Musings of an idle mind....

[BillP]

This question was originally posted by Joe on APC forums on 9/1/2016

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I was looking at one of my UPS systems, a Back-UPS 750, apart on the floor awaiting a new battery.  The idea of "perpetual motion" came to mind and I wondered what would happen if you plugged the UPS input into one of its outputs?  Would it turn on and run "forever", self destruct or is the UPS smart enough to not even power up?

Now, back to your regularly scheduled programming.

[MarkC_apc]

This was originally posted on APC forums on 9/1/2016

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I thought such thoughts were reserved for us retired folks with too much "idle" time.  One better - if we could spin that UPS around the earth at the speed of light, it will also last forever - in perpetual motion.  That would certainly help Schneider's bottom line!  

Not sure what program you're watching, but please let me know the channel.

[BillP]

This reply was originally posted by Joe on APC forums on 9/1/2016

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Hi Mark.  Good to hear from you!  Regarding the channel I am watching, i don't think politics would be appropriate for this forum.  Stay well!

[UnexpectedBill_apc · Accepted solution]

This was originally posted on APC forums on 9/2/2016

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I think that APC has a "loop detection" circuit that serves to shut down the UPS and produce an error if its input is plugged into the output. If this circuit didn't exist, I suspect the UPS might "buzz" as it switched to and from the battery very rapidly. This would greatly accelerate the wear on mechanical parts like relays and I expect it would greatly shorten the life of the UPS.

So far I haven't had a UPS of any kind that I held in sufficiently low regard to actually try it.

Whatever the outcome, the UPS definitely wouldn't run "forever". The inverter and battery charging circuits aren't anything like 100% efficient, especially when the inverter is lightly loaded. You'd unavoidably lose some energy as heat.