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Do-it-yourself UPS
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...
Coupla caveats:
.3 or .7 volts.
Put a "battery isolator", or at least a power diode with a heat sink, between the power supply and the battery. And allow for the fact that it will drop
Don't even think about wet cells inside the house. Sulfuric acid belongs out of doors. There's a reason you're allowed to ship the Concorde battery without declaring it hazardous: it won't spill. Further, a non-sealed battery will release hydrogen while it's being recharged. Is your computer room free of all ignition sources?
Fred KC7YRN
(I've seen a commercial 500 VA unit for US$40)
People often misunderstand the electrocution hazards presented by electricity. Yes, technically it's the amps that hurt you, but the volts have to be there too.
I could hold a 1 volt 300000 amp power supply's leads all day and not be hurt. The reason is Ohms law.
Your body generally has a pretty high resistance. Ohms law states that amps=volts/resistance. Your body is probably between 20,000 and 300,000 ohms, depending on which part you are talking about. Wet or sweaty parts have lower resistance. Higher voltage is more dangerous, because more amps will flow through your body. A 500 volt at 1 amp power supply would probably be lethal, especially if you had wet hands.
A rule of thumb is that anything above 50 volts should be treated very carefully. This is about the threshold of where you will normally start to conduct possibly dangerous amounts of current. If your hands are sweaty or wet, or you are grounded well for some reason, better cut that down to 30 volts.
Here's a link
The parent post is correct though, be careful in any case. Don't try this stuff unless you know what you are doing around electricity.
I've had enough abrasive sigs. Kittens are cute and fuzzy.
Be careful with this stuff. Batteries can be nasty. At my previous job we had a "switch room" which housed out 50,000kva (yes "K"va) UPS. On the wall across from it were huge "grab the handle and yank" circuit breakers...which were covered in battery acid from the previous UPS.
Now this wasn't your home little ups box, this thing would blend in with three refrigerators side by side, and would run a 500 person electronics factory, and 500 person office (PC's at least) for 8+ hours. That was a kickass battery box.
Just remember, UPS's can go "BOOM" and I wouldn't want to try my hand at making my own and seeing it for myself. Some things are better left to APC and crue.
-Pete
Soccer Goal Plans
Or, you could visit:
http://auction.apc.com/
And get refurbished, and sometimes brand-new, warranteed APC power units for pennies on the dollar.
Two years ago I purchased two 420VA refurbished backups for around $50 each. They're currently protecting my three boxen, one of which I'm on now, and have been flawlessly through brown-outs, sags, surges, etc.
Typically the refurb'd units are from companies who have agreements with APC to buy many UPSs and return them when the batteries run out. Why? Customers used to return UPSs marked as 'defective' when in fact it was simply a dead battery. So, they tape over the battery bay and simply have the customers return the units with dead batteries and pick up a new one. They replace the battery and sell the ok unit again as refurbished.
Thanks,
--
Matt
I have two UPSes -- I used to have three but one died a horrible death for no apparent reason.
:-(
The smallest unit I have is a 600VA no-name Taiwanese box with two 7A SLAs. It has no fan and, although it's just an SBS, it still runs hot as hell.
As a result of this hot running, I discovered that the SLAs tend to dry out rather quickly such that you get a much shorter time than you'd expect when the mains power goes off (as I discovered just the other night
My other box is a Siemens 1KVA full-time UPS with forced ventilation and a bunch of other cool features.
It's worth noting that even a fan-cooled UPS such as the Siemens can run way too hot -- as I discovered about a year after I installed it.
Without warning, the UPS started screeming at me with a continuous alarm buzzer. It was still working but it was not at all happy.
On touching the case I discovered why -- it was too hot to touch.
I shut things down really quickly and opened up the case to see what was wrong...
Dust!
The intake holes in the front panel have a fine wire mesh over them and, since this UPS (like most others) lives on the floor under my desk, enough dust had been sucked into the holes to totally block them.
So here's a DC-AC inverter busy delivering about 500W of power to several computers and monitors -- but without the benefit of any cooling. No wonder it wasn't happy.
I blew the filters out with compressed air, checked that the fan was okay and put it back together. It's been working fine for nearly two years since -- albeit that I check and clean the intake meshes every few months now.
That the Siemens box was smart enough to warn me it was in distress (rather than just failing) shows that nobody ever regretted buying quality.
So.. rules of thumb for UPSes...
If it runs hot-- expect the batteries to last just 18 months to 2 years -- and don't wait until the power fails to find out that you should have changed them already.
If you have a fan-cooled UPS mount it up off the floor or check that the cooling holes are clear at regular intervals.