Linking UPSs a bad idea?

sketch145 · 17 Mar 2009 at 00:24

hey all, just wondered whether it would be damaging in any way to link UPS's together to increase the time they could sustain the pc without power. (i.e. plugging one UPS into the wall socket, and then plugging another UPS into the first UPS and then plugging your computer into the second UPS)

is this a good/bad idea?

(btw I'm not planning on doing this, just wondered if it was possible)

J.B · 17 Mar 2009 at 00:26

Would that even work?

I dont know why but something in the back of my head says that wouldnt work, cant back up or justify that in any way though.

sketch145 · 17 Mar 2009 at 00:36

yeah thats what I thought, can't quite put my finger on why though.

bremen1874 · 17 Mar 2009 at 00:41

From the APC knowledge base...

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.

Amonlym · 17 Mar 2009 at 00:52

you would do much better to daisy chain batterys themselves (in parallel) to achieve the desired run time - car batterys would works very well. Spend the money saved on a good ups. - cheap modified sine wave ups's have a peak voltage well in excess of 400v which will usually exceed the rated votlage of the input caps of your psu causing them damage.

sketch145 · 17 Mar 2009 at 01:11

right, so how would one go about linking the batteries to the UPS

bremen1874 · 17 Mar 2009 at 01:37

If you've got any sense you don't (unless you have a UPS with a dedicated DC input designed for the purpose).