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

--- Quote from: tautech on May 24, 2020, 01:55:10 am ---You cannot assess a PSU with light bulb loads OR its capability if loading only one rail !

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yup on 12V rail, i can see its less than half the 450W PSU rating, ie 18A, so its only half the story. btw, last time i bought Gigabyte brand ATX PSUs for my PC, decent price. both died prematurely in less than a year, the second one only for few weeks, they only have nice nylon wires grouping sheathing, cute big fans and quality like exterior black paint, but functionally abysmal. then i thought what the heck, let me just buy the cheap $20 one (TronMonxter from Tatu) its surprised me when they can survive for like 4-6 years. the second one i just dismantled not because it blows up dead, its still working, its just the wiring near connectors becomes stiffen and broken in few pins and places making my PC shut off from time to time for sometime now. now i cant stand it so my PC is on a new cheapo PSU again only starts working for few days now, no more intermittent shut off no more corrupted hibernated data on power up. i keep reusing the nice nylon sheathing power connectors that i stripped from Gigabyte PSU to get more connectors for my many HDD/SDD/DVD etc because the cheap one has too few on it, so the dead Gigabyte is not entirely useless. i will keep 1 or 2 PSU unit in stock bought every year or 2, coz i know the working one will sometime failed unexpectedly, so keeping in stock will not leave me in the dark for a day or 2 while finding a shop that can supply me a PSU. some of them are even dirt cheap like $10 i can buy 2 or 3 units in one receipt if i want to, but i dont want to occupy much of my storage space there are many more items to store, not just ATX PSUs. so on rare occasion, this is where you buy cheaper to get better product..
wraper:

--- Quote from: Mechatrommer on May 24, 2020, 11:09:16 am ---yup on 12V rail, i can see its less than half the 450W PSU rating, ie 18A, so its only half the story.
--- End quote ---
Particular PSU has 42A/504W rating on 12V rail out of 550W total. Any modern half-decent ATX PSU has at least 80-90% of total power rating on 12V rail.
PKTKS:

--- Quote from: Mechatrommer on May 24, 2020, 11:09:16 am ---
--- Quote from: tautech on May 24, 2020, 01:55:10 am ---You cannot assess a PSU with light bulb loads OR its capability if loading only one rail !

--- End quote ---

--- End quote ---

TRUE.

The ATX  sticker ratings are meaningless - they just sum the rails.

Making tests on a single rail is also meaningless - different supervisors
sample the output in different ways.

Cheap ATX up to 500W **VERY CAREFUL CHOSEN**  can deliver
up to 300W on a well balanced load.

Apart this you have a bad setup.
I do have a lot of those cheapos - they work fine if proper balanced

Aerocool VX series can deliver 350W just fine in well balanced systems

Half bridge cheap designs they all use cheap components and require
a proper and careful load balance for proper operation.

IT IS NOT LIKE:  "HEY 500W in a single 12V rail ... exploded?"
obvious it will explode

Paul
strawberry:
What can be found in cheap psu: They use BJT even today. Input filter cap size less than ~1uF per watt. Poorly designed control loop (oscilation, voltage overshoot !) and controller. Stadard instead of low ESR. Poor quality enemaled copper wire. Heat and loss is not a thing (POWER). Rock and sand do not improve encapsolated psu heat disipation. Poor conductivity silicone rubber thermal pads.

500w psu have to disipate ~100w@80% of heat.
wraper:
Photo of this trash

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