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Anonymous Poster

Suitable Battery for UPS, 120 or 200AH?

09/09/2010 12:18 AM

Dear CR4 Engineers;

I have a UPS 220V 500VA in my home which I use for fans, lamps etc during local power break down. Last year I connected 12V 120AH lead acid battery with UPS. UPS works 1hour and remains stand (battery charging mode) by for 2-3 hours and thus it worked approximately 4-5hours (average) during 24hours. The running load on UPS was almost 200W.

After one year of battery life, now I found that during UPS working, battery voltage drops from 12.5V to 9V only in 20min with same connected load. I guessed that battery life is over. Now question is that if I connect 200AH battery instead of 120AH, is the life of new battery would be exceeded? For me, if voltage drop of battery cells (during working) would be minimum, there over all life would be exceeded. Please suggest me for the capacity of new battery.

I am sorry for my poor explanation.

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#1

Re: Suitable battery for UPS, 120 or 200AH?

09/09/2010 12:38 AM

you can contact your battery vendor to recharge the battery, you can recharge the battery instead buying new. by the way what is the battery make and type

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Anonymous Poster
#2
In reply to #1

Re: Suitable battery for UPS, 120 or 200AH?

09/09/2010 1:28 AM

I think no battery charging is needed as UPS charges the battery well. When battery was new, it charges within 1.25 hours after usage but now it doesn't charge even in two hours and its out side temperature rises during charging.

The battery is Osaka brand N-120

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Guru
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#3
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Re: Suitable battery for UPS, 120 or 200AH?

09/09/2010 1:50 AM

The problem might be the type of battery.

Lead- Acid batteries don't like deep discharge(s) and cannot handle this well, unless you go for deep cycle batteries, that are a lot more expensive.

When discharging under 10 volts, regular batteries' life shortens dramatically. (means - not taking new charge - or losing charge quickly)

The more Ah - the more backup time is evident, but don't calculate with the 200Ah in mind, since you can only use a part of it.

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#4

Re: Suitable Battery for UPS, 120 or 200AH?

09/09/2010 8:04 AM

Hi,

You can look to buy a battery but you have to take care the battery charger in the UPS is having the ratings to charge the battery otherwise your new battery is never going to charge properly or the charger will get burned up.

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#5

Re: Suitable Battery for UPS, 120 or 200AH?

09/09/2010 8:24 AM

Please suggest me for the capacity of new battery.

Step 0. A little tutorial on measurements of charge. After all, it is electrons that are stored in the battery. In phreshman fisicks we all learned that the measure of charge is the coulomb and that a single electron has 1.602e-19 coulombs of charge. One amp flowing in a wire for one second will use one coulomb of charge.

Q = I*t

where Q is the charge in coulombs, I is the current in amps and t is the time in seconds.

The amount of charge passing through that wire (conducting 1.0 amps) in 60 seconds is 60 coulombs, and in one hour you would have had said "hello" and "goodbye" to 3600 coulombs of charge.

Batteries were evidently developed by engineers who subscribed to the "whatever's easiest" system of measurement. They got tired of pulling out their slide rules to divide by 3600 every time they wanted to know how long 24000 coulombs would last them and came up with the unauthorized unit of amp-hours. Later, when smaller batteries were used they came up with milliamp-hours.

Don't be confused by the hyphen. Amp-hours means amps times hours. Divide by amps and you get hours, divide by hours and you get amps. So it isn't amps, and it isn't amps per hour, it is amp-hours. And, by the way, I have even used the term amp-seconds because when you say "coulombs" everybody goes glassy-eyed on you.

Don't get me wrong, I love amp-hours for units, it is a handy rule of thumb. Amp hours is how much charge is stored in the battery. Since a battery changes voltage during the discharge, it isn't a perfect measure of how much energy is stored, for this you would need watt-hours. Multiplying the average or nominal battery voltage times the battery capacity in amp-hours gives you an estimate of how many watt-hours the battery contains.


E = C*Vavg


Where E is the energy stored in watt-hours, C is the capacity in amp-hours, and Vavg is the average voltage during discharge. Yes, watt-hours is a measure of energy, just like kilowatt-hours. Multiply by 3600 and you get watt-seconds, which is also known as Joules.

As long as we are in the prelude, I might also mention that since the charge in a capacitor is Q=CV that a battery can be rated in farads as well. A 1.5 volt AA alkaline battery that stores 2 amp hours of charge (that's 7200 coulombs) has the equivalent capacitance of 4800 Farads. Of course a battery makes an awfully weird capacitor because the voltage doesn't drop proportionally to the stored charge, it has a high equivalent resistance, and etc.


The following method assumes that you know how many amps you need for the gadget under power. If you know the watts go to Step A below.

Step 1. Back of the envelope

If the current drawn is x amps, the time is T hours then the capacity C in amp-hours is

C = xT

For example, if your pump is drawing 120 mA and you want it to run for 24 hours

C = 0.12 Amps * 24 hours = 2.88 amp hours

Step 2. Cycle life considerations

It isn't good to run a battery all the way down to zero during each charge cycle. For example, if you want to use a lead acid battery for many cycles you shouldn't run it past 80% of its charge, leaving 20% left in the battery. This not only extends the number of cycles you get, but lets the battery degrade by 20% before you start getting less run time than the design calls for

C' = C/0.8

For the example above

C' = 2.88 AH / 0.8 = 3.6 AH

Step 3: Rate of discharge considerations

Some battery chemistries give much fewer amp hours if you discharge them fast. This is a big effect in alkaline, carbon zinc, zinc-air and lead acid batteries. It is a small effect in NiCad, Lithium Ion, Lithium Polymer, and NiMH batteries.

