HP 9000s and HP Power Trusts with new Liebert Power system.

[Jim DeSpain]

Here is what is happening at my site:
We are moving into a new "Modernized" server room with Liebert UPS and Power System, w/Emergency Power generator on a Auto Failover switch.
My question is, why would I even need the HP power supplies and batteries anymore?
Has anyone out there ever disconnected from HP UPS and relied solely on Liebert or other power?
I would greatly appreciate any/all input.

Thanks,

Jim DeSpain
UNIX Systems Administrator
Belkin Components
mailto:jimd@belkin.com

[Tim Malnati · Accepted solution]

The fact of the matter is that you will not have any need for the Powertrust units any longer. One thing you do not want to do is have your equipment powered by two different ups units in series. The first problem in this scenario is that you end up with two points of failure instead of one. There is a much more involved explanation regarding circulating currents which cause the two to end up fighting each other, but I'm not going to get into a long explanation of the theory. The bottom line is that your Powertrust ups units should be eliminated. After you have moved, it's probably a good idea to take them off your service contract and sell them off.

[Dave Wherry]

I'm glad this question was posted. We're discussing a similar issue.
Like Tim, I have been told not to use 2 UPS' in series. However, I have done it. The caveat I was told was that as long as they are "ferrite resonant"? units it works fine, and it did. This was a few years ago and as far as I know this layout is still in use at that shop.

If you use a Power Trust you can have the host and UPS talk and perform an orderly shutdown in the event of a power failure. We have an APC UPS. My question is has any one had a HP host do this communication and shutdown with a non Power Trust UPS?

[Martha Mueller]

Tim,

If you are still out there, would you please go into the involved explanation regarding circulating currents....? I have heard that this can cause malformed waveforms that damage the power supplies in the servers. I need to respond to a request to do this very thing...add a ups into a data center that is already protected.

thanks

[Chris Vail]

Yeah: its a phenomenally bad idea to use 2 UPS's in series. The Lieberts are pretty good: we use 'em here. In a real data center,
the big UPS's rule.

The hysterisis bit is overblown, methinks. In theory, its possible for back EMF to affect the circuitry of one UPS or the other.

Here's a handy tip: contact your electrical supply utility, and ask to borrow their meter. They'll be delighted to let you use it to determine how good your power is. They'll even send a consultant out to discuss it with you. Talk to their industrial customer service people: they know ALL about these issues, and are usually quite anxious to educate.


Chris