Rechargable Battery

I can only guess if you divide 45 on 12 you get an amperage then AH if you wish. 10 minutes is all you have for 45W load safety shut down. If your load is 90 W - you have less than 5 min.

As you say, we can only make educated guesses on such little information, but 45 Watts is a tiny UPS! That's barely enough power to keep a laptop going!

Now I read 12V 45W/cell as 12 Volts with 45 Watts per cell. That is a strange way to specify, but with Lead Acid batteries, 6 cells would be required, giving a total of 270 Watts.

To the Original poster: What are the physical dimensions of the 12V battery? The physical size is pretty closely related to the AH capacity of the battery, for a given voltage.

http://www.allaboutcircuits.com/vol_1/chpt_11/3.html

I read nearly all of the info in your link - I saw nothing that helps us understand the OP's problem. Nothing, that is, that I didn't already know 40 or 50 years ago...

I too would have to assume, but given the 270W (assuming 6 cells), and 12V, that'd be 22.5A (270W / 12V). Also assuming that "10 minutes" is the usable time of the UPS unit, that'd result in 3.75AH (22.5A * 1/6hr.) capacity for the 6 cell battery.

That's a LOT of assuming though... More info from the OP would certainly help!

Do a controlled discharge test and get data. Then you will know the capacity.

ChazL

The maths is straight forward enough, the question is whether the "45W/cell" is a correct spec or a typographical error.

If correct then I = 45/2 = 22.5A

Thus the battery capacity is 22.5/(10/60) = 135Ah

If it is 45W at 12V then we would get I = 45/12 = 3.75A

Thus the battery capacity would be 3.75/(10/60) = 22.5Ah

In neither case have I taken into account Peukert's effect as we don't have any info on the battery. If the OP is looking to spec a replacement then he might be looking for a gel battery of about 130Ah_C20 or 30Ah_C20 respectively. Ultimately it will probably be the physical dimensions of the space available that will dictate the choice of replacement. The actual Ah will not be critical. Following are some typical sizes for VRLA batteries around the capacities above.

160Ah AGM 12/160 Dimensions: L:485 x W:177 x H:242mm Weight: 43 Kg

140Ah (Gel) 12/140 Dimensions L:513 x W:223 x H:223 mm Weight: 49 Kg

30Ah NPC30-12 12V 30Ah Dimensions 195mm x129mm x179mm 11.25kg

I hope this helps

Chas

First of all I would like to thank all for contributing ideas to my problem.

The dimension of the said battery is : 6cm(w) x 15cm(L) x 9cm(H) there are two of it and it is use in 2000kVA ups.

I have done some test as follows :

applied 5 ampere load : ups discharge time 10 mins

applied 2 ampere load : ups discharge time also 10 mins

according to the manufacturer, it is said that this battery is 9AH capacity, but can anybody explain why the discharge time only lasted for 10 mins despite of the load current?

the battery type: yuasa NPW45-12 12V, 45W/Cell, 10min

valve regulated sealed lead-acid type rechargable battery

Looking forward for the answer for this puzzle.

so sorry guys , the ups is 2000VA , typo mistake.