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...
Be Careful (Score:5, Insightful)
Australia runs 240 V, not 220 (Score:1, Insightful)
Re:Why convert DC to AC to DC? (Score:3, Insightful)
A latop doesn't run "straight off the battery". It has a switching power supply circuit which is not entirely unlike your desktop's AC->DC supply. Most of the stuff in there runs at 3.3V, whereas the battery is 18V or more. So you still need a power supply.
For desktop PCs, a 110V->5V supply is cheaper than a DC-DC supply.
Re:why australia? (Score:2, Insightful)
As we're an Australian mag with a (mostly - we sell in New Zealand, Singapore and a few other places) Australian audience, its setup for 240V.
The UPS D-I-Y article appeared in AtomicMPC Issue 13 (latest issue is 18)
Re:Be Careful (Score:5, Insightful)
If your UPS is UL listed then there are several regulations which govern just this sort of action. Report the problem to APC, if they don't do anything about it (!!!) then report it to the UL and/or BBB.
I'm being completely serious. For it to go this bad there is certian to be more wrong with it. I wouldn't trust it to power anything worth more than $10.
-Adam
Re:Be Careful (Score:2, Insightful)
Although what you say is mostly correct from a practical point of view, try not to forget that "ohms law" is an idealization and only applies to a small class of conductors. What G. S. Ohm noticed more than a hundred years ago what the in metalic conductors at a constant temperature the ratio of electric field to current density was approximately a constant, known as the resistivity. (note that this is a microscopic statement.) Working from this assumtion that rho=E/J, and assuming an isotropic, ohmic conductor, one easily arrives at the more familliar version of ohms law: R=V/I. Now this is a very usefull result, but please remember that it was drived only after making multiple assumptions regarding the nature of the conducting material and has noting to say with regard to what is going on at a smaller scale.
Anyways, just be carefull you don't read too much into "ohms law".
A tunnel diode [tpub.com] is not a bad example of something you can hold in your hand which is most deffinately not ohmic and exhibits some interesting behavior because of this.
Electrochemical systems (such as collections of cells in a human body) are another good example of decidedly non-ohmic systems. Pick up a physical chemistry book if you want to learn more.
The take home point is: Yes, you could probably hold on to a 1v supply with no problem, but the effects of electricity on the body are not as simple as you make them seem.
And, No, I am not one of those people who think cell phones or power lines are harmfull
Standard Internet Horror Story (Score:2, Insightful)
12v DC input ATX power supplies... (Score:2, Insightful)
http://www.keypower.com/DC_power/DX-250H.htm