How to test whether the circuit board in a UPS still works?

[Wrichik Basu]

This UPS has been lying in the house for around seven years. We detached it from our desktop when it failed to provide backup. Six years back, I opened it up and found a swollen battery. At that point of time, I did not have any testing equipment, nor did I have any knowledge of electronics. So I took out the battery, reassembled the UPS and stored it inside polythene bags so that it won't collect dust. Then I forgot about it.

We worked without any UPS till date. While cleaning the room today, I found the UPS, and surprisingly it looks as good as it was originally. I have decided to repair it.

But before that, I want to test whether the rest of the circuit still works or not. Here are two pictures of the circuit board and the transformer:

The two thick wires in the PCB are supposed to be attached to the battery terminals.

My aim is to plug in the UPS and test the voltage across the AC outputs and also across the two wires that are supposed to be connected to the battery. I don't know whether it will power up at all without a battery. If it does, and if the AC outputs give the correct voltage and the battery-connecting wires show a voltage above 12V (which will mean that charging is active), can I conclude that the UPS is fine?

By the way, I still have the old battery. It is rated 12 V 7.5 Ah. Here is a small video showing how badly it has swelled up. Batteries of this rating are available online, and I am going to buy one after the lockdown is over if the circuit of the UPS is fine.

 

[scottdave]

I have owned several Uninterruptible Power Supplies over the years. I have only taken apart a couple of them. One I was able to hook into a car battery to get long lasting AC inverter. But another one (newer one) won't start up like that. It has to already be on 110 VAC then if that turns off, the inverter turns on. I do not know if there's a circuit which prevents the 12v charging leads from energizing if the battery isn't hooked up, but that's a possibility. But if you know enough about electric circuits and you have some extra wire, you should be able to test it with a car battery.

 

[Wrichik Basu]

But another one (newer one) won't start up like that. It has to already be on 110 VAC then if that turns off, the inverter turns on.

Two questions:
1. How old is this new one? (for comparison)
2. Doesn't this one even supply power to the outputs if it is connected to mains but the battery is removed?

 

[hutchphd]

The old battery is of no use to you...dispose of it in a friendly way.
If the charging circuit just contains a 60 (in USA) Hz transformer (like it seems to) then likely you will see some voltage on the battery terminals >12V (this would be the older-style circuit). Newer circuits probably have a switching supply and they likely need a battery in place to do anything. If nothing is visibly toasted on the board I think it likely that the battery failed...how old was the battery when it puffed?
The only good test I know is to put 12 V where the battery should be (and it needs to supply at least an amp for a good test). See if you get AC at milliamps and look at the battery terminal voltage when "charging"

 

[Wrichik Basu]

If the charging circuit just contains a 60 (in USA) Hz transformer (like it seems to) then likely you will see some voltage on the battery terminals >12V (this would be the older-style circuit).Newer circuits probably have a switching supply and they likely need a battery in place to do anything.

Hope that mine is an old circuit.

If nothing is visibly toasted on the board I think it likely that the battery failed...how old was the battery when it puffed?

Maybe four years. Not more than that.

 

[Borek]

I wouldn't switch it on without a 12V battery attached, at the same time any similar 12V battery should do. It is marked as an acid/lead, so any car battery will work, no matter what its capacity is.

 

[sysprog]

In my experience, when an uninterruptible power supply has failed, the problem has always been the battery, and never the circuit board; I suggest using AGM batteries.

 

[Wrichik Basu]

I conducted a few tests today.

1. Check connectivity across wires. Result: No defects found.

2. I plugged in the UPS.

The procedure to switch on the gadget is to hold the switch in "on" position for a few seconds after which there will a beep and the lights will glow. Did that but it didn't switch on. Then I discovered that there was no connection across the terminals of the switch even when I pressed it, which meant that the switch was faulty. No issue. I used a screw-driver to directly short the terminals. Still no success.

The multimeter read 26mV DC across the terminals of the switch, which meant that the circuit was receiving power from the mains.

In this condition, I measured the voltage across the wires from the PCB that were supposed to be connected to the battery (see picture in OP). The reading was 26-27 mV DC.

What I am guessing is, the circuit is "searching" for the battery, and on finding that there is no battery, it is not allowing itself to be switched on. Perhaps this is one of those newer designs that @hutchphd and @scottdave have mentioned above.

