Re: Cascading UPSs

On 1/7/2025 8:33 PM, Sylvia Else wrote:

In fairness to UPS designers, having the UPS able to start without a battery is an edge case they probably wouldn't have felt was important.

Dunno.  But I *do* know that more recent models HAVE this ability (feature?)
so it was either an intentional addition or serendipitous.
It has been handy as the few 4-hr outages we have had (equipment failures
in the network) have allowed me to run an extension cord from a (any) UPS
in the office to floor lamps and TV to (appear to) have power for those
4 hours.
[The below grade cables have been failing, one at a time, in the neighborhood.
At 40 years into their *20* year service life!  depending on which end of the
street is currently feeding us, we have at most one more outage to expect
(as the cables from us to the 'near' feed point have all been replaced)]

I had an old UPS (sadly, now long dead) that behaved this way. The battery side was completely isolated[*] from the mains by a transformer, which allowed hot-swapping of the batteries (a feature described in the manual). But this was the same transformer as was used to generate the output voltage. Consequently, they had to ensure that there was no danger of back feeding the mains, which rather precluded relays whose default position was to connect the mains.

I've never looked at them beyond their (apparent) features, size and capacity,
etc.  They are frequently discarded, here.  I suspect folks find that they
don't perform an "essential function" (if outages are infrequent, then the
cost of batteries dominates their utility:  "I had to spend $100 to get a
FEW MINUTES of 'graceful shutdown' during that ONE outage???").  I often
rescue units with usable batteries simply because someone just decided it
wasn't worth the space/whatever.  (I've even rescued several high-end
units NiB!)
*MY* usage pattern is similar:  "what does THIS unit buy me in terms of
functionality?"
For example, I rescued three SMC1500's a while back -- because their batteries
were all fully charged (verified by powering the units on while out in the
scrap yard):
 <https://www.apc.com/us/en/product/SMC1500/apc-smartups-c-line-interactive-1440va-tower-120v-8x-nema-515r-outlets-usb-and-serial-communication-avr-graphic-lcd-not-sold-in-the-us/>
I had rejoiced thinking they had finally *integrated* the network connectivity
into the units (these have in-built NICs) to save me the hassle of hunting for
network management cards (NMCs).
When I got them home, I discovered that the networking ability ONLY lets
them talk tot he manufacturer's server.  And, that I can talk to them
VIA that server.  (Really?  You're going to give some company a
beachhead inside your organization -- controlling the power to your
servers, no less -- because they can't give you DIRECT access to the
device on YOUR network???)
So, they are of limited use, to me (I have one on this machine because
this network is isolated from the rest of the house -- and, the UPS
need not be accessible from this computer).  They will make the
trip back to the surplus yard, tomorrow.  Hopefully, to be replaced
by something "older" and more useful (like SMT1500s -- even if I have
to hunt down NMCs for them!)
 <https://www.apc.com/us/en/product/SMT1500/apc-smartups-line-interactive-1500va-tower-120v-8x-nema-515r-outlets-smartslot-avr-lcd/>
[I have spent the past hour pulling the battery packs from the SMC1500s for
use in my SMT1500s]

Mind you, they also included an expensive component whose sole purpose was to ensure that the mains wasn't connected during an outage. This was perhaps a level of over-engineering that goes to explain why they no longer exist.

It seems that the UPS makers must rely on battery sales for their livelihood,
given the number of discards I find.  And, they have virtually *no* recycle
value (batteries are ~20c/lb and the rest of the unit is worth < $5 for the
minimal electronics, transformer and steel case)
And, the home/SOHO markets have got to be "one time" purchases -- either
they buy ONE and live with it or buy one and decide they don't WANT to
live with it!

Sylvia.
 [*] Which was not the case for the more recent UPS I bought to replace the old one.