UPS Battery Backup

A few years back I enjoyed no electricity for 3 days thanks to a severe ice storm.

My APC 250W UPS powered my computer for about 10 minutes before beeping the low battery warning. I opened up the UPS and extended the battery leads over to a deep discharge marine battery. This type of lead-acid battery looks just like a car battery but is designed for deep discharge. Regular car batteries are usually damaged by deep discharge cycles. My computer then ran for just under 4 hours before the low battery warning sounded (estimate computer~150W).

If the "cycle" and "float" charge voltage on the UPS is acceptable for the new battery AND you do not attempt to draw more peak power than UPS is rated for, this configuration could be used on a regular basis. NOT very portable, but very useful in my case.

What decides for how much time battery will give backup

The three major items that determine how much time you will get from the UPS are:

1. Actual Battery capacity (may be less than printed on battery due to age)

2. Batteries state of charge.

3. How much load is connected (How many watts are being used).

There are some other minor things, but these are the major items.

Tom

My computer ~150 [W]

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Original UPS had one 12 [V] 6 [A-hr] sealed-lead-acid (SLA) battery.
12[V]*6[A-hr] =72 [W-hr]

For this size and chemistry battery, 150[W] is a very high discharge rate and the losses in the battery are 50% or more.
72 [W-hr] * 0.5 = 36 [W-hr]

36 [W-hr] / 150[W] =0.24[hr] = 14.4 [minutes] (mine lasted only 10 [minutes])

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Marine battery was rated 12 [V] 50 [A-hr]
12[V]*50[A-hr] =600 [W-hr]

For this large battery, 150[W] is a fairly low discharge rate and the losses in the battery are only around 10%.
600 [W-hr] * 0.9 = 540 [W-hr]

540 [W-hr] / 150[W] =3.6[hr] (mine lasted 3.75 [hr])

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Both theoretical (calculated) and actual use times agree fairly well. You should be able to apply similar calculations to estimate your run-time.

What is Ah/20Hr written on battery?What does it mean?How to calculate how much current output battery gives? My ups is 6oowatts input240v1-3A when battery connected o/p24o at 1.2A what max. cofiguration of battery can it take without damaging it? How to calculate losses in battery?

12[V] 8.2[A-hr]/ 20[hr]

means your "battery" is intended to supply its rated energy over a 20 [hr] period.

Energy = 12[V]*8.2 [A-hr] = 98.4 [W-hr]

Rated "battery" output power = 98.4 [W-hr] / 20 [hr] = 4.92 [W]

To get the most energy out of your battery, your load should be only 5 [W] !

You can see that the full battery capacity is only available for SMALL loads. When you attempt to pull energy from the battery at a faster rate, more of that energy is lost inside the battery. There is no easy way to calculate this energy-loss curve unless the manufacturer of the battery is willing to supply it.

Without data from the battery maker, I ESTIMATE performance by assuming an internal battery resistance Ri. For this size SLA battery, I'd use a value around 0.5 [ohm].

A larger battery WILL take longer to recharge and, if designed correctly, the charging circuit should not be damaged. Without detailed schematics of your UPS, there is no way to know for certain.

Good Luck!

Thanks yar, One last question can i connect 12v5OAH lead acid battery to my 6oowatt ups without damaging it.

Need full schematics of your UPS to determine if larger battery will cause internal charger damage.

I m having only following info 6oowatt ,input 240V at 2A when battery is connected,output 230-240v at 2.5A.

Sorry, not enough information.

Ok u help me lot i will take help of my other friends. Thanks 1s again

I have a simillar UPS that is 4 yrs old with weak battery. I am using one CFL 13W during power outrages happily since last one-half-year; that is giving me 4 to 5Hrs light.

I have been using APC ups' for full wave inverters for over two years now, first with an APC 1400 and now with an APC 3000 (that I picked up on eBay for $62.50 US)

When I first contemplated the use of a UPS (full time) as a home inverter my questioning was similar (how long will the unit last?). APC and other vendors will have a "run chart" that will attempt to predict the "backup" time the included batteries will support a load - the amount of watts or amps the devices attached to the UPS will draw from the battery reserve.

By looking at the UPS model and its rating, and using the vendor "run chart" you can calculate your minutes or hours of run time.

As another member indicated, adding larger storage batteries at the input of the UPS battery connections will extend the run time. However, be sure you do not overload the charging circuit of the UPS when the UPS is "plugged" into the electrical grid.

Below is my battery supported (solar panel charged bank). With 3.8 Kwatts of solar panels, I run my refrigerator, entertainment equipment, and about 1/3 of my home CFL's and a few incandescent lamps too - 24 hours a day - as long as I get a good, sunny day. (As they say, some restrictions apply).

The most I've drawn from this battery bank - through the UPS is 22 amps, at 48 v, DC.

Members, forgive the mess, this image was taken just after I'd finished the last connections and all was working. I've cleaned and arranged all the wiring now.

Yes, I have a mixed set of batteries and capacities, but all seems to work well. Perhaps not as efficiently as it could be, but it was inexpensive.

Good luck on your own project and have fun.

You can use any type of 12 V Lead Acid battery to replace the damaged old battery. Of course the battery will be out of the UPS box frame and you must extend the leads out and connect the new battery. Even you can use 120 Ah or more. No matter it is a stationary type deep charge or a tractionary vehicle type.

However, never attempt to charge the battery with the charger integrated in the UPS. It is designed to charge 2 Ah or some higher batteries. Do not take the risk of charging high AmpH battery from your internal charger. It may damage the total UPS function.

Use an external battery charger to recharge the battery and with trickle function, when battery is full. A battery charger with 6 Amp. output may be suitable for your purpose.

Plug off the 220 Volt mains supply of your UPS.

UPS must only powered from the battery but not from your mains network. The mains network is only used to recharge your battery.

Kindest Regards

Thanks buddy it was very helful for me. On my old ups battery there was written initial current=2.1Amp what does it mean? Can i connect 12v 12Ah/20hr lead acid battery? My ups is 600watt it is input power or output?Is there any relation of this to battery configuration?

This is an addition to my previous post.

By the way get rid of the beeper inside UPS, it will continuously beep to indicate mains network is interrupted.

Plug off you UPS's 240 Volt mains network cable. Otherwise the internal battery charger will try to recharge your external battery and will damage your UPS.

Apart from the fact that most cheap UPS specs exaggerate about the actual continous max power they can provide these specs count in the fact that the build-in battery's capacity will not allow enough time for power electronics and transformers to overheat. Connecting a bigger battery that could provide hours of power all UPS passive cooling systems and most active just can't cope with that continusly and you must derate your needs accordingly. I would say by 50% for active and about 80% or worse for passive cooling systems and still not be on the safe side. I've seen 600W UPS with ~200 g of T-shaped Al heat sink with NO fins and NO air circulation in an almost closed plastic box. What can you expect from that configuration? Like 90% derate maby? Unless you're in a mood for modifications.