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#1
07-14-2008, 06:11 AM
 yudhi Guest Posts: n/a
Need Help To Calculate Battery Capacity for UPS

Hello All.

I'm new here.
I need help to calculate battery capacity for UPS I planned.
I want to buy a Inverter with UPS mode.

The inverter have :
- 24VDC Input
- 220VAC 3000Watt Output
- Eficiency 90%

I need to have 6 or 12 hours backup time at Full Load (3000Watt).
So how many AH (amps hours) I should prepare and how to calculate that ?
What I know is I need to make 2 x 12V battery in serial to get 24V.

Many thanks.
#2
07-14-2008, 06:35 AM
 JohnS Moderator Join Date: Dec 2007 Location: SE Michigan, USA Posts: 9,446 Rep Power: 19
Re: Need Help To Calculate Battery Capacity for UPS

Quote:
 Originally Posted by yudhi Hello All. I'm new here. I need help to calculate battery capacity for UPS I planned. I want to buy a Inverter with UPS mode. The inverter have : - 24VDC Input - 220VAC 3000Watt Output - Eficiency 90% I need to have 6 or 12 hours backup time at Full Load (3000Watt). So how many AH (amps hours) I should prepare and how to calculate that ? What I know is I need to make 2 x 12V battery in serial to get 24V. Many thanks.
You are going to need an enormous battery. For 3 kW out and 90% efficiency, you need 3333 W in. At 24 V dc, that's 139 A. For 6 h, that's 834 Ah, for 12 h, 1668 Ah.

That is what you need to draw, not the battery's rating. Even a deep discharge type battery should never be discharged to less than 20% of capacity, and 50% will result in much longer life. (Divide above by 0.8 or 0.5)

Discharged to 20%: 1050 Ah for 6 h, 2100 Ah for 12 h
To 50%: 1700 Ah for 6 hr, 3400 Ah for 12 h.

Those are huge batteries and you may wish to consider a much smaller UPS battery supplemented by a generator.
#3
07-14-2008, 06:47 AM
 yudhi Guest Posts: n/a
Re: Need Help To Calculate Battery Capacity for UPS

Quote:
 Originally Posted by JohnS You are going to need an enormous battery. For 3 kW out and 90% efficiency, you need 3333 W in. At 24 V dc, that's 139 A. For 6 h, that's 834 Ah, for 12 h, 1668 Ah. That is what you need to draw, not the battery's rating. Even a deep discharge type battery should never be discharged to less than 20% of capacity, and 50% will result in much longer life. (Divide above by 0.8 or 0.5) Discharged to 20%: 1050 Ah for 6 h, 2100 Ah for 12 h To 50%: 1700 Ah for 6 hr, 3400 Ah for 12 h. Those are huge batteries and you may wish to consider a much smaller UPS battery supplemented by a generator.
Wow....I need huge capacity

Generator is my last option....smoke, noisy and the fuel price is rising and never stop

Do you ever know how much is battery which have huge capacity which is used by most cellular provider at their BTS ?
I saw battery with capacity over than 2000AH.

Thanks.
#4
07-14-2008, 07:36 AM
 JohnS Moderator Join Date: Dec 2007 Location: SE Michigan, USA Posts: 9,446 Rep Power: 19
Re: Need Help To Calculate Battery Capacity for UPS

Quote:
 Originally Posted by yudhi Do you ever know how much is battery which have huge capacity which is used by most cellular provider at their BTS ? I saw battery with capacity over than 2000AH. Thanks.

I don't know. Among people who live "off grid" and use solar or wind power, batteries rated for golf carts, generally 6V, 400 Ah, are popular and relatively economical. They wire four in series for 24 V, and either operate several separate banks or parallel them for more capacity (when paralleling batteries, there may be some problems getting all of them to charge/discharge uniformly, small differences in cell voltage can be a problem).
#5
07-14-2008, 07:41 AM
 yudhi Guest Posts: n/a
Re: Need Help To Calculate Battery Capacity for UPS

Thanks a lot....its very helpful for me.
#6
04-12-2009, 12:50 AM
 kiran.elcom@gmail.com Guest Posts: n/a
Re: Need Help To Calculate Battery Capacity for UPS

My load is 3KW & I want to take inverter. How I shuld decide battery capacity Pl. tell what should be battery capacity
#7
04-13-2009, 04:51 AM
 MJWorner Guest Posts: n/a
Re: Need Help To Calculate Battery Capacity for UPS

Quote:
 Originally Posted by JohnS I don't know. Among people who live "off grid" and use solar or wind power, batteries rated for golf carts, generally 6V, 400 Ah, are popular and relatively economical. They wire four in series for 24 V, and either operate several separate banks or parallel them for more capacity (when paralleling batteries, there may be some problems getting all of them to charge/discharge uniformly, small differences in cell voltage can be a problem).
This scenario calls for 20 batteries at 100% discharge (B A D bad) or 40 batteries at 50% discharge (I would not go below that point, and not often) which makes containment, ventilation (explosion proof!) and heat dissipation into real live issues. Plus, as John says all batteries must be the same type, size and age or they will start discharging each other.

Wiring would be ten parallel banks of four batteries in series. Charging with positive at first bank and negative at last bank is proper way to keep everything equalized.

Major dollars here for a constantly deteriorating asset. Buy a lot of gas for that money, and it will be fresh with every fill up...
#8
06-11-2009, 03:58 AM
 Unregistered Guest Posts: n/a
Re: Need Help To Calculate Battery Capacity for UPS

Quote:
 Originally Posted by kiran.elcom@gmail.com My load is 3KW & I want to take inverter. How I shuld decide battery capacity Pl. tell what should be battery capacity
*rolls eyes*
Some simple maths:
V A R & W A V and for the yanks E I R & P I E same **** just using the equality values but im going to explain in base value.

Meanings: V=Volts A=Ampere R=Ohm's W=Watts

Ohms law (1) Requires to part of the calculation so any one is able to do this all you need is a multimetre to start.

Calculate:
Volts: V= AxR
Amps: A= V/R
Ohms: R= V/A

Working with watts:
Watts: W= AxV
Amps: A= WxV
Volts: V= W/A

Want an AH:
Say with a single filament 24W at a 12V supply what AH do i need to run it for lets say 24hrs?

Here now to put the above info into play:
We need the amps that is being drawn from the 24W filament so:
A=24/12 (2AMP)

So! 2A * 24HR = 48AH one thing to mention this is not for a deep charge battery! else add 20% to 48AH as we do not like to drain a deep plate as it f's it!

I can't be stuffed typin anymore lol have fun with the new info
#9
07-10-2009, 10:14 PM
 krishne Guest Posts: n/a
Re: Need Help To Calculate Battery Capacity for UPS

i want to run one sheeling fan and two tupe lights with 12 hours backup.so which battery is suitable for it and how make this calculation.thanking you
#10
08-10-2010, 07:40 PM
 Yves Guest Posts: n/a
Re: Need Help To Calculate Heat Dissipation for UPS

Hi,

I need help to calculate the total Heat Dissipation for a 20kva UPS.

Many thanks.

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