UPS turns off at load when on battery

Hi.

I have a 1000va UPS that I use for my Computer as their are numerous blackouts in my area. Recently I moved to a new location and for a few days initially, the mains voltage kept dropping too low (~170-200v instead of 220/230), during which time the UPS would go to the battery, but after it will run out in a few minutes, it will turn off (The on-battery indicating LED would turn off) but it would continue to beep and supply the same input voltage as it was getting to output (which didn't cause my computer to restart). This kept happening for about 7 days, after which the voltage was fixed (215-220v). But now since a few days, it is not charging the batteries fully (my own opinion, could be something else) as it turns off within a second or two after the power fails, if the computer is turned on when it happens. I have also noticed that one of its relay switches after few minutes of power returning, which I am guessing is the one that charges the batteries.

I am posting its front side of the main PCB in the hope that someone can please tell me what is the purpose of the two VR at the bottom left, and if I can adjust any of them to make sure that it will charge the batteries fully, or if I need to check any other components with a multimeter. There are two 12v 7Ah batteries in it, one was at ~13v and the other at 11.9v after I had it connected to mains for more than 8 hours.

P.S: When I checked its output volts on battery, without load; it was at 160-170v only.

Thank you.

hi I dont know the purpose of VR here but I think you should change the battery or change the water of battery at any battery shop.
also had same problem i changed the battery water.

The battery is a sealed one, so I guess I would have change one or both if I can make sure that the fault is with batteries. The one at 13v has the main connector that goes to the transformer (a really thick cable because of high amperes), and this connector seems to have burnt a bit too. The other battery is actually at 11v.

Open circuit measure of battery voltage with DMM does not indicate whether a SLA battery is good or bad
Remove the batteries from the circuit
Now connect an automotive 12V 15W bulb or any similar 12V bulb across the terminals of the battery and see if the bulb lights up well enough or dims out.
If the battery is all right the bulb should be well lighted
If the battery is bad the bulb will dim out within a few seconds
This way you can be sure if the battery is good or bad

Tipu606 said:

Open circuit measure of battery voltage with DMM does not indicate whether a SLA battery is good or bad
Remove the batteries from the circuit
Now connect an automotive 12V 15W bulb or any similar 12V bulb across the terminals of the battery and see if the bulb lights up well enough or dims out.
If the battery is all right the bulb should be well lighted
If the battery is bad the bulb will dim out within a few seconds
This way you can be sure if the battery is good or bad

Click to expand...

the variable shown above side seems to be for increasing/decreasing the output voltage of inverter and lower one for adjusting the 50/60 Hz frequency but its approximation.detail can be told if complete cct.diagram is available.regards

Tipu606 said:

Open circuit measure of battery voltage with DMM does not indicate whether a SLA battery is good or bad
Remove the batteries from the circuit
Now connect an automotive 12V 15W bulb or any similar 12V bulb across the terminals of the battery and see if the bulb lights up well enough or dims out.
If the battery is all right the bulb should be well lighted
If the battery is bad the bulb will dim out within a few seconds
This way you can be sure if the battery is good or bad

Click to expand...

I checked it, and the bulb does not get dim, at least not for about 5 minutes. The current through batteries when the UPS is connected to AC is about 0.10A.

@Wazir.
Thanks. I will check the variable to confirm if it increases the output voltage, but then I guess the fix isn't going to be limited to just adjusting the variable. I have a picture of PCB contacts side too, but matching all the connectors to make a circuit diagram is going to be tough/time consuming. Can you (or anyone else) point to the part of the circuit which most probably senses the voltages of batteries and consequently turns the charging on/off?