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Capacitors Provide New Maintenance-Free DC UPS

Aw 2818 Capacitor 350

Reducing downtime and routine maintenance are critical aspects of equipment design. Uninterruptible power supplies are one of the tools being used to ensure that equipment can be shut down in an orderly fashion so restarts won’t take much time.

Traditional battery backup systems provide a good solution for longer backup times, sometimes several minutes to over an hour depending on required backup current. However, battery backup systems can sometimes be bulky, with no DIN rail mounting capability on larger form factors. The new Sitop UPS500S DC UPS from Siemens Energy & Automation Inc. eliminates required battery maintenance and trims size requirements using capacitors instead of batteries.

“Capacitors have a smaller footprint than batteries for lower backup current requirements," says Kai Bronzel, Product Manager at Siemens. That can be a key factor when battery size goes beyond standard form factors, forcing automation designers to step up to larger enclosures.

The shift to capacitors also removes other issues linked to batteries. Among them is that there’s no longer a need to protect against the volatile gas emissions from a failed battery, and the service life is much longer than1-2yrs for a typical UPS battery.

The many small benefits add up to significant improvements for product designers and end users. “Total cost of ownership will be reduced with this system because there’s far less maintenance and higher temperature range capability," Bronzel says.

Capacitor back-up practically doesn’t require maintenance, nor does it have the lifetime issues that can arise when batteries are used in enclosures that have high ambient temperatures. The Siemens UPS500S is rated up to eight years of continuous service. The long-life, double-layer capacitor design can even operate safely up to 60 degrees Celsius, compared to 40 degrees for most traditional UPS batteries. 


The Sitop UPS500S provides a 24 VDC backup that gives operators enough time to properly control a shutdown sequence. For example, it provides up to 9 minutes for smaller 1-3 Amp loads.

Capacitors are also well suited to protect equipment during a series of intermittent power outages. Their recharge time is less than half the discharge time. 

The Sitop UPS500S comes in 2.5 KWs and 5 KWs models. Both have compact DIN rail mount designs that match the dimensions of Siemens’ Sitop Modular 24 VDC power supplies. That simplifies installation and wiring.

All Sitop UPS500S and UPS501S products are designed with a rugged IP20 case and certified with standard industry agency approvals, including UL 508, CSA and CE compliance. 

For more information on the UPS500S, please click here for a product brochure.


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