Regarding faulty UPS

[garvind25]

Hi,



My PC UPS (Zebronics – ZEB U725) is not giving backup when there is a power failure. It is 2.5 years old. To check it, I opened it and tested the voltages.

The battery is a 12 V, 7.0 AH sealed Lead Acid battery. The ratings of the battery are:

For cycle use: 14.6-14.8 V

For standby use: 13.7-13.9 V



The battery voltage (under open condition) is 13.39 V. The charging voltage from the UPS (under no battery connected condition) is 13.43 -13.45 V. As per the article here, the output of the battery seems to be OK for standby use but not for cycle or backup use. Pls. correct me if my interpretation is incorrect.



I wanted to ask the following:

** Which do you think has gone bad – the battery or the UPS?

** If the UPS circuitry has gone bad, how to check it?

** How to ascertain if the battery has gone bad?



Any pointers will be thankfully acknowledged.



Regards,

Arvind Gupta

 

[KlausST]

HI,

check the battery voltage in backup mode.
If it drops below 11V(or goes into low battery shutdown) --> replace the battery.

Indeed a battery voltage below 11.5V with low load means the battery is bad or at least almost discharged.

Klaus

 

[d123]

Hi,

Not good at this stuff, simple first check is if you can check battery electrolyte level, might need to top it up with distilled water.

 

[garvind25]

check is if you can check battery electrolyte level, might need to top it up with distilled water.

As already mentioned, it is a Sealed lead acid battery.

--- Updated Oct 31, 2020 ---

HI,

check the battery voltage in backup mode.
If it drops below 11V(or goes into low battery shutdown) --> replace the battery.

Indeed a battery voltage below 11.5V with low load means the battery is bad or at least almost discharged.

Klaus

As already mentioned it is not giving any backup. So how do I check voltage in the backup mode

 

[betwixt]

Get hold of a 12V car headlight lamp. With the AC power turned off, temporarily connect it across the battery terminals. If the battery is good it will light brightly and the battery voltage will stay at or above 12V. If the voltage drops significantly or the lamp is dim, the battery needs replacing.

I suggest this because a headlight lamp will draw about the same current from the battery as the UPS circuitry so it makes a good alternative load to do the testing.

If the battery is good there is a fault in the circuits and we would need a schematic to fault find it.

Brian.

 

[garvind25]

Get hold of a 12V car headlight lamp. With the AC power turned off, temporarily connect it across the battery terminals. If the battery is good it will light brightly and the battery voltage will stay at or above 12V. If the voltage drops significantly or the lamp is dim, the battery needs replacing.

I suggest this because a headlight lamp will draw about the same current from the battery as the UPS circuitry so it makes a good alternative load to do the testing.

If the battery is good there is a fault in the circuits and we would need a schematic to fault find it.

Brian.

OK. I will try with a dummy load. Since I don't have a car headlight, can you pls. suggest any alternate load for the battery. Or could you tell approx. how much current is drawn from the battery by the UPS while it is providing backup.

Thanks,
Arvind

 

[KlausST]

Hi,

As already mentioned it is not giving any backup. So how do I check voltage in the backup mode

The important point is not to measure it unloded. Any load ... maybe around 100mA ... is O.K.
When backup mode is not possible then use a resistor, an incandescent lamp, a fan ... or anything else.

Klaus

 

[Easy peasy]

Almost certainly the batteries have lost capacity - they are not of the highest quality to start with - simply replace and test ...

 

[garvind25]

Almost certainly the batteries have lost capacity - they are not of the highest quality to start with - simply replace and test ...

Yes. The battery was faulty. Replaced it. The UPS is working OK now.

 

[BradtheRad]

Congratulations on fixing it yourself.
Although 2.5 years seems short for sealed lead-acid type, it does amount to the expected few years of life in UPS batteries.