I conducted these tests before reading @Borek's post, so I have no idea if I have screwed something up. Anyway, I have nothing to do now. At this moment I can't use a car battery for the experiment. Once the lockdown is over, I will buy a new battery and test with it.

 

[sysprog]

Please be careful. I'm petty sure that you understand that volts times amps equals watts. You need wattage . . .

 

[scottdave]

I'm glad that you are still here to give us a report, after the screwdriver test, @Wrichik Basu
One thing I thought of - I think some models may have a circuit breaker with a "reset button". Does yours have that? I think you should find a battery to hook up to it. Maybe a car battery, if you can find one.
Ace Hardware carries some sizes of the UPS 12 volt batteries in my town. Also there is one of those Batteries+Bulbs nearby my home. They can dispose of your old battery - don't throw it in the garbage as it contains lead.

I was thinking that "please be careful" was referring to the "screwdriver as a switch" action @sysprog

 

[Borek]

Ace Hardware carries some sizes of the UPS 12 volt batteries in my town. Also there is one of those Batteries+Bulbs nearby my home.

Last time I checked you both lived about 8k miles apart, trying to buy a battery at Batteries+Bulbs would be quite an undertaking for @Wrichik Basu

 

[Wrichik Basu]

I'm glad that you are still here to give us a report, after the screwdriver test, @Wrichik Basu

Actually I have been through worse. Was a bit shaky before doing this, but necessary precautions were taken.

Spoiler: Description of the circuit of the switch

Following is a picture of the PCB on which the switch is connected:

Out of six terminals, four are internally connected; the remaining two are connected within themselves but not with the other four. It is evident that the switch is supposed to establish the connection between these two sets. On checking with my multimeter, I found that this connection was not being established. So I shorted the set of four with the set of two using a screw-driver at the point shown in the picture.

One thing I thought of - I think some models may have a circuit breaker with a "reset button". Does yours have that?

I checked; there is no such button.

don't throw it in the garbage as it contains lead

I have been collecting lead acid batteries for the last ten years only because of non-availability of proper disposal methods.

 

[scottdave]

If you don't have access to a good 12v battery, and you like playing around - you could get some AA batteries and solder them together to get approx 12 volts. The rechargeable AA Lithium Ion are about 1.2 volts, so 10 of them would do. Or you could try several to get more than 12v. You won't be able to run anything because the current will be too high, but maybe it would activate the charging circuit. I am remined by this guy.
He is funny. Good demonstration of what happens when you're not careful.

 

[Wrichik Basu]

If you don't have access to a good 12v battery, and you like playing around - you could get some AA batteries and solder them together to get approx 12 volts. The rechargeable AA Lithium Ion are about 1.2 volts, so 10 of them would do. Or you could try several to get more than 12v. You won't be able to run anything because the current will be too high, but maybe it would activate the charging circuit.

Yes I can do that. But the point is, whether I buy a lead-acid battery or ten AA batteries - in either case I have to wait (because none of the shops are open and the lockdown could be extended). If I buy a lead-acid battery, then I will also buy a separate 12V 2A charger with it. If the battery can't bring the UPS to life, then I will use it for powering my other experiments, and the charger would be useful in that case.

 

[sysprog]

Yes I can do that. But the point is, whether I buy a lead-acid battery or ten AA batteries - in either case I have to wait (because none of the shops are open and the lockdown could be extended). If I buy a lead-acid battery, then I will also buy a separate 12V 2A charger with it. If the battery can't bring the UPS to life, then I will use it for powering my other experiments, and the charger would be useful in that case.

You do realize that the 10 AA batteries idea is a joke, right? -- a 12v car battery is more expensive, but it has maybe 50 to 100 amp-hours, and 500 to 1000 available amps -- please be safe . . .

 

[scottdave]

You do realize that the 10 AA batteries idea is a joke, right? -- a 12v car battery is more expensive, but it has maybe 50 to 100 amp-hours, and 500 to 1000 available amps -- please be safe . . .

I guess I should've been more clear about that.

 

[scottdave]

I realize I didn't answer your questions back in post #3 above. I don't recall how old these units are, but the newest one is probably 3-4 years old. I think I should start putting date labels on these when they go into service.
The other question - all of my units have a bank of "surge suppression only" outlets, and "battery backup" outlets. On most of them, If the battery is dead or missing, the "battery backup" set of 110V outlets will not operate.