those who agree with you can do no wrong. Those who disagree can do no right.
- I'm always amazed at how many people "already knew that" after you explain it to them in detail...
 

Offline TheUnnamedNewbie

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It's also important noting that you can't just draw all that current from one supply. If a supply says 600W, it usually means x W on the 12V CPU, y W on the 12V PCIe-additional cables, z W on the 5V/3.3V rails, etc. And in the end, x+y+z will end up adding to 600W.

A 600W supply can not provide 600W on its 3.3V line. If it could, it would come with chunky cables.
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Offline madires

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What I cannot understand is why. Which are the technical reasons for this? And what one should look into the circuit to have some enlightenments about the quality of the product concerning its behavior under load?

It's the same story as why the cheap 1A USB charger for one buck (or 2 incl. shipping) delivers just 0.5A before the voltage breaks down.
 

Offline wraper

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It's also important noting that you can't just draw all that current from one supply. If a supply says 600W, it usually means x W on the 12V CPU, y W on the 12V PCIe-additional cables, z W on the 5V/3.3V rails, etc. And in the end, x+y+z will end up adding to 600W.
Not true for most and particularly any decent power supply. 12V rail is often rated close to the total power rating. Other rails have lower ratings but if you count power ratings of separate rails, usually you would come up with something like 700-750W for 600W PSU. Thus separate rail power ratings overlap within total power rating. But total output power of all rails of course should not exceed total power rating. If you see x+y+z = 600W for 600W PSU, that's a dead giveaway you are looking at piece of crap.
« Last Edit: May 25, 2020, 01:53:54 pm by wraper »
 

Offline Mechatrommer

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Not true for most and particularly any decent power supply. 12V rail is often rated close to the total power rating.
says who?

..Other rails have lower ratings but if you count power ratings of separate rails, usually you would come up with something like 700-750W for 600W PSU. Thus separate rail power ratings overlap within total power rating. But total output power of all rails of course should not exceed total power rating. If you see x+y+z = 600W for 600W PSU, that's a dead giveaway you are looking at piece of crap.
and again, says who? most likely its just "your" definition of a "crap". its like saying whoever says 1+1+1=3 is a crap math, 1+1+1 should be 4 or 5.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline PKTKS

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2cents of this jambo..

Some folks seems rather spoiled with obtaining
FULL MAXIMUM POWER from the advertised
fantasy label of those PSUs.

I never go past 70% rated single rail ...
Well balanced setup usually are fine

If you think those "value" series like Aerocool VX or KCAS
are garbage..  YOU WILL FREAK OUT WITH THESE ONES..

I use them a lot on the bench and small POS (under 150W power)
Usually with a widely available S-360 SMPS

ATX DC-DC module converters on the fly
using ANDERSON connections (above 20A)

Paul
« Last Edit: May 25, 2020, 03:06:31 pm by PKTKS »
 

Offline tunk

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I also wondered about that, so I checked these two PSUs:
Cooler Master 400W (MPX-4001-ACABW-EU) where the specs adds up to 542W.
Corsair CV450 450W (CP-9020209-EU) where the specs adds up to 617W.
« Last Edit: May 25, 2020, 02:15:58 pm by tunk »
 


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