RE: [pvusers] Need advice on using UPS as inverter

["kirk" <kirk@3rivers.net>]

It sees a voltage source and has no idea what its capacity is. It doesn't
know the size of the battery. This can be a problem if heatsink is
inadequate and it relies on the battery being small enough that charge
tapers and keeps thermal dissipation within available mass and surface area
of sink. A large cell may keep charge too high for too long. Likewise time
or duty cycle of operation may be too long for output heatsink if it is
designed for 45 minutes at max power and you want to run it for hours and
can with large bank.

Hard to believe a pure sine for $60.

Kirk

-----Original Message-----
From: Christopher Witmer [mailto:cdwitmer@spamcop.net]
Sent: Thursday, September 12, 2002 4:22 PM
To: pvusers@crest.org
Subject: [pvusers] Need advice on using UPS as inverter


In Japan I have been having a very hard time finding an affordable DC-AC
inverter; however, it isn't hard to find a large UPS that needs
batteries. For example, I just found a used APC Matrix 5000 (a pure sine
wave unit) now being sold for the equivalent of about $60. (This
particular unit is being sold without batteries.)

This UPS is designed to work with any number of add-on battery packs,
each 48v/17ah. (APC calls these "Smartcell" batteries and of course they
have a multi-wire connector of a unique design.) Instead of the
manufacturer's recommended battery packs, I want to use one BIG 48v
battery string -- e.g., something in the range of 600-1000ah.

I imagine I will have to overcome two obstacles: 1) to get the inverter
to accept a different battery than it expects, and 2) to recharge the
battery string without using the inverter's built-in recharge function.
(It takes eight hours for this UPS to recharge 10 battery packs -- just
170ah. That means it would take 35-60 hours to recharge the large
battery string I'm contemplating.)

I have access to a separate charger for the batteries, but does anyone
care to speculate how easy it will be to get the inverter to accept my
large battery string and function as I require?

Basically, I'm worried that the UPS might have some built-in self-test
function and when it detects that something is not just as expected, it
will refuse to function at all, and I won't be able to override or work
around that.

Any thoughts? Thanks!

Christopher Witmer


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