Yes, you should definitely have it tested before using.

90% of the time the only thing wrong with these things is the battery, which wears out after a few years. Replacing the battery with a compatible one is normally possible, not very expensive, and you will have a new functional UPS on your hands.

This may help: http://www.heime.org/post/17

Anyway a non-functional battery-less UPS can still serve as a (somewhat oversized 😀 ) surge protector.

dr_st wrote:

90% of the time the only thing wrong with these things is the battery, which wears out after a few years. Replacing the battery with a compatible one is normally possible, not very expensive, and you will have a new functional UPS on your hands.

^ This. Every single UPS that I have (either from people giving them to me or finding them in the trash) had nothing wrong other than worn out batteries. For the (cheap) price of sealed lead-acid batteries I've got more UPS than I'll ever need. 😁

So it's not likely to explode if I plug it in, or explode whatever I plug into it?

Where do you get replacement batteries, anyway?

Typically, in shops that specialize in repairing/refurbishing electronics/electrical equipment. They would also have the means to test it for safety.

I'd check the batteries first thing. If it is stored for too long they might've gone bad and may catch fire/explode when the recharging circuitry kicks in.

Back UPSes aren't terribly brilliant, though - they usually only switch to battery on power loss, whereas a Smart UPS is running through a topped up battery all the time. Still, can't argue with free.

Actually only SmartUPS RT are dual-conversion (running off the inverter all the time). The non-RT SmartUPS units are just like the others, only kicking in when the power goes out. I think the difference between BackUPS and SmartUPS is that BackUPS could be modified square-wave, but SmartUPS is full sine-wave.

I've got five SmartUPS units myself, from 1400VA to 3000VA. Four were "dead" but just had flat batteries (flat batteries make the units appear dead - they won't even switch on when plugged into the mains if the batteries are completely dead.) One unit was making a buzzing/arcing sound when switching from mains to the battery, which was solved by replacing an internal relay. That unit now provides backup power for my main PC and works perfectly.

Often the replacement batteries cost almost as much as a new UPS if you buy them direct from APC, so that could be why the unit was chucked. I'd just plug it in in a garage or somewhere away from combustible materials and see what happens. Almost certainly it's just a dead or dying battery. Let it sit plugged in for a minute or two then switch it off and see if there are any hotspots. Almost certainly there won't be any!

I had an UPS once, I think it was a smart one (had an inverter and RS232 port).
Is modified square-wave from an UPS safe for vintage computers ? Just askin'. My experience is quite little with that stuff.
I'm almost always using regulated, transformer based PSUs for my vintage gear if I can (less rf noise)..
Same for step-up/step-down converters, I'm using the old heavy ones with transformers.
I heard cheap converters (modified square-wave,too ?) are not good if you aim to run certain devices, like PCs or TVs.
Maybe that's wrong, but I've seen some of the more expensive ones with a "PC compatible" advertisement and this confuses me a little bit.

Modified square wave is generally meant for switch mode supplies. The important factor is whether the harmonics of the input current will cause additional heating of the main transformer. Switch mode transformers are designed to handle heavy harmonics while linear supplies don't generally function at frequencies above 400 Hz.

Ah, okay, that makes sense.
Thank you very much!

Well, the man at the battery place was astonishingly helpful. Here's what I learned today:

-Apparently even lead batteries can experience thermal runaway and start expanding when they're no good. (Fortunately that was not the case here.)
-The batteries are easily removable. If you hook them up to a voltage meter, a battery with a good charge should give 10-11 V. In my case, I was only getting about 2.5.
-Once these things have been sitting around with no charge for a while, they're probably no good anymore.
-A new battery in this particular case was about $32 CDN, and thus hardly worth replacing.
-These things are heavy and no fun at all to haul around.

Might be a good source for high powered semiconductors.

Jorpho wrote:

-Apparently even lead batteries can experience thermal runaway and start expanding when they're no good.

Oh yes, I've seen my share of bloated batteries which I find quite amusing, especially when they manage to get trapped inside the equipment. 😜

Jorpho wrote:

-A new battery in this particular case was about $32 CDN, and thus hardly worth replacing.

That's too bad, in my 3rd world country where everything is expensive a typical 7Ah SLA brick goes for roughly half that. Have you considered fitting a cheaper but not quite the same replacement battery? I once did that with a UPS that took two 6V batteries in series - it was cheaper for me to get a single 12V battery of equivalent capacity plus a block of wood for padding the empty space caused by the physically smaller replacement. 😀

The man at the shop offered to scrap the unit for me, and rather than haul it around any further I decided to take him up on his offer. It's not like it's even all that useful for me – I can't even remember the last time my building suddenly lost power while I was sitting at my computer.

I've chucked a few UPS's in the past when indeed it was only the battery.
In the past it was because company's were getting more servers so they were reaching max load anyway.
Now its because everyone is downsizing and don't need such a big unit.

I'd love to take them home, but god damn are they heavy! even without the battery