Failing UPS taken apart

Other Hardware General Electronics
1

I took apart a ups which stopped working properly in the sense that if I disconnect it from the wall, whatever is plugged into it fails.

This is a very common failure in cheap ups like centra brand here. So I opened it and took a look inside and couldn't see anything that immediately caught my attention. I tested the battery terminals and it read a healthy 12.5. I say healthy because its been unplugged for the past 2 weeks so it has managed to retain its soc.

So I'm wondering if you all could give me your ideas on what usually fails in these ups units?

2

Check the battery with a load on it and see what the voltage is. I have not looked into these units, but I would start by making sure the battery could handle a load. I have seen lead acid batteries show 12 volts with no load, but put a 5 amp load on them and the bottom drops out.

3

It's not uncommon that lead/acid batteries in a UPS fail in two years time.
Leo..

4

Marciokoko:
So I opened it and took a look inside and couldn't see anything that immediately caught my attention.

You're lucky that the high voltage on the line capacitors didn't catch your attention!

5

The batteries. The output voltage will plummet under load, I'd wager. Lead acid batteries suck.

6

aarg! :slight_smile: True, thanks for pointing that out. I guess they should be the 2 ones in the back near the heat sink?

I cant tell from the picture anymore and I already closed it back up, but Im guessing they would be 120V or so? Or could they be greater?

ups.png
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Ok so although the battery might read 12.5V, it might be shot when under load, which would be the reason why the ups beeps and turns off when it has something plugged into it.

Anything else I can salvage from it? I found the IRLB4132 in the back connected to the heat sink, which are power mosfets. What exactly do these things do in a power supply? I understand they are transistors, but voltage controlled instead of current controlled. But Im wondering if there is anything I could use these for, even tinkering?

There is a KA3843 which appears to be a PWM IC.

There are BRD-SS-112L which are relays.

So apart from the heat sink and a few LEDs or maybe some copper wire, dunno if I should keep anything else. Maybe the magnets form the coils just for fun.

7

I assume you are referring to some toroidal inductors (look like small doughnuts wound with wire) - those are typically not magnets although they do have a ferrite core. They are inductors used in the part of the power conditioning. I would not expect you to actually find any real magnets in there. As to what to keep, that depends what you want to do. If it were mine, I think I would change it around a bit to use a standard 12v car battery external to the case and continue to use it if the rest of it was working OK (but then, I am a packrat that still has vacuum tube stuff downstairs too )

8

Well I could replace the battery but it costs about as much as a new ups.

Yeah the transformer is not a motor, I was confusing it with a DC motor.

Thanks

9

If it were mine, I would use a car battery as well and keep using it. I actually need to do the same to mine. My battery is shot, though it did last almost 4 years, it will only keep my system running for about 30 secs. If you don't need it or want it, then harvest all the parts you can as you never know what you will need in the future.

Marciokoko:
Well I could replace the battery but it costs about as much as a new ups.

But, with a car battery, especially the deep cycle, would allow the system to stay on longer. A UPS with this much capacity cost $$$$.

10

That was what I was talking about. Many of the deep cycle car/rv batteries have not only the regular battery posts, but terminals with wingnuts on them as well. External to the case, but much better capacity (and easier to get a replacement) than the built in battery. Watch for the acid though - they have sulfuric acid in them - best to put the battery in a battery box and leave the top open for ventilation (they produce hydrogen when charging). Make sure you use heavy enough wire when extending the wires from the inside to the external battery (use stranded wire, not solid)

11

codlink:
But, with a car battery, especially the deep cycle, would allow the system to stay on longer. A UPS with this much capacity cost $$$$.

Of course the UPS will never actually recharge the car battery, but does that really matter? Never let the technicalities stand in the way of a truly dumb idea hey?

Small UPS's are designed to work with small batteries, with larger capacity batteries the charger circuit will do one of three things:

  1. Simply shut down on overload and never charge the battery.
  2. Fail in a (possibly) non passive manner scattering bits of "innards" around the room
  3. Go all "high voltage" and boil the battery.

gpsmikey:
That was what I was talking about. Many of the deep cycle car/rv batteries have not only the regular battery posts, but terminals with wingnuts on them as well. External to the case, but much better capacity (and easier to get a replacement) than the built in battery. Watch for the acid though - they have sulfuric acid in them - best to put the battery in a battery box and leave the top open for ventilation (they produce hydrogen when charging). Make sure you use heavy enough wire when extending the wires from the inside to the external battery (use stranded wire, not solid)

Deep cycle car/rv batteries are not designed for float operation, these do not like sitting for months on float charge, they are more likely to sulfate and fail.

Start batteries also are not designed for UPS's applications and again will most likely fail prematurely.

"Wet" batteries, the ones that can be topped up with water should NEVER be used in Home/Office situations, the highly corrosive gas given off is toxic and simply eats anything it comes in contact with.

"Maintenance Free" Automotive batteries are slightly better as they only gas if over charged but still pose hazards.

Any of the Float rated Sealed Lead Acid batteries, but preferably Absorbent Glass Mat (AGM), are the best answer. Have a chat to battery suppliers directly, don't go through Hobby Electronic stores (they charge like a wounded bull), or maybe talk with security suppliers as they use the smaller ones and may help with pricing.

One final thought, it is best to keep to the battery size supplied with the UPS, not only do you have issues charging large ah batteries, it is often a waste of time and money putting significantly larger batteries on a small UPS, especially if it is NOT fan cooled. These small UPS's are only designed to run for a short time on battery and most simply shut down after 10 - 15 minutes regardless of battery capacity, either as a standard time function (ours used to give maximum 15 minutes at 50% load) or on over temp.

12

DrAzzy:
Lead acid batteries suck.

Lead Acid batteries are like everything else, they have distinct advantages and disadvantages, in UPS applications for instance they are ideal.
In Deep cycle applications they hold their own as a balance between cost and "usability", they are less suited to small portable applications because of weight and dimensions etc, but in "static" or larger applications the cost advantage outweighs the disadvantages.