I got half a dozen UPS at a bankruptcy auction. They came with original invoices, showing them to be bought in June 2009, however no user manuals. I wish to use them for a small business, running one workstation on each UPS. These workstations were normally turned off at end of working day. Should the UPS be left on? Do the batteries last longer if always on? I measured the standby power of each one, and it would cost nearly $100 a year if I left them all running..........................................
If these are cheap $100 UPS then the batteries already have a problem. You can't let them run down to below 30% charge otherwise they will never recharge. And, typically, these things have at least 2 SLA's in series which means either one develops a fault then both batteries are lost. They may be easy to replace, but tearing the thing open to do it is usually not worth the effort -- buy a new UPS.
I've used these kinds of things they are especially useful to avoid brownouts or other glitches that (typically) happen sometime on Fri evening. :)
But it seems to matter what you do the batteries in them die after 2 or 3 years of continuous use. Their falure modes are many and various. In one we heard a buzzing, then saw a little flickering light inside. Turned out to be one of the innumerable little relays used to switch batteries in and out of the charger circuit. Others simply had a relay stick and blow up. Etc.
In my situation all machinery was on 24/7 so UPS were -- of course -- always on.
If you turn off your machines at night then it probably makes no sense to have them running o'night.
Usually these things can be controlled from a serial port or USB port or even ethernet. The s/w is very simple but pretty flexible. You can usually arrange the power supply to stage down a few mins (sometimes a couple hrs) after the PC that send the command has powered itself down.
So it's possible to make a stagedown that sees all machines power off and then later all UPS power down. The reason for doing this is simply to ensure they are fully charged and so don't drop below that 30% threshold.
R Kym Horsell
If your ideas are any good you'll have to ram them down people's throats.
I would turn them off when the computers arent on, but if there was a power failure towards the end of the working day, I would leave them on for a couple of hours to fully charge the batteries. I doubt that the batteries would be affected by sitting off charge overnight. It is a different matter if they decide to start up for any reason during the night or haven't been shut down when the comp was shut down. Maybe make sure they are turned off at the front panel of the UPS also ?
Remember also: If you have one backing up a phone system that needs to be available to receive messages or faxes or something that needs to be on 24h , then you must leave the UPS on at all times. If you use VOIP for this
- then the modem supplying the VOIP phone line will need backup power. If you have a computer that is set to power on upon certain events such as a modem/network event, this will still need power (and UPS backup)
I find at home that its an extremely good idea to backup your ADSL modem (for VOIP) so you can use the phone during a blackout, and also to be able to connect your laptop to the net if you need net access. Handy if you can't do anything else without the power and want to call a friend.
The other problem you might have with any used UPS is how long have these been sitting idle before you bought them ? The batteries tend to slowly discharge inside them, and if left long enough, (even weeks with some models) the batteries will go so flat that never hold a charge after that.
In many cases, it isnt worth replacing the batteries compared to buying an entire new UPS.
We've had half a dozen UPS here over the years; some of the smaller ones, and some of the larger APCC units. As far as I can see, they all have a definite life for the power management electronics. We've replaced batteries on a couple of the large ones, which bought us a couple more years. However, I understand the large power capacitors eventually fail, and at that stage it's usually cheaper to buy a new one, than repair the old.
It isnt hard to replace the batteries in a UPS in most cases, but you need to be careful in following the instructions to avoid getting zapped. They still carry a lethal zap even when turned off and disconnected from the power.
If I was buying 2nd hand UPS units that have been in use for 12 months or so, I'd be planning a rolling replacement of the batteries in the next year...
Yes, as it is still possible for it to be drawing current even when turned off at the front panel.
At very least, for safety all UPS I have ever seen, have a relay that is energised whenever the mains is turned on - its contacts then connect the mains input into the UPS (in order that the mains input is completely isolated from the innards of the UPS for safety). If nothing else, this relay will consume power, and some models may possibly charge the batteries or power internal electronics from the mains supply even if front panel switch is turned off.
How did you measure it? Typical power measurement devices sold in shops don't handle low power factors very well (for example, an unloaded transformer), let alone harmonic distortion, of which there's likely to be a fair amount in a charging circuit.
The true power consumption may be a lot lower than your device shows.