UPS Failure

Thread Starter


Joined Dec 5, 2004
Hello all,

I have 2 generic brand UPS's and after a few years they have both failed to support my pc's even though I change the batteries every 2 years.
They worked very well for my requirements. I measured the voltage on the battery (the block type 12v 7a) and it is about 13.3v.
I have taken apart one UPS as I read somewhere that cheaper brand UPS often kill the batteries by over-charging them to quickly but there are no pots on the board to adjust any voltages.

Here is what the board looks like.

I am wondering if it is worth changing any of the parts to save these instead of buying new ones?


Joined Jun 22, 2012
The batteries will be monitored by an op amp comparator, probably the LM324,looking at the pcb there are two positions for Vr1,Vr2, linked out,Vr3 is on the top right corner, you would need to reverse engineer the output side to see how it pulses.


Joined Jun 8, 2013

Are any of the batteries swollen? That is a sign of overcharging.
The more expensive UPS's have a load calibration test where the batteries
are allowed to discharge under load and the correct amount of trickle charge is auto adjusted.
If the batteries are not swollen, overcharging is probably not the problem.

Thread Starter


Joined Dec 5, 2004
Hi, thanks for your replies Dodgydave and eetch00.
The batteries are not swollen so I guess I will have to look an see what the LM324 are doing.