Backup battery for ups

Hi Guys !

Due to prolonged loadshedding, I want to use a backup battery for my UPS. This battery will be charged by a separate battery charger.

The question is :

What arrangement should I have to make so that when the primary battery is discharged, it is automatically switched over to backup battery. Upon restoration of power supply, both the batteries restore to their orignal charging systems.

Any idea ?

Just connect them in parallel connection, or ask some battery dealer, he'll tell you how to connect both batteries in parallel or hire a tech man from him, he'll charge you 200-400 rps and connect your batteries to increase your backup. You really don't need to have a separate charger and then attach/remove batteries again and again...

When we attach batteries in parallel, both are charged at the same rate as if each battery has its own charger. Right?

If a battery is low charged or no charged for a long time, it dies.

how will the batteries be charged if they are in parrallel incase they are discharged to different level?

and which battery will be used if both are connected in parrallel?

if both batteries are used equally the the smaller one will discharge quickly,,so how do the charger knows that one is discharged?

One thing I am still unclear is that when my UPS is unable to fully charge existing battery, how will it be able to charge another battery connected in parallel.

We have 6 hrs continuous loadshedding and the UPS has only 1 to 2 hrs for charging.

[quote=“adnan.ahmed, post:, topic:”]

Hi Guys !

Due to prolonged loadshedding, I want to use a backup battery for my UPS. This battery will be charged by a separate battery charger.

The question is :

What arrangement should I have to make so that when the primary battery is discharged, it is automatically switched over to backup battery. Upon restoration of power supply, both the batteries restore to their orignal charging systems.

Any idea ?

[/quote]

You do not need any separate charger to charge secondary battery. Just connect it in parallel with the primary battery. Make sure both primary and secondary batteries are of equal capacity. Otherwise, you will face complications like overheating of smaller capacity battery, unfinished charging of larger battery.

[quote=“hawker, post:3, topic:16778”]

When we attach batteries in parallel, both are charged at the same rate as if each battery has its own charger. Right?

If a battery is low charged or no charged for a long time, it dies.

[/quote]

In parallel, voltage remains the same but current is distributed. Suppose, the charger is of 10 amps and it has to charge two batteries connected in parallel. Current shall be equally distributed i.e. 5 amps for each battery. Now, the point is, if one battery is smaller in capacity, it shall get charged first and if charging is not cut off, it shall start getting hot and energy is dissipated in the form of heat i.e. electrical energy starts converting into heat energy.

[quote=“jhagra, post:4, topic:16778”]

how will the batteries be charged if they are in parrallel incase they are discharged to different level?

and which battery will be used if both are connected in parrallel?

if both batteries are used equally the the smaller one will discharge quickly,so how do the charger knows that one is discharged?

[/quote]

That’s the point which should be clarified. Both batteries are discharged at the equal rate. Both batteries are discharged simultaneously. But what happens when two different capacities are used in parallel, for this I give an example. Say one battery is 50 Ah and the other one is 150 Ah both connected in parallel with each other. Now, they are allowed to discharge. Both shall discharge at the equal rate but since smaller battery has only 50 Ah capacity, it empties first and gets deeply discharged but the bigger battery which has the capacity of 150 AH, it keeps discharging during the process. So, in a nutshell, it is extremely bad idea to connect different capacity batteries in parallel.

[quote=“adnan.ahmed, post:5, topic:16778”]

One thing I am still unclear is that when my UPS is unable to fully charge existing battery, how will it be able to charge another battery connected in parallel.

We have 6 hrs continuous loadshedding and the UPS has only 1 to 2 hrs for charging.

[/quote]

Oh, that’s the thing. So, in this case, you should not connect batteries in parallel with the single UPS. This will not increase the backup time as you are mentioning that UPS has only 1 or 2 hours in between the power outages to charge the batteries. So, I advise, if you can afford, buy another UPS. This will ease your troubles.

thanks blogger bro..

ah,, can u tell is there any seperate charger available in the market for lead acid battery and whats its price/brand intelligence,, means does it tells if its fully charged and trickles it ?

[quote=“blogger, post:6, topic:16778”]

You do not need any separate charger to charge secondary battery. Just connect it in parallel with the primary battery. Make sure both primary and secondary batteries are of equal capacity. Otherwise, you will face complications like overheating of smaller capacity battery, unfinished charging of larger battery.

In parallel, voltage remains the same but current is distributed. Suppose, the charger is of 10 amps and it has to charge two batteries connected in parallel. Current shall be equally distributed i.e. 5 amps for each battery. Now, the point is, if one battery is smaller in capacity, it shall get charged first and if charging is not cut off, it shall start getting hot and energy is dissipated in the form of heat i.e. electrical energy starts converting into heat energy.

That’s the point which should be clarified. Both batteries are discharged at the equal rate. Both batteries are discharged simultaneously. But what happens when two different capacities are used in parallel, for this I give an example. Say one battery is 50 Ah and the other one is 150 Ah both connected in parallel with each other. Now, they are allowed to discharge. Both shall discharge at the equal rate but since smaller battery has only 50 Ah capacity, it empties first and gets deeply discharged but the bigger battery which has the capacity of 150 AH, it keeps discharging during the process. So, in a nutshell, it is extremely bad idea to connect different capacity batteries in parallel.

Oh, that’s the thing. So, in this case, you should not connect batteries in parallel with the single UPS. This will not increase the backup time as you are mentioning that UPS has only 1 or 2 hours in between the power outages to charge the batteries. So, I advise, if you can afford, buy another UPS. This will ease your troubles.

[/quote]

Stop posting misleading information which is not accurate. :rolleyes:

Sufficiently detailed discussion on parallel batteries:

[quote=“adnan.ahmed, post:5, topic:16778”]

One thing I am still unclear is that when my UPS is unable to fully charge existing battery, how will it be able to charge another battery connected in parallel.

We have 6 hrs continuous loadshedding and the UPS has only 1 to 2 hrs for charging.

[/quote]

You would need higher capacity charger (separate from UPS if the UPS one isn’t sufficient) to first make sure that your existing battery gets nearly fully charged. If your existing battery isn’t being fully charged by your current charger, there is no point to using another battery in parallel. It would be like trying to fill up two empty glasses with half a glass of water.

[quote=“blogger, post:6, topic:16778”]

Oh, that’s the thing. So, in this case, you should not connect batteries in parallel with the single UPS. This will not increase the backup time as you are mentioning that UPS has only 1 or 2 hours in between the power outages to charge the batteries. So, I advise, if you can afford, buy another UPS. This will ease your troubles.

[/quote]

So that was my original question. Is their any means (any diode or switch etc.) which I fix in between the two batteries so that when the original battery discharges, the supply is automatically switched over to backup battery which has been charged by a separate battery charger.

[quote=“Asad, post:9, topic:16778”]

You would need higher capacity charger (separate from UPS if the UPS one isn’t sufficient) to first make sure that your existing battery gets nearly fully charged. If your existing battery isn’t being fully charged by your current charger, there is no point to using another battery in parallel. It would be like trying to fill up two empty glasses with half a glass of water.

[/quote]

Ok. My existing battery isnt fully charged by current UPS charger. Other battery would be charged separately by another charger. I want it to remain as backup and only come into play when the first battery discharges. The only concen is how the connection would be established.

A small circuit would be needed to detect the LVC for the first battery and then switch over to the other battery via some contactor, etc. If interruption in UPS operation is not a concern when switching from one battery to the other, you could also consider a high current/utility supply changeover switch commonly available in market.

you should connect your batteries with paralleled

because voltages are same in parallel combination