Re: Piggy backing UPS's

["Andy Whitfield" <andywhitfield2002@xxxxxxxxxxx>]

Hi John,

It's not recommended daisy chaining UPSs.  I've copied and pasted
APC FAQ below.  Not all APC's points are relevent to you but I've
pasted the complete FAQ.

And from my experience..... If the big UPS is double conversion then
the smaller UPS will see it OK but it is not an ideal thing to do.
The small UPS will most likely be inductive and disproportionally
load the big UPS.

Can you plug the small UPS directly in to the mains?
I have, of course, got big UPSs in stock with USB ports.  ;-)
Regards, Andy

***From APC FAQs
Question:  Can I daisy-chain UPS?

Answer:  APC does not recommend that you daisy-chain two or more
UPSs together. Each unit should be plugged directly into a properly
grounded wall outlet for maximum effectiveness.

We do not recommend this configuration for the following reasons:

1) It is not UL (Underwriters Laboratories Inc. (UL) is an
independent, not-for-profit product safety testing and certification
organization) tested, and therefore, should something go wrong and
damages be caused to your connected equipment, APC would not honor
the claim.

2) It is a waste of money because you do not increase your load
capacity in such a configuration. Plugging a Back-UPS Pro 650 in
another Back-UPS Pro 650 does not give you a total capacity of 1300;
Your maximum load capacity is still 650 VA.

3)Such a configuration increases the possibility of overloading the
first UPS in line; if the first UPS has a load on it, and then you
plug the second UPS into the first, with a load of its own,
ultimately, all of the current is being drawn from the first unit.
There is a potential for accidentally overloading the first unit.

4) In most cases, daisy-chaining UPSs does not allow for extra run
time. If you are using a UPS that outputs a step-approximated sine
wave when on battery, as soon as the fist UPS goes on battery, the
second UPS will also go on battery because it will see the step-
approximated sine wave as distorted or bad power. Both units will
discharge together, and will not provide any extra run-time to the
load.

5)This configuration does not provide any extra surge protection,
because if an over voltage that is strong enough comes in, the UPS
will fail open and prevent the surge from traveling further in
connected equipment attached to the UPS.


--- In ukha_d@xxxxxxx, "Benfield, John \(GTI EMEA\)"
<John_Benfield@...> wrote:
>
> A question possibly for Andy.
>
> I have a large rack mount UPS that has a serial connection for load
> monitoring etc. I have just purchased a NAS device that supports
UPS
> monitoring but only via USB. Would it be feasible to purchase a
small
> UPS that has UBS connectivity and attach it to the much bigger UPS
as a
> device. The idea being that the big UPS will perform as the main
battery
> backup and only in the event of that failing completely would the
small
> UPS come on line and the NAS box can then get the status from that
and
> shutdown gracefully.
>
> JB
> --------------------------------------------------------