I need to fix a broken APC UPS (inverter)

[julianf]

I was given a 6kw UPS by a friend.

Symptoms are that one of the small caps ruptured on the main board (the one with all the through hole components). My friend cleaned it up and replaced with a close (but not identical) value capacitor.

The machine would still not boot (he tried loads, batteries, no batteries etc - i know they need batteries to boot)


My plan is to replace the cap with the correct value, and go from there. Ill take photos of the boards later today, but this is really a pre-emptive email, in case anyone is familiar with these devices.

Its a 6000XLI unit. The batteries are known good (my friend pulled two cages out of his other, running, ups, and sent me away with them instead, just so i could be sure they were good / charged)


This is not an earning job - the unit is mine if i can fix it.

 

[eSCHEn]

Know it's a silly one but have you checked the internal fuses? The blown cap may have taken one or more out.

 

[MattF]

If one electrolytic had ruptured, there's a good chance some others in that area ain't too peachy. Have a look for a dark brown residue underneath the surrounding electrolytics. Usually smells akin to rotting fish, so easy to check with a good old nose test. Also check for bulging tops on the electrolytics. As Eschen says, check fuses too, both the glass ones and any PCB mount Wickman fuses in the area. Plus make sure there's no track damage from when he replaced that one. Multi layer boards are cows to work on, and easily damaged.

 

[eSCHEn]

Multi layer boards are cows to work on, and easily damaged.

This needs plus oneing so much. They are awful to work with, the vias just die so easily.

Best way I found to replace blown caps on multilayer boards is to take pliers and crush old cap from top of board, leaving its legs still soldered in. You can then tack the new one on without having to desolder. Looks a pig but much easier to do.

 

[the snooper]

I would also obtain the correct cap aswell, you don't want anything altering the frequency that the circuitry runs at

 

[MattF]

Best way I found to replace blown caps on multilayer boards is to take pliers and crush old cap from top of board, leaving its legs still soldered in. You can then tack the new one on without having to desolder. Looks a pig but much easier to do.

A lot of chaps I've worked with have used that type of technique too, to save the risk of board damage. Worth adding a bit of hot melt glue to hold the cap in place solid too, as an extra precaution, if there's room.

 

[the snooper]

A lot of chaps I've worked with have used that type of technique too, to save the risk of board damage. Worth adding a bit of hot melt glue to hold the cap in place solid too, as an extra precaution, if there's room.

the cap doesn't even need to be upright

 

[eSCHEn]

Had forgotten about the hot glue. Yes, on its side so it's easy to get at to solder. Wee dab of glue on its back to hold it in place, do soldering, slightly larger glob of glue on legs to keep 'em rigid.

 

[julianf]

The physical work does not concern me. Ive spent more of my life with a soldering iron than i really care for. And the board is just dual layer - its just simple power supply stuff, but not the power supplies im used to...

The blown cap was pretty close (in signal path) to the mains input, so im hoping that things are still pretty simple at that point. The 'brains' of the machine is on a separate board entirely, stuffed full of microprocessors.

But, yes, i need to get the camera on it.

 

[Shox Dr]

6kva That's one hell of a UPS, I've just been given a 1.6kva to put in the truck. I'd love one that size

 

[julianf]

Friends replacement was 8, with an additional battery bank too (as in all batteries duplicated)

The novel thing about the large, expensive, units is that they regenerate the waveform all the time. So, i guess, everything that goes in from the mains gets converted to DC, and then regenerated to a nice shaped sine.

The smaller units just switch between mains and inverter when things start to go wrong.

...just uploading photos.

 

[julianf]

Right, so here is the board im looking at -

The AC comes in at the bottom left hand corner. You can see the terminals marked "Blue" and "Brown"

As i understand it, the two 24v dc relays to the right of the terminals are the ones that turn on and off the mains input, according to if the batteries are present / healthy.

Here is a view of the underneath of the board. I think that the pathway is along the edge of the board (ie from top left of the photo, rightwards)
You can see the flux where the cap was soldered in just under 2/3rds of the way across the photo (from the left) - at the end of the y-shaped thinner trace thats closest (but not close) to the top left corner.

Back to the top again, and moving further across - the two relays again -

And now onto where the damage was -

Im told that the small electrolytic ruptured, and spewed its guts over some distance. We're talking the one between the TO-220 package transistor and D732 / D733.

