Gembir EG-UPS-PS3000-01

[Infineon]

Hi!

I have bought an UPS few months ago, but couple of weeks ago it failed, with a semi-loud bang and a flash. It was unpowered for few hours, and nothing was attached to it. It died exactly when it got power from wall outlet. All batteries were charged ~90%, and they still are almost fully charged.
Since it was under warranty, I have sent it for repairs. Unfortunately it was dropped few times during transportation, and plastic front panel got some cracks. Now post office and service center both point their finger at me, stating that it was my fault and nobody will repair damaged UPS. basically I got it back, with extra external damage.
I don't care about some cracks and scratches, what I care about is to get UPS working again.
After I got it back I took off cover, and now am trying to understand if I can get it repaired with some help. I disconnected wires from battery pack, and an 8-pin connector with 7 wires going into the board.

This is a UPS inside from left side:


This is a UPS inside from right side:


This is a closeup of board, with circle around a damage I've found:


This is a closeup of damaged spot:


I have no idea what kind of component was located there, but it's vaporized now, I didn't find much remaining of it inside the box.

Does anyone know what was damaged? Can UPS be fixed by just replacing this component?
Maybe somebody has same model of UPS to check what is supposed to be located in that spot?
I have basic tools like a soldering iron and multimeter, and do have some experience in soldering, but I have no idea how to fix something so complex, and I hope I can get some help here.

[TheMG]

Doesn't look like there was any component there, those are pads where another connector could have been soldered, but it was left unpopulated.

By the looks of it, I'd say something caused a short circuit between the pads labelled IP-L and IP-N (input live and input neutral). Could have been anything from a small piece of metal, an insect, or any other type of conductive debris.

Check to see if there is a fuse or breaker somewhere in line with the AC input to the UPS, that could be the only reason it's not working.

Also it looks like there is some damage to the pads/trace from the flashover, this could be an issue if the pad also doubles as a via to the other side of the board in which case the damage could have created an open circuit.

[Infineon]

Ok, I have tested UPS today, and it didn't go boom.
Thank you TheMGH!

I was hesitating to plug it into a wall socket, because last time it got plugged in a wall 20A fuse got blown in the building basement, so 1/3 of my apartment was without electricity for almost 2 days.

Now I have a new question:
I have discovered that batteries are connected in series, and there is no charging balancing. Is that safe?
I am thinking to set charging voltage to ~80% capacity in UPS software, and hook up some small 13.5V power supply to each battery independently, so that it keeps batteries topped up evenly. something like this https://www.amazon.com/Accessory-USA-Adapter-Charger-5-5mm3-0mm/dp/B00Y7RNLR6

Is it something that makes sense?

[Manul]

I have discovered that batteries are connected in series, and there is no charging balancing. Is that safe?
I am thinking to set charging voltage to ~80% capacity in UPS software, and hook up some small 13.5V power supply to each battery independently, so that it keeps batteries topped up evenly. something like this https://www.amazon.com/Accessory-USA-Adapter-Charger-5-5mm3-0mm/dp/B00Y7RNLR6

Is it something that make sense?

I think it is ok how it is. They should balance naturally while being charged to the top if some small trickle charge current is going. And for discharge balancing, well, there is none, so better not use UPS till 0%. Lead batteries generally like to stay fully charged and without deep cycling (even ones, which allow deep discharge).

[Infineon]

Ok, I guess those guys know what they do when they design UPS.
But now I have a question that I was not sure about for a long time.
When I was a student and didn't have any money for UPS but still wanted one, I got an UPS with dead battery for free. I didn't want to buy a new 7Ah battery, so I decided to hook up a 12V 60Ah car battery that was laying around in dad's garage. UPS worked just fine in a "UPS" mode for few minutes, but as soon as I have connected it to wall outlet it died spectacularly with green plasma and some smoke.
I am still unsure why would that happen? I mean - you can charge a car battery with cheapest ac/dc power brick, how come UPS didn't manage to perform?

Why do I have this question now? As you can see inside of UPS there is a spot for 4 more batteries. I can make a retaining piece from a sheet metal easily, but I am not sure if UPS will survive adding in parallel 4-in-series wired batteries, basically doubling the capacity. Will it go up in flames like the one I had many years ago? Some online sources say you can easily do this, but my experience tells me otherwise. I'm confused 

[Manul]

Well, there is no guarantee, that "UPS with dead battery" had only a dead battery and no other faults. Or maybe you used long leads? I would avoid that, long leads add inductance which might in some conditions cause problems. Hard to say, normally it should not be a problem.

[Infineon]

I did use Battery->jump starter wires->UPS leads->UPS
Didn't want to do any soldering before it is tested to work properly.

[Manul]

Yeah, maybe long leads was a problem. Inductance may cause voltage transients, ringing. Maybe that circuit was not well protected from such events and got damaged by high voltage.

[fzabkar]

AFAICT, J43 and J11 are wired in parallel. Assuming that the manufacturer did install a component in that unpopulated location, the only thing that would make sense would be a MOV. However, if that were the case, then where are its pins?

Could we see the other side of the PCB?