UPS as inverter - sources, models, fix for high stby? - bob g, scottsAI, others?

[DSinOR]

Hey guys.

I've done some reading here and on other boards, but haven't found the "definitive" answers...

I like the idea of using a low- or no-cost discarded UPS as an inverter.  My plan would be to add cooling/sinks and use it with a ~500AH 12v deep cycle battery bank.  Working load would be ~300watt, with occasional peaks to 800ish. 

I see lots of talk about super cheap or free UPS discards, but I'm not finding them myself.  I looked on ebay - mostly pricey with exhorbitant shipping costs.  Where are you guys finding the deals? 

Is there such an animal as a 3000VA UPS that will make 110vAC from 12vDC battery bank?  Model recommendation?

What is the solution to the high UPS STBY current?  Are certain models better than others in terms of lower stby current?  Did anyone ever come up with a PIC circuit design for effective load sensing?  Can the stby load be reduced by disabling certain UPS functions?

Are UPS's pure sine wave or MSW?  Or does it vary from model to model?

What about 220vAC to allow sporadic use of my 220V 0.5HP 400watt (650 peak) water well?  Is there such an animal as a 220v UPS with 12v batteries?  24v batteries?  48V? 

Lastly, a general design question:  Assume a sub-panel with two 15A 110v breakers plus one 220v breaker for the water well.  The water well only comes on a few times per day to fill a pressure tank.  The 110v loads are intermittent: lighting, computer, internet.  If I use either a 220v inverter, or a 110v inverter plus a 1:2 step-up transformer, to push 220v at the panel, is it acceptable to run a few 110v loads from the panel while the well is not in use?  IOW - the 110v loads would only be using one leg of the "220v supply".  Is this kosher, or disastrous, or

I know...lot's of questions!  But hey - I'm searching for knowledge!   

Thanks!

[bob g]

in my experience any ups that is 3kva or larger will be 48volt dc at least, some 72, 120, 196volts and up!

i know of none that operated on 12volts dc these days, the smaller apc units start out at 24volts

yes there are dc to 240volt ups systems, although more commonly 208volts ac

all of the apc ups systems over 700 kva are sine wave, very clean at less than 5% thd

thats as much as i can tell you off the top of my head, that i think i know

as for standby draw, i haven't figured out how to get around that, if it is running it will be eating
about 40-50watts continuously, any modifications to the pc board usually has horrible results so i wouldn't recommend
poking around there.

probably best to come up with a way to turn the thing on to power a load, and then turn it off

all of the apc ups units i have tested from 700, 1000, 1400 and 2200kva are between 84-86% efficient, that at
about 3/4 load or better, they are dreadful at very low load levels, because of the 50watt base load.

bob g

[ghurd]

ebay and shipping?
You may be seriously underestimating the size of the larger units.

If I had a free discarded unit, it would probably cost over $20 to package it for shipping.

And they are heavy.
I went on a road trip with 'Nothing to Lose' to collect a few cheap ebay UPS'.  Seems like they were 3000VA or 5000VA Matrix rack mount units, without batteries or battery boxes.  He decided it was worth his time and effort to drive about 29 hours and 1700 miles round trip.  We each grabbed a side to carry them to the van, and they were still pretty heavy (one person could deal with one, but it was like 250 yards from the storage place to the van).

G-

[zap]

Where are you guys finding the deals?

If you can't find them on the curb or in a dumpster... try craigslist.  If you're in a heavily populated area, chances are good you'll find some, possibly free and if not, certainly cheap.
2 or 3 months ago a friend called me up to let me know that one of the Habitat for Humanities recycle centers here in town had around 200 500watt(ish) sized ups in a big pile and another pile of the batteries out of those units.  I had too much work to do to go have a look see.

I'll second everything bob g has said and add that I've 'seen' some of the smaller wattage units efficiency levels in the mid 90s but usually you have to load them up over 75% load to approach that... much the same as any inverter.

[bob g]

DSinOR

if you are in oregon, (from your screen name) and you ever make it as far north as tacoma, let me know
i can hook you up with more apc ups units than you likely want to cart off.

ok, maybe not the case, but i have many i would part with for very little cash, some just to get them out of my
shop and to a good home.

the majority are 24volt dc 120vac output, ranging from 700va to 1400va or so, maybe a bit bigger but i think
they are 48volt units

and no i do not want to package and ship them



bob g

[DSinOR]

Guys - thanks for all the replies, and for helping me along the curve. 

i will do some more reading and thinking on this. 

bob g - Thanks!  I have family in Puyallup, and visit approx once per year.  I'll drop you a line before the next trip.  I'm in rural eastern OR, where many folks do not yet have a pc!.  Discarded UPS's are not so common out here.