3 ms·

>a standby UPS where the battery failed, it turned off the UPS I assume this would be because the power is always flowing through the battery/inverter? Wouldn'

• snuxoll 6y ago
  Standby UPS topologies like the APC Back-UPS lines keep the battery out of the loop until a loss of power from the AC input is detected, at which point the inverter kicks on the the transfer switch takes the feed from there. This is a design choice from APC, money is on the control electronics being powered off the battery meaning a dead or missing battery means the entire unit is non-functional. Making the unit resilient to this probably costs as much as a line-interactive unit, however, so you might as well just tell people to get a better unit than make a middle-ground solution.
  • formerly_proven 6y ago
    I have a line-interactive APC and it most definitely is just a UPS-shaped brick without a battery. Might have changed in newer models, I wouldn't know.
    • zaarn 6y ago
      My APC BackUPS Pro (supposedly line interactive) runs fine without battery (ran it with a tab from shipping still in the case), might depend on the setup. Generally line interactive makes little sense why it wouldn't work without battery since the power rail is shared.
• jcrawfordor 6y ago
  Using a DC auxiliary power supply for backup is common in telecommunications equipment and by extension common in network appliances - "redundant power supply" for network equipment typically means a built-in AC power supply and then DC connections for an external aux power supply that provides battery, often called an RPS. This isn't common for servers though which, if equipped for redundant power, have two AC power supplies. I think this just comes down to the higher current draw usually associated with servers, running even 48VDC power can become costly and impractical when you need to supply say a couple thousand watts per rack, so the extra space and thermal load of an AC power supply in each unit becomes preferable. The downside is that while redundant power supply is usually a "standard" feature on switches and routers (that is, they always have the connection whether or not you buy an RPS is up to you), you need to specify and pay extra for dual AC power supplies up-front in servers, so you don't get as smooth as an upgrade path. That said in datacenter environments you often buy servers, racks, and power systems all at once so it's not as much of a concern. There's a similar tradeoff that exists around bottom-of-rack UPS and central (building or area) UPS---bottom-of-rack UPS tends to be more expensive, higher maintenance, higher thermal load, etc for large installations, so usually large installations use one (or two for A+B power) large central units which may be hybrid between different technologies like flywheel and battery (and you could view the transfer to generators as a "third stage" of a central UPS system), but it also makes your cabling a little more complicated and you have a bit of an "eggs in one basket" situation. Central UPS generally have internal redundancy so their risk of failure is low, and often a bypass device where if a non-recoverable failure of the UPS is detected a contactor "shunts" the entire UPS removing it from the circuit so you don't lose power due to a UPS failure, but that doesn't necessarily save you when the HVAC pours water directly into the UPS control cabinet causing widespread failure of the control electronics... a situation that I have somehow seen twice. I bet on bigger installs you can get an external bypass with some sort of health monitoring though? If HP/Tandem taught is one thing it's that you can always through more redundancy into your very special basket.