Any issues with using a APC77250 transfer switch to 'cacade' UPS power?

[BillP]

this may fall into the category of a 'dumb question' but here goes.

I would assume that it is possible to use a transfer switch to effectively double-up UPS units?

So If I have two UPS units, the transfer switch would allow the servers to use up the runtime on the first UPS, then switch to the second UPS?

The practical issues I can see is that the second UPS, though lightly loaded, would be using runtime when the power goes off. And PowerChute network shutdown would need to be configured in the second UPS only.

Of course the advantage of using a ATS is that I could take either UPS offline for service. The other advantage is that I can retain the ability to remotely cycle power to each server via my APC MasterSwitch PDU. Since I only have one master switch, if I add another UPS for one or two servers, they cannot be controlled with it...as the MasterSwitch only has one power input.

But in theory, if there were a long power outage, and the load is within the limits of the UPS, then the servers would draw down the batteries of the first unit until it dropped the load, then the transfer switch would transfer the load to the second UPS. A UPS without a load on it would run for a very long time, I would assume. I have APC PowerChute configured to shed load by shutting down less critical servers first.

[BillP]

this may fall into the category of a 'dumb question' but here goes.

I would assume that it is possible to use a transfer switch to effectively double-up UPS units?

So If I have two UPS units, the transfer switch would allow the servers to use up the runtime on the first UPS, then switch to the second UPS?

The practical issues I can see is that the second UPS, though lightly loaded, would be using runtime when the power goes off. And PowerChute network shutdown would need to be configured in the second UPS only.

Of course the advantage of using a ATS is that I could take either UPS offline for service. The other advantage is that I can retain the ability to remotely cycle power to each server via my APC MasterSwitch PDU. Since I only have one master switch, if I add another UPS for one or two servers, they cannot be controlled with it...as the MasterSwitch only has one power input.

But in theory, if there were a long power outage, and the load is within the limits of the UPS, then the servers would draw down the batteries of the first unit until it dropped the load, then the transfer switch would transfer the load to the second UPS. A UPS without a load on it would run for a very long time, I would assume. I have APC PowerChute configured to shed load by shutting down less critical servers first.

[BillP]

i assume you got the part numbers mixed up. We only have AP7750 or AP7723, AP7724, AP7750, etc so I am not sure which one you mean.

the purpose of an ATS is to provide redundant to power to devices that may not have dual power cords.

with an ATS connected to two UPS for its input sources, yes, if UPS A goes to battery, the ATS will not switch input sources. UPS A will rundown its battery and when it is depleted, it will switch to UPS B.

if you configure Powerchute Network Shutdown in a multiple UPS scenario, PCNS will not shutdown the server until it receives an on battery or shutdown signal from both UPSs it is monitoring. generally, you wouldnt use an ATS in that scenario though, you'd have dual corded power supplies connected to each UPS. in an ATS scenario, the equipment is connected directly to the ATS, rather than the UPS. i dont see why you couldnt use PCNS to monitor these UPSs though. I'd have to sit and think about every scenario that may come up that could cause an issue there.

here is a brochure on Rack ATSs by the way -> http://www.apcmedia.com/salestools/THON-7GTPY6_R4_EN.pdf

[BillP · Accepted solution]

Thanks, it's a 7750.

I may be the only APC customer with the following in his home server rack:

Two APC SUA1000RM2U with AP9617 mgt cards
One Netbotz RackBotz 400e
Two APC MasterSwitch AP9211 units
One APC 7750 ATS

The Netbotz acts as the SNMP trap target, and of course the other devices play well with the Netbotz.

APC makes some very rugged and reliable gear, as most of these units are over ten years old and just keep going and going.....