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19452
April 16th, 2004 14:00
Power circuit requirements for UPS and Servers
I'm trying to determine how many additional electrical circuits to have installed in my machine room. I've recently purchased 3 DELL 1440 VA Smart-UPS units to power three rack mounted servers. I expect to add as many as 3 more UPS powered servers. The servers are DellPowerEdge 1750's.
I currently have 1-120V power outlet (with 2 plugs/recepticles). The electrician tells me that the outlet is on a 20 amp circuit (attached to an emergency generator). According to his math, the UPS units would consume 18.6 amps each, I therefore need one 20 amp circuit for each UPS. Is that correct? He was not sure about the power requirements of the UPS, but he calculated 18.6 assuming the UPS was 2.2 KVA: 2.2 * 1000 / 118 volts = 18.6 Amps.
Is it true that I need a separate 20 amp circuit for each UPS, or could I attach two or more to each circuit (how many can I attach to each circuit). The cost of these circuits may be expensive since they are powered by an emergency power generator.
Quino
153 Posts
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April 16th, 2004 15:00
We always connect each UPS to a distinct circuit. You load of 1 server per UPS would not be at the max load, however..... but it is good practice to assume max load on a UPS and plan circuits accordingly, so you dont get into trouble in the future.
Why are you using three UPS's to power three servers? One UPS could handle that load?
We typically install two circuits to a rack, and then two UPS's..... for redundancy (not for load) and then connect one power supply per server to the upper UPS, and the other power supply to the lower UPS. Even this is overkill for most..... I am curious why you have a single UPS per server?
joel_hammond
2 Posts
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April 16th, 2004 17:00
Thanks for the response. Perhaps I don't need so many UPS units. The reason I was using multiple UPS units was so a power failure at the UPS would trigger a gracefull shutdown on the server. Since each UPS has only one serial connection, any other server would not get the message that the power was about to go off. I knew that a pricier UPS and software would allow multiple servers running off a single UPS but I never explored the options. My new UPS' came with Powerchute Business Edition. I have'nt installed it so I don't know what it does. Maybe it will do the trick.
Joel
Quino
153 Posts
0
April 16th, 2004 20:00
Yeah, sure sounds like you have UPS overkill!
Just to get graceful shutdowns.... you have lots of options. Using a single UPS, most of the APC Smart-UPS line has a "smartslot" in which you can add a $100 card:
http://www.cdw.com/shop/products/default.aspx?EDC=048353
Which is a serial port expander which allows you to add two more servers to monitor the UPS.
Another option, is to simply create a shutdown script on a single server, and when the UPS reaches a critical battery condition, have the UPS software execute that script, which first shuts down the other servers, and then shuts itself down.
Lots of options.... and cheaper than three UPS's... with distinct power circuits for sure.