Can you switch-on an UPS when the main is off?

Yes, this will happen with most UPS. Because you may have UPS of capacity just meeting req of all your equipments put to gether. If equipments are running, they draw just working current. At power-on any electrical device will draw much-higher current. So, if you try to turn them on, directly on UPS it will not allow. Then you have two lalternatives:

1. Turn-on your devices one after another - in your req importance. Stop when it trips! Rest of equipments you can not use on UPS.
2. Buy a UPS of atleast 50% higher rating, of your need. And then apply method-1.

Hope this will solve your problerm.

With warm regards.

Yours Truly
Hitesh Mahant
Vital Technologies,
www.vital4all.com

In case of mains failure,battery shall supply load,for time duration till it gets discharged. However,when mains are switched off,the battery may self-discharge and after some hours,all charges might get drained.The battery will then need re-charging from mains. Self discharge can be prevented,if battery terminals are kept disconnected,when not in use for long time.

Of course I agree with all the pionts. But I like toadd:
1. Start UPS off-lod. If it runs Next ..2
If not >> Design Fault.

2. Put load one by one & see how much it can withstand. I f all the load can be handled by UPS adopt this procedure otherwise you have to consider for at least 50% abondoned capacity.

Points to consider:
Equipment like Motors,TV & Monitors [conventional] take surge currents on switch-on.
UPS switch-mode design may not take such loads as mostly these are Square-wave supplies, Sine-wave supplies can handle such loads.

Regarding point 1. of haajee; if UPS do not do cold-start, still it may not be faulty design. Some models have no-load protection, so if no-load is connected, it may enter power-down mode immediatel. So in this case it is recommended to conenct some minimal load, like Speaker.

Rest all, I also agree with.

Hitesh

Of course there may be some such designs, but they are normally Switched-Mode supplies & not recommended to be started off-load. Thanks

Why not leave the UPS on all the time - it will be as charged as possible. Turn the lights and computer off when you are not there. If the computer must be on all the time (or as much as possible) leave the UPS on, the computer on, but turn off all accessories, the lights and monitor.

It might be considered a design fault that you can't switch on after the power fails, maybe something in the software. You don't state unit type, but for a battery-inverter type unit the best fix is to install a switch downstream of the UPS Unit, and leave the unit connected and on all the time. If it's a small office type unit, just unplug the loads when you leave. This will insure a fully charged battery and prevent the unit from discharging into unused loads when you are not present.

Not enough info.

1. What size APC UPS? How many amp hours?

2. Is it dying under load when the power goes out in your absence?

If the lights are connected as well as computer equipment, you might consider making them supplied seperately from another UPS. That way if the lights are drawing down the battery, you still may be able to use the computer.

More battery is always good for UPS.

Tripp-lite makes a series of UPS units that allow you to cold start the ups with a load and no main power. I agree with one of the other responders that you should apply the load in stages if possible.

First let's redefine your situation.
You have a computer and a light bulb (but not an entire lighting loop?) connected to the UPS's power interface (to it's protected and/or unprotected AC outputs). You might--just might--be running the UPS without a user-computer-UPS serial communictions (i.e. GUI) inteface--this assumption derives from your implicit statement: that the backup battery discharges to deadpoint, because you are not in attendance--thus, it seems, there is no UPS service that has been programmed (using computer input) to shut down the UPS before the battery goes dead. Now you say that the UPS is an APC, but you don't say which APC class it is. Typically, APC UPS services are provided by Microsoft within its operating system; at least that is true for Windows XP. The Windows UPS services are found under Power Options in the XP control panel. Of course, if you install the APC interface (there are several to choose from if you are running Windows), you will also need to install the RS232 inteface cable between your UPS and your computer. When you get the interface installed--depending on the UPS's design technology--you will then be able to configure the UPS to always Save Date and shut down...before the battery reserve has been exhausted. (There is this common, but mistaken, perception out there that running UPSs without software is somehow safer. Not true.) So then, if your UPS is properly programmed to shut down before battery depletion, you might find that your problem has been eliminated...meaning, that you will not be trying to actuate the UPS's startup relays with no power--no power from the mains, and no power from the battery/inverter. Of course all this depends to some degree to the capabilities available with your particular UPS. Now for a more fundamental point...

It appears that you might have Novice understanding of UPSes; and Novice expectations of what a UPS can be used for. By that I mean: it appears you are attempting to use the UPS in a situation where a backup generator is called for. UPS's are not designed or intended to replace a backup generator--but, based on your description of how you're using the computer and the UPS, it appears that this is what your are expecting of the UPS. (That is to say: you're situated where mains can go off-line for extended durations; you sometimes operate the computer for extended durations using battery power; you leave the computer (and light?) running unattended for extended periods.) So--to simplify--your best resolution appears to be as follows...

1. Acquire a generator and transfer switch and connect it to the loop to which your UPS is connected. (If it is necessary for you to leave the computer running unattended for long periods, you will need to have automatic (not just manually actuated) transfer switching and generator-start capability). The generator need not be large and expensive--only enought capacity to supply your computer and light bulb is required--up to the ratings of your UPS.
2. Fill the generator's tank with fuel.
3. Keep your computer-UPS hook-up as is, or modify as desired.
4. Forget about trying to start the UPS with no power...and keep on keeping on.

PS. If you want a good UPS-computer interface software kit with which to program your UPS services, send me a message. I might have one you will really like.

Rating of UPS shall be at least the sum total of individual loads / devices connected to UPS. Most of the times the load demand of individual devices is assumed or estimated.Manufacturers catalogues also do not provide this information. Can you please advise scientific and safe method for arriving at the consumption of devices and arriving at the capacity / KVA requirement of UPS? What is the basis of sizing UPS? Thanks

Nymani, Please stand by. I am preparing a detailed response to your request. Should have it in a few days. Cowanon