On 11/17/10 12:30 PM, Daniel Clark wrote:
> On Wed, Nov 17, 2010 at 12:25 PM, Chris Hoogendyk
> <[email protected]> wrote:
>> I have no idea how that home brew UPS you linked would have performed in a
>> similar situation.
> Thanks - at least one useful thing I've gotten from this thread is
> that whatever I end up doing, it would seem to make sense to have
> smaller COTS "front end" UPS units, connected to whatever backend (be
> it COTS or DIY), and have separate "front end" units for servers and
> HVAC.
I didn't keep the whole thread, so I'm replying to this member of the thread.
Around the middle of the thread, there was an exchange between Brad Knowles and
Doug Hughes
regarding connecting one UPS to another (daisy-chaining UPSs).
The thread was pretty well hashed over, but I just got the latest APC
(Schneider Electric)
"Currents" newsletter (glossy extended advertisement). Inside the back cover is
a page titled
"Frequently Asked Questions" that addresses this issue. They list 4 reasons to
NOT to daisy-chain
UPSs. Abbreviating, (1) not UL tested (voids your warranty), (2) no extra surge
protection, (3)
increased chances of overloading the first UPS, and, at more length,
(4) "In most cases, daisy-chaining UPSs does not allow for extra runtime. If
you are using a UPS
that outputs a step-approximated sine wave when running on battery, as soon as
the first UPS goes
into battery operation, the second one will also do so because it will see the
step-approximated
sine wave as distorted or bad power. Both UPSs will discharge together and will
not provide any
extra runtime to the load."
They recommend a larger UPS or one designed with extra batteries for longer
runtime.
Since they listed item 4 and said, "in most cases," one might assume that the
UPSs they manufacture
and sell still provide a step-approximated sine wave when running on battery
power. Looking for
details on their web site, the Smart UPS series claim a pure sine wave on
battery, but the Back UPS
series have nothing regarding sine wave, square wave or step-approximated. They
don't say anything.
I guess you don't advertise the shortcuts you take on less expensive hardware.
--
---------------
Chris Hoogendyk
-
O__ ---- Systems Administrator
c/ /'_ --- Biology& Geology Departments
(*) \(*) -- 140 Morrill Science Center
~~~~~~~~~~ - University of Massachusetts, Amherst
<[email protected]>
---------------
Erdös 4
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