UPS Battery Number Calculation

There are efficiency curves provided by the battery manufacturer. You will find that batteries are rated at 10 or 20 hour discharge rates. If you discharge them over a 1 hour period you might multiply the nameplate rating (AH) by a factor as small as 0.6.

Dear Sir,

I appreciate the response. That is new information to me. But I am told that with that amount of info provided, it is completely possible to design/suggest the system.

Apparently people charge professional charges for providing a solution! So, I wanted to know how this is done.

Thanks

I don't know how much solisitation you are allowed to do here but you might be interested in the Silent Sentry. check www.onstatpower.com

Here's a paper with everything you ever wanted to know about UPS selection criteria.

Hi. There thanks for the great help.

It is recommended to use no more that 50% of battery capacity to maintain an acceptable battery life. These are approximate calculations based on your numbers.

12 [V] * 200 [A-hr] * 0.5 = 1200 [W-hr/battery]

Estimated energy requirement is close to 9600 [W-hr]

9600 [W-hr] / 1200 [W-hr/battery] = 8 [batteries] minimum

I would build the system with room for 2-4 more batteries (10-12 total) and make allowance for easy change of batteries when maintenance/repair is required.

Good Luck!

Hi, Thanks for the details. Please allow me to show you my calculations:

Total Wh=9216

Max avaialable from battery is 12*200=2400

Considering efficiencies,

No of batteries=9216/(0.5*0.8*2400)=9.6 batteries. Please help me find the actual value!

Thanks

Thank you all for the wonderful ideas and assistance. Yes, I did get some help from a "professional." He also said I will need about 8 batteries. Seems he was right! Thanks again, but I will be back if I have more queries!

Not sure how often you will NEED back-up power, but your posting implies relatively frequent use.

If that is the case, you would be much better off with a "simple" UPS system with maybe 2 batteries and a back-up generator. The UPS is only there to ride through until the generator is up and running at full power- maybe 10 to 30 seconds OR to allow orderly shut down IF the back-up generator does not work.

Hello,

Surely two heads think much better than one! I appreciate the great input. However, all I am trying to clarify is the exact METHOD of CALCULATING the required number of batteries. The procedure on how-to is my target thanks. The system is just to back up light loads like computers for some time. Thanks

Well, think of Amp-hours as 'fuel'. A battery can contain so much, then it's full.

Battery size is in amp-hours: amps x hours. but don't lose sight of the fact that battery amps are at 12 vdc and inverter output is at 120 vac, so you must do a ratio 10 conversion. then derate by inverter efficiency, then rapid discharge efficiency, add reserve capacity, and inverter idling loss if applicable.