Do-it-yourself UPS 388
Giampiero writes "Over at dansdata.com some guy named Dan creates a UPS out of some spare parts. To sum it up, "if you're looking for an industrial-capacity UPS solution, and don't like the prices of the off-the-peg options, it might be easier than you think to roll your own."" Of course you can mentally substitute U.S. 110 volts for Australian 220 volts wherever necessary...
Why convert DC to AC to DC? (Score:4, Interesting)
Of course, PCs don't actually use AC power: there's a big box in the back that converts all the AC input back to DC. So why not save some money and bypass this, by running the PC straight off the battery (like a laptop)?
Great solution... (Score:1, Interesting)
220V (Score:1, Interesting)
Lacking some features (Score:2, Interesting)
UPS maintenance (Score:3, Interesting)
By contrast, UPS batteries are designed to discharge at a slower rate, but charge very very quickly to be able to work if the power suddenly cuts out two or more times in a row.
The problem with using one battery where another is required is that a memory effect can develop. That slow discharge on a car battery can cause it to lose capacity and in as little as 6 months it'll be useless for any power failures over about 5 seconds.
How much does a car battery cost? about $50. But, you're going to need one every 6 months or so, making a home built UPS actually many times more expensive than one you buy at Comp USA.
I know it's counter-intuitive, but many things about batteries are.
Re:Why convert DC to AC to DC? (Score:5, Interesting)
Taking DC, converting to AC so the PC power supply is happy, then the power supply converts to DC... it would be nice if it could just be DC all the way.
The problem is that your monitor, modem, etc. all expect AC power. It's easiest just to make a UPS that provides standard AC power, and plug everything in.
Someday, I think we will have "smart" plugs. Wall power outlets will not be live by default; they will only serve power when a proper coded request goes in over a smart plug. The device will be able to tell the wall outlet what kind of power it wants, and the outlet will be able to tell the device what kinds of power it can offer. Then little kids will stick butter knives into wall outlets and not get fried; PCs and monitors will ask for +5 and +12 volts DC and get it; and UPSes will be able to feed +5 and +12 volts DC to those PCs and monitors.
Actually, if you have the complicated smart power system I envision, there will probably be a UPS integral to the system. When your home loses power, the smart power system would broadcast a "power interrupted" signal and devices like your refrigerator and your laser printer will power themselves down; your PC will run for about 5 minutes and then power itself down (unless you are there and override it) and medical devices will run indefinitely. Maybe only the DC devices in your home will be on the UPS by default?
steveha
been there done that (Score:1, Interesting)
-Matt
This is dumb and dangerous. (Score:2, Interesting)
Also the cost for these components is *much* higher than a $59 APS UPS.
However, if you wanted to roll your own you would ditch the inverter and simply regulate the gel-cel down to the +12, +5, +3.3, +2.2, etc that your computer needs, and use a DC-DC converter chip [maxim-ic.com] to get the -12 and -5volts.
That's much more efficient and somewhat safer.
You wouldn't want a person without a CS degree writing software; we shouldn't have folks without EE degrees designing power supplies.
Don't-do-it-yourself UPS (Score:2, Interesting)
Re:UPS maintenance (Score:3, Interesting)
experiment. Imagine an industrial table
full of physics equipment. It drew more power
than any desktop or small server but needed
to run for hours. We bought a single AGM sealed
valve regulated deep cycle battery for $80 and
it has worked well. It provided power continuosly
for more than 4 hrs and as far as we can tell
has not lost much capacity yet (i.e. after a few dozen fairly deep discharge cycles). It has also
worked for a couple of years now without a hickup.
So from personal experience, this scheme works
very well, but a quality setup will run you ~$300.
Look at boating and RV sites and newsgroups for
names of good battery manufacturers and compare
prices. We have nothing but good things to say
about Concorde's Chairman batteries.
Re:Be Careful (Score:2, Interesting)
Re:VA? Watts? (Score:2, Interesting)
W == less then E*I for inductive loads, like computers, motors, etc... anything with a power factor less then 1. On the other hand, VA == E*I for any device, and gives the total amount of power required by the device, not how much it is using.
(E == volts, I == amps)
Re:Why convert DC to AC to DC? (Score:2, Interesting)
Immediately have quiet and attentive students.