[chadh]

I was just looking at uninterruptable power supplies (UPSs) to keep my aquarium running when the power goes out.  There are several different designs - but some (the "in-line" or "double inversion" UPSs) work in a really cool way.  The items powered by the UPS always draw power from the internal battery.  And while the mains power is operational, the battery is continually recharged.  As a result, the battery never runs down unless the mains power is cut, and at that stage you have however many minutes/hours of power delivered by the battery.

Do people use these in audio applications?

In an audio application, the power backup itself seems unimportant.  BUt wouldn't this UPS design provide excellent power conditioning?  One could run all of one's system through the UPS (well, maybe not people with humungous amps) and be drawing only pure battery power at 120v, but would never need to be concerned with recharging the unit or limiting the listening session.

Is the cost of in-line UPSs simply prohibitive?

I found one link that suggested that UPSs are usually discarded when the battery fails because it's expensive to replace the batteries in a unit that has possibly quickly become obsolete.  They suggested trying to pick up an old one and wire in a car battery.  Good or bad idea?  Of course, one positive thing about this plan is that, as back-up power is hardly the important issue, a smaller (in terms of amp-hours) and cheaper battery would be needed.

Apparently there's some issue of whether the inverter actually produces a proper sine wave - but you'd think that they'd sort that out if they were using these things to protect expensive computer gear.

Hmmm...maybe this is what "power regenerators" do...

Chad

[ctviggen]

Supposedly, they don't produce a good sinewave, which isn't a big deal for computers, which convert to DC anyway. The best ones supposedly charge the battery on "one end" while your equipement is connected to the "other end" of the battery.  The cheaper ones use the same connection to charge the battery.  For instance, the UPS I had would cause my computer to come out of hibernation (but not restart) because the UPS didn't switch to battery power fast enough.  The batteries are expensive.  I think the battery for my old one is more expensive than buying a new UPS.

[chadh]

Battery cost shouldn't be such an issue.  

A cheap UPS is truly just a battery backup.  The appliances attached draw power from the mains until the mains power disappears, then a switch causes the battery power to come online.  If this doesn't happen quickly enough, then your pc might hibernate.  These types of units tend to provide batteries delivering up to 750, or maybe 1000 amp hours (from what I can tell).  An expensive UPS of the "inline" variety might provide a battery of 5000 amp hours.  Now, these batteries are likely to be EXPENSIVE!  But for an audio application, there would be no need to use such a big battery, since the battery life is never a real issue (unless you're committed to the idea of listing to your system during a power outage).  So the idea would be to find an old "inline" unit, where the battery has died, and replace the battery with a deep charge 12v car battery (which might cost you $50-$200, depending on the technology you like).

The issue of producing a nice sine wave might be more of an issue.  I know that the types of inverters used in these applications are marketed in different ways - some of them produce a "modified sine wave", and others claim to produce a "true sine wave."   It seems most use something called "pulse width modulation" to produce a wave - I have no idea what this is or how accurate it could possibly be.  However, if PS Audio is charging in excess of $1000 for a "power regenerator", where the difficulty lies in producing a perfect sine wave, I'd be prepared to believe that these inverters may do a shoddy job.

It's clear though that there are many applications where the good sine wave is important.  For example motors run off modified sine waves will be prone to break down, which becomes important for those of us who would like to use the power to run water pumps in an aquarium  when the AC goes out.  So some technology is invested in sine wave production.

Chad