Modular DIN-rail UPS uses LiFePO4 or supercap power : Page 2 of 2

December 20, 2018 //By Nick Flaherty
 Modular DIN-rail UPS uses LiFePO4 or supercap power
Bicker Elektronik in Donauwoerth, Germany, has launched a DIN-rail uninterruptible 12V and 24V DC power supply for fail-safe designs.

For short and medium bridging, ultracapacitors provide over 500,000 charging and discharging cycles. Unlike batteries, which store energy by the detour of a chemical reaction, Supercaps are based on electrophysical principles and are loaded and ready for use within a very short time. Energy storage with supercapacitors convince with high current carrying capacity, power density and reliability. The Bicker BP-SUC-D energy storage units have an integrated control and protection circuit as well as a Connect / Disconnect Power function and work in the extended temperature range.

For longer bridging times,it is advisable to take a closer look at the cathode material used. Especially in cells with chemically and thermally unstable cathode material such as lithium-cobalt-oxide (LCO) or lithium-nickel-manganese-cobalt-oxide (NMC), in-cell exothermic chemical reactions can occur under certain conditions which ultimately result in an uncontrollable "thermal runaway". For this reason, Bicker Elektronik decided to use lithium iron phosphate (LiFePO4) for the cathode material which, compared to LCO / NMC, has a much more stable chemical compound with increased safety and around ten times higher cycle stability (6,000 charging and discharging cycles). The BP-LFP-D battery packs also have an integrated high-performance battery management system (BMS) to optimize lifetime and safety. The BMS monitors and controls the complete charging and discharging process of each battery cell of the energy storage. The integrated cell balancing ensures a balanced and uniform charge of all cells, so that the full capacity of the lithium-ion battery pack remains permanently usable.

With the Battery Relax mode, Bicker Elektronik addresses the problem that in many DC UPS systems the battery pack is often operated for a very long time (possibly for months) to end-of-charge voltage on the charger, in order to guarantee full UPS readiness at any time. However, when lithium-ion cells remain in the end-of-charge state for such a long period of time, the lifetime of cells decreases sharply after a few months.
To protect the cells, it is therefore necessary that after a defined time the charging MOSFET is deactivated at end-of-charge. The discharge MOSFET remains active, so that a discharge is possible at any time. When discharge is detected (UPS operation after power failure), the previously deactivated charge MOSFET is immediately reconnected, so that the current flow through the body diode lasts only a few microseconds and the charger returns to the regular operating mode. Protecting the battery pack by the Relax Mode results in a significantly longer lifetime and thus an increased system availability.

The minimum load detection of the UPSI control unit monitors in backup mode (battery mode) the output load supplied from the energy storage system. If the load at the output falls below a certain threshold, the energy storage is automatically disconnected from the UPSI charging and control unit, so that the energy storage is not unnecessarily emptied by the DC UPS electronics. For PC-based controllers and computer systems, the integrated reboot function automatically restarts the PC system after a shutdown and a recurring supply voltage without the intervention of a service employee being necessary. In addition, a battery start function allows to manually activate the (separated) energy storage and thus initially start the system out of the battery, for example to carry out a diagnosis.

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