calculation of battery capacity for UPS 1

[geeny]

I would like to know how can you calculate the size and quantity of batteries (lead acid and nickel cadmium)to withhold a load of of 30 kw and 100 kw for 30min. and for 1hour.
please show me how and where such information can be provided...many thanks to all

 

[IRstuff]

watt*second = joule
watt*hr = watthour

TTFN

 

[YIGO]

Here is an outline of a way to do it. You need to select the battery system voltage V, then given the load P (30 kw or 100 kw)the battery has to supply a current I=P/V. From known batteries I(t) and V(t) curves select the ones that can deliver the current needed for 30 mn (1hr) without the voltage dropping to a critical level for the batteries or the system.

Hope it will help.

Yigo

 

[alehman]

UPS's are a constant kW load for the battery. As the battery voltage falls, current increases. So it's difficult to relate ratings in amp-hours to kW-hours. For this reason, manufacturers of batteries intended for UPS systems normally furnish capacity tables rated in kW per cell to a specified final discharge voltage.

1. Determine the required DC bus voltage.
2. Determine the minimum allowable discharge voltage.
3. Determine the battery kW (including inverter and cable losses)
4. Divide battery kW by the number of cells to get cell kW.
5. Look in mfg's tables to find appropriate type of cell based on required kW, discharge voltage and operating temperature.

Some UPS's will tolerate a range of DC voltage, so you can adjust the number of cells to obtain the exact run time needed.