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need help understanding passive PSU's

post #1 of 16
Thread Starter 
ok to whom it may concern (sin? phaedrus? anyone? biggrin.gif )

what are the primary differences between something like a super flower SF-500P14FG / kingwin stryker STR-500 which have LARGE heatsinks even tho it's a platinum rated unit vs something like a seasonic SS-520FL2 which has significantly smaller heatsinks yet offering 20w more rated power? both units are platinum rated so heat generation wise, there should be negligible difference so why such a large difference in thermal design?

also the up coming enermax 650w fanless unit which has SIGNIFICANTLY higher rated power yet doesn't seem to use any more heatsink then the super flower unit? what are the things I should look for in terms of evaluating that unit when it finally hits the streets? what can be the cause of it putting out so much more power while keeping cool? it's not the fan biggrin.gif and heatsink wise they are not that much different. efficiency wise they should be within a percent or 2 of each other so.... what am I looking for?

thx in advance for any wisdom smile.gif
post #2 of 16
Something to think about is the STR-500 is capable of 600W at a gold rating.
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post #3 of 16
Am no expert on the mechanical side but i think what caps they use and what temps they are rated for plays a big part

Dont think you will se any CapXon/Teapo and Samxon in units like that

Think its all Rubycon/Hitachi/Panasonic/Nippon Chemi-Con capacitors

Or am i just guessing???
Edited by shilka - 8/1/13 at 5:29pm
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post #4 of 16
Well the cooler a PSU runs the better its efficiency. PSU with smaller heat sinks may drop under the rated efficiency if the get hot enough. So having a larger heatsinks ensure better efficiency in warmer environment.

Then there is the question of the quality and "size" of the internals. Better internals generate less heat as they allow current to flow more freely and thus a unit with exceptionally good internals needs less cooling then a unit with lower tier parts.

So at the end of the day its a balancing act for the PSU manufacturers. Spend money on the internals and save on the heatsinks or use cheaper internals and slap on a bigger piece of copper/aluminium.

The there are naturally thous that make sub par units that have both cheap parts and small heatsinks and thus can not necessarily keep up the rated efficiency if the unit is run in warm conditions. Similarly there is also companies that make premium products that not only use excellent parts but also use large sized heatsinks in order to ensure the unit performs well even in adverse conditions.
    
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post #5 of 16
Quote:
Originally Posted by Bit_reaper View Post

Well the cooler a PSU runs the better its efficiency. .

Its the other way around
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post #6 of 16
Quote:
Originally Posted by shilka View Post

Its the other way around

Nope. Why do you think supper conductors are cooled with LN2? The more resistance the more power is wasted. That translates in to efficiency.

http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

A PSU in a 20C room will be more efficient than a PSU in a 30C room. Similarly if you have two PSU's with identical internals, the one with better cooling will be more efficient.
Edited by Bit_reaper - 8/1/13 at 5:54pm
    
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post #7 of 16
Quote:
Originally Posted by Bit_reaper View Post

Nope. Why do you think supper conductors are cooled with LN2? The more resistance the more power is wasted. That translates in to efficiency.

http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

A PSU in a 20C room will be more efficient than a PSU in a 30C room. Similarly if you have to PSU's with identical internals the one with better cooling will be more efficient.

Well then it works both ways

Higher efficiency means less power wasted less wasted less turned into heat less heat = better
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post #8 of 16
Thread Starter 
ok let me try to explain my question alittle better.

ALL of the units in question are "super premium" units. ONLY the best components are used for a fanless unit for the obvious reason and ALL units involved are "true" platinum rated units (anything less would require a fan at max load) so what makes 1 unit requiring a LARGE heatsink (super flower) better/worse then another unit with relatively small heatsink (seasonic). reputation of the manufacture and their respective knowledge in the field of PSU construction are not up for debate. both are the top of their class in terms of reputation. components used for such premium units aren't going to be in question either so that's not really an issue.

so what makes a 520w use smaller heatsinks then a 500w unit? and how can enermax (also not a bad PSU company, maybe not in the same league as seasonic or super flower, but not bad either) claim a unit that can go 650w completely fanless? what should i be looking for in terms of reviews or components used to justify this vast improvement in rated power output?
post #9 of 16
Actually Enermax is right up there with Seasonic and SF. As for the larger heat sinks in the SF design, simply put, it's overdone... it's a proper fanless unit that can dissipate the conversion generated heat under no airflow whatsoever, Seasonic on the other hand leverages the fact that no case is absolutely neutral when it comes to air pressure, so whether it is positive or negative, there's always some air moving through the perforations of the PSU. Not that it wouldn't work in the absence of any airflow, it's just that it's preferable to have some with the Seasonic unit, the same thing is true for the Super Flower Golden King 550W, not a fanless unit per se, but the fan only engages when you reach the ~500W mark (DC draw, it varies with efficiency which in turn varies with AC input voltage).
The Golden King 550 uses the exact same topology as the Golden Silent 500 (which only sees the PCB slightly rearranged to accommodate the massive heat sinks), the Golden King engages the fan at high loads for lifetime reliability reasons (caps degrade when baked), and it does have similarly sized heat sinks to those inside the Seasonic fanless units, on the other had, the Golden Silent unit couldn't care less, the entire casing takes care of dissipation.

Anyway, unless you're building a fanless system (fanless CPU cooler, fanless VGA, etc), there's little point in buying a fanless PSU these days (unless, of course, you get a fantastic deal on such a unit).
Edited by Original Sin - 8/1/13 at 7:38pm
post #10 of 16
I'm not so sure about absolute-best components or anything like that...

Also, I'm not really an expert, but maybe I have some insights you might not have thought about.


The majority of the heat is produced by the active electronics in the circuit, the silicon transistor-based stuff. It's switching losses from a little charge that gets built up and is discharged every cycle (from stray capacitive elements of gates and so on), stray resistances here and there, and so on. These high-power silicon components through which most of the power passes through are what get heatsinked. At higher operating temperatures, the amount of power they can handle decreases, and the amount of heat dissipated also increases.

When we're looking at fanless units, the most fragile components are some of the active electronics and then the capacitors (on a normal unit, the fan is also a concern for longevity). Note that the capacitors are not heatsinked, and they respond poorly to higher temperatures.

If you're thinking about handling higher power, you could (1) choose higher-grade components in some sense, like lower Rds(on) or possibly from some trusted manufacturer or whatnot, (2) increase the number of components in parallel like the number of +12V rectifiers so each handles less current and is in a less stressful part of the operating curve, or (3) use a better heatsink to reduce the operating temperatures a little.

As for the capacitors, depends on what their role is in the circuit and the temperatures they'll expect to see. If one is in an area that won't get much convective airflow and is right next to one of those big, hot heatsinks, that's a bad sign. Their survival depends on the physical layout and thus temps they'll see, how much the capacitors are asked to filter, quality, and so on.

It looks like the Enermax is a little larger than the others; possibly this results in increased component spacing and lower temps to certain stuff and/or more parallel and redundant electronics.

Also keep in mind that some companies may simply be more cavalier about rated wattages, warranties, and fanless units. Some fanless power supplies are more overbuilt than others, and they're counting on different amounts of airflow. Pretty much everyone using a fanless power supply doesn't like noise and isn't using really high-power multi-GPU systems that are relatively noisy, so you can mostly count on them not to actually run the fanless power supply near capacity much.
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