correct use of UPS? leave on if not used?

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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..........................................

Re: correct use of UPS? leave on if not used?
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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.


If your ideas are any good you'll have to ram them down people's throats.
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Re: correct use of UPS? leave on if not used?

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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

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

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

My 2 cents...



Re: correct use of UPS? leave on if not used?
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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

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.

Re: correct use of UPS? leave on if not used?
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I switch mine off at the front panel of the UPS when the computer is not
in use, never at the wall. Would it be better to switch off the input
power to the UPS too?

Long-time resident of Adelaide, South Australia,
which probably influences my opinions.

Re: correct use of UPS? leave on if not used?
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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

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Re: correct use of UPS? leave on if not used?
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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.


Re: correct use of UPS? leave on if not used?
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most PCS don't and monitors have an off switch on the front panel.
did you turn the disconnect the load from the UPS during the test.

Do you mean 'idle', (UPS on, no load)
or 'standby' (UPS off at front panel but connected to mains power)?

the model you have may be different, but in general.

turning them off at the front panel and then at the mains should
put them to sleep correctly

This should do no damage to the batteries as long as they're powered up
every few months.

what you propose may even prolong their life.

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