UPS Input Current Calculation

28.7

What voltage?

On average, the input current must be a bit higher than the output, but if the batteries and the output circuitry support it, the output current can occasionally be higher.

There is no such simple answer with the information that you provided. There are many information required for calculating the UPS input current (note, when we say UPS input current, it is basically the UPS charger input current). The UPS input current is not always same; it depends on the type of the UPS operation (on-line and off-line) and the status of the battery charging. For an on-line UPS, if the battery is fully charged, the input current is required for supplying the load currents and the losses in the inverter and charger. On the other hand, if the batteries are fully discharged and/or require charging, the input current required supplying the battery charging current in addition to supplying the load currents and the losses in the inverter and charger. See these equations for UPS input current:

When battery is charging: UPS input current ∞ Load current + Losses + Battery charging current (varies over the time)

When battery is fully charged: UPS input current ∞ Load current + Losses

(∞ indicates proportional, not equal)

If you are interested to see the detail calculation for the UPS input current, see this thread (especially the comment # 9): http://cr4.globalspec.com/thread/38821

Note: It may happen that the UPS input current is lower than the UPS output current on some conditions such as (1) the input voltage is higher than the output voltage or (2) the input is three phase but output is single phase or both (1) and (2).

- MS

33.1

That's a brilliant question. The answer can be found by using the telephone and making a call to the manufacturer of the <...10 KVA UPS...> under consideration.