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I have a x-ray machine rated at 8KW, 230V AC. I have a 5KW UPS with 100Ah battery bank. Obviously I cannot use this as a power source for the x-ray machine. Therefore I am planning for a 10KW UPS. The UPS needs to supply power to the x-ray machine at 230V AC only when the x-rays are produced, i.e a maximum of 5 sec at a time. The UPS will normally require 96V DC battery bank. My question is can I replace the battery bank of the 10KW UPS with a capacitor bank ? If yes what should be the rating of the capacitor bank? The idea is to charge the capacitor bank with my existing 5KW UPS and then use it to power the 10KW UPS. If this is possible I can get rid of 8 nos of 12v DC batteries required for the new 10KW UPS. Any suggestions?

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Capacitors store energy so, yes, you could replace the batteries with a capacitor bank.

To size the capacitor bank, you'll need to specify the required energy for the 5 second interval, which you haven't done, as well as the allowed change in voltage across the bank.

The energy stored in a capacitor is proportional to the square of the voltage across. Thus, as the capacitor bank discharges, the voltage will decrease. So, you will need to specify the voltage at the start and end of the 5 second interval to properly size the capacitance.

However, I think you'll find that the cost is far, far greater than for batteries. See this for example.

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  • \$\begingroup\$ The capacitor bank will also be much bigger, physically. The energy density of a typical supercap is about 1/20 that of a lead-acid battery, the sort typically used in UPSes. If you switch to LiIon, the factor is about 1/100. \$\endgroup\$ – Warren Young Dec 12 '13 at 3:51

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