berman@me.ri.cmu.edu (Steven Berman) (08/11/87)
Regarding a recent query about quality of UPS (uninterruptible power supply)
output:
I have recently spent some time researching UPS technology of today.
There is a wide range of equipment available, good, bad, and ugly! Beware
that there are major differences in implementation. What follows is a short
summary of several technologies.
OFF-LINE UPS:
This machine has a feed-through from main power to output
with some filter caps across it. When power fails, a switch-over
circuit connects the battery to an inverter circuit, which supplies
the output. An active battery charge circuit keeps the cells
charged when "off-line". This is the least expensive UPS and
by far the worst for computer-related applications. It's plusses
are 100% off-line efficiency, quiet operation. Minuses: dirty
switchover. Up to 30 msec switch time. Really intended for
brute-force loads, that can handle the spikes, and drop-out.
ON-LINE UPS:
This is a good middle-of-the-road machine. It uses a battery
charge circuit to both keep up the cells AND supply an inverter.
The inverter is the only source to the output. This means that
switch-overs have EXACT wave-form synchronization. Pluses:
Near zero switch-over time. Modest cost, small. Minuses:
VERY noisy, inverter tends to squeal at 5-30 KHz. (very annoying)
Can be destroyed by a dirty power feed-in. (Real Life example:
Gasoline Generators feeding UPS: Blew out all the inverter
transistors after only 100-hours of up-time.) Sola makes these.
FERRO-RESONANT UPS:
The cream of the crop! Theese machines use a HUGE transformer
fed from the main to supply the output. When power fails, the
batteries kick-in and the enormous L of the transformer maintains
the synchronization of the sine-wave. These machines have small
switch-over times (~5 msec), but the big plus is that perfect
sine-wave. They are quiet, since they use the transformer
when on-line, and are more efficient than the ON-LINE models.
BEST Power Tech. makes these, and I bought three recently.
Hope this helps,
I'll gladly provide more details through mail.
I have a file that compares ~10 companies with cost/KVA.
~Steve
--
------------------------------------------------------------------------------
Steven Berman
Mechanical Engineering-Robotics
The Robotics Institute
also Computer Science Department
Carnegie-Mellon University
ARPA: berman@me.ri.cmu.edu
UUCP: {harvard | ucbvax | seismo}!me.ri.cmu.edu!berman
SNAIL: 5668 Darlington Rd. Pittsburgh, PA 15217
This does not represent the opinion or policy of my employer...yet.larry@kitty.UUCP (Larry Lippman) (08/12/87)
In article <1003@me.ri.cmu.edu>, berman@me.ri.cmu.edu (Steven Berman) writes: > ON-LINE UPS: > This is a good middle-of-the-road machine. It uses a battery > charge circuit to both keep up the cells AND supply an inverter. > The inverter is the only source to the output. A well-designed UPS has a "reverse transfer" feature using a solid-state switch that switches output power load back to the AC line in the event of inverter failure and/or output load overcurrent. > This means that > switch-overs have EXACT wave-form synchronization. Pluses: > Near zero switch-over time. Modest cost, small. Minuses: > VERY noisy, inverter tends to squeal at 5-30 KHz. (very annoying) Admittedly they can be noisy, but with 60 Hz/120 Hz hum - which is much more tolerable than a high-frequency inverter whine. > Can be destroyed by a dirty power feed-in. (Real Life example: > Gasoline Generators feeding UPS: Blew out all the inverter > transistors after only 100-hours of up-time.) I don't see this being a problem on a well-designed UPS. The battery charger circuit is going to "float" the battery with a small net positive current flow above demand. As a result, the float charging circuitry will be both current and voltage limited so that any AC line input overvoltage will either be harmless or will trip an overcurrent device (on the charger circuit only) before harm can occur. A sign of a well-designed UPS is one which has panel metering and failure alarms. Some of the best designed UPS systems which work on the above principles are made by Elgar and Lorain Power Products, and I am admittedly partial to both vendors. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|seismo|utzoo}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
dhesi@bsu-cs.UUCP (Rahul Dhesi) (08/12/87)
In article <1003@me.ri.cmu.edu> berman@me.ri.cmu.edu (Steven Berman) writes: >OFF-LINE UPS: [...] >It's plusses >are 100% off-line efficiency, quiet operation. Minuses: dirty >switchover. Up to 30 msec switch time. Really intended for >brute-force loads, that can handle the spikes, and drop-out. A common error. By definition, a UPS (uninterruptible power supply) has zero switchover time. The above is more correctly called a standby power supply. -- Rahul Dhesi UUCP: {ihnp4,seismo}!{iuvax,pur-ee}!bsu-cs!dhesi