From: david.brown@hesbynett.no   
      
   On 27/09/2025 10:14, Thomas Koenig wrote:   
   > Michael S  schrieb:   
   >> On Fri, 26 Sep 2025 12:10:41 -0000 (UTC)   
   >> 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.   
   >>>   
   >>   
   >> Are you sure?   
   >> Indeed, in industry, outside of transportation, asynchronous AC motors   
   >> were that most wide-spread  motors by far up to 25-30 years ago. But my   
   >> imressioon was that today various type of electric motors (DC, esp.   
   >> brushlees, AC sync, AC async) enjoy similar popularity.   
   >   
   > I can only speak from poersonal experience about the industry I   
   > work in (chemical).  People used to use DC motors when they needed   
   > variable motor speed, but have now switched to asynchronous (AC)   
   > motors with frequency inverters, which usually have a 1:10 ratio   
   > of speed.  There are no DC network in chemical plants.   
   >   
   > If you have high-voltage DC system (like in an electric car) then   
   > using DC motors makes more sense.   
   >   
      
   These are not "DC motors" in the traditional sense, like brushed DC   
   motors.  The motors you use in a car have (roughly) sine wave drive   
   signals, generally 3 phases (but sometimes more).  Even motors referred   
   to as "Brushless DC motors" - "BLDC" - use AC inputs, though the   
   waveforms are more trapezoidal than sinusoidal.   
      
   And whenever you have a frequency inverter, the input to the frequency   
   is first rectified to DC, then new AC waveforms are generated using PWM   
   controlled semiconductor switches.   
      
   Really, the distinction between "DC motor" and "AC motor" is mostly   
   meaningless, other than for the smallest and cheapest (or oldest)   
   brushed DC motors.   
      
   Bigger brushed DC motors, as you say, used to be used in situations   
   where you needed speed control and the alternative was AC motors driven   
   at fixed or geared speeds directly from the 50 Hz or 60 Hz supplies.   
   And as you say, these were replaced by AC motors driven from frequency   
   inverters.  Asynchronous motors (or "induction motors") were popular at   
   first, but are not common choices now for most use-cases because   
   synchronous AC motors give better control and efficiencies.  (There are,   
   of course, many factors to consider - and sometimes asynchronous motors   
   are still the best choice.)   
      
      
   >>   
   >>>>   
   >>>> 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?   
   >>   
   >> Yes, transistors. DC-to-DC convertors are made of FETs. FETs are   
   >> transistors.   
   >   
   > I'm more used to thyristors in that role.   
   >   
      
   It's better, perhaps, to refer to "semiconductor switches" as a more   
   general term.   
      
   Thyristors are mostly outdated, and are only used now in very high power   
   situations.  Even then, they are not your granddad's thyristors, but   
   have more control for switching off as well as switching on - perhaps   
   even using light for the switching rather than electrical signals.   
   (Those are particularly nice for megavolt DC lines.)   
      
   You can happily switch multiple MW of power with a single IGBT module   
   for a could of thousand dollars.  Or you can use SiC FETs for up to a   
   few hundred kW but with much faster PWM frequencies and thus better control.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)