From: david.brown@hesbynett.no   
      
   On 26/09/2025 14:10, Thomas Koenig wrote:   
   > BGB  schrieb:   
   >   
   >> Brings up a thought: 960VDC is a semi-common voltage in industrial   
   >> applications IIRC.   
   >   
   > I've never encountered that voltage.  Direct current motors are   
   > also mostly being phased out (pun intended) by asynchronous motors   
   > with frequency inverters.   
   >   
      
   True DC motors - with brushes - are rarely found outside of very small   
   motors (where they are cheap and simple).  But there are a wide variety   
   of AC motors controlled in many different ways.  Asynchronous AC motors   
   are only one type.  There are lots of other topologies for motors and   
   their controllers, with different pros and cons and suitable applications.   
      
   >> What if, opposed to each computer using its own power-supply (from 120   
   >> or 240 VAC), it uses a buck converter, say, 960VDC -> 12VDC.   
   >   
   > That makes little sense.  If you're going to distribute power,   
   > distribute it as AC so you save one transformer.   
   >   
      
   There are lots of advantages of distributing power as DC.  Transformers   
   are only a good choice at higher voltages - once you get to the levels   
   that can be handled well by semiconductor switches, they are smaller and   
   more efficient, and work best for DC-to-DC.  1200V switches are cheap   
   and common now, though there are devices that handle a few thousand   
   volts.  Electric car charger standards are 400V and 800V, with some new   
   ones at 1000V or up to 1500V.   
      
   It makes to distribute locally at something like 48V or 60V DC.   
   Connections are simpler, you can take it directly from an UPS, and the   
   local conversions to low voltage power lines is simpler than with 120V   
   or 240V AC.   
      
   So for a data centre, using perhaps 800V DC (taking advantage of the   
   electric car industry standards) to the rack, then 48V DC to the devices   
   on the rack would seem a good setup to me.  DC also makes life much   
   easier and more efficient when you have UPSs and battery backup -   
   locally in a rack, or wider in the higher level supply.   
      
      
   >>   
   >> Or, 2-stage, say:   
   >>     960V -> 192V (with 960V to each rack).   
   >>     192V ->  12V (with 192V to each server).   
   >>   
   >> Where the second stage drop could use slightly cheaper transistors,   
   >   
   > Transistors?   
      
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