For lead acid batteries the rated capacity (i.e. the number of AH stamped on the side of the battery) is typically given for a 20 hour discharge rate. If you are discharging at a slow rate you will get the rated number of amp-hours out of them. However, at high discharge rates the capacity falls steeply. A rule of thumb is that for a 1 hour discharge rate (i.e. drawing 10 amps from a 10 amp hour battery, or 1C) you will only get half of the rated capacity (or 5 amp-hours from a 10 amp-hour battery). Charts that detail this effect for different discharge rate can be used for greater accuracy. For example the data sheets listed in http://www.powerstream.com/BB.htm

For example, if your portable guitar amplifier is drawing a steady 20 amps and you want it to last 1 hour you would start out with Step 1:

C=20 amps * 1 hour = 20 AH

Then proceed to Step 2

C' = 20 AH / 0.8 = 25 AH

Then take the high rate into account

C''=25 /.5 = 50 AH

Thus you would need a 50 amp hour sealed lead acid battery to run the amplifier for 1 hour at 20 amps average draw.

Step 4. What if you don't have a constant load? The obvious thing to do is the thing to do. Figure out an average power drawn. Consider a repetitive cycle where each cycle is 1 hour. It consists of 20 amps for 1 second followed by 0.1 amps for the rest of the hour. The average current would be calculated as follows.

20*1/3600 + 0.1(3559)/3600 = 0.1044 amps average current.

(3600 is the number of seconds in an hour).

In other words, figure out how many amps is drawn on average and use steps 1 and 2. Step 3 is very difficult to predict in the case where you have small periods of high current. The news is good, a steady draw of 1C will lower the capacity much more than short 1C pulses followed by a rest period. So if the average current drawn is about a 20 hour rate, then you will get closer to the capacity predicted by a 20 hour rate, even though you are drawing it in high current pulses. Actual test data is hard to come by without doing the test yourself.



If you know the watts instead of amps, follow the following procedure

Step A: Convert watts to amps

Actually, watts is the fundamental unit of power and watt-hours is the energy stored. The key is to use the watts you know to calculate the amps at the battery voltage.

For example, say you want to run a 250 watt 110VAC light bulb from an inverter for 5 hours.
Watt-hours = watts * hours = 250 watts * 5 hours = 1250 watt hours

Account for the efficiency of the inverter, say 85%

Watt-hours = watts * hours / efficiency = 1250 / 0.85 = 1470 watt-hours

Since watts = amps * volts divide the watt hours by the voltage of the battery to get amp-hours of battery storage

Amp-hours (at 12 volts) = watt-hours / 12 volts = 1470 / 12 = 122.5 amp-hours.
If you are using a different voltage battery the amp-hours will change by dividing it by the battery voltage you are using.

Now go back to Steps 2-4 above to refine your calculation.

Refer to the links in the article for battery chemistry FAQs.

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Anonymous Poster
#6
In reply to #5

Re: Suitable Battery for UPS, 120 or 200AH?

09/09/2010 11:42 AM

This is a good explanation,but why you move this good technical information so easily from USA to the Third world ?

Didn't you the lesson so far ?

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Guru

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#7
In reply to #6

Re: Suitable Battery for UPS, 120 or 200AH?

09/10/2010 3:36 AM

Information that is not proprietary is to be shared with all - not hoarded for personal gain.

RDGRNR is doing what is correct and fair - hats off to all with attitudes like him!

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Anonymous Poster
#8
In reply to #7

Re: Suitable Battery for UPS, 120 or 200AH?

09/10/2010 6:18 AM

Well,take the information then use it to commit massacres against humanity.

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Anonymous Poster
#9
In reply to #8

Re: Suitable Battery for UPS, 120 or 200AH?

09/10/2010 7:46 AM

information is power for everybody. good information is like a cool drink of water. so what does this information have to do with a massacres against humanity. when you keep information from humanity than they are kept in bondage.

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Guru

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#10
In reply to #9

Re: Suitable Battery for UPS, 120 or 200AH?

09/10/2010 9:08 AM

I agree with you - It seems the other guest is 1) a coward as he probably has a user name, 2) some kind of psychological problem 3) some very strange politics and 4) no idea of what is useful to bad guys and what is not

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Anonymous Poster
#11
In reply to #9

Re: Suitable Battery for UPS, 120 or 200AH?

09/10/2010 9:44 AM

This Guest is russ123 and is hiding his user name and then came back with his name in the next post.

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Guru

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#12
In reply to #11

Re: Suitable Battery for UPS, 120 or 200AH?

09/10/2010 12:49 PM

Sorry bout that - I am not hiding or making stupid points - only responding to them.

I reported your lying about the post to admin - just for your information.

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Anonymous Poster
#13
In reply to #12

Re: Suitable Battery for UPS, 120 or 200AH?

09/10/2010 6:26 PM

Lying birth place is the Middle East.

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#14
In reply to #13

Re: Suitable Battery for UPS, 120 or 200AH?

09/11/2010 12:05 AM

We should care?

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#15

Re: Suitable Battery for UPS, 120 or 200AH?

11/18/2010 5:08 AM

Hi all

I am a muslim and pakistani I am Electrical Engineer with Masters from UK .Let me be honest with you what is actually happening in Middle east .I have very good friends from US and UK and they are real friends regardless of nationality or religion it is above all that .What my personal experince is about Middle east specially arabs is they follow a simple rule "copy and paste " I have worked with huge companies in middle east I couldnt believe when i heared b*llsh*t from them and my collegues from UK and US asked me question and i feel shame on all that stuff .My request is pass information to those who can really make this world heaven not like dumbs .

Please accept my appology if some body gets hurt

God Bless you all

Excellent answer by RDGRNR keep the good work for good people

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