[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 ?
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.
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?
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.
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.