Backup time of 24v UPS vs 12v UPS with same batteries

Does a 24v UPS provide longer backup than a 12v UPS with the same capacity batteries.

e.g if a 24v UPS (1000VA) is connected to 2 [12v 80AH] batteries in series it provides 1 hr backup at full load. Now what will be the theoretical backup time of a 12v 1000VA UPS connected to the same capacity batteries in parallel????

Please tell the benefits of using 24V vs 12V UPS!!!!

Regards

You cannot gain any more energy than what is in the batteries however you connect them. Using a 24v system would have slightly lower resistive losses maybe. Essentially though not much difference at all unless the batteries are on longish leads, then 24v would help, assuming the core size of the cable remains constant.

From some real tests on one of our UPSs (designed to work with 12 or 24V batteries, with only very small changes in some components) and with 2x 9Ah batteries (in series=24V or in parallel=12V), the runtime can be even 40% higher with 24V than 12V.
If the load is not too high, the difference is much lower.

Those differences are mainly due to:
- much more resistitive losses with lower voltage (you have to double your supply current to get same power)
- less strain to the batteries: half current when they are put in series. If you take a look at the discharge curves you'll understand what I mean

This is one of the reasons why it is always suggested to work with at least 24V when your power requirements are higher than 5-600W.

P.S. if the capacity of your battery is much higher than 7.2/9Ah (80Ah), the main difference will be due to the resistitive losses because the internal resistance of the 80Ah battery will be low enough to minimize the second point.

I agree with bepobalote at high current the effect is more pronounced, hence battery power tools having ever increasing voltage batteries. However in my experience, at more moderate levels its not that noticeable. Certainly if you can use 24v, go for it, no real disadvantages.

the main advantage using higher volt battery is to reduce the current hence reduce the heat generated by mosfet, if a good Low RDSon will give good results