Electronics > Projects, Designs, and Technical Stuff
switching-PSUs: why can't you usually exceed the 50% of declared power?
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madires:

--- Quote from: 0db on May 23, 2020, 08:43:06 pm ---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?

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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.
wraper:

--- Quote from: TheUnnamedNewbie on May 25, 2020, 10:36:57 am ---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.

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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. 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.
Mechatrommer:

--- Quote from: wraper on May 25, 2020, 01:51:28 pm ---Not true for most and particularly any decent power supply. 12V rail is often rated close to the total power rating.

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says who?


--- Quote from: wraper on May 25, 2020, 01:51:28 pm ---..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.

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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.
PKTKS:
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
tunk:
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.
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