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You have thought this out very well. I have just recently
"more or less officially" ended my own project on this subject.
1) The choice of 36 VDC UPS and inverters is too limited. The
popular (low-cost) brands seem to be 12/24/48.
2) The DC connectors on the battery packs are made by AMP and
they have a name and a color to indicate their capacity. I couldn't locate a
source that would discuss sale of small quantities or samples.
As so often happens the project went a different direction. I
was able to get "free for removal" some 20 year old lead-calcium cells
(telephone back-up) that I had originally installed in 1986! Although
maintenance has been spotty, they cleaned up well and load-tested (c/20 rate) at
100% of label rating- They are 150 amps in a 24 cell/48 volt string. The rated
life-span is 25 to 30 years, and I am already old, so...
The next item to turn up was a commercial grade APC
1500watt/2200VA sine-wave UPS. I got this by horse-trading, but a new one is
about $750. It has 48 volt internal pack and the plugs
for adding more boxes 'o batteries. I had to hard-wire the batteries (yes there
is an added fuse) because of that darn AMP connector. The internal and
add-on battery packs appear to be 17 amps at 48 VDC. I programmed the UPS
to believe that it has 9 extra packs attached- this is max, and the unit is too
smart for it's own good- I am not enough of a logic controller guy to change
anything else. Documentation is spotty- just how the manufacturer wants it,
I'm sure.
In any case, the test consisted of running the window A/C in
my shop last summer for 12 hours straight- remaining battery capacity was above
40%.
Rate of recharge: in this unit, the charger is efficient but
not fast- takes 48 hours to bring back my (total) 167 amp pack. But float
voltage is tightly controlled- no issues with water use in almost a
year. I recently finished the project by running a
feeder to my home office from the shop- it runs everything including lights and
laser printer. I got rid of the small UPS systems that were in the
office.
A small bank of manual transfer switches allows me to apply
UPS power to sump pump, oil boiler, well water pump as needed. Plugging in
an extension cord would allow addition of the freezer or refrigerator during an
extended outage.
So, success! What remains?
1) the UPS raises constant insufferable AM radio interferance
that I have yet to filter- input and output wiring carries it. Who cares? My
other hobby is old radio;-(
2) maybe... I could generate DC from an old ElecTrak motor
belted to my gas tractor and feed it into the battery bank, let the UPS clean it
up.... and there is still that 225 amp at 36 VDC tractor pack just sitting
there...
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