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Putting UPS's in series?

 
 
YKhan
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      06-01-2010, 09:56 AM
I'm wondering if there are any dangers or precautions to putting a
couple of UPS's in series to increase their power-on time?

Yousuf Khan
 
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Robert Redelmeier
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      06-01-2010, 11:46 AM
In comp.sys.ibm.pc.hardware.chips YKhan <(E-Mail Removed)> wrote in part:
> I'm wondering if there are any dangers or precautions to putting
> a couple of UPS's in series to increase their power-on time?


Even presuming sufficient VA (=W/PF), few UPSes produce
nice sine waves on their outputs while most expect them on
their inputs. There may be problems [overheating] with the
second UPS. UPS should be able to handle poor powerfactor
draws since most computing devices are miserable.

It would be vastly preferable to put them in parallel
where you can split loads, like one for the CPU,
one for monitor & wallwarts.



-- Robert

 
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YKhan
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      06-01-2010, 02:50 PM
On Jun 1, 5:46*pm, Robert Redelmeier <(E-Mail Removed)> wrote:
> In comp.sys.ibm.pc.hardware.chips YKhan <(E-Mail Removed)> wrote in part:
>
> > I'm wondering if there are any dangers or precautions to putting
> > a couple of UPS's in series to increase their power-on time?

>
> Even presuming sufficient VA (=W/PF), few UPSes produce
> nice sine waves on their outputs while most expect them on
> their inputs. *There may be problems [overheating] with the
> second UPS. *UPS should be able to handle poor powerfactor
> draws since most computing devices are miserable.
>
> It would be vastly preferable to put them in parallel
> where you can split loads, like one for the CPU,
> one for monitor & wallwarts.
>
> -- Robert


That's what I was afraid of. I remember hearing something about that
sometime back, but I couldn't remember if I heard it right or what the
reason was, so I asked here.

Yousuf Khan
 
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Strobe
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      06-01-2010, 05:37 PM
On Tue, 1 Jun 2010 07:50:50 -0700 (PDT), YKhan <(E-Mail Removed)> wrote:

>On Jun 1, 5:46*pm, Robert Redelmeier <(E-Mail Removed)> wrote:
>> In comp.sys.ibm.pc.hardware.chips YKhan <(E-Mail Removed)> wrote in part:
>>
>> > I'm wondering if there are any dangers or precautions to putting
>> > a couple of UPS's in series to increase their power-on time?

>>
>> Even presuming sufficient VA (=W/PF), few UPSes produce
>> nice sine waves on their outputs while most expect them on
>> their inputs. *There may be problems [overheating] with the
>> second UPS. *UPS should be able to handle poor powerfactor
>> draws since most computing devices are miserable.
>>
>> It would be vastly preferable to put them in parallel
>> where you can split loads, like one for the CPU,
>> one for monitor & wallwarts.


If you do this, don't forget to put a small lamp on one of them.
Bad enough coping with a power outage without having to do it in the dark.

>That's what I was afraid of. I remember hearing something about that
>sometime back, but I couldn't remember if I heard it right or what the
>reason was, so I asked here.


Have you looked into replacing the UPS battery with a larger capacity one?
This is the preferred (and more elegant) way to get longer power-up time.

--

Terry V.
 
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Rick Jones
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      06-01-2010, 06:51 PM
In comp.sys.intel Strobe <(E-Mail Removed)!beep!.com> wrote:
> If you do this, don't forget to put a small lamp on one of them.
> Bad enough coping with a power outage without having to do it in the dark.


That's what all the blinking lights are for - all real computers have
blinking lights right?-)

rick jones
--
oxymoron n, Hummer H2 with California Save Our Coasts and Oceans plates
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...
 
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Bill Davidsen
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      06-01-2010, 07:38 PM
YKhan wrote:
> I'm wondering if there are any dangers or precautions to putting a
> couple of UPS's in series to increase their power-on time?
>

In general it's more effective to split load or use a bigger UPS. With few
exceptions the output of a UPS is ugly with high frequency harmonics, resulting
on a bunch of losses.
 
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Steve Thompson
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      06-01-2010, 07:43 PM
On Tue, 1 Jun 2010, Rick Jones wrote:

> In comp.sys.intel Strobe <(E-Mail Removed)!beep!.com> wrote:
>> If you do this, don't forget to put a small lamp on one of them.
>> Bad enough coping with a power outage without having to do it in the dark.

>
> That's what all the blinking lights are for - all real computers have
> blinking lights right?-)


Absolutely. Anyway, we have a nice illuminated EXIT sign which is on
emergency power and so stays on when the power is out. The computers are
not, because the emergency power is turned off once every month for
"testing". Really.

Steve
 
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LSMFT
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      06-01-2010, 10:45 PM
YKhan wrote:
> I'm wondering if there are any dangers or precautions to putting a
> couple of UPS's in series to increase their power-on time?
>
> Yousuf Khan


Series would double the voltage and blow your stuff up.

--
LSMFT

I haven't spoken to my wife in 18 months.
I don't like to interrupt her.
 
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Bryce
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      06-07-2010, 12:37 AM
Sam E wrote:

> On Tue, 01 Jun 2010 18:45:10 -0400, LSMFT
> <(E-Mail Removed)> wrote:
>
>>YKhan wrote:
>>> I'm wondering if there are any dangers or precautions to
>>> putting a couple of UPS's in series to increase their
>>> power-on time?
>>>
>>> Yousuf Khan

>>
>>Series would double the voltage and blow your stuff up.

>
> That's funny. I hadn't thought of connecting the OUTPUTS
> in series.


In 'normal' mode, most consumer-grade UPS devices just pass
through the input mains power. Any attempt at connecting the
outputs in series would either result in total output
voltage equaling mains voltage, or zero and an immedite
shutdown by either unit's short-circuit protector.

When operating off-line (i.e., during a line power failure)
it would be possible to obtain much more than rated voltage
with the series connection, but it would be weird. The two
UPS units would not be phase synchronized and probably would
not even operate at exactly the same frequency. Output
voltage would vary unpredictably.
 
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Rick Jones
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      06-07-2010, 09:30 PM
William R. Walsh <(E-Mail Removed) m> wrote:
> This does not always work, especially if the UPS manufacturer never
> intended for larger batteries to be used.


Doesn't that then also imply that the UPS is being used in a context
for which the UPS manufacturer never intended?

rick jones
--
firebug n, the idiot who tosses a lit cigarette out his car window
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...
 
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