aurgathor wrote in message
news:1101811497.9+GL3fFjQIKbD+bAQSNOqw@teranews...
I have a 650VA APC UPS (Back-UPS Pro 650)
that has worn batteries (occasionally, it starts to
beep and the red battery light comes ON) .
The UPS is there to ride through brownouts and
outages lasting usually less than 10 seconds (have
quite a few of those) so if the batteries are less
than perfect, I don't care as long as it can last for
10 - 20 seconds.
Yes.
So, how does the UPS's circuitry determines if
the battery is going bad? Is it simply a voltage
measurement, or something more sophisticated?
How difficult would be to modify the UPS to
lower the treshold for a bad battery?
That, of course, depends on the UPS. Some just
watch the potential at the battery REGARDLESS
OF LOAD. Others apply a fixed (known) load and
note how the battery voltage changes. Others
*measure* the load and note the rate of change
of battery voltage. Etc. The Back-UPS 650 Pro isn't
a particularly "high end" unit so I wouldn't expect
much sophistication, there. I'll have to look at the
schematic to see what facilities *are* available to
determine battery state...
Alternatively, how would the unit work if I were
to connect a marine or car battery instead of
the manufacturer supplied battery?
Again, it depends on the UPS and the battery chosen.
Let's assume we stick with the same battery *technology*
(i.e. lead acid) so you don't have to address differences in
charging techniques, discharge characteristics, etc.
Typically, the rate a battery is charged is related to the
capacity of the battery. C/10 and C/20 are common
rates. The higher rate obviously leads to greater
*perceived* convenience though usually is tougher
on the battery itself.
One of the risks you run when replacing a battery with
one of a different capacity (physical volume is a rough
parallel to actual capacity -- for a given number of cells)
is that the charger is probably designed with the
*assumption* that a particular battery (capacity) is in place.
Replacing it with a smaller battery could lead to excessive
heating (in the battery) as the battery is now being charged
at a "higher than typical rate". Replacing it with a larger
(capacity) battery could lead to lengthier charge times.
In either case, if the UPS monitors the charge cycle actively,
it can erroneously deduce a battery failure ("Why is this
battery taking so long to charge?" or "Wow! That battery charged
awfully fast! I wonder if that's just a surface charge...")
Using a "car battery" always poses the risk of outgasing which,
if not vented well, can be a fire hazzard. Also, you have to
worry about leaks, spills, etc. as these are not gelled electrolytes.
And, of course, maintenance if the cells are not "mainetenance free".
I had a 3500W unit that ran off 120VDC. I considered using
a set of (10) auto batteries as a cheap way of getting "capacity".
Of course, 10 batteries aren't likely to fit in the living area.
And, with the high charge rate that the UPS used, I was
fearful of putting them in the garage -- 10 batteries potentially
venting into an enclosed space with open sources of ignition
(think gas water heater, automobile, etc.) seemed like an
insurance claim waiting to happen!
So, the only real alternative would be to locate the batteries
outside the garage and run 120VDC through the wall. Then,
run AC from the UPS into the house to support the loads.
But, that means building a shelter to keep the batteries out of the
sun, rain, etc. And, protecting against wildlife chewing on
the wiring, etc. Way too much work!
So, I now use lots of little UPS's. Since outright *outages* here are
rare (a bigger concern are the "2 second wink-outs" you mentioned),
a 500VA - 650VA unit by each critical load is quite adequate.
And, when the machine in question is powered off, there is no
need for the UPS to run at all! (A 3500W UPS wastes a LOT
of power just *idling*!)
The Back-UPS 650 Pro *wants* an 11AHr battery (based on volume).
But, a nice 7AHr will do just fine for you (though you will have to
"pad" it a bit to prevent it from flopping around inside). At most,
that should run you $15 - $18. I think you can even buy the 11AHr
battery for around $20 ("off brand").
What is an outage -- even a 2 second "reboot" -- worth to you?
If it is NOT worth $18, then why are you bothering with a UPS
at all?? (sort of like the folks who spend $50 on a tape backup
system -- that they only use once a month -- and then complain
when they have had a crash and discover last backup they made
is "unreliable")
shrug
--don
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