(Elementary user)

We have a server with two 980 Watt power supplies. Our voltage is 240V. The idea is that should one of the power supplies fail, the server will continue to function seemlessly.

Am I correct in thinking that:

a) Both power supplies should be plugged in to the UPS?
b) I must calculate a battery requirement for 1800 Watts?

Best regards

Not a lot of info to work off of since you don't mention required uptime, if there is other equipment getting plugged in, if you actually want power redundancy or just wanting to plug in both power supplies because they are there. So I will make a few assumptions to show you my thought process.

Split your two power supplies to two separate UPS(s). Having a 3000va or better will more than cover the load plus give you a few minutes of uptime (about 26 minutes with just the one power supply connected; 109 minutes adding one battery unit). Having both power supplies plugged into this one unit would change the dynamic to where you would need the add-on battery unit to get any type of run-time and you would be at about 75% utilization of the UPS's capability.
Another option, you could do a different sizing scenario where you have a big UPS for one power supply and a smaller UPS for the other power supply. So maybe a 5-6Kva for the first UPS and a smaller 3000va for the second.
Yet another option would be to just battery protect one of the power supplies and plug the other into a PDU which in turn plugs into your second dedicated electrical circuit (so no battery protection on that one power supply). Of course with this option, should the power go out, the only power supply working would be the one on UPS protection till power is restored.

Just some thoughts.

 

The idea behind having dual power supplies on a server is to lessen the chance of failures.  One input should be plugged into a properly sized UPS and the other should be plugged into a Utility Source.  If either one fails the other should pick up the load.  Your primary input should be plugged into the UPS and the secondary source should go to utility.  If your secondary sources are plug into the UPS and you lose utility you run the risk of overloading the UPS.

Good Luck