Re: Using an APC battery backup for other things - help!
From: Walter Roberson (roberson_at_ibd.nrc-cnrc.gc.ca)
Date: 11/22/03
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Date: 22 Nov 2003 21:04:03 GMT
In article <bwpatter-1EAE65.14561122112003@news.verizon.net>,
Blake Patterson <bwpatter@bellatlantic.net> wrote:
:The sump pump in the put activates
:rarely, but in really moist periods it comes on every 20 mins, for 3-4
:seconds, or so. I worry about what would happen if power went out.
:Rather than just having a standby generator, could I use a computer
:batter backup system, like these from APC:
Yes, generally speaking you can use "computer" UPSes for other
purposes such as pumps. The trick is to size the UPS properly.
There are [at least] four important considerations in choosing a
UPS:
1) Does the UPS do the kind of power cleaning that is important to you. The
cheapest variety of UPSes pretty much just pass power through raw until
the power fails, and then kick in the battery. There might be some
power spike filtering, and there would be some amount of protection
against brownouts and blackouts, but you can still end up with some
pretty ugly power inbetween those limits. These are called "standby"
UPSes. The kind of UPSes that clean the power up the most are called
"online" or "double conversion" UPSes, but they are -much- more
expensive. There is a third intermediate "single conversion" kind of
UPS.
2) Can the UPS handle the voltage and amperage you need in total?
You can do a worst-case calculation by looking at the specifications
of the devices, multiplying voltage by rated amperage and totalling the
results over all of the devices, and buying a unit that handles
that many VA (Volt-Amps); this will often come out noticably
higher than you really need, but extra doesn't hurt [other than
pricetag].
If the UPS is rated in Watts, then you have to be careful
in how you do the VA to Watts conversion: there is a phase angle
involved in the calculation and the angle is much more favourable for
computer equipment than for motors such as pumps: you need a more
powerful unit (in Watt terms) to handle motors than you do modern
computer equipment that looks to have the same rating.
3) If the UPS goes out, can the UPS handle the drain for as long
as you need? In your case, the time the pump would be most needed
would be during a storm, but a storm is the time the electricity
would be most likely to go out. If you had a really bad storm,
could the pump end up running effectively continuously? Take the
highest expected load and look through the manufacturer's tables of
how long the model could support that load, and figure out whether
that's long enough for you. Are you trying to protect against power
going out for 5 minutes? For 2 hours? For all day?
4) How long is the unit going to last? How much is it going to cost
to change the batteries a few years down the road [the batteries
lose their effectiveness over time, depending how far down
you draw them, and depending on how exactly they get recharged.]
5) Does the UPS have enough of the right kind of outlets for all of
your equipment? Examine all the specifications *very* carefully;
it's very easy to end up with the wrong kind of receptacles
if you don't make a list and check it four times. In the case of your
pump, you might find that you need to "hardwire" the connection --
the pump might not *have* a plug of any sort. If the unit you are
looking at does not have exactly the right kind of connections, it
is possible that the next one along will... but every once in awhile
you find a plug type that a particular manufacturer just doesn't support.
Four major UPS manufacturers that I can think of at the moment are APC,
Powerware, Tripp-Lite, and Liebart. APC has more than half the market,
but I would not say that they are always the best value for your
money, and their lower-end equipment does not always last as long
as some of the other manufacturers (but you would definitely
want to look at APC if you were putting together a "911" call
centre or other establishment combining high power with high
availability.) There are hundreds of lesser-known UPS manufacturers,
some of which produce excellent devices, and others of which
don't. Shopping around can really pay off... but it can also take
a long time to decide between multitudes of similar units with
similar prices.
-- Perposterous!! Where would all the calculators go?!
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