Bargain Hardware Thread

[kladner]

Originally Posted by Mark Rose

If I were planning to run a 2 kW system, I'd spec a more efficient power supply than that, like this one that's 90%+ efficient, and save 277 watts over an 80% efficient unit.

Even with an 800 to 900 watt system, a Platinum supply made a noticeable improvement over its Gold predecessor. It is also a 1200 w supply, instead of 1 KW, so it runs a bit more in its sweet spot. On the downside, it is too long for me to put anything larger than a 92mm fan in the bottom port of the case, where previously I had a 140mm.

[Xyzzy]

Wouldn't it be more efficient to run stuff off of DC and have just one big (very efficient?) AC/DC converter?

[retina]

Originally Posted by Xyzzy

Wouldn't it be more efficient to run stuff off of DC and have just one big (very efficient?) AC/DC converter?

Only if you have superconducting cables to each cabinet and your converter is very reliable. Otherwise it is better to have lower currents for less cable loss and also to distribute the conversion among many PSU for redundancy.

[LaurV]

Originally Posted by Mark Rose

If I were planning to run a 2 kW system, I'd spec a more efficient power supply than that, like this one that's 90%+ efficient, and save 277 watts over an 80% efficient unit.

There is no such a think like 90+ for 2KW power supplies. The one you link to it is guaranteed 80+, and the specs say it is 90% when 50% load, which is a marketing trick in fact. Put it at work and measure it, like measure input and output energy and you may get 75% when under heavy load. When close to nominal, you lose by heating, switching frequency out of optimal, etc. Also, consider that most stuff in your computer runs at 5V, 3.3V, down to 1.8V. Say an average of 4V (pulled out of my butt, but let's say), then P=U*I, I=P/U, 2000W/4V=500 Amps going through all those wires. No matter what you put in between, mosfets, diodes, spaceships, per total, there are 500 amps going through all that "sheaf" of wires, which may look like in your avatar, which I love, or may look like newest mobos, which I may not love, but at the end, those 500 Amps give out a lot of heat. There is no way you could transform those 240V AC into 12V, 5V, 3.3V etc without losing a lot on the way, short of using some supercondutor wires. For example, at 50 amps you lose 0.2V in the 40 cm of (AWG) wires between the power supply and the mobo: the PSU gives 5.15V, and the mobo gets 4.95V. Measure it! This is already 0.2 from 5, or 4% of the "efficiency". Gone! Pufff!

And we talk about 300-500Amps stepped down in one or more steps (like, 1.8 core voltage, made from 3.3, made from...) not about a single stepped 50 amps.

Advertising and marketing, yeah, full!
But reality is different.

I go to bed now... Midnight here, Loy Krathong is gone, but these idiots around me just discovered firecrackers, fireworks and petards, they discover them every year, and they are very enthusiastic about making lots of noises and smoke, scaring the ghosts away, whatever, like children having new toys... In spite of official bans - every year the buildings look like after the war, and the hospitals are full with guys having accidents, damaged eyes, ears, fingers... Few cretins even try to put firecrackers in their mouth or in their asses every year, this is not a joke!... worse than darwin awards. And they don't learn...

[chris2be8]

There must be a point where you want the fans driven by a mains powered electric motor. A three phase induction motor is at least as efficient as a brushless dc motor, but doesn't go through the PSU so saves about 20% there.

The limit is the thicker insulation for mains voltage, so it doesn't scale down to only a few watts.

Chris

[danaj]

My last job upgraded their network gear and gave away the old equipment to employees. I picked up a nice Dell 3224 24-port switch. It works, but t took less than 5 minutes for my family to scream at me to turn the bloody thing off. It's a rack mount unit and has two small howling fans in the back.

[Madpoo]

Originally Posted by LaurV

...
I am still wondering how they solve all those problems. I would really like to work in a company that design or produce those toys...

Not only all that, but I've seen ambient temp differences of 5-10 degrees F between systems on the bottom of a cabinet and those on the top (of a loaded cabinet, that is).

Heat rises, and unless you have a LOT of airflow from front to back, some of the heat from the lower systems migrates up the cabinet. Now that I think about it, a top-mounted fan to vent up and out seems like it would draw air up that way on purpose, rather than rely on the systems to move the air front-back.

Besides that, some cabinets are just too stinkin' shallow to mount your network gear in the front. It's very common to mount your net gear (switches, firewalls, etc) facing backwards where there's more room for copper or fiber to stick out. Plus it helps wire routing since all the servers have their ports in the back.

But what that means is you now have the exhaust from your switches or whatever blowing from the hot aisle to the cold. Doh! But it's truly unavoidable unless you have a nice (expensive) cabinet with more room up front where the door won't crimp your fiber when you close it. Honestly, it drives me nuts that they don't take that into consideration.

I just suck it up, mount 'em backwards and put them as high up in the cabinet as I can so the heat coming out won't get "sucked" back into any server intakes.

[fivemack]

Originally Posted by Madpoo

But what that means is you now have the exhaust from your switches or whatever blowing from the hot aisle to the cold. Doh! But it's truly unavoidable unless you have a nice (expensive) cabinet with more room up front where the door won't crimp your fiber when you close it. Honestly, it drives me nuts that they don't take that into consideration.

I notice that http://www.colfaxdirect.com/store/pc...p?idCategory=7 explicitly have 'front to back airflow' and 'back to front airflow' on some of the switches. Those little box fans that 1U devices use look as if they rotate through 180 degrees without all that much kludging.

[Xyzzy]

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[Mark Rose]

Originally Posted by Xyzzy

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Pretty sure I saw that on /r/cableporn the other day.

[xilman]

Originally Posted by Xyzzy

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Extremely rare that you see network cables that tidily arranged. Usually looks like a plate of spaghetti.