Rack Mounted UPS In Series

[Anonymous user]

Do you have any information on or heard of rack mounted UPS units in series with the house ups system? A Customer wants to do this in my data center.

[BillP]

i have not. what model UPS are you looking at? what are they hoping to achieve with this set up? what type of UPS home system do they have?

[Anonymous user]

Hi,

House UPS's are Liebert 610s, I found this link this is considered daisy chaining,

http://emea-en.apc.com/app/answers/detail/a_id/397/~/daisy-chaining-ups

[BillP]

oh ok, you should not daisy chain UPSs for those reasons. i wasnt sure if they were trying to achieve something else such as monitoring them all or something else, i dont even know what.

[BillP]

i believe they intend to connect the units in a parallel configuration, either redundant or capacitive installation.
in any case, the liebert 610 can be paralleled by a sync box. APC would not be able to assist with this request, as it is a 3rd party unit.

[upsguy_apc]

I can't begin to think of a reason you would want to parallel rack mount UPS for either capacity or redundancy.... The hassle and cost couldn't justify any gains of doing this.

Same goes for UPS in series. The only recommended method is with Large UPS systems and that is to feed the Bypass of the Primary UPS with the output of the secondary UPS. This is called ISO Redundant and would accomplish the same basic function. Most small rack mount UPS however do not have the option of dual mains input.

If you really need the redundancy of two UPS I would recommend installing a rackmount transfer switch which can be fed by the House UPS and the Rackmount UPS and in the event either fails the load would still have a UPS source available.

http://www.apc.com/products/family/index.cfm?id=14

[Anonymous user]

It is not uncommon to do this, many colocation customers in large data centres install their own UPS which is naturally fed off the site UPS. As long as there is say 5 times size difference between the two it shouldn't cause a problem.

[upsguy_apc]

Adding in components between a protected source and the load only decreases reliability. As parts count goes up you increase single points of failure. The idea of a UPS feed by a UPS may seem like a good idea but a small single phase UPS isn't nearly as reliable as a large 3 phase UPS system and your only introducing a greater risk of failure of doing this.

Just because some people do this in colocation data centers doesn't make it right. A proper colo data center should have a reliability factor multiples higher than a single UPS. If you put a small UPS in series with the protected power path it would negate the entire reason for placing your servers in a colocation data center in the first place.

As stated before if you really want to add an additional UPS for redundancy, use the redundant power supply in the server. If its a single corded device I would use an ATS if you feel your primary UPS is unreliable.

[Anonymous user]

There are many reasons to be in a colo other than UPS, and while it does introduce another potential failure point there are always stories of major data centres going down when they really shouldn't. At least if a local UPS is used the owner has control over that and can take whatever steps they feel are necessary to maintain uptime such as replacing the whole UPS every 3 years with a new one if they wish.

The OP was asking whether it is possible and Yes it is, the additional failure point is their customer's problem.

[BillP · Accepted solution]

Rack mounting refers to the Computer servers designed for rack-mounting can include a number of extra features to make the server easy to use in the rack:

The sliding rails can lock in various extended positions to prevent the equipment from moving when extended out from the rack for service.
The server itself might have locking pins on the sides that just drop into slots on the extended rail assembly, in a manner similar to a removable kitchen drawer. This permits a very easy server installation and removal since there is no need for the server to be held in midair while someone fastens each rail to the sides of the server with screws.
Some manufacturers of rack-mount hardware include a folding cable tray behind the server, so that the cables are held into a neat and tidy folded channel when inside the rack, but can unfold out into a long strip when pulled out of the rack, allowing the server to continue to be plugged in and operating normally even while fully extended and hanging in midair in front of the rack. This piece of equipment thus simplifies maintenance, but at the cost of providing a restriction to airflow.
Rack-optimized servers might duplicate indicator lights on the front and rear of the rack to help identify a machine needing attention, or provide a separate "identify" LED indicators on both sides of the server (which can be turned on in software or by pushing an associated button). Since some configurations permit over fifty 1U servers in a single rack, this provides a simple method to determine exactly which machine is having a problem when at the rear of the rack.
A handle may be provided at the rear of the server rails, to help pull or push the server without having to pull on the cables.

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