Online/double-conversion UPS economy/high efficiency modes?

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1

Hi folks,

I'm looking at several brands of rackmount 3kva double-conversion
UPSes, such as Tripp Lite and Eaton Powerware. I'm specifically
looking for something that will work as a line-interactive UPS until
the power starts to misbehave and will then switch to
double-conversion mode until a while after the last power bump.

Basically I want the best of both worlds: save money on my power bill
most of the time (double-conversion UPSes generally waste 10%-15% of
the consumed kilowatt hours) but switch to nice clean
double-conversion when the storms roll through and the power gets
rough.

Here's where I'm looking for help: the vendor web sites have scanty
details about how the UPSes behave in their high efficiency modes. I'm
hoping folks here have used some of the UPSes with this feature and
can offer feedback.

When does the UPS decide to switch to double-conversion? When does it
decide to switch back? Are the options tunable? Through what
interface? Can I write software that monitors a weather report and
sends an SNMP message to switch the UPS to double conversion mode
ahead of a storm?

Eaton's 9130 says "On the High Efficiency setting, the UPS operates
normally on Bypass, transfers to inverter in less than 10 ms when
utility fails, and transfers back to Bypass in 1 minute after utility
returns. The indicator illuminates when the UPS transfers to Bypass."
http://lit.powerware.com/ll_download.asp?file=Eaton%209130%20UPS.pdf

Tripp Lite's SU3000RTXL3U only says "If the UPS has been placed into
Economy Mode (available on select UPS systems), it configures an
online UPS to function as a switching UPS. When the UPS system is in
Economy Mode, it operates at increased efficiency while AC utility
power is available (within +/- 10% nominal) and switches to battery
power if AC utility power is interrupted."
http://www.tripplite.com/shared/techdoc/Owners-Manual/932471.pdf

What others should I consider? Can anyone offer details?

Thanks,
Bill

2

I recently went to the tripplite 16kva online double conversion ups and did note the increased ineffeciency. However, the financial cost of that ineffeciency doesn't appear to be more than $40 - $60 / mo. So I am wondering at your scale with only a 3kva model, really, what is the final dollar cost to you versus the effort and dubious benefits of writing scripts or depending on embedded logic to do the right thing? The whole reason you have online double conversion vs line interactive, is to have the best available protection, and when you are on line interactive - even if it can switch - you are still taking that risk of power issues that will jump your ups and hit your connected equipment anyways.

Mike-

3

That is so old-school FUD re line-interactive vs double-conversion. Very
much the tubeless vs tubed tire debate all over again. Buy well-engineered
quality brand products (ie Emerson/Liebert, Schneider/APC) then it will be a
non-issue.

4

> I'm looking at several brands of rackmount 3kva double-conversion
> UPSes, such as Tripp Lite and Eaton Powerware. I'm specifically
> looking for something that will work as a line-interactive UPS until
> the power starts to misbehave and will then switch to
> double-conversion mode until a while after the last power bump.

Not entirely the topic asked, but we have good experience doing this at the 500 kva module level. We are using the 'eBoost' method from GE, which is more or less what you ask for. It keeps the inverter and rectifier alive and energized, but current flow is via the bypass static switch.

We have used this for about a year or so now, and even including hurricane sandy craziness, have seen in excess of 98% usage of eBoost. When in that mode, system efficiency jumps from about 92% to 99.8% efficient. A huge savings per 500 kva / 450 kw.

450 kw * 24h * 30d * 7.8% increase in efficiency is 25,272 kw-hrs saved per month, or at $0.12/kw-hr is $3,032/month/450 kw of load.

The point is that it works, works well, and is green.

http://www.gedigitalenergy.com/products/brochures/PowerQuality/brochure-eBoost-GEA-D1050-GB.pdf

To this point:

even if it can switch - you are still taking that risk of power issues that will
jump your ups and hit your connected equipment anyways.

If the overall power system is designed correctly, this should never be an issue. We did pretty extensive testing on this.

I don't know if anyone does this at the very-small level. I know GE's smallest unit is 300 kva for eBoost.

"Question everything, assume nothing, discuss all, and resolve quickly."

-- Alex Rubenstein, AR97, K2AHR, alex@nac.net, latency, Al Reuben --
-- Net Access Corporation, 800-NET-ME-36, http://www.nac.net --

5

I have a 700VA 9130 rackmount that I recently bought to give it an eval
run (although the first was a dud). There is a 3kVA model. For my small
load it reports a PF of 0.91 online.

It is selectable between normal and high efficiency mode through the
front panel. I would assume the tolerance settings in there related to
bypass availability would trigger online mode. If it does kick over to
online from high efficiency bypass it'll stay there for a minute to
watch for stability before going back.

The network card (Network Card-MS) is extremely sparse in being able to
configure it remotely. It's mainly just for status. It does not have an
option in the web interface to toggle the mode or change the bypass
tolerance settings, however, there is a MIB object for "power strategy"
that says it's read-write but I haven't tried writing to it yet. I guess
I can try it and report back.

~Seth

6

I have a 700VA 9130 rackmount that I recently bought to give it an eval run
(although the first was a dud). There is a 3kVA model. For my small load it
reports a PF of 0.91 online.

PF, as in power factor? That has nothing to do with UPS efficiency.

7

I apologize for mentioning it; thanks for taking the time to point out such data could not possibly be useful.

~Seth