Basic UPS Question

[mcasazza]

Sorry for the basic question. I am more a network and computer person, but this question came up recently. Can you replace a UPS's batteries with batteries that have much greater capacity (AH rating) so long as the voltage remains the same? Basically, I have a client with a several UPS systems rated from 1.4KVA to 750VA and they want to replace the batteries with 75AH batteries. The intended benefit is extended run time. And of course they want to hire me to do the install/upgrade. Based on my knowledge of the way these devices work I see no problem, but I want a second opinion.

Thanks,

Mark C

 

[itsmoked]

This is a commonly asked question. The short answer is no. The long answer is maybe. Generally, the smaller UPS's will not tolerate this abuse. The abuse rises from the fact that the UPS's charging circuits are as cheap as they can be made and have no remaining capacity for charging extra batteries.

Larger units, especially those that allow optional extended battery units to be plugged into them, tolerate this well. APCs "BackUPS" like the RS 1500 series is an example. You can purchase a battery pack "RS/XS" that more than doubles its original capacity.

One of the concerns are such things as the way UPS decides the battery has reached end-of-life or are perhaps distressed for some reason. With far more batteries connected, the UPS can make incorrect adjustments and decisions.

A second concern is a UPS is normally UL listed and this is a function of its enclosure, fusing, and other safety features inherent in the enclosed case of batteries and controls.

Another concern is again the batteries. If not safely and enclosed and terminals properly insulated, could in certain failure modes rupture, explode, or burn.


You probably need to look at this closely, because being hired to do this makes you highly liable if something goes wrong. Which of course is somewhat different from the average person trying to extend the UPS under their desk at home.