• • • UPS & STANDBY POWER • • • Lifetime – A false sense
of security? Lead-acid batteries have a very limited lifetime. The “long lifetime” frequently stated according to Eurobat is misleading. This applies only under ideal conditions, typically 20°C ambient temperature, and does not take into account aging of the battery occurring during storage. Temperature has the greatest influence on the reduction in lifetime. Increasing the temperature by 10°C halves the stated life. If one also does not consider the aging by storage, then a 6-9 year lifetime battery, according to Eurobat, quickly becomes one which requires replacement after only 1.5 years when taking these effects into account These problems are removed when using
Electrochemical Double Layer Capacitors. The capacitors are permanently installed in the device and cannot be replaced and have the same lifetime expectancy as the power supply unit itself when the buffer module is correctly designed. In practice, this is longer than 10 years in a typical application. The storage time of Electrochemical Double
Layer Capacitors is practically unlimited. They do not have to be recharged regularly and do not cause any issues if an installation should be put into service after a lengthy storage period.
Full Power between
-40°C and +60°C Electrochemical Double Layer Capacitors are not affected by cold and can tolerate temperatures down to -40°C. This makes these components ideal for applications outdoors, in mobile systems
and applications in solar or wind energy projects. With lead-acid batteries, the hydrogen freezes
on charging at temperatures below -10°C and damages the battery. Only expensive pure lead batteries are suitable for such applications. Electrochemical Double Layer Capacitors provide their full capacity even up to +60°C, which makes it possible to use them inside an enclosed non- ventilated switchgear cabinet. With lead-acid batteries hydrogen typically escapes at temperatures greater than +45°C, which creates a destructive process or can cause an explosion. It is not without reason that installing lead-acid
batteries outside switchgear cabinets is recommended. In contrast to lead-acid batteries, Electrochemical Double Layer Capacitors emit no hydrogen and ventilation of the switchgear cabinet as required by EN 50272-2 for lead-acid batteries is not required.
A New Unit – kWs or kJ The capacitor voltage is reduced continuously on discharge. Therefore, stating the energy in Ah (ampere hours), as is the practice for batteries, makes no sense and so the energy is stated in Wh (watt hours) or in kWs (kilowatt seconds). It is also frequently stated as kJ (kilojoule). 1kJ corresponds exactly to 1 kWs. 1 kWs means that the device can supply 1 kW for one second or 100W for 10 seconds. The energy in a capacitor is calculated according to the following formula: This describes the energy to completely discharge to zero volts. However, in practice, the converters cannot work down to zero volts, so that one cannot use the full energy. Caution is therefore required here: The buffer modules are classified according to their nominal energy and not according to the usable energy. When determining the buffer time, always use the data sheets or diagrams and not the simple equation stated above.
Energy (Ws) = ½ CU2 PULS offers two buffer modules with different
storage capacities; the UC10.241 with 6kWs storage capacity and the UC10.242 with 12kWs. These devices are designed for 24VDC systems and can be used in the normal mode and in the buffer mode with up to 15A. In both devices, the capacitor storage unit is installed together with the electronic controls in a compact housing for DIN-Rail installation. Smaller buffer modules with shorter buffer times and a 48V version are also available. The series connection of the single capacitors is equipped with an active balancing circuit, which provides long lifetime for the capacitors. The device is equipped with signalling contacts and display elements for monitoring and diagnostics. If buffering is not required, it can be disabled with the inhibit input.
32 ELECTRICAL ENGINEERING • NOVEMBER 2022
electricalengineeringmagazine.co.uk
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