Plugging a UPS into a UPS.
Posted on 2008-10-16
We have a Liebert UPS that provides power to most of our building, including the Cold Room. I would like to make it so that the Liebert unit is not a single point of failure, and the first option is to install some APC SmartUPS units in the Cold Room. It would be setup so that the servers are plugged into the APC UPSs, and the APC UPSs would be running off the Liebert UPS. The design would be that each server power supply would be plugged into a separate UPS; so that one UPS going out would not kill the server. Right now, if the Liebert UPS goes out, we lose the servers. Or, if the Liebert goes on Stand-By, we lose power protection for the servers. Either way, that single point of failure concerns me.
I asked a Liebert Field Tech about this configuration and he said they do not recommend installing one UPS in series with another UPS. He said a lot of people do this, but it can cause problems on the power lines.
I have considered bypassing the Liebert UPS altogether (for the servers), but that would mean we would not be on the Emergency Generator; which would mean we'd have to shut down the servers during extended power outages. I'm not sure if we could insert the APC UPSs between the Auto Transfer Switch and the Liebert UPS; so that the Emer Gen would supply power during power outages.
Do any of you have any recommendations/thoughts?