Is daisy chaining UPSs safe? Does it add any benefit or cause more problems?

Question

Is it safe and is their any benefit to daisy chaining multiple UPSs together?

Answer 1

Depending on how the UPSes operate, there is a chance this can work. HOWEVER, with most UPSes and the way they operate, you can end up damaging the devices. In the best case, with most UPSes, you will just end up draining the batteries faster than they normally would.

The reason is that the power a UPS produces can appear as a power surge to the second UPS. The second UPS will then "return" the power back to the first UPS over ground. End result is the power from the first UPS goes to ground and the power from the second UPS powers your equipment until it runs out.

I would warn you that daisy chaining UPSes can void your warranty depending on manufacturer and/or model.

If you still want to do this, then before you do, check with the manufacturer. Their support should be able to tell you if it is safe to chain particular UPSes together or not.

I always recommend people play it safe and split the load between your UPSes. This helps to prevent overloading your UPS as well.

Answer 2

Not really a good idea with most of them - Most "Computer UPS's" output modified square wave, not sine wave power. But they expect real sine wave power on their input. Daisy-chaining them would probably not be a good thing for that reason, at least.

If they all actually work (do some basic testing with real loads and a timer, don't put too much faith in most "self-tests") you'd be better off to divide up any loads you need to power during an outage among the 4 UPSes, according to their rated power and the loads' draw.