Home
| Calendar
| Mail Lists
| List Archives
| Desktop SIG
| Hardware Hacking SIG
Wiki | Flickr | PicasaWeb | Video | Maps & Directions | Installfests | Keysignings Linux Cafe | Meeting Notes | Linux Links | Bling | About BLU |
I think it was Apple (Apple II) that used the first switching power supply, but that was at the time when competition was limited to a few hobby computer builders (about 1977). On 10/13/2011 12:29 PM, Tom Metro wrote: > Edward Ned Harvey wrote: >> Hold it. P=VI is a DC rule. Power is more complex in AC. >> What's the difference between VA and W? >> >> If you have inefficient power supplies, you might be overpaying 30% >> for power. > You're referring to power factor: > http://en.wikipedia.org/wiki/Power_factor > > The power factor of an AC electric power system is defined as the > ratio of the real power flowing to the load over the apparent power in > the circuit,[1][2] and is a dimensionless number between 0 and 1 > (frequently expressed as a percentage, e.g. 0.5 pf = 50% pf). > [...] > Circuits containing purely resistive [loads] have a power factor of > 1.0. Circuits containing inductive or capacitive elements (electric > motors, solenoid valves, lamp ballasts, and others ) often have a > power factor below 1.0. > > So when PF=1.0, VA==Watts. The better the quality of your power supply, > the closer its PF will be to 1.0. In the last decade it has become > common for name brand computer power supplies to specify a PF as a > selling point. > > See also: > http://en.wikipedia.org/wiki/Switching_regulator#Power_factor > > for discussion of PF with respect to computer power supplies. > > >> When you're talking about 208, you're talking 3-phase. > You can attach single phase loads to a multi-phase supply, as long as > they are balanced: > http://en.wikipedia.org/wiki/Three-phase_electric_power#Single-phase_loads > > >> If you want to use 3-phase 208, you need a special power supply in the >> server. Generally you don't have such a thing... > Old power supplies used to have a 120V/240V mechanical switch. Most > modern switching supplies will work fine with any input voltage from > like 90V up to 250V (check your supply specifications). The ability to > handle a wide input range is a byproduct of the switching regulator design: > > http://en.wikipedia.org/wiki/Switching_regulator > > -Tom > -- Jerry Feldman<gaf at blu.org> Boston Linux and Unix PGP key id:3BC1EB90 PGP Key fingerprint: 49E2 C52A FC5A A31F 8D66 C0AF 7CEA 30FC 3BC1 EB90
BLU is a member of BostonUserGroups | |
We also thank MIT for the use of their facilities. |