OT: Continuous mode UPSes

[Jim Kuzdrall]

On Sunday 19 April 2009 21:34, Bruce Dawson wrote:

> I need a continuous mode UPS that will be used 24x365 and it needs to
> supply at least 500 watts for 15 minutes. Note: This needs to be
> *continuous mode*; line-interactive and standby will *not* work (we
> have too many phase changes here). The usual contenders such as APC,
> TrippLite, ... don't seem to have continuous mode UPSes.

    Be sure you get a unit that allows hot-swapping the battery.  
Unfortunately, the time that you find out the battery is going to fail 
in 60 seconds is while the UPS is running during an outage.  (Battery 
charge-state instrumentation is not terribly reliable.)
    
    You may find this super-conservative approach useful, but you will 
need to make an EE-type investigation before buying.

    I had trouble with short power interruptions here due to an arcing 
feeder line (denied by PSNH for months).  The non-continuous UPS would 
delay 8 or 16ms before coming on, which would cause most of the 
attached equipment to power-reset.

    The non-continuous UPS I had, an APC 1100 (1100VA), was a high-end 
model that puts out a stepped voltage approximation of a sine wave 
rather than a square wave of equal rms voltage (which is OK for running 
lamps, stoves, motors.)

    I bought a Trip-Lite SU1000RT2 (1000VA, 800W) which is the 
"continuous" type you refer to.  It solved the line-arc-reset problem 
nicely.  But rather than discard the APC, I have them hooked in tandem, 
the less capable APC feeding the Trip-Lite.

    I have been using the series combo for about 6 years now - long 
enough to have battery failure in both units.  The failed unit beeps 
etc, but cannot interrupt power to the equipment.  The Trip-Lite 
batteries can be hot-swapped.  The APC can be turned off for battery 
removal.  Independent electronics and batteries may offer more 
protection than an extra battery for one unit.

    Both units have a serial port computer warning/status output that is 
supposedly Linux compatible, but I never had the time or need to hook 
it up.
>
>... If it
> can use my batteries (deep-discharge marine type), ...
> I've tried building my own with inverters and chargers, but have had
> problems with the batteries dying prematurely (min: 3 months, max: 9
> months).

    "Deep discharge" is the problem.  The chemistry and plate design for 
high-current, rapid discharge batteries leads to an irreversible lead 
sulphide build-up on the plates if they are only partially discharged 
and recharged several cycles.  Also, some of them don't like continuous 
trickle charge.  (This is from vague memories, so double-check before 
accepting it as accurate.)

Jim Kuzdrall