Calculating which Generator to use

[B657]

Hi there,

Sorry for my complete lack of understanding here, but here is the scenario.

We have a 2000va UPS, and this powers a few critical items in our comms rack- a couple of servers, network switches, telephone system and routers. We get about a 30 minute run time here.

What I would like to do is buy a generator so that when we have a power outage, we can just unplug the mains power and replace with the generator.

The idea being that the generator just replaces the mains power and keeps things running.

What I need to know, is how we spec what size generator is required to keep the UPS battery topped up?

And of course any other advice that anyone has.

Kind Regards.

 

[normntwrk]

a few things...do you have AC and should you be including that in the equation ? Is the UPS that you have generator certified ? Do you require automatic cutover or will a manual cutover suffice (huge cost difference)

Norm

 

[B657]

Thanks Norm,

1) AC- I have no idea. Its a standard office environment.
2) Havenn't bought it yet. It would be an APC 2000VA UPS.
3) No automatic. We would start the generator and plug into the IEC connector on the UPS.

 

[normntwrk]

AC in this case stands for Air Conditioning...depending on the size of the room it can get pretty hot pretty quick without AC with multiple servers running

If it is a Smart UPS it should be fine
but you may have to run a constant load on it (IE 300 watt bulb or electric heater will work) to smooth out the genset

The best thing to do would be to add up the wattage of all the devices and multiply times 1.5 and get a genset that has at least that much capacity (might want to think of future expansion also). Of course if all you will be plugging in is the UPS use the wattage from that x 1.5

 

[beljunchoclit]

General rule of thumb is make the genny double the UPS size.

 

[rudenate3]

I used to work at APC and we always recommended 3-5x larger than the UPS you will be backing up. Another heads up, if your generator isn't generating perfect power, you may have problems with your total harmonic distortion. If you hear your unit clicking, and it's switching from battery to utility somewhat rapidly, you are going to want to switch the sensitivity to a lower setting. Easiest way to do it is through the software.