UPS

ron said:
We have backfed the UPS output from a temp upstream feeder. See if there is a spare on the UPS output panel that can accept a temp back feed big enough to support the load. Wire the temp backfeed breaker 1st, then the cutover is quick (closed transition, make before break). Then you could take your time to either replace the upstream panelboard or if they want UPS protection during that time, you then have more than 10 min to provide a temp UPS input feeder as the load is energized on the load side.
You could also provide a temp UPS to do the load side back feed, then you can have lots of time to do the upstream panel change.
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I see your idea, what if the ups output panel does not have a spare breaker? Can electrican add new breaker into the panel while the panel is live?
 
ModbusMan said:
Not really, no... I don't know how many times I had to stop sales reps from saying the exact same thing, not least because the batteries are never directly connected in parallel to the DC bus. Ripple currents are death to VRLA batteries, and I can't imagine lithium is much happier, so the batteries get their own charging circuit independent of the main power flow. You'll also find that the battery bus is lower than the inverter bus, and there's a DC boost between the two because even though large units typically have ~540VDC for their battery float, the bus under discharge will drop almost instantly to 480VDC, and by end of discharge it's down to 400-420 (depending on configuration). The inverter bus by comparison can be nearly 800VDC on the newest systems.
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Yes of course there is some battery charging circuitry in there. OF course its a bit more complicated then the rectifier, batteries and inverter input all connected with some big blue wirenuts..... I think you are trying to be super literal and exact on the topology, and I was just giving a very basic rough "block diagram" overview that I felt was adequate for the question asked. The primary reason a double conversion is used is for the zero transfer time. Many people often use them for "clean power", but that is rarely ever actually needed.
 
ModbusMan said:
Ug... no. It does not run off the batteries unless the power goes out... can't discharge and recharge batteries at the same time, y'know. During normal operation, a rectifier front-end charges a capacitor-buffered high voltage DC bus, which the inverter then pulls from. Hence why I say they're more like a VFD than an MG.
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I believe another term for that type of UPS is Always On, as there is NO transfer upon power loss.
 
Double-conversion or full-online (as opposed to line-interactive).

BTW, I've never seen a large USP with a battery charger separate from the DC inverter supply; it's always been a controlled rectifier feeding a large capacitor bank in parallel with the batteries (and the inverter input). Granted that I'm not on the absolute latest designs.
 
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