I have not powered up the board at all yet - need to find some space on the table. I wonder if the TO-220 package cooked the electrolytic some, however, replacing the electrolytic (with the incorrect value mind!) has certainly not cured the issue. Ive since been told that the correct part is a 33uF 35V, and the part currently fitted is a 47u 25v.


One final shot of the brains of the machine -

You can see its a much fancier board, plugging into the one im working on using its edge connector (female sockets are both covered, and just round the back of the heatsinks, which is why you cant see them in the shot)

 

[Wendelspanswick]

Right, so here is the board im looking at -

The AC comes in at the bottom left hand corner. You can see the terminals marked "Blue" and "Brown"

As i understand it, the two 24v dc relays to the right of the terminals are the ones that turn on and off the mains input, according to if the batteries are present / healthy.

Here is a view of the underneath of the board. I think that the pathway is along the edge of the board (ie from top left of the photo, rightwards)
You can see the flux where the cap was soldered in just under 2/3rds of the way across the photo (from the left) - at the end of the y-shaped thinner trace thats closest (but not close) to the top left corner.

Back to the top again, and moving further across - the two relays again -

And now onto where the damage was -

Im told that the small electrolytic ruptured, and spewed its guts over some distance. We're talking the one between the TO-220 package transistor and D732 / D733.

I have not powered up the board at all yet - need to find some space on the table. I wonder if the TO-220 package cooked the electrolytic some, however, replacing the electrolytic (with the incorrect value mind!) has certainly not cured the issue. Ive since been told that the correct part is a 33uF 35V, and the part currently fitted is a 47u 25v.


One final shot of the brains of the machine -

You can see its a much fancier board, plugging into the one im working on using its edge connector (female sockets are both covered, and just round the back of the heatsinks, which is why you cant see them in the shot)

We change out UPS's regularly, as we are trying to have one uniform size and make on each site. There are various brands and sizes we have recovered, I know there are some APC ones in the recovered pile.
Next time I go to our store I will have a root around and see if I can find an APC 6000XLI and pull the boards.

 

[julianf]

That would be great : )

I replaced the cap on this one, and half assembled it, and now ive realised something, which has me confused -

So far as i can tell, the cap that went is on the mains *input* side.
Now, of course, the very purpose of these things is to run without mains...

So it should boot from the batteries, even if i drilled holes in the mains input section. But it doesn't.

Ill have to take it apart again, and apply a less aggressive DC voltage, and see if i cant trace it a little. (im not sure if i like the idea of working on a 200v DC device)

 

[MattF]

So it should boot from the batteries, even if i drilled holes in the mains input section.

Not necessarily. Some UPS's won't allow you to fire them up when there's no mains supply present, or if that side of the circuit isn't working.

Ill have to take it apart again, and apply a less aggressive DC voltage, and see if i cant trace it a little. (im not sure if i like the idea of working on a 200v DC device)

Is there any life in the thing whatsoever when it's powered from the mains and you try to turn it on? I'd do some cold checks on the mains input circuitry before you start over thinking it. Just check all input fuses first and go from there.

 

[wookie]

Not necessarily. Some UPS's won't allow you to fire them up when there's no mains supply present, or if that side of the circuit isn't working.

I've looked on the APC site, your UPS is cold start capable, so even without the mains if the batteries are charged it should startup up and run from the batteries.

If it doesn't do that then you have bigger problems than just a blown psu capacitor.

 

[julianf]

That's what i feared.

Odd that two systems should fail at the same time - i would not have thought somthing so close to to the start of the mains input to make something fail right over on the other input chain.

...but it would seem that may be the case.

 

[julianf]

Another UPS, coming my way (this one works, but i am having to pay for it) -

8kva, and has the additional add-on battery pack. You would not want to put your tongue across those terminals!



Why do i want one?

Firstly, to keep the cnc machine running through brown outs etc.
Secondly, i have a 1950s single cylinder lister. Ive been trying to get that hooked up to the house electrics for some time, but have never been able to work out a way to not just cause issues (a grid tie inverter was my first plan, but then the engine wont track the load. i then thought about current shunts and servos, but never got around to it)

Anyhow, a large ups between the generator and the house will allow for short term overloads (ie pulling more power than the generator can supply) without needing the generator on full power all the time.

 

[Shox Dr]

How much was that if you do mind me asking

 

[julianf]

£140, with the additional battery pack. But, as ive found out above, APC units are a total gamble - no schematics or anything available when they die.