katzman@harvard.ARPA (Cynthia Katzman) (09/26/85)
Ok... so I get the message-net.lan doesn't mind getting filled with discussion on Broadband Cable issues. Good. We are considering investing in either a UPS or a Stand-by power supply. My gut feeling is that we don't really need to spend the money on a UPS for the cable plant, nor the head-end equipment. (including a 68000 micro processor made by Momentum which is the Sytek Network Control Center.) I really think that a Stand-by would do the trick. (When we have power failures, the NCC is usually not affected.) Anyway, while I have calculated the max. amps needed to protect everything, I have not figured out how long I have before the cable plant goes out, and users, both data and video, are affected. (All my amps., both trunk and distribution, and presently powered by the Power Supply in the Head-end.) I'm seperating the back-up power for the cable plant, and that of the actual Head-end equipment. Does anyone out there have stand-by power? Does anyone have an automatic switch or some protection should the main PS fail? My feeling is that the cable plant could most likely support a 20 milisecond AC out, (for stand-by power) but I really don't have any facts to support this. Cynthia Katzman katzman@harvard.uucp
phil@amdcad.UUCP (Phil Ngai) (09/29/85)
I expect that most standby power supplies can switch fast enough to
keep your equipment alive. We are using one from Topaz which switches
in about 10 mS. As long as it is less than one cycle of 60 Hz power
you will probably be in good shape. I tested the Topaz on a florescent
lamp: it stayed alive.
If you do go with the much cheaper standby instead of a true UPS, make
sure you have a regular testing program for the standby. (e.g. unplug
it from the wall every month or so) Otherwise you could be driving
around with a flat spare.
--
God made atheists too.
Phil Ngai (408) 749-5720
UUCP: {ucbvax,decwrl,ihnp4,allegra}!amdcad!phil
ARPA: amdcad!phil@decwrl.ARPAhes@ecsvax.UUCP (Henry Schaffer) (09/29/85)
> I expect that most standby power supplies can switch fast enough to > keep your equipment alive. We are using one ... which switches > in about 10 mS. > -- > Phil Ngai (408) 749-5720 When switching the AC power to equipment, and trying to do it fast - sometimes problems relating to phase coherency of the power sources can arise. In high current equipment (which your's probably is not) you can have a very high current inrush if your standby current is switched in out of phase with the current which previously was there. (It has to do with the remanant magnetic field in the transformer. It can get particularly tricky when powering large AC motors.) This doesn't happen (of course) when switching between two DC sources. --henry schaffer
phil@amdcad.UUCP (Phil Ngai) (10/01/85)
In article <505@ecsvax.UUCP> hes@ecsvax.UUCP (Henry Schaffer) writes: > When switching the AC power to equipment, and trying to do it >fast - sometimes problems relating to phase coherency of the power >sources can arise. Good point. I should add that our unit is a 400VA model. -- Arthur Rudolph believed that technology is morally neutral and so, therefore, are those who create it. Phil Ngai +1 408 749-5720 UUCP: {ucbvax,decwrl,ihnp4,allegra}!amdcad!phil ARPA: amdcad!phil@decwrl.ARPA