COMPUTER UPS AS AN INVERTER?

 Has anyone tried this?

Lots of UPS units for computer backup are going cheap because the
batteries are nuked. After a while, they just wont charge any more and
they cost a lot of money to replace. The inverter part is still
functional. Now......can these inverters be used as always-on units to
feed rectified dc into the grid? The output should be very high
quality...you wouldnt run expensive computer gear on a square wave
right? How much modification would it take to make this inverter feed
power from solar or battery or other source back into the grid. Right
now I'm not as interested in the "non-islanding" issues as simply
making the connection safely and efficiently. I can get several 5 k
units....yeah they backed up some pretty big computers....and it would
be a lot cheaper than buying brand new inverters, but only if they
dont need a lot of expensive or impractical modification.  Any ideas?

 
Nope. In order to be "grid tied", the inverter must be able to
synchronize with the AC phase of the grid. Computer UPSs are not
designed to synchronize with and backfeed to the grid.


High quality as to voltage, but it isn't a neat sine wave output.
Most UPS units use a "modified square wave" inverter and call it a
"modified sine wave".


If you were a skilled enough electrical engineer to do that, you could
design and build your own inverter from scratch.


"Non-islanding" IS a safety issue! Grid synchronization is also a
safety issue - an "out of synch" inverter could act like a short
circuit.


Find out the input voltage for these units - at that size the
batteries would be much higher voltage than 12 volts! If you can
arrange the proper input voltage from solar panels and batteries you
can use them to power things directly, not "grid tied".

 I bought a couple of 1700 watt Tripplite UPS's off eBay. The guy claimed
they ran great, just the batteries were dead. It used two 33 amp 12 volt
lawn tractor style batteries wired in series. They were selling for less
than a quarter of what they went for new. I got them, bought new batteries,
and found a host of troubles including blown bridge rectifiers (marked "bad"
in pencil under the heat sink ?)  in the charging circuit and many bad
relays. The company who made the boxes refused to sell parts to the general
public but it was easy to get the exact replacement parts directly from the
suppliers via the internet. Cumbersome to repair due to design but the
circuit was rather simple.

 

CM wrote:


    UPSs in the 5kw neighborhood are usually 48 VDC nominal.
This is to keep them under the 50 volt 'low voltage' section of the
laws and regulations dealing with electrical safety.   Big UPSs, of
the tens of kw or larger, tend to be moter-generator sets with large
battery banks.
    5kw units are rarely ( I've never heard of one ) capable of
synchronizing to an external source.  If you have units that are of the
always on variety, they have inverter sections that are designed for
full time use.  Most UPSs are standby type units, and the inverters
are not designed, or rated for continuous use.

    --Dale

 On Wed, 03 Sep 2003 23:28:45 -0400, blank@adelphia.com wrote:


Cannot be used as grid-tie because it won't syncronize. Works OK for
off-grid if you can keep them cool.