On Mon, 29 Nov 2010, [email protected] wrote: > Brad Knowles wrote: >> This is on systems where they provide high voltage DC power direct to >> the container, so at most you need a DC-DC voltage conversion (to step >> the power down to the 5VDC and 12VDC that most computers need on >> input), which is a lot less wasteful than doing an AC-DC conversion. > > Is DC-DC much better than AC-DC? IIRC, DC-DC conversion typically uses > a switched-mode power supply (buck or boost) that's from 60-95% > efficient, or a 3-terminal regulator that's not so efficient, or a zener > diode which is terribly inefficient. Perhaps this is going off topic, > sorry.
the first step in an AC-DC power supply is to convert the AC power to DC (rectifier and filter), and then it uses the same switching technology to produce the low voltages for the system there are a couple of things in a DC powered datacenter that make it a win. 1. the DC power is typically distributed at a higher voltage than AC power, resulting in less line loss (although DC does have more of a loss than AC at the same total power, 300v DC will give you the same RMS power as ~420v AC, either of which is considerably less loss than 240v or 120v AC power) 2. the DC power is frequently distributed directly from the main UPS, which avoids the loss you get from converting the power from the UPS to the distribution voltage. In addition, converting to sine-wave output is a very inefficient process, it's almost always cleaned up by having to filter out harmonics, which throws away a fair bit of power (the naive approach of producing a square wave and then filtering ou the harmonics would throw away 1/3 of the output power IIRC). the need to do this filtering without overheating anything and without throwing away too much power is a large part of the reason that good UPS systems are so expensive. David Lang _______________________________________________ Tech mailing list [email protected] https://lists.lopsa.org/cgi-bin/mailman/listinfo/tech This list provided by the League of Professional System Administrators http://lopsa.org/
