UPS for high load short time

Hi there, we have a server room in a place that is backed up by a diesel generator but does not have an UPS, so that the electricity can go down for about
1 minute before the generator can be fully working.
We a lot of new servers now which can draw up to 12KW, tri-phase (but it could probably be brought to single-phase 220V if needed).
We would like to buy an UPS but we have space and money constraints. All the UPSs I see at APC are both expensive and also have a low maximum load, while they have an unnededly long running time for us. We would like an UPS which can provide 12KW for just 1 minute, possibly small and cheap. Where should we look?
Thank you
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There's no getting around the need for a large, expensive UPS. Where you can skimp a little is battery capacity, but batteries are cheap compared to the cost of the rest of the unit. Extending run time is inexpensive and easy, increasing peak capacity is relatively expensive and difficult.
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You need to be careful when selecting a UPS to work with a generator. Be sure to mention this to the UPS sales guy.
Newsey

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newsey wrote:

Why, what could be the problem?
Thanks everybody
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kunt wrote:

If the UPS is expecting a stable 60 Hz (or 50 Hz) and the generator is off by a fraction of a cycle, it is considered unstable, and the UPS doesn't switch over.
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On Sat, 22 Mar 2008 22:18:57 -0400 Michael A. Terrell
| | kunt wrote: |> |> newsey wrote: |> > You need to be careful when selecting a UPS to work with a generator. |> > Be sure to mention this to the UPS sales guy. |> |> Why, what could be the problem? | | | If the UPS is expecting a stable 60 Hz (or 50 Hz) and the generator | is off by a fraction of a cycle, it is considered unstable, and the UPS | doesn't switch over.
The "double conversion continuous online" UPS types generally do not have this problem. These are the ones that convert the incoming AC power to DC, parallel it with the battery (under control of a circuit that manages how the battery is charged, etc), and invert the DC back to AC (usually with a sine wave inversion, although a cheap square wave version might exist). It's possible to make such a UPS picky about the input frequency. But ones I have looked at (and selected one from) generally support frequencies in the range 47-63 Hz. Some will make the output AC match the input frequency either exactly, or will select 50 Hz or 60 Hz depending on which is closest to the input (by default, though with many you can select the frequency for the output in the control panel). The more expensive models (usually of a lot higher capacity) tend to have the smarter features.
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Agree entirely Also this type of UPS will be more expensive.
Newsey

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The big cost of a 12KW UPS is going to be in the transformers and switching circuitry. There is just no way it's going to be "cheap." To have enough battery capacity to keep up a 12KW load you'll be forced to have more running time than you think you'll need. That's a physical limitation of how fast you can draw current from a battery. No way around it.
Bill Ranck Blacksburg, Va.
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kunt wrote:

Surplus, and buy new batteries. A few years ago there were several working units available near here for $150 -$250, plus the trucking costs. They didn't sell, and ended up at the local scrap yards for the copper.
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| Hi there, | we have a server room in a place that is backed up by a diesel generator | but does not have an UPS, so that the electricity can go down for about | 1 minute before the generator can be fully working. | | We a lot of new servers now which can draw up to 12KW, tri-phase (but it | could probably be brought to single-phase 220V if needed). | | We would like to buy an UPS but we have space and money constraints. All | the UPSs I see at APC are both expensive and also have a low maximum | load, while they have an unnededly long running time for us. | We would like an UPS which can provide 12KW for just 1 minute, possibly | small and cheap.
It won't be all that much cheaper. The electronics still has to be the same because it is load based. You need less battery capacity, but the market tends to want more capacity, not less, especially in these mid sized units. Additionally, a smaller battery would not tend to have the current delivery capability to do more power in less time.
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Liebert or Powerware are the 2 that come to mind first. But they wont be cheap. You could try the used market but the usual risks are involved.
Or you could split you loads and get a bunch of smaller units.
I am assuming you need the UPS to hold the servers until a generator kicks in.
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kunt wrote:

I haven't read the entire thread, so someone may have alrady covered this:
I have worked on several sites where this requirement was met with a specially adapted diesel generator set incorporating a very large mass flywheel kept spinning by mains power under normal conditions.
When the mains failed, the slowing mass of the flywheel generated the power until the diesel(s) had reached operating speed.
I have seen some where the flywheel itself was used to get the diesel started. Others where compressed air was used.
It may be my bad luck, but every single one of these sites had problems. Usually put down to the stored energy in the flywheel being inadequate.
The most "exciting" solution I came across was an on-site one. Baffles were welded in the U cross-section flywheel and it was filled with water, when up to speed. This attempt at increasing the mass of the flywheel without replacing it was very ingenious - unfortunately the many gallons of water decided to add their energy to the switchboard and motor, rather than the baffles, when the mains supply was removed.
A slight variation was a battery bank linked to an auxiliary motor on the drive train. When the electric supply failed, the main ac motor was automatically declutched and the auxiliary motor powered-up and clutched in. The only problem was the choice of clutches. Each consisted of a chamber containing an input and output "fanblade" and filled with oil when "clutched in". The main motor chamber was above the auxiliary one and the idea was very simple - a big plate was held in place between the two chambers (top full, bottom empty) by the incoming supply. On supply failure, the plate fell away and the oil dropped into the lower chamber. Thus making sure that it wasn't possible for both clutches to be engaged simultaneously and prducing something that was extremely simple.
You can probably guess what happened..
-- Sue
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